(pv) Solar System...

Intro:

The Solar System Project Report (1)

It’s obviously that every single day the main sources of power are going more expensive than ever “oil, gas, nuclear power …etc”, so the main objective nowadays is to find a good replacement for such a problem PV Idea: Photovoltaic cell (PV) is used to convert directly the solar radiation into electricity -The PV cells are usually connected in series and parallel to construct a PV module -The PV modules once more are connected in series and parallel to form a PV generator in order to produce higher power. Photo: This is the Greek word of Light. Volt: it is the voltage we can get after we make it in a circuit. Photovoltaic power conditioning units are used to supply electrical power to appliances of different voltage forms (Dc or AC) such as the public electricity grid, telecommunication stations on highways, houses or villages appliances, and solar boot, etc… DC/DC Converter Module used to provide a regulated current and a regulated voltage with very small voltage ripples at the consumer terminals. It should provide high efficiency over the desired voltage range, as well as consider the characteristics of the other different modules (MPP, power supply and battery controller. DSP-Kits are a microprocessor unit. Its basic task is to control the DC/DC converter. Electricity generation using photovoltaic’s (PV) represents an alternative solution for clean energy source. Especially if the continuous increase of the oil prices and the escalation of the environmental problems are continued. Therefore, PV as renewable energy source with the energy efficient Light emitting diodes LED diodes are of high interest.

When the Sunlight hits the “n-type surface” it will generate Kind of “-“and “+” voltage which We need to use in our devices It’s a simple example of how it work But we need some more researches For that. So we will start from the beginning, what We can call solar cells for dummies…

Energy received from the solar cells is used to power the system during sun-on periods, and to recharge the battery pack for sun-off periods. During solar eclipse, the battery is used as the primary power source. The main power line (connected to the solar cells and battery) feeds into a number of DC-DC power converters, which provides the necessary supply voltages for the electronics.

Light Energy IN

Photovoltaic Cells Conversion

Electrical Energy OUT

Photovoltaic Panels cells are made up Of two thin layers usually made from Silicon which is small amounts of Substances. The first layer is called the P-type layer created by treating Silicon with small amounts of Boron that Causes a shortage of electrons and a positive charge. The second layer is Called the n-type layer that is treated with Phosphorous creating a surplus of electrons And therefore a negative charge. The barrier between these two layers is called The p-n junction. When light energy is Applied, the electrons are given enough energy to Move across this junction. Explanation step by step: Radiant energy passes through a glass cover and an anti-reflective coating Inside the cell itself we got a silicon sandwich, this is the working part of the PV cell, the silicon atoms are arranged in a cubic pattern. The top “n-layer” of silicon has electrons to spare; the bottom “p-layer” is missing electrons. So in general it has electron holes. The cell has a positive side and a negative side, just like a battery. A permanent electrical field called a “junction” separates the tow layers. Electrons can flow through the junction from the p-layer to the n-layer, but not the other way. When a photon of sunlight hits the n-layer, it knocks an electron free. These electrons stay in the n-layer. When a photon of sunlight hits an atom in the p-layer, it knocks an electron free. These electrons easily cross into the n-layer. Extra electrons accumulate in the n-layer. A metal wire attached to this layer gives the electrons someplace to go. They enter a DC electrical circuit. Electrons flow from the negative side of the cell, through the circuit, and renter the cell at the positive side. As long as sunlight is corning in, the electrical current will keep flowing. The current delivers electrical energy to a load for instance. So for example:

If we use a light bulb, the current will give us the light we need, and if we put more efficient fluorescent bulb in our circuit, the same amount of power will give us five times more light. Any power we don’t use can go towards reaching a battery. The battery will push electrons through the circuit after the sun has set.

