T1.docx

“TECHNICAL SEMINAR TOPIC”

Bachelor of Technology In Electrical and Electronics Engineering Submitted by: Name :K.Tejavardhan Yadav H.T.NO:15H51A0285

Technical Seminar Coordinator

Mr.Ch.Sankar Rao, Assoc.Prof. Dept. Of EEE, CMRCET

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

CMR COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous)

(NAAC Accredited with ‘A’ Grade & NBA Accredited) (Approved by AICTE, Permanently Affiliated to JNTU Hyderabad) KANDLAKOYA, MEDCHAL ROAD, HYDERABAD - 501401. 2018-19

ABSTRACT ELECTRICICY FROM OCEANS WAVES Wave power is the capture of energy of wind waves to do useful work – for example, electricity generation, water desalination, or pumping water. A machine that exploits wave power is a wave energy converter (WEC).

Wave power is distinct from tidal power, which captures the energy of the current caused by the gravitational pull of the Sun and Moon. Waves and tides are also distinct from ocean currents which are caused by other forces including breaking waves, wind, the Coriolis effect, cabbeling, and differences in temperature and salinity.

Wave-power generation is not a widely employed commercial technology, although there have been attempts to use it since at least 1890.[1]

INTRODUCTION The consumption of energy all over the world is estimated to rise over the next decades. The conventional methods of energy generation are contributing to severe environmental effects that are still obscure. The jeopardy of further use of fossil fuels have brought renewable energy technologies under a spotlight. The renewable energy resources like wind, solar, ocean, biomass and geothermal heat are among the emerging resources of energy in today’s world. After wind, solar and biomass energy, ocean energy is the most imminent resource of energy. Upto 70 percent of earth’s surface is covered up with oceans which constitutes ample amount of energy in the form of wave, tidal, marine current and thermal gradient. The wave energy is developed due to the winds interacting with the surface of the ocean. The process of wave power extraction does not produce any waste or emit CO2; it does not induce any noise pollution and is also ecological. Also, compared to other renewable energy resources, wave energy can yield power throughout the year. The energy flux attainable in the wave energy is more then that attainable from solar, wind, and other renewable sources. The energy in the waves is a concentrated form of solar energy: the sun heats the atmospheres unevenly and the differences in pressure create currents in the atmospheres (known as winds), and winds blowing over the ocean surface transfer their energy to the oceans in the form of waves. Wave generation depends on three parameters of the wind: the wind speed, fetch (the distance in the sea over which the wind transfers its energy to the waves) and duration.

Wave energy technologies Wave energy technologies consist of a number of components: 1) the structure and prime mover that captures the energy of the wave, 2) foundation or mooring keeping the structure and prime mover in place, 3) the power take-off (PTO) system by which mechanical energy is converted into electrical energy, and 4) the control systems to safeguard and optimise performance in operating conditions. There are different ways in which wave energy technologies can be categorised,1 e.g., by the way the wave energy is converted into mechanical energy or by the technology used. In this technology brief, we use a very broad categorisation for oscillating water columns (OWCs), oscillating body converters and overtopping converters Oscillating Water Columns are conversion devices with a semisubmerged chamber, keeping a trapped air pocket above a column of water. Waves cause the column to act like a piston, moving up and down and thereby forcing the air out of the chamber and back into it. This continuous movement generates a reversing stream of high-velocity air, which is channelled through rotorblades driving an air turbine-generator group to produce electricity.

One way to categorise wave energy technologies is by how the device extracts the surge, heave or sway motions of the wave (or a combination of each) (EMEC, 2014). In general, point absorbers convert the “heave” to drive a piston up and down, terminators and oscillating wave surge converters convert the “surge”, and attenuators convert the “pitch” of the wave to drive a rotor. Over half (53%) of WEC concepts developed are point absorbers, 33% terminators, and 14% attenuators (IRENA, 2014). Ocean Wave Energy Technologies The wave energy devices being developed and tested today are highly diverse, and a variety of technologies have been proposed to capture the energy from waves. Some of the more promising designs are undergoing demonstration testing at commercial scales.

