Tech Briefs

TECHNOLOGY BRIEFS Overview of Advanced Electric Delivery Technologies

August 2004

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United States Department of Energy Office of Electric Transmission and Distribution

PREFACE This document was prepared for the U.S. Department of Energy’s Office of Electric Distribution and Transmission (OETD). OETD’s mission is to lead a national effort to help modernize and expand America's electric delivery system to ensure economic and national security. That effort includes managing technology development programs, conducting research and development activities, reducing regulatory and institutional barriers to efficient T&D, acting as a neutral facilitator of solutions that benefit everyone, and providing a national vision for building strong public-private partnerships. The purpose of this document is to provide stakeholders with an overview of grid-enhancing advanced electric delivery technologies. It is intended to give the audience general information on advance electric delivery technologies. The Technology Briefs provide an overview of various technologies that can enhance the electric delivery system. The covered technologies correspond to the ones listed in Section 1224, Advanced Transmission Technologies, of Senate Bill S. 2095. This document is a dynamic document and will be updated as the state of advanced electric delivery technologies evolves. The following people provided valuable insights and strong support for the document: Larry Mansueti, Lead, Electric Markets and Technical Assistance, OETD; David Jopling, Regulatory Analyst, Florida Public Service Commission; Robert Hawsey, Oak Ridge National Laboratory; Joe Eto, Lawrence Berkeley National Laboratory; Dale Bradshaw, Tennessee Valley Authority; Andrew Spahn, National Association of Regulatory Utility Commissioners (NARUC).

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TECHNOLOGY BRIEFSOVERVIEW OF ADVANCED ELECTRIC DELIVERY TECHNOLOGIES

Table of Contents INTRODUCTION ............................................................................................................................... 1 A. CABLES AND CONDUCTORS .................................................................................................... .2 A1. Superconducting Power Cables................................................................................................ 3 A2. High Voltage DC Technology.................................................................................................. 5 A3. Composites and Ceramics (including high temperature low-sag conductors) ......................... 7 A4. Multiple Phased Transmission Lines ....................................................................................... 9 A5. Underground Transmission Cables ........................................................................................ 10 A6. Other Cable and Conductor Technology................................................................................ 12 B. INTELLIGENCE AND CONTROLS ............................................................................................. 13 B1. Real-Time Monitoring............................................................................................................ 14 B2. Distributed Intelligence .......................................................................................................... 17 B3. Communications Systems ...................................................................................................... 18 C. MODULAR EQUIPMENT .......................................................................................................... 20 C1. Superconducting Transformers .............................................................................................. 21 C2. Superconducting Fault Current Limiters................................................................................ 23 C3. Power Electronics................................................................................................................... 25 C4. High-Performance Ceramics (e.g., connectors, insulators)................................................... 27 C5. Flexible Alternating-Current Transmission Systems (FACTS) ............................................. 29 C6. Superconducting Synchronous Condensers ........................................................................... 31 D. ENERGY STORAGE ................................................................................................................. 33 D1. Batteries.................................................................................................................................. 34 D2. Flywheels ............................................................................................................................... 36 D3. Compressed Air Energy Storage ............................................................................................ 38 D4. Pumped Hydro Energy Storage.............................................................................................. 40 D5. Superconducting Magnetic Energy Storage (SMES)............................................................. 42 D6. Other Energy Storage Technology......................................................................................... 44 E. DISTRIBUTED ENERGY ........................................................................................................... 45 E1. Industrial Gas Turbines .......................................................................................................... 46 E2. Microturbines ......................................................................................................................... 48 E3. Fuel Cells ............................................................................................................................... 50 E4. Reciprocating Engines............................................................................................................ 52 E5. Photovoltaics .......................................................................................................................... 54 E6. Demand Response.................................................................................................................. 57

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INTRODUCTION The Technology Briefs provide an overview of various technologies that can enhance the electric delivery system. The covered technologies correspond to the ones listed in Section 1224, Advanced Transmission Technologies, of Senate Bill S. 2095. The purpose of this document is to provide regulators and other stakeholders with an overview of grid-enhancing advanced electric delivery technologies. Each technology brief includes a technology readiness paragraph that describes the commercial availability of the technology. Each brief also includes a technical description, cost and performance characteristics, market applications, and future technology goals (if applicable). The Technology Briefs have been organized into the following five technology classifications: • • • • •

Conductors and Cables Intelligence and Controls Modular Equipment Energy Storage Distributed Energy

Conductors and cables are the equipment that comprises the power lines that connect electricity users with power plants. They are the backbone of the electric delivery infrastructure. Conductor designs range from a single copper wire to cables consisting of several types of wires, including copper and aluminum and newly-designed high-strength, lightweight composites. Advanced conductors and cables use new materials and designs to expand current carrying capacity without the need for new real estate or rightsof-way. Intelligence and controls can be added to the electric delivery infrastructure to improve grid operation, enable real-time detection and system restoration, and control the devices working together on the grid. These systems and software can automate decision making and expand data acquisition capabilities. Visualization tools can aid grid operators to respond to data and enhance operations in real time to lower costs and increase reliability. Modular equipment includes a variety of devices such as transformer banks, switchgear, and capacitors. Advanced modular equipment designs can lower costs and increase durability and reliability. Standardized, flexible technologies that can easily be installed throughout the electric delivery system are needed so that the equipment does not have to be designed uniquely for a specific site. Energy storage technologies can address peak load problems, power quality disturbances, and improve the stability of the electric system. Storage equipment can be applied at the power plant, in support of transmission systems, at various points in the distribution system, and on particular appliances on the customer’s side of the meter. Distributed energy technologies are installed at or near the point of consumption. Power generation technologies such as industrial gas turbines, reciprocating engines, and fuel cells can be installed by users to improve their power quality and reliability. By reducing peak demand, these technologies can lead to a reduction in the need for “upstream” investments in electric generation, transmission, and distribution.

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A. CABLES AND CONDUCTORS A1. Superconducting Power Cables A2. High Voltage DC Technology A3. Composites and Ceramics (including high temperature low-sag conductors) A4. Multiple Phased Transmission Lines A5. Underground Transmission Cables A6. Other Cable and Conductor Technology

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A1. SUPERCONDUCTING POWER CABLES Technology Readiness Superconducting power cables are not commercially deployed. Prototypes are currently being developed and field tested. Prototype superconducting power cables in Ohio and New York will be energized by 2006-2007. Technology Description High-capacity underground high-temperature superconducting (HTS) cables are capable of serving very large power requirements at medium voltage ratings. Over the past decade, several HTS cable designs have been developed and demonstrated. All HTS cables have a much higher power density than copper-based cables. Moreover, because they are actively cooled and thermally independent of the surrounding environment, they can fit into much more compact installations than conventional copper cables. This advantage reduces environmental impacts and enables compact cable installations with three to five times more capacity than conventional circuits at the same or lower voltage. In addition, HTS cables exhibit much lower resistive losses than occur with conventional copper or aluminum conductors. At present, there are two principal types of HTS cable under development: Warm dielectric design • This simpler design is based on a single conductor, consisting of HTS wires stranded around a flexible core in a channel filled with liquid nitrogen coolant. • This cable design employs an outer dielectric insulation layer at room temperature. • It offers high power density and uses the least amount of HTS wire for a given level of power transfer. • Drawbacks of this design relative to other superconductor cable designs include higher electrical losses (and therefore a requirement for cooling stations at closer intervals), higher inductance, and required phase separation to limit the effects of eddy current heating. • Most of the HTS cable demonstrations undertaken to date have been based on the warm dielectric design. Cold dielectric design An alternative design that employs concentric layers of HTS wires and a cold electrical insulation system. • Liquid nitrogen coolant flows over and between both layers of wire, providing both cooling and dielectric insulation between the center conductor layer and the outer shield layer. • Cold dielectric HTS cable offers several important advantages, including higher current-carrying capacity, reduced AC losses, and low inductance. • The reduction of AC losses enables wider spacing of cooling stations and the auxiliary power equipment required to assure their reliable operation. •

Cost and Performance The U.S. Department of Energy (DOE) Superconductivity Program, as part of its Superconductivity Partnerships with Industry (SPI) activity, is cost-sharing the development, installation, and field-testing of several HTS power cable systems.

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SPI Demonstrations Cost and Performance Characteristics Power Capacity (MVA) Voltage (kV) Current (A) Length (m) Year Energized (Scheduled) Demonstration Project Cost ($M) (includes 50% cost share, DOE and industry)

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Southwire, GA Facility 27 12.4 1150 30 2000 15.3

AEP, Columbus Cable 69 13.2 3000 200 2006 8.65

NiMo, Albany Cable 48 34.5 800 350 2007 26.0

LIPA, Long Island Cable 600 138.0 2400 610 2006 30.0

A conservative cost estimate of the first market entry HTS cables is about $10 million per mile on an installed basis, including ancillary equipment. As the HTS cable technology matures, per-mile installed costs are expected to fall well below this level. Even though HTS cable can be more expensive than conventional solutions on a mile-for-mile basis, the ability of HTS cables to solve power flow problems with shorter lengths of cable, at lower voltages, and in a shorter timeframe due to simplified siting and permitting requirements can offset these costs leading to a lower installed-cost system solution. While HTS cable remains an early-stage, low-volume product, initial projects are likely to be focused on highly congested grids in urban areas. As volumes increase and costs decline, its advantages can be expected to expand to a broader range of applications. Market Applications

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HTS cables may make an excellent choice for the replacement of existing underground cables in urban areas where additional underground space is extremely limited and valuable. Their use would allow a significant increase in the current being delivered to power-starved cities around the country.

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HTS cables can increase the capacity and flexibility of the grid without further raising system voltages. Short HTS cable segments can bridge transmission bottlenecks and improve overall power system efficiency and lower total system costs. HTS cables have the potential to create an efficient “electricity superhighway.”

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American Superconductor’s Very Low Impedance (VLI) concept where an HTS VLI AC parallel section can readily unload exiting overhead lines or underground cables. It can be easily controlled with small changes in phase angles using a small phase angle regulator, and the VLI section acts like a power electronic static series synchronous compensator (SSSC). Technology Goals

The R&D goals are to solve the general engineering challenges of integrating dielectrics and cryogenic systems at high voltage operation. Cables using second generation HTS wire need to be designed, fabricated, and tested. The ultimate goal is to demonstrate the efficiency, performance, reliability, and equivalent cost (on a life cycle cost basis) compared to a conventional cable by 2010. Demonstration goals are as follows: • By 2006: 34.5 kV, 50 MVA, 0.2 miles • By 2007: 138 kV, 600 MVA, 0.5 miles • By 2009: 138 kV, 600 MVA, 2.0 miles • By 2010: 345 kV, 750 MVA, 2.0 miles Sources: American Superconductor Corporation DOE Superconductivity Program Website (www.electricity.doe.gov)

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A2. HIGH VOLTAGE DC TECHNOLOGY Technology Readiness High voltage DC (HVDC) is commercially available and used across the world. It is cost competitive with AC transmission technology when large amounts of power (>500 MW) needed to be transmitted over long distances (>500 km or 310 miles) and to link asynchronous control areas. Technology Description • • •

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In a high voltage DC (HVDC) system, electrical current is converted from AC to DC in order to be transmitted by a line or cable and then converted from DC to AC for distribution and end use. The distinguishing component of this technology is the converter station at the end of each line. There are three types of converters: − Natural Commutated Converters − Capacitated Commutated Converters − Forced Commutated Converters There are three primary types of systems: − point-to-point transmission (monopolar and bipolar systems) − back to back station (asynchronous interconnection) − multi-terminal system (two or more converter stations) HVDC systems usually have a power capacity of more than 100 MW, many are in the 1,000-3,000 MW range. The Pacific HVDC Intertie spans 1361 km (845 miles) from Sylmar (just north of Los Angeles) to Ciello, Oregon and has a power capacity rating of 3100 MW. Cost and Performance Characteristics

A number of factors affect the cost of an HVDC transmission system. Valves and converter transformers are the biggest cost issue. Below is a diagram that depicts the cost structure of a typical system.

Sourse: World Bank; http://www.worldbank.org/html/fpd/em/transmission/technology_abb.pdf

Below is a graph showing cost in relation to length of a DC line compared to an AC line.

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Market Applications • • • • • • • • •

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Undersea power transmission Transmission of bulk power to or from remote locations Increasing capacity of the grid without the need for siting additional lines Power transmission between unsynchronised AC distribution systems Connecting distributed generation facilities, particularly off-shore wind farms Capable of carrying power over very long distances Power flow can be controlled quickly and accurately The only means through which energy from windfarms can be converted to DC Advantages over AC transmission lines: − Transmit electricity over greater distances − more compact design (less environmental footprint) − more control of power flow − faster control of real and reactive-power HVDC can carry more power per conductor because, for a given power rating, the constant voltage in a DC line is lower than the peak voltage in an AC line. This voltage determines the insulation thickness and conductor spacing. Many are operating in markets today including some in Texas, WSCC, and the Eastern Interconnection. Technology Goals

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Reduce cost of converter station at the end of each line. TVA and Vanderbilt University are conducting basic research to develop a high voltage, rugged and robust, chemical vapor deposition diamond edge or tip field effect transistor, diode, or triode in a vacuum which reduces the costs of HVDC valves.