Sensors

Battery

Battery

DC-DC Convertors

An Electrical Device

The Project Side: We need to design a system with the next features : The ability to transfer the Light energy into a useful electrical energy, and after we understand the physical part, we can start with the Circuit and we will need the following steps for that: -Solar panels (The Cells) or the PV transformers. -The DC-DC convert. -A Rechargeable Batteries. -A Battery Sensors, to detect the Full Charge and the Low Charge situations, and start the charging process automatically, and when we got a full charge it has to start to get the energy we need directly from the cells to the circuit no need to use the battery, but we can't detect any sun light the same sensors will be in charge to turn on the batteries to get the energy amount we need .

Project objective Design and implementation of a controller with the following specifications: - Over charge and Low charge protection of the battery.

Light bulb (energy hog because houses 60-100 watts have lots of lights, and it's easy to leave them on when they're not being used)

Fans 100 watts Floor fan or box fan (high speed) Ceiling fan (Bigger fans and faster 15-95 watts

speeds use more energy. My 2004 42" Hampton Bay uses 24/28/42 watts on low/med/high respectively, according to the manual. Progress Energy says on high speed fans use 55/75/95 watts for 36"/48"/52" models respectively.)

Computers 140-330 watts Desktop Computer & 17" CRT monitor 1-20 watts Desktop Computer & Monitor (in sleep mode) 120 watts 17" CRT monitor 40 watts 17" LCD monitor 45 watts Laptop computer

Solar Cells Solar cells are usually made from silicon, the same material used for transistors and integrated circuits. The silicon is treated or "doped" so that when light strikes it electrons are released, so generating an electric current. There are three basic types of solar cell. Monocrystalline cells are cut from a single large crystal of silicon whilst polycrystalline cells are made from a number of crystals. The third type is the amorphous solar cell. Amorphous Solar Cells Amorphous technology is most often seen in small solar panels, such as those in calculators or garden lamps, although amorphous panels are increasingly used in larger applications. They are made by depositing a thin film of silicon onto a sheet of another material such as steel. The panel is formed as one piece and the individual cells are not as visible as in other types. The efficiency of amorphous solar panels is not as high as those made from individual solar cells, although this has improved over recent years to the point where they can be seen as a practical alternative to panels made with crystalline cells. Crystalline Solar Cells Crystalline solar cells are wired in series to produce solar panels. As each cell produces a voltage of between 0.5 and 0.6 Volts, 36 cells are needed to produce an opencircuit voltage of about 20 Volts. This is sufficient to charge a 12 Volt battery under most conditions. Although the theoretical efficiency of monocrystalline cells is slightly higher than that of polycrystalline cells, there is little practical difference in performance.

Solar Power Batteries In stand-alone systems, the power generated by the solar panels is usually used to charge a lead-acid battery. Other types of battery such as nickel-cadmium batteries may be used, but the advantages of the leadacid battery ensure that it is still the most popular choice. A battery is composed of individual cells; each cell in a lead-acid battery produces a voltage of about 2 Volts DC, so a 12 Volt battery needs 6 cells. The capacity of a battery is measured in Ampere-hours or Amp-hours (Ah). Battery Types The number of times a battery can be discharged is known as its cycle life, and this is what determines its suitability for use with solar cells. Car batteries are the most common type of lead-acid battery, but will survive only 5 or 10 cycles so are unsuitable for our purposes. For solar applications a battery needs to be capable of being discharged hundreds or even thousands of times. This type of battery is known as a deep-cycle battery, and some of the many different types are explained here. Leisure Batteries Leisure batteries or caravan batteries are usually the cheapest type of deep-cycle battery. They look similar to a car battery but have a different plate construction. Their capacity is normally in the range of 60 to 120 Ah at 12 Volts, making them most suitable for smaller systems. The cycle life of leisure batteries is limited to a few hundred cycles, meaning that they are most suitable for systems which will not be used every day, such as those in caravans or holiday homes.