Wave technologies have been designed to be installed in the nearshore, offshore, and far offshore locations. While wave energy technologies are intended to be installed at or near the water's surface, there can be major differences in their technical concept and design. For example, they may differ in their orientation to the waves or in the manner in which they convert energy from the waves. Although wave power technologies are continuing to develop, there are four basic applications that may be suitable for deployment on the Outer Continental Shelf (OCS): point absorbers, attenuators, overtopping devices, and terminators.  

   

Terminator devices extend perpendicular to the direction of the wave and capture or reflect the power of the wave. These devices are typically onshore or nearshore; however, floating versions have been designed for offshore applications. The oscillating water column is a form of terminator in which water enters through a subsurface opening into a chamber, trapping air above. The wave action causes the captured water column to move up and down like a piston, forcing the air though an opening connected to a turbine to generate power. These devices generally have power ratings of 500 kW to 2 MW, depending on the wave climate and the device dimension Attenuators point absorber Overtopping devices Oscillating water column

Attenuators attenuators are long multisegment floating structures oriented parallel to the direction of the waves. They ride the waves like a ship, extracting energy by using restraints at the bow of the device and along its length. The differing heights of waves along the length of the device causes flexing where the

segments connect. The segments are connected to hydraulic pumps or other converters to generate power as the waves move across. A transformer in the nose of the unit steps up the power-to-line voltage for transmission to shore. Power is fed down an umbilical cable to a junction box in the seabed, connecting it and other machines via a common subsea cable to shore.

Structural elements The structure is a steel structure that can be built locally using standard construction techniques available at most shipyards. The device structure has been designed using standard offshore construction principles, and a leading offshore technology consulting firm independently verified the design. there are different barriers that generation of wave energy has yet to pass, but one of the biggest ones is its costs. The predicted cost of energy from these technologies is relatively high compared to other renewables, but significant cost reduction potential is expected in the long term. Waves have the characteristic that once created they can travel for many kilometres practically without energy losses.In that sense, the energy from the sun reaches the coasts, where most of the populations of coastal countries are located, in a concentrated and fairly continuous way. the right type of location is done under a careful techno-economic evaluation. We have identified 4 different types of wave energy capturing devices that even though all of them are installed at the surface or near the surface of the ocean they differ in the way they interact with the waves, capture the wave energy and the way they convert this energy into electricity.

Mooring The mooring consists of a 3-point slack-mooring configuration. The mooring allows the device to turn into wave direction within its mooring constraints. The mooring and survivability of the system has been simulated theoretically and tested in wave

Source: Pelamis Wave Power

Source: Pelamis Wave Power

tanks. While the mooring is probably the least mature element in the overall system and will need to be looked at closely and adapted to the specific site requirements, it does not raise any concerns. The mooring and survivability has been independently analysed and verified by one of the leading offshore technology consultancy firms and is designed to withstand the 100-year storm wave.

Performance The device is able to rapidly tune to the incident wave climate

using a digitally controlled hydraulic system and detune to oversized waves. A large amount of effort has gone into optimizing

power conversion train has an average efficiency of 80% and future versions will likely show improvements in conversion efficiencies and the capacity factor is of 40%. Survivability The Pelamis has excellent survivability characteristics. Being a relatively narrow device, which will point into the wave and is able to completely de-adjust to large waves, it will always minimize loads on its mooring system. The power take off and control subsystems have been designed with many redundancies in place to minimize reactive maintenance such as the required intervention after a storm. The estimated life duration of this device is 15 years. Operation&Maintenance The device is designed to be quickly disconnected from its mooring and towed into a nearby port for maintenance overhauls. Many subsystems, such as power modules, are

designed in such a way that they can be lifted out with a crane and replaced with a tested subsystem. Remote diagnostic capability, extensive instrumentation and a high level of redundancy will minimize the physical intervention requirements and will allow O&M activities to be carried out during suitable weather windows.

Point absorber Structural elements The structure is made of steel and can be built locally using standard construction techniques available in most shipyards. The structural elements were designed using finite element analysis.