Sources: World Bank; http://www.worldbank.org/html/fpd/em/transmission/technology_abb.pdf National Transmission Grid Study

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A3. COMPOSITES AND CERAMICS (INCLUDING HIGH TEMPERATURE LOW-SAG CONDUCTORS) Technology Readiness Composites are currently used in composite core conductors that are commercially available. Ceramics are advanced materials used in HTS technology. Ceramic-based wires and tapes (bismuth compounds) are currently being manufactured. 2nd Generation wires and tapes (yttrium compounds) are being developed for power applications. Technology Description Composites • Research is underway to develop composite conductors that could replace the steel in existing steel-reinforced or supported aluminum conductors to enable lighter, stronger lines with higher carrying capacity. New conductors will also have less sag. • Composite conductors are used in overhead transmission lines. • Composites can be used as conductor core, instead of conventional ferromagnetic core. The aluminum composite core can run cooler, allowing the conductor to operate at higher temperatures without significant line sag. The higher aluminum content also reduces line losses. Ceramics High temperature superconductivity (HTS) offers the opportunity to transmit electricity with zero line losses. In order to maintain this capability, HTS materials must be cooled to liquid nitrogen temperature (77 K). Advanced material applications make this possible. • Using nanotechnology, researchers have been able to configure the atomic structure of certain materials and composites to create a type of “super-lattice” capable of transmitting electricity with little to no resistance or losses. •

Cost and Performance Characteristics Performance Indicators for 2G HTS Wire Metric Current Status 2005 2006 2007 2008 2009 2010

A/cm width 77K, SF 250 300 500 500 800 900 1000

Length

Cost

10 m (~32.8 ft) 20 m (~65.6 ft) 100 m (~328 ft) 1000 m (~3280 ft) 1000 m 1000 m 1000 m

— — — $50/kA-m $30/kA-m $20/kA-m $10/kA-m

Annual Production — — — 200-1000 km 1000 km 2000 km 10,000 km

Properties of 3M’s Composite Core

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The application of advanced materials and HTS wire can increase the carrying capacity of the grid by as much as five times without the need for new rights-of-way. • National laboratory, university, and private sector researchers are exploring potential applications: superlattices, artificially structured multilayers of thin film, may find use in detectors; coils for use in energy storage, motors, generators, and electric distribution equipment are also being designed and tested. • Composite core conductors, because of their performance characteristics, can be used in environmentally sensitive areas, long-span crossings, capacity upgrades, heavy ice regions, replace aging structures, and changing clearance requirements. (Source: 3M Company) Composite conductors can be used to replace current aluminum steel reinforced conductors (ASCR). Technology Goals • • • • • •

Continue basic research to identify higher temperature superconducting materials. Develop advanced conductor materials using alloys and composites of aluminum, copper, polymers, carbon, dielectrics, magnets, supercapacitors, and others. Develop advanced conductor designs for increased carrying capacity, low line losses, low-cost manufacturing, installation, and maintenance. Develop lower cost construction and installation techniques for re-conductoring existing facilities and building new facilities, for both overhead and underground lines. Continue investment in the manufacturing scale up of 2nd generation HTS wire while using the best available, first-generation wire in immediate applications to ready the market. Lower cost of manufacturing of HTS technologies for widespread market application.

Sources: National Electric Delivery Technologies Roadmap, January 2004 3M Company, http://www.3m.com/market/industrial/mmc/accr/design_guide.jhtml “Composite Core Conductors Emerge to Boost Capacity,” National Rural Electric Cooperative Association, Cooperative Research Network, Technology Surveillance newsletter, November 2003.

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A4. MULTIPLE PHASED TRANSMISSION LINES Technology Readiness Multiple phased transmission lines are not currently available. There have been experiments with multi-phases but none are installed commercially. Technology Description •

Currently, three-phase transmission lines are used in our electricity infrastructure. Multiple phase transmission lines—six-phase and twelve-phase lines—could possibly provide a technology solution that increases the carrying capacity of existing lines without taking up more space, thus avoiding increased difficulties that come with siting higher-powered transmission lines. Researchers have experimented with designs of 462 kV six-phase and 462 kV and 312 kV twelvephase lines. The first six-phase test line was completed in 1983 with funding from DOE and New York State Energy Research and Development Authority (NYSERDA). The test line was an open circuit line, 1200 feet long and was used to measure voltage related environmental effects. High phase order (HPO) transmission lines can provide power transfers of equal magnitude to three-phase lines with less right-of-way requirement. Lower phase-ground voltage than three-phase systems.

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Cost and Performance Characteristics •

The most important cost saving factor is lack of necessity to site new rights-of-way for transmission line construction and operation. • 3,000 MW capacity multi-phased system (317 kV, 12 phase) costs about $1,000,000 per mile less than the ultra high voltage (UHV) alternative. • 6,000 MW capacity system (462 kV six and twelve phase) costs are about $500,000 less per mile than the UHV alternative. Characteristics of Multi-Phase Lines Number of Line kV Spacing Minimum Ground Thermal Line Capacity Phases Requirements Clearance (MW) 3 6 12 12

1200 462 462 317

78.7 feet 61.25 feet 71 feet 50 feet

15 feet 15 feet 10 feet

23,900 17,900 17,900 13,400

Market Applications • • •

Multi-phased lines can have the same voltage capacity as three-phase system with less rights-ofway requirements, and same electrical field, audible noise level, and orders of magnitude increase in transmission capacity. Requires smaller transmission structures (towers, etc). Reduces ground level electric and magnetic fields. Technology Goals

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Experimental verification of the predicted behavior of twelve-phase systems. Determine efficiency of widespread market applications.

Source: EHV High Phase Order Power Transmission, DOE/ET/29297-3, U.S. Department of Energy, September 1983

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A5. UNDERGROUND TRANSMISSION CABLES Technology Readiness Underground cables are commercially available and are installed where overhead transmission is impractical or unpopular. Undergrounding is more expensive than overhead transmission and decision makers tend to struggle over when and where to install underground cables and how to cover the costs of undergrounding, since burying the lines cannot always be justified by economic data alone. Technology Description The most common installed underground cables today are self-contained, fluid-filled cables, which carry the highest levels of power in AC and DC systems, and mass impregnated paper insulated cables, which cover the longest distances. Both technologies have intrinsic limitations: • Self-contained, fluid-filled cables are limited in distance by the oil feeding hydraulic system. • Mass impregnated paper insulated cables are limited in power by the electrical and thermal performances of kraft paper. The state-of-the-art technologies in underground cables today are fluid-filled polypropylene paper laminate (PPL) and extruded dielectric polyethylene (XLPE) cables. PPL cables are more commercially mature than XLPE cables, with improved performance and reduced electricity losses over traditional cables, but XLPE cables have several advantages over PPL cables: • Lower dielectric losses • Simpler maintenance • No insulating fluid to affect the environment in the event of system failure • Smaller insulation thickness Advanced underground cable technologies include gas-insulated transmission lines (GIL), which are still under research and are considered to hold promise for future applications. GILs have a relatively large diameter tubular conductor sized for the gas insulation surrounded by a solid metal sleeve, which provides lower resistive and capacitive losses, no external electromagnetic fields, good cooling properties, and reduced total life-cycle costs compared to other types of cables. However, the gas used to insulate the lines would be considered a greenhouse gas if it were to leak into the environment. Cost and Performance Characteristics New underground systems cost approximately $1 million per mile – more than 10 times the cost of installing overhead electricity lines. 1 One reason the cost of underground cables is higher than above-ground cables is because access for installation, repair, and replacement is more labor and resources intensive. Above-ground lines can be visually inspected, whereas underground lines require special equipment to locate the problem and repair it. Excavation (trenching or boring) and restoration costs of placing electrical transmission cables underground can approach 75% of total project costs. However, underground cables offer some benefits over above-ground cables that could be translated into cost savings: • • • • • •

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Protection from severe weather Fewer rights-of-way issues with siting and installation Reduced motor vehicle accidents Less economic harm as a result of fewer outages and increased property values Improved efficiency of electric system Trees do not have to be trimmed to avoid power lines

“Out of Sight, Out of Mind?,” Brad Johnson for the Edison Electric Institute, January 2004, page 5

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Market Applications Underground cables are used to transmit power in areas where overhead transmission is impractical or unpopular. Compared to above-ground lines, underground cables tend to have fewer power outages but outage duration tends to be longer. Underground lines are not immune to outages during storms, due to water seeping underground, particularly after heavy flooding. The potential reliability benefits from underground versus above ground cables are uncertain; thus, the economic benefits are not necessarily high enough to justify the cost. The most significant benefit of burying power lines is improved aesthetics, which is real and substantial to communities and individuals who want electric lines out of sight. Community and government decision makers tend to struggle over when and where to install underground cables and how to cover the costs of undergrounding, since burying the lines cannot always be justified by economic data alone. Technology Goals Research and development is focused on cutting the costs of undergrounding cables and improving the reliability of the installed lines. Cost control measures are being undertaken in cable design, construction, refurbishment, operation, and maintenance. Researchers, including the Electric Power Research Institute and Pirelli, are working to develop innovative diagnostic monitoring systems for cable life extension, operational tools to increase reliability, and improved designs for “self healing” cables. Industry is looking for cost reduction methods that use more standardized circuit ratings and cable sizes, selecting more optimal routes for installation, and reducing cross-section areas of excavation trenches. Since excavation and restoration account for the highest portion of installation costs, research into alternative burying methods is critical. Open cut trenching, the traditional method for installing underground cable, is not suitable for burying power lines in many urban and suburban areas. The underground environment is becoming more congested and deeper trenches are required to go under existing utility infrastructures. Researchers are developing innovative, trenchless construction methods that use boring from one point to another and then pulling the lines through the bore. Research is being done to improve horizontal boring methods so that issues with performance, equipment, and job specification and design can be resolved, and that the costs and reliability of this undergrounding method become more competitive. Sources: Pirelli (www.pirelli.com/en_42/cables_systems/energy/innovation/ppl1.jhtml) National Transmission Grid Study Issue Papers, May 2002, page F-34 “High Temperature Superconductivity: The Products and Their Benefits,” Oak Ridge National Laboratory, December 31, 2002 “Going Underground,” UtiliPoint IssueAlert, February 5, 2004 Electric Power Research Institute “Out of Sight, Out of Mind?,” Brad Johnson for the Edison Electric Institute, January 2004 “Underground Cable that Heals Itself,” NRECA Connections, October 2003

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A6. OTHER CABLE AND CONDUCTOR TECHNOLOGY Wireless Power Transmission Wireless power transmission, also known as power beaming, involves using a laser or microwave radiation to transmit electricity. Space applications are the nearest-term uses of wireless power transmission, and longer-term applications may be remote sites that are far away from the electric grid or separated from the grid by impassible terrain. Wireless transmission may even be used someday for aesthetic or economic reasons. Source: National Transmission Grid Study Issue Papers, page F-36 www.wirelesspowertransmission.com

Ultra-High Voltage Transmission Lines Ultra-high voltage lines (UHV) are over 1 MV (1000kV) and can carry more power than lower voltage lines, but require larger right-of-ways than lower voltage lines, which can lead to higher costs. UHV increases the need for reactive power reserves and requires larger, modified towers. Several issues have hindered the application of UHV lines in the United States including concerns about increased electro magnetic fields (EMFs) and increased rights-of-way. UHV lines are unlikely to have a large impact in the United States due to cost issues and public concern about possible safety issues pertaining to EMFs. 1000 MV lines are currently being used in Japan. Source: National Transmission Grid Study Issue Papers and the National Transmission Grid Study.

Ethernet Cables Ethernet cables, commonly used for data transmission, are beginning to be used to provide power. The cables are able to transmit only 13 watts, a standard set by the Institute of Electrical and Electronics Engineers in June 2003, which is enough electricity to power items such as telephones, security cameras, loudspeakers, and wireless network access points. Data and electricity can be transmitted using the same wires because they are at opposite ends of the frequency spectrum. A connected system of appliances attached to an Ethernet can be shut down at once instead of being turned off individually. Ethernet power is uniform, and has the potential to be a worldwide common standard for power. Research and development is being conducted to improve Ethernet cables so that they can transmit enough power to run a typical laptop computer. New standards, and possibly new computer hardware, would need to be developed for higher capacity Ethernet cables to power larger items. The added heat would require more resilient components and new safety standards. Source: “No Outlet? Don’t Worry, an Ethernet Cable May Do,” The New York Times, March 18, 2004

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B. INTELLIGENCE AND CONTROLS B1. Real-Time Monitoring B2. Distributed Intelligence B3. Communication Systems

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B1. REAL-TIME MONITORING Technology Readiness Real-time monitoring technologies are commercially available. These technologies including sensing devices that monitor individual devices as well as the entire systems and software technologies that integrate and analyze the data collected by the sensing devices to enable better control of the power grid. Emerging technologies include devices that can collect data over wide areas, software that offers improved visualization information, and systems that incorporate the information in to improved controls. Technology Description Real-time grid monitoring devices are key to help operators recognize, analyze, and respond to system anomalies and predict performance under various circumstances. Improved monitoring can help determine the limits in real time of individual system components and measure the state of the grid. Real-time monitoring includes several integrated hardware and software elements. Hardware Power System Device Sensors help determine the limitations of individual devices such as transmission lines, cables, transformers and circuit breakers. The limits of each of these devices are determined by the thermal characteristics. There is to develop improved sensors that dynamically determine the limits by directly or indirectly measuring temperature. • Conductor Sag Sensors can determine the line capacity by measuring the sag on the overhead transmission line. The conductor sag is the major limiting factor for overhead transmission lines. As the wires heat, they expand, and cause sag, which can eventually result in a short circuit due to arcing from the line to trees, poles, or whatever object may be underneath the wires. Conductor sag can be measured directly or indirectly, by estimating sag by measuring the conductor temperature with a device directly mounted on the line and/or a second device that measures the conductor tension at insulator supports. • Transformer Coil Temperature Monitors dynamically determine the transformer capacity. The transformer capacity is limited by thermal constraints. Transformer constraints are caused by localized hot spots on the windings that result in degradation of insulation. • Underground/Submarine Cable Monitoring/Diagnostics detects potentially hazardous situations for underground and submarine cables to support preventative maintenance, mitigate risk failure, and maximize the use of the transmission asset. Some of the sensing functions that are being incorporated in cable design include cable temperature, dynamic thermal rating calculations, partial discharge detection, moisture ingress, cable damage, and hydraulic condition. Direct System-State Sensors are used to quickly measure region-wide phenomena such as transient stability limitations, oscillatory stability limitations, an voltage stability limitations. The voltage magnitudes and angles at the system buses ultimately determine the system state. • Power-System Monitors collect essential signals from local monitors and forwards the appropriate data to the regional operator. Existing SCADA and Energy Management Systems provide low-speed data access for the utility’s infrastructure. A network of high-speed monitors will help verify system performance. Bonneville Power Administration (BPA) has developed a network of high-speed data collection with dynamic monitors- the power system analysis monitor (PSAM) and the portable power system monitor (PPSM). • Phasor Measurement Units (PMUs) are synchronized digital transducers that stream data in realtime to phasor data concentrator units. PMU networks have been deployed at several utilities across the country. They have their highest value in mission critical applications that involve wide area measurements.