Traction Batteries The term traction battery relates to all batteries used to power electric vehicles. This can mean anything from a mobility scooter to a fork-lift truck, so encompasses capacities from 30 or 40 Ah to many hundreds. The smaller traction batteries are usually 6 or 12 Volt units, where the largest are single 2 Volt cells. Traction batteries are ideal for solar power applications, as they are intended to be fully discharged and recharged daily. The larger traction batteries can withstand thousands of discharge cycles. There are also batteries known as semi-traction batteries, which can be thought of as higher quality leisure batteries, exhibiting a greater cycle life. Marine batteries also fall into this category. Sealed Batteries There are many types of sealed lead-acid batteries, ranging from those of 1 or 2 Ah to single cell traction batteries of hundreds of Amp-hours. The advantages of sealed batteries are obvious; they need no maintenance and are spill-proof. They do have disadvantages however; they are more expensive than other battery types, they require more accurate charging control and can have a shorter life, especially at high temperatures. Sealed batteries are most appropriate where the solar power system will need to operate for long periods without maintenance.

Charge Controllers Most solar power systems will need a charge controller. The purpose of this is to ensure that the battery is never overcharged, by diverting power away from it once it is fully charged. Only if a very small solar panel such as a battery saver is used to charge a large battery is it possible to do without a controller. Most charge controllers also incorporate a low-voltage disconnect function, which prevents the battery from being damaged by being completely discharged. It does this by switching off any DC appliances when the battery voltage falls dangerously low. Controller Types Solar charge controllers are specified by the system voltage they are designed to operate on and the maximum current they can handle. The system voltage is usually 12 or 24 Volts, or occasionally 48 Volts. The maximum current is determined by the number and size of solar panels used. A single panel would need a controller of between 4 and 6 Amps rating, while larger arrays may need controllers of 40 Amps or more. Different settings are needed if sealed batteries are used. The controller shown is available with ratings of 8, 12, 20 and 30 Amps, and automatically selects between 12 and 24 Volts. How it Works The principle behind a solar charge controller is simple. There is a circuit to measure the battery voltage, which operates a switch to divert power away from the battery when it is fully charged. Because solar cells are not damaged by being short or open-circuits, either of these methods can be used to stop power reaching the battery. A controller which short-circuits the panel is known as a shunt regulator, and that which opens the circuit as a series regulator. Optionally there may also be a switch to disconnect the power from the appliances or loads when the battery voltage falls dangerously low.

Inverters Many different types of inverter can be used in a solar power system. There are dedicated inverters for solar power available, but what's important is that the correct inverter is used for the job it has to do. This job is converting a certain amount of power from low voltage DC to 230 Volts AC to power mains appliances. The right inverter will deliver enough power but will be no bigger than necessary, and will have the right output waveform. How it Works Most people are familiar with the idea of a transformer. A transformer is a device that converts one voltage into another, so why do we need an inverter? Well the problem with a transformer is that it can only work with alternating current or AC. The power from the battery in a solar power system is direct current or DC. Roughly, what an inverter does is to turn this DC into AC by rapid transistorized switching, and then use a transformer to convert it to the correct AC voltage. Depending on how this is done, the result can be either a sine wave like the mains or a modified sine wave which approximates to the mains. Inverter Types Inverters come in many different sizes. The smallest and cheapest, like the one shown, are basic modified sine wave devices designed to be plugged into a lighter socket. The top end of the market provides inverters rated at many kilowatts, with a sine wave output and additional features such as generator control. As a rule, a smaller system will use a small inverter to power exceptional loads, whereas a larger system may have everything powered from the inverter. The choice of waveform is dependent on the loads; a modified sine wave inverter is likely to be cheaper and more efficient, so a sine wave inverter would be chosen only if mains-quality power is specifically needed, for example for a high-quality sound system.