Power Take Off The hose pump delivers water into an accumulator to smooth the power output over the wave cycles. The water pressure is then discharged, driving a hydraulic impulse turbine. The power take off can be designed as a closed loop or open loop system. Regulation for the device is accomplished by slowly changing the pressure level in the hydraulic accumulator (the device cannot be rapidly adjusted to each wave that passes through). The lack of the power take-off system’s ability to rapidly modify the system will reduce its performance. Grid Connection The AquaBuOY is synchronized with the grid using a variable speed AC-DC-AC converter and the voltage is increased with a step-up transformer. Flexible riser cables connect the devices to a junction box on the ocean floor. This aspect is standard and does not raise any significant concerns.

Installation As the AquaBuOY is a relatively small device, it can be easily towed into a nearby port for major overhaul activities. In order to tow it into a nearby port, it would be required to be brought into horizontal position. This can be accomplished using a crane to bring the counterreaction tube into horizontal position or by pumping air into sub-sea compartments. Performance Power Output comparison of wave tank testing and theoretical models developed by the company revealed an uncertainty in performance predictions. The root of the

uncertainty may be that the system has only modelled the counter reacting tube as a mass without considering hydrodynamic interactions. The performance of this device will be limited by the capabilities of the power take off, which is only able to slowly adjust the device to the dominant wave period as outlined in the power take off section. The manufacturer also quotes a capacity per device of 250 kW, with an associated capacity factor of about 12% (assuming a 25kW/m wave climate). It is predicted that a capacity factor of around 40% could provide a near optimal economic value of electrical energy for this type of a device. Survivability The AquaBuOY has successfully solved the end-stop problem. If the hose pumps are elongated to a certain point, the piston assembly in the counter reacting tube will come into an area where the reaction tube widens. As a result, the water inside the tube is able to bypass the piston assembly and discharge without creating further dynamic stresses in the device structure. As such, it is an effective overload mechanism. The estimated life duration of this device is 20 years. Operation & Maintenance Remote monitoring and supervisory controls have not yet been designed. Ease of maintenance concerns come from the difficulty of assessing submersed components. These will likely include the hose pumps, piston assembly and

check-valves. In order to carry out any repair on these components, the system will be required to be floated into horizontal position in order to access them. Turbomachinery elements are likely accessible within the buoy hull. Alternative O&M strategies are under investigation by the manufacturer that would relieve some of these issues.

The cheapest cost/performance site studied was North Uist for the attenuator device, while the most expensive one was Tenerife for the point absorber. In terms of power performance, the point absorber device had a wide range of functionality in different sea states, but the attenuator device higher operating availability (capacity factor). Wave energy is still a very costly energy mainly due to the environment where it operates in, and has yet a long ride to reach its competitor, offshore wind energy

Overtopping devices Overtopping terminators, also referred to just as terminators, are devices that take advantage of wave energy to generate electricity. Scientists have been doing research since the 1990s to develop overtopping devices, but not until recently has significant progress been made (Bevilacqua & Zanuttigh, 2011). The overtopping terminator is a large device that is categorized as a wave capturer. This means that instead of using a wave’s kinetic energy to generate power like other wave energy devices, the terminator captures waves and takes advantage of their potential energy (Katofsky, 2008). In fact, the terminator got its name because of the way it absorbs or “terminates” all of a wave’s power. (Bedard et al, 2010). Plans have been proposed to install overtopping terminators both on and offshore. However, after Demark made great improvements with the offshore model it became the primary method of development and the onshore method’s progress diminished (Bevilacqua & Zanuttigh, 2011). Now overtopping terminators are described as large, floating reservoirs with ramps and reflectors extending off the end and turbines located at the bottom of the reservoir. The terminators are up to 390 meters wide and can hold between 1,500 and 14,000 cubic meters of water. The average cost to build and install one of these devices is a steep $10 to $12 million but its high efficiency makes it worth the cost in the long run (US Dept of Energy, 2009). When waves first approach an overtopping terminator, they bump into its reflectors. These reflectors are attached to the main body of the floating device and are angled outward in order to direct as much wave energy up to the device as possible.

Oscillating wave surge converters extract energy from wave surges and the movement of water particles within them. The arm oscillates as a pendulum mounted on a pivoted joint in response to the movement of water in the waves. Overtopping devices capture water as waves break into a storage reservoir. The water is then returned to the sea passing through a conventional low-head turbine which generates power. An overtopping device may use ‘collectors’ to concentrate the wave energy The overtopping devices are like hydroelectric turbine system as they utilize the wave kinetic energy to lift the sea water higher ; in other word they transfer kinetic energy of the wae into potential energy of the water. After being lifted upp, the water is contained in reservoir for later uses. The water is then dropped through a hydro turbine in order to make electricity.In some other case other mechanical energy conversion system can be used instead of the hydro turbine. An example of this type of device is the Wave Dragon.