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Software •

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Supervisory Control and Data Acquisition (SCADA) systems provide real time monitoring of the utility system status. SCADA systems include hardware and software components. The hardware gathers and feeds data into a computer that has SCADA software installed. The computer then processes these data and presents it in a timely manner. SCADA also records and logs all events and warns when conditions become hazardous by sounding alarms. Energy Management Systems The Synchronized Phasor Measurement Tools, which take data snapshots many times per second and display the data visually, allow grid operators to examine the exact shape of the 60cycle wave form—even noting transient phenomena that may have been missed by the current technology that uses 4-second intervals for a single snapshot. With this more accurate picture, operators can verify that their systems are operating within safe margins. This information is critical to supporting reliable regional and inter-regional electricity transfers, particularly in the Eastern Interconnection. The VAR-Voltage Management Tool provides a three-dimensional, geographically oriented, visual depiction of system voltage levels across an entire interconnection area and displays reactive reserve margins at critical grid locations. Since the same display also includes sensitivity calculations, distances from voltage collapse and remedial action options, operators and reliability coordinators can use a single tool to recognize warning signals, diagnose potential problems, and maneuver the system to safer operating regions before major reliability threats occur. The Area Control Error (ACE)-Frequency Real-Time Monitoring System creates a real-time visual display of the power grid using data generated every four seconds from more than 100 control areas in the United States, which is then made available to all 18 reliability coordinators in the Eastern and Western Interconnections. The data immediately lets the coordinators know when an area is out of compliance with the North American Electric Reliability Council (NERC) rules, which are designed to ensure the reliable supply of electricity. Frequency and load flow abnormalities allow operators to quickly identify the control areas where the violation occurred in time to address the situation and ward off an unplanned outage. Wide Area Measurement System (WAMS) is a smart, automatic network that applies real-time measurements in intelligent, automatic control systems to operate a reliable, efficient, and secure electric transmission infrastructure. Cost and Performance Characteristics

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Traditional SCADA systems (non-web based) cost anywhere from $100,000 to couple of millions. Market Applications

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Real-time monitoring can be used for measuring conductor sag, coil temperature, and grid management. WAMS is in place in the West, where it continuously monitors grid performance across the power system. It provides operators with high-quality data and analysis tools to detect impending grid emergencies or to mitigate grid outages. Technology Goals • •

In the future, WAMS will monitor the grid parameters in real time, facilitate calculating location marginal prices in real time to support market designs, and assist in providing customer transparency. There are further needs for improved sensors, advanced visualization tools, wide area measurement tools, and advanced controls that apply real-time monitoring. EPRI is working on a Fast Simulation Model (FSM) that will be able to visually show thermal, voltage, and transient stability problems faster than real time.

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Sources: “Web-Based SCADA Offers Co-ops New Alternative”, National Rural Electric Cooperative Association, Cooperative Research Network, Technology Surveillance newsletter, First Quarter, 2003. “Opening the AMR Cash Register”, Energy Customer Management, A Supplement to Public Utilities Fortnightly, Spring 2003 Office of Electric Transmission and Distribution Website “Advanced Transmission Technologies”, National Transmission Grid Study Issue Papers, May 2002.

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B2. DISTRIBUTED INTELLIGENCE Technology Readiness Technology Description Distributed intelligent systems are multiple entities (such as agents or robots) that integrate perception, reasoning, and action to perform cooperative tasks under circumstances that are insufficiently known in advance, and dynamically changing during task execution. • Low-cost physical sensors will be used to measure voltage, current, temperature, phase angle, and will have other electric distribution and grid system characterization applications. • The system architecture will be dependent on the ability of intelligent agents to diagnose and forecast local faults. This will involve placing a number of sensors, intelligent agents, and controllers at strategic locations. • The sensing, communication, and information analysis required for intelligent decision making must happen in real time or near real time (in seconds), sufficiently faster than the time required to affect coordination, control, and protection schemes. • Communications must take place to advise the central controller of the local system status, perform critical nonrepudiating functions to manage the electricity commerce, and enable real-time markets for energy and ancillary services. • A Grid-Friendly appliance controller, based on the gate array chip, is being developed to monitor the power grid while controlling on-off operations of household appliances (refrigerators, air conditioners, water heaters, etc.) in response to power grid overload. Cost and Performance Characteristics •

Current cost for the grid friendly appliance is $15 for 100; when manufactured in higher quantities, costs are expected to drop to about $5-10/unit or lower. Market Applications

• •

The Grid friendly appliance device developed by Pacific Northwest National Laboratory (PNL) has been tested in a laboratory environment and is ready for installation in the next generation of appliances. A wireless end-device controller is being installed at more than 200 facilities in southwest Connecticut, with the goal of controlling 2-3 megawatts of electricity on a real-time, dispatchable basis. The controller collects real-time, energy-use information and controls end-use loads (lighting, vending machines, etc.) to manage system peak demand.

Intelligent neighborhood controller modules are being developed to demonstrate a smart, technologically sophisticated, but simple, efficient, and economical solution for aggregating a community of small distributed generators into a virtual single large generator capable of selling power or other services to a utility, Independent System Operator, or other entity, in a coordinated manner. Technology Goals Prototype sensors and communication systems, as well as assessment methods for the intelligent agents, are needed to demonstrate robust and reliable energy management software. Sources: U.S. Climate Change Technology Program – Technology Options for the Near and Long Term, November 2003 Pacific Northwest National Laboratory

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B3. COMMUNICATIONS SYSTEMS Technology Readiness Powerline carriers are commercially available and broadband over powerlines is currently being developed and field tested. Technology Description Communication systems can consist of powerline carriers (PLC), which includes broadband over powerline (BPL), and fiber optics. PLC transmits high-speed data communications, such as internet traffic, home device monitoring, and alarm devices, by high-frequency radio waves over a shared electrical power distribution network. • PLC superimposes a telecommunications signal on a utility’s distribution lines. • Powerline adaptors at substations take data that is sent over the internet and convert it to frequencies that can be transmitted over the distribution lines. Power-socket modems split the data from the electricity so that the two do not interfere with each other and disturb the connection. • The distribution transformer blocks the powerline networking signal from crossing the main power grid, but does little to stop a signal in one of the homes that the transformer powers from propagating to another home using the same transformer. • Fiber optic cable can be installed along existing rights-of-way. There are two types of optical fiber, multimode and singlemode, that are currently used in data networking and telecommunications applications. Cost and Performance Characteristics • Throughput data rates have been achieved 18.8 Mb/s over a distance of 0.2 miles on overhead medium voltage lines and data rates of 15 Mb/s over 1000 ft on underground medium voltage lines. • The table below shows performance of three automated meter reading (AMR) systems using PLC technology: End Point Information and Control (EPIC), Two-Way Automatic Communication System (TWACS), and Electronic Metering and Control System (EMETCON). AMR Systems Using PLC EPIC Transmission Medium

TWACS

Power Line Communication

Power Line Communication

EMETCON Power Line Communication

Performance End Point Response Time

15 minutes

9 sec

6 sec

Age of Data

24 h

9 sec

5 sec

Resistance to Power Line N/A Disturbance

Re-acquire data after a delay of 9 seconds

Rerecord data after a delay of 6 seconds

System Integrity

30 Days of Data Retrieval

24 Hours of Data Retrieval

24 Hours of Data Retrieval

Throughput

9,000 meter reads per day per 16,000 hourly interval reads substation bus per substation bus

600 hourly meter reads per substation bus

Access to Solid State Meter

No

Direct Register Read

Direct Register Read

Data Storage

Host Server, 30 days at Substation

Server and 24 hours of data in end point

Server and 24 hours of data in end point

Modulation Technique

Frequency Division Multiple Access

Channel and Time Division Multiplexing

Coherent Phase Shift Keying

Ultra Narrow Band

Power Frequency Modulation

Carrier Frequency (9 kHz, 12.5 kHz)

Signal Frequency

Source: Bi-directional PLC AMR: A Market Snapshot, National Rural Electric Cooperative Association, Cooperative Research Network, Technology Surveillance newsletter, March 2003.

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• • • • •

• •

•

Market Applications Because utilities are connected with every home and building in their network, they can easily reach their customers at a low cost to offer them value-added services. PLCs can provide utilities with automatic meter reading and energy-saving services such as power quality monitoring, substation to substation communication, outage reporting, peak shaving, and theft protection. Two-way PLC systems can run programs for time–of-use, real-time pricing, and demand metering. PLCs can enable home networking. Data can be transmitted throughout different areas of the home using the electrical wiring, instead of installing new cables. Rural electric cooperatives offer internet service to their customers and BPL offers another technology for them to competitively provide internet service to their area. Technology Goals BPL technology is currently being tested in many areas. PLC performance varies with frequency. Frequency variations may be caused by switching power supplies or plugging a device into a power line. In addition to dealing with a transfer function problem, PLC faces interference problems. Interference sources can range from brush motors, such as those in vacuum cleaners or hair dryers, dimmer switches, lamps, and amateur band radio transmitters. The interference results in bit error in the data bits. Circuit breakers can have substantial attenuation. In home networking many homes only have a physical connection to other circuits via the circuit breaker that can create 20 dB of loss at frequencies below 1 MHz.

Source: Bi-directional PLC AMR: A Market Snapshot, National Rural Electric Cooperative Association, Cooperative Research Network, Technology Surveillance newsletter, March 2003. HomePlug Standard Brings Networking Home, www.commdesign.com, December 2000. Powerline Communications, www.plcform.org

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C. MODULAR EQUIPMENT C1. Superconducting Transformers C2. Superconducting Fault Current Limiters C3. Power Electronics C4. High-Performance Ceramics C5. Flexible Alternating Current Transmission Systems (FACTS) C6. Superconducting Synchronous Condensers

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C1. SUPERCONDUCTING TRANSFORMERS Technology Readiness High temperature superconducting (HTS) transformers are not commercially available. High-capacity (30 MVA and higher), compact HTS transformers are expected to be available in 2007. Technology Description • • • • • • • • •

•

Transformers lower or raise system voltages in order to transport electricity more efficiently. Electricity generally passes through at least three transformers before reaching the end consumer. A transformer is composed of two conductor coils, or “windings,” wound around a magnetic core. Via electromagnetic induction, current flows into the primary coil and out of the secondary coil. Ideally, the input power equals the output power, resulting in lossless voltage transformation; however, since the coils in conventional transformers are made of copper wire, resistance in the wire causes a one to two percent loss of energy. HTS transformer coils, made of HTS wire, incur substantially less resistance loss, bringing the efficiency rate of the transformer closer to its theoretical potential (100%). The copper or aluminum conductors of conventional transformers are replaced by an HTS conductor incorporated into a HTS transformer coil design. There are eddy and AC losses in the windings that require refrigeration power. The HTS coils will be operated at liquid nitrogen temperature (77oK, or -196oC). These losses are small compared to losses due to resistive heating in conventional transformer windings. HTS transformers offer the possibility of operating with low losses and at 10 to 30 times greater current density than conventional transformers. The windings are electrically insulated with dielectric material, which is designed to meet ANSI standard dielectric tests for system voltages and the associated basic impulse insulation test levels. Additionally, HTS transformers can develop greater flux densities and magnetic fields within a smaller coil, which also increases device efficiency per unit volume. Conventional transformers are extremely heavy because of the magnetic core, copper winding, and insulting/cooling oil. HTS transformers will be lighter and will require no oil. Cost and Performance Characteristics

•

• •

•

HTS transformers have potential advantages over conventional transformers in the following areas: − about 30% reduction in total losses − about 45% lower weight − about 20% reduction in total cost of ownership These advantages are based on a 100 MVA transformer with HTS wire providing a critical current density of 10 kA/cm2 and AC losses of 0.25 mW/A-m in a parallel field of 0.1 tesla. Additional benefits include: − two times the overload rating capability for extended periods without insulation damage or loss of lifetime − unprecedented fault current limiting functionality, which is expected to protect and reduce the cost of utility system components − reduced operating impedance, which will improve network voltage regulation In addition to greater efficiency than conventional transformers, HTS transformers eliminate oil cooling, thus reducing fire and environmental hazards associated with oil-based systems. These benefits enable HTS transformers to have higher power densities so they will be lighter and more compact allowing them to be sited in high-density urban areas and inside buildings.

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HTS Transformers Cost and Performance Characteristics Connection Primary/Secondary Voltage Primary/Secondary BIL Primary/Secondary Current Overload Ratings 3-Day Power Outage Handling Cooling System Instrumentation Cost per unit1

5/10 MVA 3-Phase 24.9 kV/4.2 kV 150 V/50 kV 67 A/694 A 2-sec 10X, 48-hr 2X Backup Motor/Generator Cryocoolers Local Demonstration Project2: $8.84 million

30/60/MVA 3-Phase 138 kV/13.8 kV 550 kV/110 kV 72 A/1255A 2-sec 10X, 48-hr 2X Backup Motor/Generator Cryocoolers Remote $750,000

1 The present price of a conventional 30 MVA transformer is about $500,000. Waukesha believes that early market entry at $750,000 for a HTS transformer is commercially viable. Initial HTS transformers are expected to cost 30% higher with ownership costs 10% higher than conventional units. Lower cost HTS transformers will become available at comparable first cost and 10-20% lower total ownership costs than conventional units as cost and performance targets for HTS wire and cryogenic systems are reached. The cost of the superconductor is assumed to be 10% of the total cost of the transformer. 2 Demonstration project includes design, build, and test 1 MVA prototype and 5/10 MVA prototype. Cost includes 50% cost share DOE and industry.