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Inverters: How To Choose An Inverter For An Independent Power System The inverter is one of the most important and most complex components in an independent energy system. To choose an inverter, you don't have to understand its inner workings, but you should know some basic functions, capabilities, and limitations. This article gives you some of the information you'll need to choose the right inverter and use it wisely. WHY YOU NEED AN INVERTER Independent electric energy systems are untethered from the electrical utility grid. They vary in size from tiny yard lights to remote homes, villages, parks, and medical and military facilities. They also include mobile, portable, and emergency backup systems. Their common bond is the storage battery, which absorbs and releases energy in the form of direct current (DC) electricity In contrast, the utility grid supplies you with alternating current (AC) electricity. AC is the standard form of electricity for anything that "plugs in" to utility power. DC flows in a single direction. AC alternates its direction many times per second. AC is used for grid service because it is more practical for long distance transmission. An inverter converts DC to AC, and also changes the voltage. In other words, it is a power adapter. It allows a battery-based system to run conventional appliances through conventional home wiring. There are ways to use DC directly, but for a modern lifestyle, you will need an inverter for the vast majority, if not all of your loads (loads are devices that use energy). Incidentally, there is another type of inverter called grid-interactive. It is used to feed solar (or other renewable) energy into a grid-connected home and to feed excess energy back into the utility grid. If such a system does not use batteries for backup storage, it is not independent from the grid, and is not within the scope of this article. NOT A SIMPLE DEVICE Outwardly, an inverter looks like a box with one or two switches on it, but inside there is a small universe of dynamic activity. A modern home inverter must cope with a wide range of loads, from a single night light to the big surge required to start a well pump or a power tool. The battery voltage of a solar or wind system can vary as much as 35 percent (with varying state of charge and activity). Through all of this, the inverter must regulate the quality of its output within narrow constraints, with a minimum of power loss. This is no simple task. Additionally, some inverters provide battery backup charging, and can even feed excess power into the grid. DEFINE YOUR NEEDS To choose an inverter, you should first define your needs. Then you need to learn about the inverters that are available. Inverter manufacturers print everything you need to know on their specification sheets (commonly called "spec sheets"). Here is a list of the factors that you should consider. APPLICATION ENVIRONMENT Where is the inverter to be used? Inverters are available for use in buildings (including homes), for recreational vehicles, boats, and portable applications. Will it be connected to the utility grid in some way? Electrical conventions and safety standards differ for various applications, so don't improvise.

ELECTRICAL STANDARDS

The DC input voltage must conform to that of the electrical system and battery bank. 12 volts is no longer the dominant standard for home energy systems, except for very small, simple systems. 24 and 48 volts are the common standards now. A higher voltage system carries less current, which makes system wiring cheaper and easier. The inverter's AC output must conform to the conventional power in the region in order to run locally available appliances. The standard for AC utility service in North America is 115 and 230 volts at a frequency of 60 Hertz (cycles per second). In Europe, South America, and most other places, it's 220 volts at 50 Hertz. Safety Certification An inverter should be certified by an independent testing laboratory such as UL, ETL, CSA, etc., and be stamped accordingly. This is your assurance that it will be safe, will meet the manufacturer's specifications, and will be approved in an electrical inspection. There are different design and rating standards for various application environments (buildings, vehicles, boats, etc.). These also vary from one country to another. POWER CAPACITY How much load can an inverter handle? Its power output is rated in watts (watts = amps x volts). There are three levels of power rating-a continuous rating, a limited-time rating, and a surge rating. Continuous means the amount of power the inverter can handle for an indefinite period of hours. When an inverter is rated at a certain number of watts, that number generally refers to its continuous rating. The limited-time rating is a higher number of watts that it can handle for a defined period of time, typically 10 or 20 minutes. The inverter specifications should define these ratings in relation to ambient temperature (the temperature of the surrounding atmosphere). When the inverter gets too hot, it will shut off. This will happen more quickly in a hot atmosphere. The third level of power rating, surge capacity, is critical to its ability to start motors, and is discussed below. Some inverters are designed to be interconnected or expanded in a modular fashion, in order to increase their capacity. The most common scheme is to "stack" two inverters. A cable connects the two inverters to synchronize them so they perform as one unit. POWER QUALITY -- SINE WAVE vs. "MODIFIED SINE WAVE" Some inverters produce "cleaner" power than others. Simply stated, "sine wave" is clean; anything else is dirty. A sine wave has a naturally smooth geometry, like the track of a swinging pendulum. It is the ideal form of AC power. The utility grid produces sine wave power in its generators and (normally) delivers it to the customer relatively free of distortion. A sine wave inverter can deliver cleaner, more stable power than most grid connections. How clean is a "sine wave"? The manufacturer may use the terms "pure" or "true" to imply a low degree of distortion. The facts are included in the inverter's specifications. Total harmonic distortion (THD) lower than 6 percent should satisfy normal home requirements. Look for less than 3 percent if you have unusually critical electronics, as in a recording studio for example. Other specs are important too. RMS voltage regulation keeps your lights steady. It should be plus or minus 5 percent or less. Peak voltage (Vp) regulation needs to be plus or minus 10 percent or less. A "modified sine wave" inverter is less expensive, but it produces a distorted square waveform that resembles the track of a pendulum being slammed back and forth by hammers. In truth, it isn't a sine wave at all. The misleading term "modified sine wave" was invented by advertising people. Engineers prefer to call it "modified square wave." The "modified sine wave" has detrimental effects on many electrical loads. It reduces the energy efficiency of motors and transformers by 10 to 20 percent. The wasted energy causes abnormal heat which reduces the reliability and longevity of motors and transformers and other devices,