Overtopping theory The theory [VI.]for modeling overtopping devices varies greatly from the traditional linear systems approach used by most other WECs. A linear systems approach may be used with overtopping devices. This considers the water oscillating up and down the ramp as the excited body, and the crest of the ramp as a highly nonlinear power take-off system. However due to the non-linearities it is too computationally demanding to model usefully. Therefore a more physical approach is taken. The time series of the overtopping flow is modeled, thus, relying heavily upon empirical data. Figure 8 shows the schematic of flows for the Wave Dragon. Depending on the current wave state (Hs, Tp) and the crest freeboard Rc (height of the ramp crest above mean water level, MWL) of the device, water will overtop into the reservoir (Qovertop). The power gathered by the reservoir is a product of this overtopping flow, the crest freeboard and gravity. If the

reservoir is overfilled when a large volume is deposited in the basin there will be loss from it (Qspill). To minimize this, the reservoir level h must be kept below its maximum level (hR). The useful hydraulic power converted by the turbines is the product of turbine flow (Qturbine), the head across them, water density and gravity. Within the field of coastal engineering there is a considerable body of work looking at the overtopping rates on rubble-mound breakwaters, sea walls and dykes. The studies of Van der Meer and Janssen (1994) provided the basis of the theory on the average expected overtopping rate. Gerloni et al. (1995) investigated the time distribution of the flow. However this work was focused on structures designed to minimize the rate of overtopping, counter to the aims of the Wave Dragon. Kofoed (2002) performed laboratory tests on many permutations of ramp angles, profiles, crest freeboard levels in a variety of sea states, all with heavy overtopping rates. These studies showed the Wave Dragon's patented double curved ramp to be highly efficient at converting incident wave power. When comparing results between different scales of model testing it is very useful to use nondimensional figures to describe the variables. Results from the model scale can then simply be used for any size of device.

Categorization of overtopping WECs Overtopping devices have been designed and tested for both onshore and offshore applications. So, they are categorized in two groups: coast based and floating structures

a) Coast based devices Among the few WECs that have been built and tested is the Norwegian TAPCHAN (TAPered CHANnel). This device is equipped with the same machinery as a low pressure hydroelectric power station with a reservoir and a Kaplan

turbine. The reservoir is fed by waves trapped by a broad channel opening that reaches into the sea. Towards the reservoir the channel is tapered and bent in such a way that the waves pile up and spill over the channel margin. Studies have also been performed on a variation of this coast based approach where overtopping water is not used to produce power but to recirculate water in harbors (in a project called Kingston harbor pump). This approach can be useful at locations where only a small tide exists and therefore only insufficient flushing of the harbors occurs. As the coast based overtopping devices work best in areas with small tidal ranges this can be a very useful application.

b) Floating device The coast based devices are most applicable in coastal regions with deep water close to a rocky coastline. Therefore for countries where the coast generally consists of gentle sloped beaches, such as Denmark, the coast based devices are not appropriate as the waves lose the majority of their energy content through bottom friction and wave breaking before they

reach the shore. Thus a number of floating WECs utilizing wave overtopping have been proposed. The fact that these devices are floating not only makes it possible to move them to regions with larger wave energy density but also solves problems associated with tide and enables relatively easy control of the crest level of the slope. Among the first devices to use this approach was the Sea Power WEC from Sweden. This device has been tested in prototype scale. In Denmark one of the WECs which has been most developed is the Wave Dragon (WD). The WD combines ideas from TAPCHAN and Sea Power and is a floating structure equipped with wave reflectors that focus the waves towards the slope.