Market Applications • • • • •

One-half of all U.S. power transformer sales will be in the class of 30 MVA, 138-kV/18.8-kV transformer rating for the next two decades. It is envisioned that HTS transformers will primarily be used at substations within the electric utility grid. The first applications for HTS transformers are in urban and other substations that are space constrained yet need to increase capacity. Super-efficient, quiet, lightweight, compact, and oil-free HTS transformers can be used where transformers previously could not be sited, such as in high-density urban areas or inside buildings. An alpha prototype 5/10 MVA HTS transformer has been built by Waukesha Electric. This prototype will demonstrate the technical and economic feasibility of 30/60 MVA and larger HTS transformers. The 30/60 MVA transformer represents the largest target market. Technology Goals

HTS transformer product design and demonstration will focus on the following targets: • Demonstrate 5/10 MVA HTS transformer in the Wisconsin electricity grid, 2004. • High-capacity (30 MVA and higher) HTS transformers to be available in 2007. • Improve designs anticipating better HTS conductors and better insulation to allow higher power and higher voltage in same frame size: − 2004: 24.9 kV, 10 MVA − 2007: 138 kV, 50 MVA − 2010: 345 kV, 340 MVA • Improve designs anticipating better cryogenics to provide enhanced performance and reliability. Sources: High Temperature Superconducting Electric Power Products Modernizing the Existing Electricity Infrastructure, DOE High Temperature Superconductivity: The Products and Their Benefits, Oak Ridge National Laboratory DOE Superconductivity Program Website

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C2. SUPERCONDUCTING FAULT CURRENT LIMITERS Technology Readiness Superconducting fault current limiters (FCLs) are not commercially available. Field tests are ongoing and DOE plans to cost share with industry the design, fabrication, and testing of a 138 kV high temperature superconducting (HTS) FCL beta prototype in a transmission system by 2006. Technology Description A current limiter protects against sudden momentary surges of current that can destroy expensive utility equipment and cause power outages. For instance, if lightning sends an uncontrollable surge of power through the utility grid that is beyond its capacity, a circuit will be tripped, as a preventive measure, causing a power outage. Utilities have traditionally relied on more expensive transformers, currentlimiting reactors or single-use fuses to deal with this problem. Fault current limiters (FCLs) provide a more advanced option to help deal with these electrical disturbances. • Strategically placed in the utility grid, these devices can effectively limit current spikes that are experienced by circuit breakers allowing utilities to increase systems loads, reliability, and power quality without upgrading these circuit breakers. • HTS materials are perfectly suited to this role because they are natural FCLs, being able to quickly change from a zero to a high impedance state. • HTS current controllers have the ability to detect power surges and redirect them to HTS coils that can then safely absorb the excess energy without tripping the circuit breakers or causing an outage. • A number of FCL concepts have been proposed. FCL designs typically fall into one of three generic categories: resistive, inductive, and hybrid (including bridge FCL with power electronics). The resistive class of FCLs is the least complex and the most viable using HTS conductors. • The HTS FCL allows enhanced operating capacity of utility systems. Conventional copper-based current limiters (i.e., line reactors) can cause voltage instability in the electrical system by adding reactance (a resistance to the flow of current) to the system. This forces the utility to add expensive capacitance to the system to counter-balance the reactive element. No capacitive correction is needed with HTS FCL devices, since it has no reactance and is passive during non-fault conditions. Cost and Performance Characteristics • • • • •

•

Utilities can reduce or eliminate the cost of upgrading circuit breakers and fuses by installing HTS current limiters. Fault current levels on a typical transformer can be as high as 10 to 20 times the steady state current. One conventional solution to limiting fault current is the use of higher rated circuit breakers and power fuses. Large capital costs are incurred not only to upgrade the circuit breaker, but also the entire substation buswork. By design, the superconducting current controller will limit fault current to 3 to 5 times the amount of steady state current, reduce standby energy losses, protect and extend the life of transformers and associated utility equipment, and provide improved flexibility in the use of existing lower-rated circuit breakers and fuses. An ideal HTS FCL would have zero impedance throughout normal operation; provide sufficiently large impedance under fault conditions; provide rapid detection and initiation of limiting action (within less than one cycle, or 16 ms (16/1000 s)); provide immediate (within a half-cycle, or 8 ms) recovery to normal operation after the clearing of a fault; be capable of addressing two faults within a period of 15 s; and be compact, lightweight, inexpensive, fully automatic, and highly reliable with a long lifetime.

Since FCLs represent a new class of equipment, no specific cost data are available. To be commercially feasible FCLs must be economically competitive with conventional solutions such as upgrading or replacing circuit breakers, building new substations, or bus splitting. HTS FCL design specifications for each major market application are shown in the following table. Energetics, Incorporated

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Superconducting FCL Performance Characteristics

Bus Tie Application Basic

Feeder Breaker Applications

Power Quality

Basic

Underground

Industrial

Transformer Applications Basic

Underground

Steady-State Current (kA)

0.6-1.2

0.6

0.6

0.6

1.2

2.5

1

Fault Current (kV)

1.8-5.0

1.8

3

3

<20

7.5

3

Hold time (msec)

100

100

400

400

400

600

100

Re-closing Requirement

No

No

Yes

No

No

Yes

Yes

Instant Recovery

No

No

Yes

No

No

Yes

No

Source: American Superconductor Corporation

•

•

Key parameters affecting the FCL design are: − Steady-state current, − Limiting current during a fault, − Fault duration (hold-time), and − Re-closing of the circuit immediately after a fault is cleared (instant recovery). It is difficult to satisfy all of these requirements in a given device. Market Applications

HTS FCLs have applications throughout the electric transmission and distribution system. HTS FCL applications include: • Generator protection that simplifies interconnection of new generation sources. • Bus tie that maintains tie to maximum flexibility. • Line protection, which allows users to avoid upgrade to more expensive line breakers (circuit breakers reaching 80 kA upper limit). • Transformer protection (some HTS experts suggest that HTS FCLs and HTS transformers may well be sold together or in an integrated design because of the inherent benefits of this configuration) • Feeder protection. • Closing open loop. • In-rush current controller for self-start induction and synchronous motors. Technology Goals The anticipated progress in demonstrating a transmission level (138 kV) HTS FCL is: • By 2004, build a scaled pre-prototype HTS FCL (8 kV, 800 Arms, single phase) and conduct nongrid connected tests. • By 2005, build and demonstrate a 138 kV HTS FCL alpha prototype. • By 2006, design, fabricate, and test a 138 kV HTS FCL beta prototype in a transmission system. Sources: High Temperature Superconducting Electric Power Products Modernizing the Existing Electricity Infrastructure, DOE High Temperature Superconductivity: The Products and Their Benefits, ORNL DOE Superconductivity Program Website

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C3. POWER ELECTRONICS Technology Readiness Power electronics have been commercial for several decades; however, they remain very expensive when used in newer applications such as Flexible AC Transmission Systems. Technology Description Power electronics are fast silicon semiconductor switches that can withstand low to medium voltages and high currents. Power electronics are essential in the electricity world as they help transform DC power to AC power and allow dynamic voltage control. They are used in inverters, rectifiers, power conditioning systems, and Flexible AC Transmission Systems (FACTS). (FACTS are discussed in greater detail in section C5). Cost and Performance Characteristics Market Applications • • • • • •

•

Power electronics have several market applications as displayed in the table below. Power electronics in inverters and rectifiers can convert high frequency AC electricity from flywheels and microturbines to 60 hz electricity that can be used in the electric grid and distributed generation. They are the advanced electronics that allow switching power AC to DC or vice versa at multiple locations in the electric system. They are also used in fault current limiters needed to control fault current levels on utility distribution and transmission networks. The fault current limiters can operate effectively without adding impedance to electric circuits during normal operations. Static VAR compensators, built partially with power electronics, can be used in several ways: − To control the switching of capacitors and reactors − To control voltage fluctuations − To mitigate the effect of switching in conventional capacitor and reactors and dynamically control reactive power flow in electric systems. The latest use of power electronics resides in the design of FACTS. FACTS systems allow dynamic voltage support and control of inter line power flows in the electric grid. Power Electronics Applications

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Technology Goals •

R&D efforts are focused on developing lower cost and more reliable power electronics to achieve more safety and simplicity during the interconnection process of distributed generation. Key Technical Challenges

Top Priority R&D Needs

• Lowering the cost of manufacturing and installing power electronic devices • Improving the efficiency, durability, and current handling capacity • Finding better materials for improving performance and lowering costs • Decreasing the cost and increasing the efficiency and reliability of distributed energy resources

• Develop power electronics devices for integrating distributed energy resources into grid operations for safe two way power flows • Develop power electronics devices for distribution system operations including switches, transformers, and power conditioning • Develop power electronics devices for transmissions system operations including switchgear, fault current limiters, and static VAR compensators • Develop advanced materials for power electronics devices to increase durability, efficiency, and reliability and to lower costs • Develop distributed energy devices and combined heat and power systems for customer and utility applications

• Diamond based power electronic devices offer tremendous promise. They would have a very small footprint and would be lossless in the off state. Source: National Electric Delivery Technologies Roadmap, Office of Electric Transmission and Distribution, January 2004

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C4. HIGH-PERFORMANCE CERAMICS (E.G., CONNECTORS, INSULATORS) Technology Readiness Ceramic electrical insulators have had a large impact on society. They were first invented in 1860 to ignite fuel for internal combustion engines and are still being used for this purpose today. High voltage insulators make it possible to safely carry electricity to houses and businesses. Technology Description The term ceramic is used to describe a broad range of materials that include glass, enamel, concrete, cement, pottery, brick, porcelain, and chinaware. Ceramics can be either crystalline or glass-like. They can be either pure, single-phase materials or mixtures of two or more discrete substances. Most ceramics are polycrystalline materials, with abrupt changes in crystal orientation or composition across each grain in the structure. • Ceramics have a wide range of electrical properties including insulating, semi-conducting, superconducting, piezoelectric, and magnetic. • Ceramic spark plugs are electrical insulators. They were first invented in 1860 to ignite fuel for internal combustion engines, and are still being used for this purpose today. • High voltage insulators make it possible to safely carry electricity to houses and businesses. Alumina Today’s high-performance electrical insulators are often made from high-purity alumina, which maintains its insulating properties at temperatures and voltages that would break down porcelain. • Alumina is the most versatile engineered ceramic because of its high temperature service limit and its chemical, electrical, and mechanical properties. • It is relatively low-cost and is easily formed and finished using a number of fabrication methods. • Alumina tubes are highly impermeable to gases, a necessity for electrical feed-through lines in instruments that require high-vacuum systems. •

High Voltage Transmission Lines Transmission lines with higher system-voltage carry greater power flow. These lines serve the role of trunk feeder in the delivery of power. Instability in line operation can cause a negative impact on the entire power system. Thus, insulators for these transmission lines require not only endurance against higher electrical and mechanical stress, but must also uniformly ensure high quality to maintain the reliability of system operation. Cost and Performance Characteristics

Source: Advanced Ceramics Technology Roadmap, December 2000, www.advancedceramics.org/ceramics_roadmap.pdf

Level of increases in the key structural characteristics of strength, toughness, and Weibull Energetics, Incorporated

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Modulus (measurement of the uniformity of strength).

Source: DOE/ORO 2076: Opportunities for Advanced Ceramics to Meet the Needs of the Industries of the Future, December 1998, http://www.ms.ornl.gov/programs/energyeff/cfcc/doe2076.htm

Market Applications •

•

•

NGK Insulators, Ltd., Nagoya, Japan, manufactures a variety of insulators for large-capacity transmission lines, which are subject to severe operating conditions, such as heavy contamination and earthquakes. Insulator contamination is a concern for many utilities. The contamination is typically caused by super cooled drops and/or droplets from fog, drizzle, or rain (salt water is particularly damaging). NGK’s bushing shell for 1,000-kV ultrahigh voltage (UHV) transmission systems is the world’s largest porcelain product, with a height of 11.5 meters (~38 feet) and a maximum diameter of 1.6 meters (~5 feet). These insulators have been distributed throughout the world. According to NGK, successful long-term service experience in higher system voltage illustrates the reliability and quality of these insulators. NGK has also developed products such as transmission line arresters and insulator washing equipment which prevents reduction of insulator performance caused by contamination. These products contribute to the reliability of power supply. Technology Goals

•

NGK Insulators, Ltd., Nagoya, Japan, has been developing new technologies for transmission lines and substations. Their High Voltage Laboratory is equipped with world's largest-level UHV research facilities.