including some appliances and computers. The choppy waveform confuses some digital timing devices. About 5 percent of household appliances simply won't work on modified sine wave power at all. A buzz will be heard from the speakers of nearly every audio device. An annoying buzz will also be emitted by some fluorescent lights, ceiling fans, and transformers. Some microwave ovens buzz or produce less heat. TVs and computers often show rolling lines on the screen. Surge protectors may overheat and should not be used. Modified sine wave inverters were tolerated in the 1980s, but since then, true sine wave inverters have become more efficient and more affordable. Some people compromise by using a modified wave inverter to run their larger power tools or other occasional heavy loads, and a small sine wave inverter to run their smaller, more frequent, and more sensitive loads. Modified wave inverters in renewable energy systems have started fading into history. EFFICIENCY It is not possible to convert power without losing some of it (it's like friction). Power is lost in the form of heat. Efficiency is the ratio of power out to power in, expressed as a percentage. If the efficiency is 90 percent, 10 percent of the power is lost in the inverter. The efficiency of an inverter varies with the load. Typically, it will be highest at about two thirds of the inverter's capacity. This is called its "peak efficiency." The inverter requires some power just to run itself, so the efficiency of a large inverter will be low when running very small loads. In a typical home, there are many hours of the day when the electrical load is very low. Under these conditions, an inverter's efficiency may be around 50 percent or less. The full story is told by a graph of efficiency vs. load, as published by the inverter manufacturer. This is called the "efficiency curve." Read these curves carefully. Some manufacturers cheat by starting the curve at 100 watts or so, not at zero! Because the efficiency varies with load, don't assume that an inverter with 93 percent peak efficiency is better than one with 85 percent peak efficiency. If the 85 percent efficient unit is more efficient at low power levels, it may waste less energy through the course of a typical day. INTERNAL PROTECTION An inverter's sensitive components must be well protected against surges from nearby lightning and static, and from surges that bounce back from motors under overload conditions. It must also be protected from overloads. Overloads can be caused by a faulty appliance, a wiring fault, or simply too much load running at one time. An inverter must include several sensing circuits to shut itself off if it cannot properly serve the load. It also needs to shut off if the DC supply voltage is too low, due to a low battery state-ofcharge or other weakness in the supply circuit. This protects the batteries from over-discharge damage, as well as protecting the inverter and the loads. These protective measures are all standard on inverters that are certified for use in buildings. INDUCTIVE LOADS and SURGE CAPACITY Some loads absorb the AC wave's energy with a time delay (like towing a car with a rubber strap). These are called inductive loads. Motors are the most severely inductive loads. They are found in well pumps, washing machines, refrigerators, power tools, etc. TVs and microwave ovens are also inductive loads. Like motors, they draw a surge of power when they start. If an inverter cannot efficiently feed an inductive load, it may simply shut down instead of starting the device. If the inverter's surge capacity is marginal, its output voltage will dip during the surge. This can cause a dimming of the lights in the house, and will sometimes crash a computer. Any weakness in the battery and cabling to the inverter will further limit its ability to start a motor. A battery bank that is undersized, in poor condition, or has corroded connections, can be a