Oscillating Water Columns (OWCs) are a type of Wave Energy Converter (WEC) that harness energy from the oscillation of the seawater inside a chamber or hollow caused by the action of waves. OWCs have shown promise as a renewable energy source with low environmental impact. Because of this, multiple companies have been working to design increasingly efficient OWC models. OWC are devices with a semi-submerged chamber or hollow open to the sea below, keeping a trapped air pocket above a water column. Waves force the column to act like a piston, moving up and down, forcing the air out of the chamber and back into it. This continuous movement force a bidirectional stream of high-velocity air, which is channelled through a Power-Take-Off (PTO). The PTO system converts the airflow into energy. In models that convert airflow to electricity, the PTO system consists of a bidirectional turbine. This means that the turbine always spins the same direction regardless of the direction of airflow, allowing for energy to be continuously generated. Both the collecting chamber and PTO systems will be explained further under "Basic OWC Components. Wave energy stands out among the different renewable energy sources not only for its high potential – which, according to the International Energy Agency, can reach up to 80,000 TWh / year – but also for its high energy density, the highest of all renewables

Wave energy is derived from the winds as they blow across the oceans, and this energy transfer provides a convenient and natural concentration of wind energy in the water near the free surface. Once created, waves can travel thousands of kilometres with little energy loss. The power in a wave is proportional to the square of the amplitude and to the period of the motion. Therefore, long period (7÷10 s), large amplitude (about 2 m) waves have energy fluxes commonly averaging between 40 and 70 kW per m width of oncoming wave. Nearer the coastline, the average energy intensity of a wave decreases due to interaction with the seabed. In the Mediterranean basin, the annual power level off the European countries coasts varies between 4 and 11 kW/m, the highest values occurring in the area of the south-western Aegean Sea. This area is characterized by a relatively long fetch and high energy potential. The entire annual deep-water resource along the European coasts in the Mediterranean is of the order of 30 GW, the total wave energy resource for Europe resulting thus to 320 GW. Oscillating Water Column (OWC) systems are one of the most popular technologies for wave energy conversion [4, 5]. They consist of a partially submerged chamber with an underwater opening on its front and an air turbine. Waves

impinging on the device cause the water column inside the chamber to oscillate, which gives its name to the system. As a result of these oscillations, the water column acts like a piston, forcing the air in the upper part of the chamber to flow alternatively out of the chamber and into it, driving the turbine in the process. OWC converters present two main advantages over other Wave Energy Converters (WECs). Firstly, their simplicity, they consist exclusively of the two aforementioned elements, the chamber and the air turbine. Secondly, their low maintenance cost relative to other WECs, which is a result of both their simplicity and the absence of mechanical elements in direct contact with seawater. The chamber and turbine are, therefore, the two essential elements of an OWC converter. Two main types of self-rectifying turbines are used: Wells turbines or impulse turbines [6, 7]. As regards the chamber, a number of works were carried out with the aim of studying and optimising the design of the chamber [8, 9, 10, 11 and 12]. It is worth noting that, in most of the studies carried out so far, these two elements of an OWC converter, the air turbine and the chamber, are investigated separately - in spite of the fact that the coupling between both plays a fundamental role in the performance of the system . In effect, the turbine should ideally provide the pneumatic damping (pressure drop through the turbine) for the chamber to work at, or near, resonant conditions, and the chamber should provide the amount of pneumatic power that maximises the turbine output. The design of the air turbine and turbine type are strictly related to the wave frequency and amplitude. Several authors proposed different design procedure experiments and mathematical modelling in different seas. As known by the authors, in literature there are no studies of using mini or micro OWCs on board of vessels. For this purpose, in this paper, a preliminary study of a micro OWC converter using straight-bladed Darrieus

type air turbine is presented. In particular, a laboratory scale system was realized and analysed by means of Particle Image Velocimetry methodology.

Conclusions In the present paper a transparent Oscillating Water Column Wave Energy Converter simulator was built and tested. The system is able to run performance tests with different air turbines at different wave frequency and amplitude. Moreover, flow characteristics and velocity field around turbine rotor can be measured by means of Particle Image Correlation method. In particular, in this paper a straight-bladed Darrieus type air turbine was tested. Using the PIV system velocity field around the turbine rotor was measured. On the basis of the obtained results the system allows to study velocity field in the air column and around the rotor, while carrying out air turbine

performance assessments. This tool can be used to obtain reference experimental data to validate OWCWEC and air turbine design procedure, as well as to calibrate and verify 1D/3D mathematical model predictions