Sources: The American Ceramics Society, www.ceramics.org Purdue University chemistry department web site, www.purdue.edu Today’s Chemist at Work, May 2002 issue. NGK Insulators, Ltd., http://www.ngk.co.jp/english/index.html

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C5. FLEXIBLE ALTERNATING-CURRENT TRANSMISSION SYSTEMS (FACTS) Technology Readiness After more than 20 years of R&D, some FACTS devices are now entering utility service. Others are still in various stages of development. The Static VAR Compensator, for example, is an example of a FACTS technology that is already well-established. Technology Description The term “Flexible Alternating-Current Transmission Systems” or “FACTS” describes a variety of power electronic devices used to improve control and stability of the transmission grid. As electricity travels through the system, many transmission lines become overloaded, while others are underutilized. FACTS devices can be used to alleviate this problem. • The technology consists of high power semiconductors configured in a three phase inverter. • Voltage is then injected into the transmission system to control the flow of power on a given transmission line. By combining high-voltage, high-current electronic devices with communication links and automatic controllers, FACTS devices enable electrical power transmission circuits to operate at a level that is closer to the thermal limit of the transmission wire. Thus, the strain on overused transmission wires is reduced and capacity on underused lines is increased. • Because FACTS devices respond quickly and precisely, power can be added to the line very quickly, and, thus, the transmission system becomes more stable and reliable in a way that offers a power supplier much flexibility. • A supplier could load a line up near its thermal limit when necessary, and reduce the amount of power on the line when such generation is not needed. • The supplier can also relocate power within the system to meet increased demand in different sectors of the service area. FACTS devices may also allow for alternative energy sources to be connected to the existing transmission network without installing additional transmission lines to accommodate the new sources. Examples of FACTS devices include: • Static VAR compensators, which provide a dynamic source of reactive power; • Thyristor-controlled series capacitors, which provide variable transmission-line compensation (thus “shortening” the line length and reducing stability problems); • Synchronous static compensators, which provide a dynamic source of reactive power; and • Universal power-flow controllers, which control both real- and reactive-power flows. Cost and Performance Characteristics FACTS technology is still not entirely mature even though it is based on concepts that are two decades old. As has been the case with several other promising technologies, FACTS has not been utilized by the electricity industry at the rate that it should, based on its apparent technical merits. • Many utilities believe that FACTS devices are not cost effective because of their high installation price; traditional, passive AC devices are perceived to have a cost advantage. • FACTS devices are attractive, they are not well understood, and operating experience with other innovative technologies suggests that use of new control devices may result in significant and unforeseen interactions with other equipment, which could be costly. • FACTS devices generally require the support of a wide-area measurement system (WAMS), which currently exists only as a prototype. • Without a WAMS, a FACTS or any major control system technology cannot be adjusted to deliver its full value and, in extreme cases, may interact adversely with other equipment. • FACTS technology can provide transmission “muscle” but not necessarily the “intelligence” for applying it. A recent WAMS/FACTS installation in Brazil links two regional systems with an AC line plus two Thyristor-Controlled Series Capacitor units. Prior to this, a DC line would have been the inevitable and more expensive choice. Energetics, Incorporated

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The technical and economic benefits of FACTS devices must be compared with those of conventional facilities on a case-by-case basis to determine if FACTS would be a viable alternative. Specially-trained technicians are needed to fully understand the coordinated control strategy of these devices as they penetrate the system. At the 20 MW power level, estimated costs range from $250/kW to $450/kW. The chief impediment to practical deployment is the initial investment required. Market Applications After more than 20 years of R&D, some FACTS devices are now entering utility service. Others are still in various stages of development. The Static VAR Compensator, for example, is an example of a FACTS technology that is already well-established. • The New York Power Authority (NYPA) developed, built, and is currently testing a Siemens FACTS device at their Marcy Substation. The $48 million project was initiated in 1999 and consists of a Convertible Static Compensator, currently operating at the Frederick R. Clark Energy Center. The installation has resulted in a 60-percent increase in the amount of power that can be released over the Center’s transmission lines. • American Electric Power has also implemented a Siemens FACTS system located at the Inez Substation in Kentucky. Installed in 1998, the system is the world's largest inverter. The system has proven to be effective at regulating voltage and is also capable of controlling power flow. • In November 2003, Pacific Gas & Electric awarded a $12 million contract to ABB to install FACTS technology to supplement its electric transmission network in San Francisco, California. The FACTS installation will be located adjacent to a generation plant in San Francisco. Once in service, PG&E will be able to retire the old generators. The project is scheduled for completion in November 2004. Additional applications: The idea of combining FACTS technology with energy storage systems (such as battery storage or superconducting magnetic energy storage) is currently being researched since short-term energy storage can aid in power flow control. Recent work shows that even a small amount of storage can significantly enhance the performance of some FACTS devices. • FACTS devices may allow for alternative energy sources to be connected to the existing transmission network without installing additional transmission lines to accommodate the new sources. •

Technology Goals The major challenge is to reduce the cost of FACTS systems to achieve widespread use. New power electronics advances are needed to lower the costs of these systems and accelerate their application on the network. New semiconductor materials (such as silicon carbide, gallium nitride, and thin-film diamond) could dramatically lower the cost of FACTS devices by providing the basis for developing a power electronic equivalent of the integrated circuit. Sources: Utility Automation & Engineering T&D, November 2003. “Advanced Transmission Technologies” issue paper, National Transmission Grid Study, U.S. Department of Energy, May 2002. Energy Info Source’s Transmission Insight newsletter, “Tech Brief: Flexible AC Transmission Systems,” Vol 1, Issue 3, June 2002. “Transmission Planning And The Need For New Capacity,” Eric Hirst and Brendan Kirby, Consulting in Electric-Industry Restructuring, Oak Ridge, Tennessee 37830, December 2001, Prepared for National Transmission Grid Study, U.S. Department of Energy. Electric Power Research Institute (EPRI) Electricity Technology Roadmap, July 1999.

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C6. SUPERCONDUCTING SYNCHRONOUS CONDENSERS Technology Readiness Superconducting synchronous condensers are currently being field tested by the Tennessee Valley Authority (TVA). TVA is testing American Superconductor Corporation’s SuperVAR™ Dynamic Superconducting Condenser (DSC) 8 MVAR prototype unit and has plans to conduct tests on five 10 MVAR production units. Technology Description • •

• • •

Synchronous condensers are generally employed to improve system stability and to maintain voltages within desired limits under varying load conditions and contingencies. Synchronous condensers can provide both inductive and capacitive VARs to maintain voltage levels under varying load conditions. They are capable of generating or absorbing reactive power (MVARs) at various locations on the power grid. DSCs are capable of continuous steady-state as well as dynamic reactive compensation while having multiples of their rated output in reserve for transient events. Synchronous condensers can incorporate high-temperature superconducting (HTS) wires that result in more effective and efficient operation than conventional machines. HTS synchronous condensers can help stabilize grid voltages, increase service reliability, and maximize transmission capacity. The standard synchronous condenser uses power-dense rotor coils made of HTS wires. The HTS rotor enables the condensers to provide up to eight times their rated capacity for short periods and do not have the typical high rotor maintenance costs. HTS DSCs do not experience thermal fatigue of the field coils as the VAR output changes from zeroload to full-load. Cost and Performance

• •

The American Superconductor SuperVAR DSC has a footprint of 6 ft wide by 12 ft long by 6 ft tall and weighs 20,000 lbs. The DSC requires about 50 kW of auxiliary power and suitable dry type transformer to interface with a 13.8 kV station bus. HTS synchronous condensers have lower standby losses, higher output, lower cost, and higher reliability than conventional synchronous condensers. Specifications of the SuperVAR Synchronous Condenser

Market Applications • •

•

DSC synchronous condensers can be used for peaking as well as base load applications without loss of life due to frequent load changes. HTS synchronous condensers can be used to alleviate voltage problems for: • reactive compensation in transmission and distribution systems • steady state voltage regulation for long radial delivery systems • dynamic power factor correction in large industrial sites • flicker mitigation for sensitive power quality in steel mills, electric arc furnaces, etc. The first SuperVAR synchronous condenser is being used by the Tennessee Valley Authority (TVA) to alleviate voltage flicker at a steel mill in Gallatin, Tennessee.

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Technology Goals Sources: American Superconductor Corporation, AMSC “Superconducting Dynamic Synchronous Condenser for Improved Grid Voltage Support”, Published in Proceedings of IEEE T&D Conference, Dallas, TX, September 2003 “A Synchronous Machine Using High Temperature Superconducting Wire to Mitigate Voltage Flicker”, Michael R. Ingram, P.E., Tennessee Valley Authority.

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D. ENERGY STORAGE D1. Batteries D2. Flywheels D3. Compressed Air Energy Storage D4. Pumped Hydro Energy Storage D5. Superconducting Magnetic Energy Storage D6. Other Energy Storage Technology

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D1. BATTERIES Technology Readiness Lead acid batteries are the most common energy storage technology for stationary and mobile applications. Other batteries that are currently being developed and not yet widely available are lithium-ion, lithium polymer, nickel metal hydride, zinc-air, zinc-bromine, sodium sulfur, and sodium bromide. Technology Description Batteries represent the first energy storage invented since the nineteenth century. They all store and release electricity through the same electrochemical process. Batteries have electrode plates, made of chemically reactive materials, that are placed in an electrolyte. Electricity flows in the battery through the transfer of ions from one electroplate to another. The negative electrode gives up electrons, which migrate to the positive electrode, during the discharge cycle. The flow of electrons results in electricity that can be supplied to any load connected to the battery. The process is reversed during charging. Batteries produce and store DC power only, so they need inverters to be tied into the electric grid. •

•

•

•

•

The most mature battery systems are based on lead acid technology. There are two major kinds of lead acid batteries: flooded lead acid batteries and valve-regulated-lead-acid (VRLA) batteries. Flooded lead acid batteries were invented first and have the following disadvantages: the need for periodic addition of water, and the need for adequate ventilation because they release hydrogen gas when charging. VRLA batteries are sealed batteries fitted with pressure release valves. They are considered low-maintenance batteries because they do not require periodic adding of water, unlike flooded batteries. They have a smaller footprint than flooded lead acid batteries as they can be stacked horizontally as well as vertically. They are more expensive than flooded batteries and more sensitive to the charging cycle used. They often display reduced battery life and performance when exposed to high temperatures. There are several rechargeable, advanced batteries under development for stationary and mobile applications, including lithium-ion, lithium polymer, nickel metal hydride, zinc-air, zinc-bromine, sodium sulfur and sodium bromide. These advanced batteries promise several advantages over lead acid batteries in terms of cost, energy density, footprint, lifetime, operating characteristics, reduced maintenance, and improved performance. The zinc-bromine battery consists of a zinc positive electrode and a bromine negative electrode separated by a microporous separator. An aqueous solution of zinc/bromide is circulated through the two compartments of the cell from two separate reservoirs. Zinc-bromine batteries are currently being demonstrated in a number of hybrid installations, with microturbines and diesel generators. Sodium bromide/sodium bromine batteries are similar to zinc-bromine batteries in function and are under development for large scale, utility applications. These flow battery technologies have the following advantages: low cost, modularity, scalability, transportability, low weight, flexible operation, and easily recyclable components. Their major disadvantages are that they offer relatively low cycle efficiency. Other advanced batteries include the lithium-ion, lithium-polymer and sodium sulfur batteries. Lithium batteries have specific energies four times higher that those of lead acid batteries. Sodium sulfur batteries operate at high temperature and are being tested for utility load leveling applications. Cost and Performance Characteristics

•

•

•

Energy storage systems for large-scale power quality applications (~10 MW) are economically viable now– with very strong sales from several manufacturers such as East Penn, Exide, GNB, Enersys, Yuasa, CND and Fiamm between 2000 and 2001. Lead acid battery annual sales have tripled between 1993 and 2000. The relative importance of battery sales for switchgear and UPS applications has shrunk during this period from 45% to 26% of annual sales by 2000. VRLA and flooded battery sales were $534 and $171 million, respectively, in 2000. Sales for lead acid batteries have dropped recently with the collapse of battery demands from the telecommunications industry in 2001. There was significant growth in sales in 2000, due to the demand from communications firms and investments in production and marketing. Many manufacturers have been subject Energetics, Incorporated

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to mergers and acquisitions. A few dozen manufacturers in the United States and abroad still make batteries. EnergyRelated Cost ($/kWh) Lead-acid Batteries (Flooded Cell) Lead-acid Batteries (VRLA) Ni/Cd High Temp Na/S

Characteristics of Battery Technologies used for Bulk Storage PowerBalance Efficiency Replacement Replacement Related of Plant (AC to AC) Cost Frequency Cost ($/kW) ($/kW) ($/kWh) (yr)

Fixed O&M

150

125

150

0.75

150

6

($/kWyr) $15/yr

200

125

150

0.75

200

5

5

600 250

125 150

150 50

0.65 0.7

600 230

10 10

5 20

Source: Long vs. Short Term Energy Storage Analysis, A Study for the DOE Energy Storage Systems Program, SANDIA Report, Printed August 2003.

Market Applications •

• •

•

The first application of batteries is stationary applications for the following industries: telecommunications, utility switchgear and control, uninterruptible power supplies (UPS), and photovoltaic and nuclear power plants. Installations can be any size. The largest system to date is a 40 MW Nickel Cadmium Battery from Saft installed in Fairbanks, Alaska. Lead acid batteries are the most common energy storage technology for stationary and mobile applications. They offer maximum efficiency and reliability for a wide variety of stationary applications such as power quality, peak shaving, spinning reserve, and other ancillary services. Government and private industry are currently developing a variety of advanced batteries for transportation and defense applications: lithium-ion, lithium polymer, nickel metal hydride, sodium metal chloride, sodium sulfur, and zinc bromine. Rechargeable lithium batteries are also being used in consumer electronics. Technology Goals

• • •

Lead-acid batteries are likely to remain a strong technology in the future because they provide the best longterm power in terms of cycles and float life. Battery manufacturers such as Exide, Saft, NKG, GNB and Sanyo are working on incremental improvements in energy and power density. The battery industry is trying to improve manufacturing practices and build more batteries at lower costs to stay competitive. Gains in development of batteries for mobile applications will likely crossover to the stationary market.