weak link in the power chain. The inverter cables and the battery interconnect cables must be big, and I mean REALLY big, perhaps the size of a large thumb! The spike of DC current through these cables is many hundreds of amps at the instant of motor starting. Follow the inverter's instruction manual when sizing the cables, or you'll cheat yourself. Coat battery connections with a protective coating to reduce corrosion. IDLE POWER Idle power is the consumption of the inverter when it is on, but no loads are running. It is "wasted" power, so if you expect the inverter to be on for many hours during which there is very little load (as in most residential situations), you want this to be as low as possible. Typical idle power ranges from 15 watts to 50 watts for a home-size inverter. An inverter's spec sheet may describe the inverter's "idle current" in amps. To get watts, just multiply the amps times the DC voltage of the system. LOW SWITCHING FREQUENCY vs. HIGH SWITCHING FREQUENCY There are two ways to build an inverter. Without diving into theory, I'll simply say that there are differences in weight, cost, surge capacity, idle power, and noise. A low switching frequency inverter is big and heavy (generally about 20 pounds (10 kg) per kilowatt), and more expensive. It has the high surge capacity (four to eight times the continuous capacity) needed to start large motors. Beware of the acoustical buzz that low switching frequency inverters make. If you install one near a living space, you may be unhappy with the noise. A high switching frequency inverter is much smaller and lighter (generally about 5 pounds (2.5 kg) per kilowatt), and also less expensive. It has less surge capacity, typically about two times the continuous capacity. It produces little or no audible noise. The idle power is generally higher. If the inverter is oversized for motor starting, its idle power will be higher yet, and may be prohibitive. Most homes that have a well pump or other motors greater than 1 HP will find a low switching frequency inverter to be more economical. Both types of inverter have their virtues. Some people "divide and conquer" by splitting their loads and using two inverters. This adds a measure of redundancy. If one ever fails, the other one can serve as backup. AUTOMATIC ON/OFF Inverter idling can be a substantial load on a small power system. Most inverters made for home power systems have automatic load-sensing. The inverter puts out a brief pulse of power about every second (more or less). When you switch on an AC load, it senses the current draw and turns itself on. Manufacturers have various names for this feature, including "load demand," "sleep mode," "power saver," "autostart," and "standby." Automatic on/off can make life awkward because a tiny load may not trigger the inverter to turn on or stay on. For example, a washing machine may pause between cycles, with only the timer running. The timer draws less than 10 watts. The inverter's turn-on "threshold" may be 10 or 15 watts. The inverter shuts off and doesn't come back on until it sees an additional load from some other appliance. You may have to leave a light on while running the washer. Some people can't adapt to such situations. Therefore, inverters with automatic on/off also have an always-on setting. With it, you can run your low-power night lights, your clocks, fax, answering machine and other tiny loads, without losing continuity. In that case, a good system designer will add the inverter's idle power into the load calculation (24 hours a day). The cost of the power system will be higher, but it will meet the expectations of modern living. PHANTOM LOADS and IDLING LOADS High tech consumers (most of us Americans) are stuck with gadgets that draw power whenever they are plugged in. Some of them use power to do nothing at all. An example is a TV with a remote control. Its electric eye system is on day and night, watching for your signal to turn the