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D2. FLYWHEELS Technology Readiness Low-speed flywheels are commercially available and have multiple units in the field. Prototype highspeed flywheels are being developed and tested in the field. Technology Description Flywheels use a mechanical process to store kinetic energy in a rotating mass. The amount of stored energy is dependent on the speed, mass, and configuration of the flywheel. The most common use for flywheels is as short-term energy storage devices for propulsion applications such as engines for large road vehicles. • Flywheel energy storage systems are usually categorized as either low-speed or high-speed. Highspeed wheels are made of high strength, low-density/weight composite materials, making these systems considerably more compact than those employing lower-speed metallic wheels. However, the low-speed systems are still considerably less expensive per kWh. Flywheels systems require power conditioning and balance-of-plant components. A dozen companies are actively developing flywheels. Low-speed, steel flywheels are commercially available now and composite, high-speed flywheels are rapidly approaching commercialization. Cost and Performance Characteristics Utilities require that energy storage offer high reliability and per-kilowatt costs less than or equal to those of new power generation ($400–$600/kW). The major barrier for all storage technologies including flywheels is cost reduction. Low-speed (7000-9000 rpm) steel flywheels are commercially available for power quality and UPS applications. There are at least two companies developing flywheels in the 10 – 20 kW range for distributed generation. A 50 kW system has projected energy costs of $1000/kWh and power conditioning system costs of $300/kW. Flywheels require very low maintenance. Its bearings and other systems need replacement on a three- to five-year basis. Flywheels used in power quality applications have higher energy costs that vary depending on the manufacturer. The table below shows all costs of flywheels used in DC applications. Characteristics of High Speed Flywheels, 18 kW, 37 kWh for DC Applications EnergyRelated Cost

PowerRelated Cost

Balance Efficiency of Plant (AC to AC)

Replacement Replacement Parasitic Cost Frequency Loss

Fixed O&M

($/kWh)

($/kW)

($/kW)

($/kWh)

(yr)

($/kW-yr)

1,000

300

0

0

None

0.95

0.05%/hr

$1000/yr

Source: Long vs. Short Term Energy Storage Analysis, A Study for the DOE Energy Storage Systems Program, SANDIA Report, Printed August 2003.

Market Applications •

•

Flywheels are primarily used in transportation, defense, and power quality applications. Flywheels can also be used for energy storage applications. However, there are barriers such as parasitic losses due to windage and bearings. They can be used in load management to have energy stored during offpeak hours discharged at peak hours, achieving savings in peak energy, demand charges, and a more uniform load. In addition, flywheels are under development for vehicle applications. Flywheels can handle angular instabilities and provide low cost frequency regulation, and can provide power balancing for wind energy systems.

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Technology Goals High-speed flywheels need further development to improve reliability and weight. There is also research to reduce parasitic load and make flywheels attractive for small uninterruptible power supplies and small energy management applications. Europe and Japan are the leaders in flywheels research and development efforts. In the United States, there has been more industry investment than government research.

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D3. COMPRESSED AIR ENERGY STORAGE Technology Readiness Compressed Air Energy Storage (CAES) is commercially available, but requires available storage media locations such as salt domes, mines, or aquifiers. There are two CAES plants currently in operation: one in Germany was constructed in 1978 and the other in Alabama was constructed in 1991 and is operated by the Alabama Electric Cooperative. Technology Description CAES stores compressed air in an underground cavern during off peak hours and releases the air through turbines to produce electricity when energy is needed. CAES systems are usually greater than 100 MW. • During charging, an electric motor uses electricity (usually during off-peak hours) to drive a compressor to pump air into an underground facility, such as a salt dome or aquifer, to store for later use. • When electricity is needed, the compressed air is released from the underground facility, heated by natural gas in combustors, and run through high-pressure and low-pressure turbines to power the generator. • A turbine can reach efficiencies with compressed air 3 times greater than a conventional turbine because a conventional natural gas turbine consists of a compressor, which compresses the gas prior to combustion. The compressor consumes nearly two-thirds of the mechanical energy that is delivered to the shaft of the turbine. Cost and Performance Characteristics CAES systems have two distinct cost components–the storage media and the power-related costs (combustion turbines, ancillary equipment, etc.) • Storage media costs are generally inexpensive where the locations are available–salt domes, mines, aquifiers, or old oil and gas areas. The energy-related costs are estimated at $3/ kWh (SNL). • Power-related costs for modern equipment are approximately $425 /kW. Generation Power Train Characteristics Heat Rate

< 4,300 Btu/kWh

Charging Ratio

0.75 MWh compression/ 1 MWh generation

Emissions

50% of standard simple cycle combustion turbine

Output

No degradation to high ambient temperatures or altitude

Start-up

0 to 100% in less than 10 minutes

Ramp Rate

50%-100% in less than 15 seconds

Part load

Minimal heat rate and environmental degradation down to 50% of capacity

SCADA/AGC

Capable

Black Start

Capable Source: Ridge Energy Storage and Grid Service, LP

Capital Cost Estimates for CAES Plants Rock

Salt

Aquifer

Plant Minus Storage ($/kW)

439

425

414

Storage ($/kW per hour)

30

1.1

8

Hours of Storage

x 10

x 10

X 10

Total Capital Cost ($/kW)

739

436

494

Source: Tennessee Valley Authority

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Market Applications There are two CAES plants currently in operation: one in Germany was constructed in 1978 and the other in Alabama was constructed in 1991 and is operated by the Alabama Electric Cooperative (AEC). Both systems use solution-mined salt caverns as the reservoir. • Renewables- CAES plants can be combined with wind or solar energy. When the renewables produce more energy than is in demand the extra energy can be used to compress the air. When it is no longer sunny or the wind stops blowing, air can be released and used to generate electricity. • Peaking- CAES plants can store energy during off-peak times when electricity is the cheapest and provide energy during peak times, reducing the need to bring expensive generation on-line • Grid Management- By siting a CAES plant close to a transmission bottleneck, the CAES plants can help relieve transmission grid congestion bottlenecks and reduce the need to build expensive transmission upgrades. CAES plants can also help provide balancing and voltage support for the transmission grid. Technology Goals The efficiency of CAES needs to be optimized and costs need to be reduced (an estimated 30 percent of the total energy cost of the central plant is from the CAES). A methodology to quantify the central plant efficiency of the CAES is needed. Sources: Tennessee Valley Authority Long vs. Short-Term Energy Storage Technologies Analysis, Sandia National Laboratories, August 2003 Ridge Energy Storage and Grid Service, LLP. California Energy Commission

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D4. PUMPED HYDRO ENERGY STORAGE Technology Readiness Pumped hydro energy storage is commercially available. There are more than 19 gigawatts of pumped storage capacity in the U.S. (2.7 % of total generation). Technology Description Pumped hydroelectric energy storage is based on conventional hydropower technology. Generally, pumped hydropower plants pump water from a lower reservoir to an upper reservoir when demand for electricity is low. Water is stored in an upper reservoir for release to generate power during periods of peak demand. For example, in the summer, water is released during the day for generating power to satisfy the high demand for electricity for air conditioning. At night, when demand decreases, the water is pumped back to the upper reservoir for use the next day. A typical pumped hydro energy storage plant consists of the following components: Dam (upper reservoir). Controls the flow of water and increases the elevation to create the head. The reservoir that is formed is, in effect, stored energy. Penstock. Carries water from the reservoir to the turbine in a power plant. Reversible Turbine. Turned by the force of water pushing against its blades and also spins backward to pump the water from the lower reservoir to the upper reservoir. Generator. Connects to the turbine and rotates to produce the electrical energy. Transformer. Converts electricity from the generator to usable voltage levels. Transmission lines. Conduct electricity from the hydropower plant to the electric distribution system. Cost and Performance Characteristics • • • • • • •

Pumped hydroelectric storage plants range in size from 300 MW to 1800 MW. Existing plant capital costs were low. The Tennessee Valley Authority’s pumped storage plants were $250 kW in the early 1980s. Efficiencies range from 60% (old units) to 78% (newer units). Cold start usually takes 1 to 4 minutes. Change over from pumping to generating takes 5 to 40 minutes. Operate as little as once a week to 8 times per week. Capacity factors from 15% to 35%. Availability is high, between 90-98% and starting reliability is 99%. Market Applications

• • •

•

Most popular large storage technology in the world with 19 gigawatts in the United States (2.7 % of total generation) Used for price arbitrage and reduced price volatility and also ancillary services, such as VAR support and voltage regulation. While pumped storage facilities are net energy consumers, they are valued by a utility because they can be rapidly brought on-line to operate in a peak power production mode. The pumping to replenish the upper reservoir is performed during off-peak hours when electricity costs are lowest. This process benefits the utility by increasing the load factor and reducing the cycling of its baseload units. In most cases, pumped storage plants run a full cycle every 24 hours. Pumped hydro can be very useful if used with intermittent energy sources such as solar or wind power. Some regions may produce excess wind or solar energy than is in demand; this extra energy can be used to pump water to a high reservoir. When it is no longer sunny or the wind stops blowing, water from the upper reservoir can be released and used to generate electricity. Technology Goals

Experts have determined that the best sites for pumped hydro storage plants in the United States have been used and the remaining sites are in remote areas that may require new transmission to utilize the technology. There are also many environmental impact issues to deal with at potential pumped hydro plant sites. Energetics, Incorporated

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•

New capital costs range from $1,100 to $2000 per kW. These costs are non-competitive with existing technology, such as combustion turbines.

Sources: Energy Storage Council Tennessee Valley Authority, www.tva.gov Office of Energy Efficiency and Renewable Energy, www.eere.energy.gov

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D5. SUPERCONDUCTING MAGNETIC ENERGY STORAGE (SMES) Technology Readiness Superconducting Magnetic Energy Storage (SMES) technology has been under development around the world for many years. Currently, American Superconductor is offering various types of SMES units for commercial sale under the name D-SMES. Low temperature superconducting (LTS) SMES is commercial. Technology Description A SMES system stores energy in the magnetic field created by the flow of direct current in a coil of superconducting material. To maintain the coil in its low-temperature superconducting (LTS) state, it is immersed in liquid helium contained in a vacuum-insulated cryostat. SMES systems have a high cycle life and, as a result, are suitable for applications that require constant, full cycling and a continuous mode of operation. Although past research was conducted on larger SMES systems in the range of 10 to 100 MW, recent focus has been on the smaller SMES devices in the range of 1 to 10 MW-second. SMES devices are available commercially for power quality applications. • Commercial SMES products utilize LTS material – though HTS SMES products are under development. • Since the SMES coil is a DC device, a power converter system is required at the coil/grid interface. The power converter system uses standard solid-state DC-AC converters as well as other filtering and control circuitry. • In addition to the superconducting coil and the power converter system, the only other major elements comprising a SMES plant are the cryogenic refrigerator systems (including cryostat). • SMES technology has been under development around the world for many years. Currently, American Superconductor is offering various types of SMES units for commercial sale under the name D-SMES. Cost and Performance Characteristics D-SMES Performance Characteristics Cost and Performance Characteristic

D-SMES System

Voltage

69-500 V

Reactive Power

Up to 8 MVAR continuous Up to 18.4 MVAR instantaneous

Response Time

Subcycle

Magnetic Power Discharge

3 MW

Magnetic Energy Storage

3 MJ

Recharge Time

< 90 seconds

The cost for a D-SMES unit is about $250/kW. Six D-SMES units were deployed on the Wisconsin Public Service Grid (115 kV) for transmission stabilization at a cost of approximately $4 million. Market Applications Due to the ability to store and release large amounts of energy very quickly, the SMES is well suited for uninterruptible power supply applications. The SMES overcomes the most prevalent type of powerquality problem, which are momentary voltage sags. These are drops in voltage that typically last much less than one second (causing lights to flicker), but long enough to knock out sensitive manufacturing equipment or to cause voltage instabilities in transmission systems. The applications of SMES in the utility sector go well beyond simple energy storage and have the ability to significantly increase transmission capacity through enhanced line stability. • •

D-SMES systems are employed by electric utilities and are connected to their grids at substations. D-SMES systems increase transfer capacity and protect utility grids from the destabilizing effects of

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•

• •

•

short-term events, such as voltage dips caused by lightning strikes and downed poles, sudden changes in customer demand levels, and switching operations. In many cases, D-SMES is a cost-effective way to reinforce a transmission grid without the costly and environmentally intrusive construction of new lines. Rather than protecting one individual customer, a D-SMES system consists of a number of SMES units placed at strategically selected locations on the utility system. By improving the stability of the entire transmission grid, a D-SMES system can cost-effectively increase system capacity and improve the reliability and quality of electric service to thousands of customers simultaneously. D-SMES is a shunt connected Flexible AC Transmission (FACTS) device designed to increase grid stability, improve power transfer, and increase reliability. Unlike other FACTS devices, D-SMES injects real power as well as dynamic reactive power to compensate more quickly for disturbances on the utility grid. Fast response time prevents motor stalling, the principal cause of voltage collapse. Larger SMES (10-180 MW), when developed, would be appropriate for load-leveling applications. Technology Goals

LTS SMES is commercial. There are no R&D goals. There may be some R&D opportunities for larger SMES devices and incorporating HTS conductors into the larger SMES designs. Source: American Superconductor Corporation website, www.amsuper.com

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D6. OTHER ENERGY STORAGE TECHNOLOGY Ultracapacitors Ultracapacitors are also known as supercapacitors, Electric Double Layer Capacitors, or pseudocapacitors. They store energy as an electric charge in polarized liquid layers between an ionically conducting electrolyte and conducting electrodes. They are considered electrochemical devices, even though no chemical reactions occur in the energy storage mechanism. Their rate of charge and discharge is determined solely by their physical properties, enabling them to release energy much faster (i.e., with more power) than a battery, which relies on slow chemical reactions. Ultracapacitors have 100 times the power density of conventional capacitors and 10 times the power density of ordinary batteries. They require power conditioning and balance of plant components to be tied into the grid. They are ideal for power quality and short-term energy storage needed for a few seconds to a few minutes. They can store large amounts of energy when designed accordingly. Ultracapacitors are alos being integrated with ETO based cascade multi-level converters to control transient and angular instabilities and also to act as a low cost Unified Power Flow Control device. They are used in consumer electronics, power quality devices, and transportation and defense applications, and have potential use in combination with distributed generation equipment for following rapid load changes. An 8 kJ ultracapacitor typically costs between $50 and $100, resulting in an energy cost of $45,000/kWh. One R&D goal is to increase production enough to have the energy cost at $25,000/kWh. Ultracapacitor development needs improved energy density from the current 1.9 W-h/kg for light-duty hybrid vehicles. Manufacturers include Nanolab, Cooper Maxwell, and NEC.

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E. DISTRIBUTED ENERGY E1. Industrial Gas Turbines E2. Microturbines E3. Fuel Cells E4. Reciprocating Engines E5. Photovoltaics E6. Demand Response

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E1. INDUSTRIAL GAS TURBINES Technology Readiness Industrial gas turbines are commercially available. They have been used for power generation for decades and generally range in size from 1 to 60 MW. There are over 8,000 MW of installed industrial gas turbine capacity. In 2003, as a result of a public-private partnership through the U.S. Department of Energy’s Advanced Turbine Systems Program, Solar Turbines commercialized the Mercury 50 industrial gas turbine. The unit is commercially available at 4.8 MW and has a 38.5% electric efficiency and an initial warranty level of 5 ppm NOx and 10 ppm CO emissions. Technology Description A gas turbine is a heat engine that uses high-temperature, high-pressure gas as the working fluid. Gas turbines are compact, lightweight, quick starting, and simple to operate. They are used widely in industry, universities and colleges, hospitals, and commercial buildings to produce electricity, heat, or steam. In such cases, “simple cycle” gas turbines convert a portion of input energy from the fuel to electricity and use the remaining energy, normally rejected to the atmosphere, to produce heat. This waste heat may be used to power a separate turbine by creating steam. The attached steam turbine may generate electricity or power a mechanical load. This is referred to as a combined cycle combustion turbine since two separate processes or cycles are derived from one fuel input to the primary turbine. Cost and Performance Characteristics Simple cycle efficiencies (i.e., without external use of exhaust heat) range from 21 - 40%. Turbines produce high quality heat that can be used to generate steam for combined cycle or combined heat and power applications, significantly enhancing efficiency. Industrial Gas Turbine Performance Characteristics Turbine Characteristics

>500 to 2000 kW >2000 kW

Capacity, kW Equip/Interconnect/HR ($/kW) Installation ($/kW) Other/Eng/Fin/PM ($/kW) Total ($/kW) Electric Efficiency (HHV) RH Efficiency – Exhaust RH Efficiency – Water Recoverable Heat (MMBtu/hr) Heating Cost ($/kW) w/HP ($/kW) Cooling Single Stage (tons) Cooling Cost ($/Ton) w/CHP ($/kW) NOx Uncontrolled (lb/MWh) NOx Controlled (lb/MWh) Control Cost ($/kW) O&M Cost ($/kWh) CO (lb/MWh) CO2 (lb/MWh)

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1000 $1,180 $460 $290 $1,930 21.9% 45.5% N/A 7.09 inc $1,930 414 360 $2,079 2.43 0.24 162 0.0096 0.71 1815

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5000 $660 $260 $150 $1,070 27.1% 42.0% N/A 26.6 inc $1,070 1,553 250 $1,148 1.16 0.11 90 0.0059 0.56 1480

August 2004

Market Applications •

•

• •

Domestic and global potential markets for advanced turbines are large. At least half of all new power generating capacity to be added between now and 2010 is likely to use gas turbines. In addition, mid-sized turbines have tremendous potential for use as baseload, combined heat and power (CHP), peaking, and standby/backup power in commercial and industrial settings. Turbines produce waste heat in the exhaust gas at temperatures in the 950-1000°F range, which is suitable for supplying a variety of commercial and industrial needs. They can be coupled with heat recovery devices to operate in a CHP mode for complexes such as office buildings, hospitals, and light industrial applications. Remote power applications also are generally base-load operations. In locations where power from the local grid is unavailable or extremely expensive to install, turbines can be a competitive option. Units may be connected in parallel to serve larger loads and provide reliability. Turbines can be applied at substations to provide incremental peaking capacity and grid support. Such installations can defer the need for transmission and distribution system upgrades, can provide temporary peaking capacity within constrained areas, or be used for voltage support. Technology Goals

The next generation of turbine product designs will focus on the following DOE performance targets: • High Efficiency and Performance: Increase the fuel-to-electricity conversion and improve the overall performance of turbines through the use of advanced materials. • Environment: The emissions target is less than 5 parts per million nitrogen oxides and 25 parts per million carbon monoxide with no post-combustion controls. • Durability and Sustainability: The goal is 8,000 hours of operation between major overhauls. • Fuel Flexibility: Should be capable of using alternative fuels including natural gas, hydrogen, diesel, ethanol, landfill gas, and other bio-mass derived liquids and gases. The durability and sustainability of advanced materials need to be increased without increasing costs. Sources: The Installed Base of U.S. Distributed Generation, Resource Dynamics Corporation, 2003

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E2. MICROTURBINES Technology Readiness Microturbines are commercially available in sizes ranging from 30 kW to 100 kW. Worldwide, over 2,100 units have been sold totaling over 79 MW of power. Technology Description Microturbines have few moving parts, a compact size, are light weight, have high efficiency, low emissions, low electricity costs, and waste heat utilization opportunities. Waste heat recovery can be used in combined heat and power (CHP) systems to achieve energy efficiency levels greater than 80 percent. They are fuel flexible machines that can run on natural gas, biogas, propane, butane, diesel, and kerosene. Microturbines consist of a compressor, combustor, turbine, alternator, recuperator, and generator. Cost and Performance Characteristics Design life is estimated to be in the 40,000 to 80,000 hour range. Microturbines have not been in commercial service long enough to provide definitive data. Microturbines range in size from 30-400 kW. Microturbine Performance Characteristics

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Market Applications Microturbines can operate in CHP modes or power only modes. Power-only applications include peak shaving, premium power, remote power, and grid support modes. • Microturbines produce waste heat in the exhaust gas at temperatures in the 400-600 °F range, which is suitable for supplying a variety of building and light industrial needs. They can be coupled with heat recovery devices to operate in a CHP mode for complexes such as office buildings, hospitals, and light industrial applications. • Peak shaving is applicable to customers with poor load factor and/or high electricity demand charges. In general, current market-entry microturbines are too costly to provide economic peaking power in most regions of the United States. However, peaking may develop into a significant microturbine application if the potential for lower capital costs and increased efficiencies can be achieved as microturbine markets develop and the technology matures. • Customers who require high power reliability such as data centers, financial institutions, and other mission-critical facilities are willing to pay a premium for it. The current high prices of microturbines may be justified, based on their potential advantages in terms of low emissions, reduced vibration, ease of installation, potential for high availability and reliability, and good power quality. • Remote power applications also are generally base-load operations. In locations where power from the local grid is unavailable or extremely expensive to install, microturbines can be a competitive option. • Units may be connected in parallel to serve larger loads and provide reliability. Microturbines can be applied at substations to provide incremental peaking capacity and grid support. Such installations can defer the need for transmission and distribution system upgrades, can provide temporary peaking capacity within constrained areas, or be used for voltage support. Technology Goals The next generation of "ultra-clean, high efficiency" microturbine product designs will focus on the following DOE performance targets: • High Efficiency – By 2007, achieve fuel-to-electricity conversion efficiency of at least 40 percent. • Environment – By 2007, achieve NOx < 7 ppm (natural gas). • Durability – By 2007, 1,000 hours of reliable operations between major overhauls and a service life of at least 45,000 hours. • Cost of Power – By 2005, system costs < $500/kW, costs of electricity that are competitive with alternatives (including grid) for market applications (for units in the 30-60 kW range). • Fuel Flexibility – By 2007, options for using multiple fuels including diesel, ethanol, landfill gas, and bio-fuels. Sources: Power Technologies Databook, National Renewable Energy Laboratory (NREL) Gas-Fired Distributed Energy Resource Technology Characterization, National Renewable Energy Laboratory (NREL) DOE Distributed Energy Program Website

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E3. FUEL CELLS Technology Readiness Fuel cells are not widely available. There are only 200 fuel cell installations in operation. Fuel cells still face many technical and financial barriers in reaching widespread market adoption. Technology Description A fuel cell is an electrochemical energy conversion device that converts hydrogen and oxygen into electricity and water. This unique process is practically silent, nearly eliminates emissions, and has no moving parts. • Similar to a battery, fuel cells have an anode and a cathode separated by an electrolyte. • Fuel cell systems today typically consist of a fuel processor, fuel cell stack, and power conditioner. • The fuel processor, or reformer, converts hydrocarbon fuels to a mixture of hydrogen-rich gases and, depending on the type of fuel cell, can remove contaminants to provide pure hydrogen. The fuel cell stack is where the hydrogen and oxygen electrochemically combine to produce electricity. The electricity produced is direct current (DC) and the power conditioner converts the DC electricity to alternating current (AC) electricity, for which most of the end-use technologies are designed. As a hydrogen infrastructure emerges, the need for the reformer will disappear as pure hydrogen will be available near point-of-use. Fuel cells are categorized by the kind of electrolyte they use. Alkaline Fuel Cells (AFCs) were the first type of fuel cell to be used in space applications. AFCs contain an electrolyte made up of a potassium hydroxide (KOH) solution and operate at temperatures between 60 and 250°C (140 to 482°F). The fuel supplied to an AFC must be pure hydrogen. Carbon monoxide poisons an AFC, and carbon dioxide (even the small amount in the air) reacts with the electrolyte to form potassium carbonate. Phosphoric Acid Fuel Cells (PAFCs) were the first fuel cells to be commercialized. These fuel cells operate at 150-220°C (302-428°F) and achieve 35 to 45% fuel-to-electricity efficiencies on a lower heating value basis (LHV). UTC Fuel Cells has delivered over 250 200 kW PAFC systems worldwide. Proton Exchange Membrane Fuel Cells (PEMFCs) operate at relatively low temperatures of 70100°C (158-212°F), have high power density, can vary their output quickly to meet shifts in power demand, and are suited for applications where quick start-up is required (e.g., transportation and power generation). The PEM is a thin fluorinated plastic sheet that allows hydrogen ions (protons) to pass through it. The membrane is coated on both sides with highly dispersed metal alloy particles (mostly platinum) that are active catalysts. Molten Carbonate Fuel Cell (MCFC) technology has the potential to reach fuel-to-electricity efficiencies of 45 to 60% LHV. Operating temperatures for MCFCs are around 650°C (1,200°F), which allows total system thermal efficiencies up to 85% LHV in combined cycle applications. MCFCs have been operated on hydrogen, carbon monoxide, natural gas, propane, landfill gas, marine diesel, and simulated coal gasification products. Solid Oxide Fuel Cells (SOFCs) operate at temperatures up to 1,000°C (1,800°F), which further enhances combined-cycle performance. A solid oxide system usually uses a hard ceramic material instead of a liquid electrolyte. The solid-state ceramic construction enables the high temperatures, allows more flexibility in fuel choice, and contributes to stability and reliability. As with MCFCs, SOFCs are capable of fuel-to-electricity efficiencies of 45 to 60% LHV and total system thermal efficiencies up to 85% LHV in combined-cycle applications.

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Cost and Performance Characteristics Types of Fuel Cell Technologies Fuel Cell Type AFC PEMFC PAFC MCFC

SOFC

Electrolyte KOH Nafion Phosphoric Acid Lithium, potassium, carbonate salt Yttrium & zirconium oxides

Electrical Efficiency (% LHV)

Typical Size Range

Cost ($/kW)

O&M costs ($/kW/yr)

Start-up time (hours)

35-45 35-45

5-250 kW 200 kW

$4,500 $4,500

$81 $81

<0.1 1-4

45-60

250 kW2MW

$2,800

$96

5-10

45-60

5-250 kW

$3,500

$84

5-10

Market Applications •

• • •

Fuel cell systems can be sized for grid-connected applications or customer-sited applications in residential, commercial, and industrial facilities. Depending on the type of fuel cell (most likely SOFC and MCFC), useful heat can be captured and used in combined heat and power systems (CHP). Premium power applications are an important niche market for fuel cells. Multiple fuel cells can be used to provide extremely high (more then six-times) reliability and high-quality power for critical loads. Data centers and sensitive manufacturing processes are ideal settings for fuel cells. Fuel cells also can provide power for vehicles and portable power. PEMFCs are a leading candidate for powering the next generation of vehicles. The military is interested in the highefficiency, low-noise, small-footprint, portable power. Technology Goals

According to the Business Communications Company, the market for fuel cells, which was about $218 million in 2000, will increase to $2.4 billion by 2004, and will reach $7 billion by 2009. • Fuel cells are being developed for stationary power generation through a partnership of the U.S DOE and the private sector. • Industry will introduce high-temperature natural gas-fueled MCFC and SOFC at $1,000 -$1,500 per kW that are capable of 60% efficiency, ultra-low emissions, and 40,000 hour stack life. • DOE is also working with industry to test and validate the PEM technology at the 1-kW level and to transfer technology to the Department of Defense. Other efforts include raising the operating temperature of the PEM fuel cell for building, cooling, heating, and power applications and improve reformer technologies to extract hydrogen from a variety of fuels, including natural gas, propane, and methanol. Source: Power Technologies Databook, NREL The Installed Base of Distributed Generation, Resource Dynamics Corporation, 2003

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E4. RECIPROCATING ENGINES Technology Readiness Reciprocating engines have been around for more than 100 years. Engines are the most widely used distributed generation technology. There are more than 10 million engines, ranging from 0.01 – 30 MW, installed in the United States. Technology Description Reciprocating engines, also known as internal combustion engines, require fuel, air, compression, and a combustion source to function. They make up the largest share of the small power generation market and can be used in a variety of applications due to their small size, low unit costs, and useful thermal output. • • •

Reciprocating engines fall into one of two categories depending on the ignition source: spark ignition (SI), typically fueled by gasoline or natural gas; or compression ignition (CI) typically fueled by diesel oil. Reciprocating engines also are categorized by the number of revolutions it takes to complete a combustion cycle. A two-stroke engine completes its combustion cycle in one revolution and a fourstroke engine completes the combustion process in two revolutions. Reciprocating engine systems typically include several major parts: fuel storage, handling, and conditioning, prime mover (engine), emission controls, waste recovery (CHP systems) and rejections (radiators), and electrical switchgear. Cost and Performance Characteristics