screen on. Every appliance with an external wall-plug transformer uses power even when the appliance is turned off. These little demons are called "phantom loads" because their power draw is unexpected, unseen, and easily forgotten. A similar concern is "idling loads." These are devices that must be on all the time in order to function when needed. These include smoke detectors, alarm systems, motion detector lights, fax machines, and answering machines. Central heating systems have a transformer in their thermostat circuit that stays on all the time. Cordless (rechargeable) appliances draw power even after their batteries reach a full charge. If in doubt, feel the device. If it's warm, that indicates wasted energy. How many phantom or idling loads do you have? There are several ways to cope with phantom and idling loads: * You may be able to avoid them (in a small cabin or simple-living situation). * You can minimize their use and disconnect them when not needed, using external switches (such as switched plug-in strips or receptacles). * You can work around them by modifying certain equipment to shut off completely (central heating thermostat circuits, for example). * You can use some DC appliances. * You can pay the additional cost for a large enough power system to handle the extra loads plus the inverter's idle current. Be careful and honest if you contemplate avoiding all phantom and idling loads. You cannot always anticipate future needs or human behavior. POWERING A WATER SUPPLY PUMP At a remote site, a water well or pressure pump often places the greatest demand on the inverter. It warrants special consideration. Most pumps draw a very high surge of current during startup. The inverter must have sufficient surge capacity to handle it while running any other loads that may be on. It is important to size an inverter sufficiently, especially to handle the starting surge. Oversize it still further if you want it to start the pump without causing lights to dim or blink. Ask your supplier for help doing this because inverter manufacturers have not been supplying sufficient data for sizing in relation to pumps. In North America, most pumps (especially submersibles) run on 230 volts, while smaller appliances and lights use 115 volts. To obtain 230 volts from a 115 volt inverter, either use two inverters "stacked" (if they are designed for that) or use a transformer to step up the voltage. If you do not already have a pump installed, you can get a 115 volt pump if you don't need more than 1/2 HP. A water pump contractor will often supply a higher power pump than is needed for a resource-conserving household. You can request a smaller pump, or it may be feasible (and economical) to replace an existing pump with a smaller one. You can also consider one of a growing number of high-effiency DC pumps that are available, to eliminate the load from your inverter.

BATTERY CHARGING FEATURES Backup battery charging is essential to most renewable energy systems because there are likely to be occasions when the natural energy supply is insufficient. Some inverters have a built-in battery charger that will recharge the battery bank whenever power is applied from an AC generator or from the utility grid (if the batteries are not already charged). This also means that an inverter can be a complete emergency backup system for on-grid power needs (just add batteries). A backup battery charger doesn't have to be built into the inverter. Separate chargers are, in some cases, superior to those built into inverters. This is especially true in the case of low switching frequency inverters, which tend to require an oversized generator to produce the full rated charge current.

The specifications that relate to battery charging systems include maximum charging rate (amps) and AC input power requirements. The best chargers have two or three-stage charge control, accommodation of different battery types (flooded or sealed), temperature compensation, and other refinements. Be careful when sizing a generator to meet the requirements of an inverter/charger. Some inverters require that the generator be oversized (because of low power factor, which is beyond the scope of this article). Be sure to get experienced advice on this, or you may be disappointed by the results. QUALITY PAYS A good inverter is an industrial quality device that is proven reliable, certified for safety, and can last for decades. A cheap inverter may soon end up in the junk pile, and can even be a fire hazard. Consider your inverter to be a foundation component. Buy a good one that allows for future expansion of your needs. YOUR FINAL CHOICE Choosing an inverter is not a difficult task. Define where it is to be used. Define what type of loads (appliances) you will be powering. Determine the maximum power the inverter will need to handle. Is the quality of the power critical? Does size and weight matter? The inverter selection table will help you to determine what type of inverter is best for you. Your next step is to learn what inverters are available on the market. Study advertisements and catalogs, or ask your favorite dealer. It is best to listen to professional advice, and to purchase your equipment from a trained and experienced dealer/installer. We hope this article helps you make the right choice.