• • • •

Commercially available engines have electrical efficiencies (LHV) of approximately 40% and yield NOx emissions of 1.5 lbs/MWh. Installed cost for reciprocating engines range between $600 and $1,600/kW depending on size and whether the unit is for a straight generation or cogeneration application. Operating and maintenance costs range 2 cents to 2.5 cents/kWh. Exhaust temperature for most reciprocating engines is 700-1200°F in non-combined heat and power (CHP) mode and 350-500°F in a CHP system after heat recovery. Noise levels with sound enclosures are typically between 70-80 dB. Market Applications

•

• •

Reciprocating engines can be installed to accommodate baseload, peaking, or standby power applications. Commercially available engines range in size from 50 kW to 6.5 MW making them suitable for many distributed-power applications. Utility substations and small municipalities can install engines to provide baseload or peak shaving power. However, the most promising markets for reciprocating engines are on-site at commercial, industrial, and institutional facilities. With fast start-up time, reciprocating engines can play integral backup roles in many building energy systems. On-site reciprocating engines become even more attractive in regions with high electric rates (energy/demand charges). When properly treated, the engines can run on fuel generated by waste treatment (methane) and other biofuels. By using the recuperators that capture and return waste exhaust heat, reciprocating engines can be used in CHP systems to achieve energy efficiency levels approaching 80%. In fact, reciprocating engines make up a large portion of the CHP or cogeneration market. Technology Goals

• •

High Efficiency- Target fuel-to-electricity conversion efficiency (LHV) is 50% by 2010. Environment – Engine improvements in efficiency, combustion strategy, and emissions reductions will substantially reduce overall emissions to the environments. The NOx target for the Department of Energy’s Advanced Reciprocating Engine System (ARES) program is 0.1 g/hp-hr, a 90%

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• • •

decrease from today’s NOx emissions rate. Fuel Flexibility – Natural gas-fired engines are to be adapted to handle biogas, renewables, propane and hydrogen, as well as dual fuel capabilities. Cost of Power – The target for energy costs, including operating and maintenance costs is 10% less than current state-of-the-art engine systems. Availability, Reliability, and Maintainability – The goal is to maintain levels equivalent to current state-of-the-art systems.

Sources: Power Technologies Databook, National Renewable Energy Laboratory Diesel and Gas Turbine Worldwide

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E5. PHOTOVOLTAICS Technology Readiness Photovotaic (PV) systems are commercially available. Worldwide, about 288 MW of PV were sold in 2000 (more than $2 billion worth); total installed PV is more than 1 GW. The cost of PV is high and many states offer subsidies for PV, such as California who subsidizes PV systems because it is considered cost-effective to reduce their dependence on natural gas, especially for peak daytime loads for air-conditioning, which matches PV output. Technology Description PV arrays convert sunlight to electricity without moving parts and without producing fuel wastes, air pollution, or greenhouse gases (GHGs). •

•

•

Flat-plate PV arrays use global sunlight; concentrators use direct sunlight. Modules are mounted on a stationary array or on single- or dual-axis sun trackers. Arrays can be ground-mounted or on all types of buildings and structures (e.g., see semi-transparent solar canopy, right). PV DC output can be conditioned into grid quality AC electricity, or DC can be used to charge batteries or to split water to produce hydrogen. Flat-plate cells are either constructed from crystalline silicon cells, or from thin films using amorphous silicon. Other materials such as copper indium diselinide (CIS) and cadmium telluride also hold promise as thin-film materials. The vast majority of systems installed today are in flat-plate configurations where multiple cells are mounted together to form a module. These systems are generally fixed in a single position, but can be mounted on structures that tilt toward the sun on a seasonal basis, or on structures that roll east to west over the course of the day. Photovoltaic concentrator systems use optical concentrators to focus direct sunlight onto solar cells for conversion to electricity. A complete concentrating system includes concentrator modules, support and tracking structures, a power-processing center, and land. PV concentrator module components include solar cells, an electrically isolating and thermally conducting housing for mounting and interconnecting the cells, and optical concentrators. The solar cells in today's concentrators are predominantly silicon, although gallium arsenide-based (GaAs) solar cells may be used in the future because of their high-conversion efficiencies. Cost and Performance Characteristics

The cost of PV-generated electricity has dropped 15- to 20-fold; and grid-connected PV systems currently sell for about $5–$10/Wp (20 to 50¢/kWh), including support structures, power conditioning, and land. They are highly reliable and last 20 years or longer. • •

•

• •

Crystalline silicon is widely used and the most commercially mature photovoltaic material. Thinfilm PV modules currently in production include three based on amorphous silicon, cadmium telluride, and CIS alloys. About 288 MW of PV were sold in 2000 (more than $2 billion worth); total installed PV is more than 1 GW. The U.S. world market share is about 26%. Annual market growth for PV has been about 25% as a result of reduced prices and successful global marketing. In recent years, sales growth has accelerated to almost 40% per year. Hundreds of applications are cost-effective for offgrid needs. Almost two-thirds of U.S.-manufactured PV is exported. However, the fastest growing segment of the market is grid-connected PV, such as roof-mounted arrays on homes and commercial buildings in the United States. California is subsidizing PV systems because it is considered cost-effective to reduce their dependence on natural gas, especially for peak daytime loads for air-conditioning, which matches PV output. Highest efficiency for wafers of single-crystal or polycrystalline silicon is 24%, and for commercial modules is 13%–15%. Silicon modules currently cost about $2-$3/Wp to manufacture. During the past two years, world record solar cell sunlight-to-electricity conversion efficiencies were set by federally funded universities, national laboratories, or industry in copper indium

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• •

gallium diselenide (19% cells and 12% modules) and cadmium telluride (16% cells, 11% modules). Cell and module efficiencies for these technologies have increased more than 50% in the past decade. Efficiencies for commercial thin-film modules are 5%–11%. A new generation of thin-film PV modules is going through the high-risk transition to first-time and large-scale manufacturing. If successful, market share could increase rapidly. Highest efficiencies for single-crystal Si and multijunction gallium arsenide (GaAs)-alloy cells for concentrators are 25%–34%; and for commercial modules are 15%–17%. Prototype systems are being tested in the Southwestern U.S. desert. Market Applications

•

•

• •

• • •

Crystalline Silicon - Most PV systems installed to-date have used crystalline silicon cells. That technology is relatively mature. In the future, cost-effectiveness will be achieved through incremental efficiency improvements, enhanced yields, and advanced lower cost manufacturing techniques. Even though some thin-film modules are now commercially available, their real commercial impact is only expected to become significant during the next three to 10 years. Beyond that, their general use should occur in the 2005-2015 time frame, depending on investment levels for technology development and manufacture. Thin films using amorphous silicon, which are a growing segment of the U.S. market, have several advantages over crystalline silicon. They can be manufactured at lower cost, are more responsive to indoor light, and can be manufactured on flexible or low-cost substrates. Other thin-film materials will become increasingly important in the future. In fact, the first commercial modules using indium gallium diselinide thin-film devices were produced in 2000. Improved manufacturing techniques and deposition processes will reduce costs and help improve efficiency. Substantial commercial interest exists in scaling-up production of thin films. As thin films are produced in larger quantity, and as they achieve expected performance gains, they will become more economical for the whole range of applications. Multijunction cells with efficiencies of 38% at very high concentrations are being developed. Manufacturing research and supporting technology development hold important keys to future cost reductions. Large-scale manufacturing processes will allow major cost reductions in cells and modules.

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Technology Goals PV Characteristics and Performance Targets

Source: Power Technologies Databook, NREL

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E6. DEMAND RESPONSE Technology Readiness Demand response programs incorporate the load management elements of what use to be known as “Demand-Side Management (DSM)” programs and also involve distributed generation—have been producing economic and environmental benefits for years. Technology Description Demand response is an all-encompassing term covering a range of mechanisms designed to give electricity customers the ability to reduce their electricity consumption in response to system reliability or price events. A demand response program allows utilities to interface with energy users to reduce peak or post-contingency demand, lessening the need to run higher-cost generation or to purchase additional power at costly spot market prices or to have generator reserves available. Demand response programs generally involve customer load reduction (through curtailment, distributed generation, or load shifting) in response to price signals or directions from distribution utilities, energy marketers, or system operators. Customers can be compensated for reducing electricity consumption at times when: •

The reliability of the system is at risk. Load response during periods of high demand alleviates strain on the system and increases system reliability. Load response can also be used as short-term response to system contingencies.

•

Wholesale electricity prices are very high. Load response can be performed for procurement cost minimization purposes (e.g., load bidding)

For these demand response mechanisms, the utility or independent system operator would determine when the electricity demand would be reduced, and the customer would be compensated. However, price response can also be performed directly by end-use customers for bill management purposes. Load response is typically attained through interruptible tariffs and direct load control programs. Price response can be attained through time-of-use rates, dynamic pricing, and demand bidding programs. Cost and Performance Characteristics •

•

• • •

Demand response programs—also known as “Demand-Side Management (DSM)” programs— have been producing economic and environmental benefits for years. Utilization of demand response is a cost-effective solution to transmission reliability problems from an engineering, economic, and environmental standpoint since it is a “non-wire” solution. Benefits include avoided energy, avoided capacity (transmission and generation), and avoided reserves (ancillary services). A study by e-Meter in March 2002 revealed that by using demand response options in California the total annual cost will be less than one-eight of the fixed costs of adding 5,000 MW of peaking plant capacity. A study by McKinsey Co. states that consumers could save nearly $15 billion annually if all states implemented real-time pricing strategies, and that the savings would be almost evenly split between the industrial and residential sectors. ISO New England says that the reduction of 50 MW in a congested zone would improve reliability by 30 percent. EPRI found that a two percent reduction in energy usage in California in the summer of 2001 would have cut wholesale electricity expenditures by $700 million.

The cost of advanced meters, which are needed for some demand response applications, is a Energetics, Incorporated

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consideration. An advanced meter allows the energy provider to remotely communicate with and measure time-differentiated customer energy usage. The meters are significantly more expensive than traditional meters. To make advanced metering and demand response programs economically attractive to utilities, Congress has supported tax incentives in the past. Market Applications The main drivers for utilizing demand response programs are to prevent future electricity crises and to reduce average electricity prices. Additional goals for price responsiveness include equity (through cost-of-service pricing) and customer control of electricity usage and bills. Load Response • Interruptible tariffs - Customers who are willing to take a greater risk that their power will be reduced in a power shortage can pay less for electricity under an interruptible tariff structure. The interruptible tariff also represents a way to “ration” power by creating a priority list of customers who will be cut back and by how much. Customers able to plan and manage their power usage can benefit by paying a discounted rate during periods when their electricity needs are less critical. •

Direct load control programs - The objective of a direct load control program is to achieve load reduction during emergencies resulting in load reduction at times of electric capacity shortfall. Reduction in system peak demand is achieved by the direct remote control of selected load by the utility without prior notice to the customer. Loads can be interrupted by the utility through remotely activated signals. Examples include the utility interrupting the operation of air conditioners or water heaters.

Price Response Dynamic pricing – Customers typically do not know when electricity is unusually expensive and therefore have no motivation or incentive to reduce demand during those times. Dynamic pricing tariffs could be used as a strategy for avoiding forced outages because of electricity demand-supply imbalances and/or mitigating high prices because of scarce supply resources. One form of these tariffs would offer rate discounts when system conditions are normal (most of the time) and charge higher rates when the grid is approaching an overloaded state, or during wholesale price spikes. Dynamic rates can also signal to the market wholesale electricity costs, which tend to be highest when electricity demand is unusually high or when supply is unusually low. Current retail electricity rates do not reflect such unexpected changes in wholesale prices.

•

•

Demand bidding programs - One approach to increasing demand responsiveness is to promote demand side bidding in electricity or reserves markets. Demand bids are treated as equal to generator bids and, thus, contribute to the determination of the market clearing price of electric energy. Currently, several ISOs operate bid-based energy and reserve markets. The ISO determines market-clearing prices and quantities on an hourly basis based on bids submitted by market participants. The details of the auctions vary among the ISOs.

Demand Responsive Load Coupled with Distributed Generation • Distributed generation may include reciprocating engines, microturbines, and combustion gas turbines. These resources provide the opportunity for end-users to self-supply energy or provide energy to the marketplace in times of scarcity. Many loads already require higher quality and more reliable power than utilities can offer. By tapping into this preexisting market where the need for distributed generation is driven by power quality and reliability needs of the load, transmission providers may be able to find resources that are willing to bid into a demand response market. Demand responsive load, when coupled with distributed generation to provide continued load operation, may improve the reliability of that load’s service by preventing power disruption. It may also provide the load with a wider choice of power supply options and may be developed more quickly than central station generators. Placing alternative power resources close to where the power is needed provides an energy solution at the “right” location. Distributed resources may produce savings on Energetics, Incorporated

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electricity rates by allowing loads to self generate during high-cost peak power periods in addition to adopting relatively low-cost interruptible power rates. Technology Goals Technological progress is providing the tools necessary to allow better demand response and help create more efficient energy markets. Several new technologies make it easier for customers to react to and participate in the electric market. Metering technologies now allow the metering of electrical customers in real-time. Systems are also being developed to communicate the pricing signals from the marketplace that customers need in order to evaluate and coordinate their consumption decisions. Demand response research, development, demonstrations, and technology transfer continues to occur. Research on policies, programs, and tariffs to promote demand response needs to be completed, as well as insight into consumer and institutional behavior in an effort to boost success of programs. Sources: New England ISO Demand Response Program web site and presentations “Demand Responsiveness in Electricity Markets,” Office of Markets, Tariffs and Rates, Federal Energy Regulatory Commission, January 15, 2001 “Energy Conservation Squeezed,” March 30, 2004, IssueAlert.

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