Batteries Controllers A charge controller is an essential part of nearly all power systems that charge batteries, whether the power source is PV, wind, hydro, fuel, or utility grid. Its purpose is to keep your batteries properly fed and safe for the long term. The basic functions of a controller are quite simple. Charge controllers block reverse current and prevent battery overcharge. Some controllers also prevent battery overdischarge, protect from electrical overload, and/or display battery status and the flow of power. Let's examine each function individually. Blocking Reverse Current Photovoltaic panels work by pumping current through your battery in one direction. At night, the panels may pass a bit of current in the reverse direction, causing a slight discharge from the battery. (Our term "battery" represents either a single battery or bank of batteries.) The potential loss is minor, but it is easy to prevent. Some types of wind and hydro generators also draw reverse current when they stop (most do not except under fault conditions). In most controllers, charge current passes through a semiconductor (a transistor) which acts like a valve to control the current. It is called a "semiconductor" because it passes current only in one direction. It prevents reverse current without any extra effort or cost.

In some controllers, an electromagnetic coil opens and closes a mechanical switch. This is called a relay. (You can hear it click on and off.) The relay switches off at night, to block reverse current. If you are using a PV array only to trickle-charge a battery (a very small array relative to the size of the battery), then you may not need a charge controller. This is a rare application. An example is a tiny maintenance module that prevents battery discharge in a parked vehicle but will not support significant loads. You can install a simple diode in that case, to block reverse current. A diode used for this purpose is called a "blocking diode." Preventing Overcharge When a battery reaches full charge, it can no longer store incoming energy. If energy continues to be applied at the full rate, the battery voltage gets too high. Water separates into hydrogen and oxygen and bubbles out rapidly. (It looks like it's boiling so we sometimes call it that, although it's not actually hot.) There is excessive loss of water, and a chance that the gasses can ignite and cause a small explosion. The battery will also degrade rapidly and may possibly overheat. Excessive voltage can also stress your loads (lights, appliances, etc.) or cause your inverter to shut off. Preventing overcharge is simply a matter of reducing the flow of energy to the battery when the battery reaches a specific voltage. When the voltage drops due to lower sun intensity or an increase in electrical usage, the controller again allows the maximum possible charge. This is called "voltage regulating." It is the most essential function of all charge controllers. The controller "looks at" the voltage, and regulates the battery charging in response. Some controllers regulate the flow of energy to the battery by switching the current fully on or fully off. This is called "on/off control." Others reduce the current gradually. This is called "pulse width modulation" (PWM). Both methods work well when set properly for your type of battery. A PWM controller holds the voltage more constant. If it has two-stage regulation, it will first hold the voltage to a safe maximum for the battery to reach full charge. Then, it will drop the voltage lower, to sustain a "finish" or "trickle" charge. Two-stage regulating is important for a system that may experience many days or weeks of excess energy (or little use of energy). It maintains a full charge but minimizes water loss and stress. The voltages at which the controller changes the charge rate are called set points. When determining the ideal set points, there is some compromise between charging quickly before the sun goes down, and mildly overcharging the battery. The determination of set points depends on the anticipated patterns of usage, the type of battery, and to some extent, the experience and philosophy of the system designer or operator. Some controllers have adjustable set points, while others do not. Control Set Points vs. Temperature The ideal set points for charge control vary with a battery's temperature. Some controllers have a feature called "temperature compensation." When the controller senses a low battery temperature, it will raise the set points. Otherwise when the battery is cold, it will reduce the charge too soon. If your batteries are exposed to temperature swings greater than about 30? F (17? C), compensation is essential. Some controllers have a temperature sensor built in. Such a controller must be mounted in a place where the temperature is close to that of the batteries. Better controllers have a remote temperature probe, on a small cable. The probe should be attached directly to a battery in order to report its temperature to the controller. An alternative to automatic temperature compensation is to manually adjust the set points (if possible) according to the seasons. It may be sufficient to do this only twice a year, in spring and fall. Control Set Points vs. Battery Type The ideal set points for charge controlling depend on the design of the battery. The vast majority of RE systems use deep-cycle lead-acid batteries of either the flooded type or the sealed type. Flooded batteries are filled with liquid. These are the standard, economical deep cycle batteries.

Sealed batteries use saturated pads between the plates. They are also called "valve-regulated" or "absorbed glass mat," or simply "maintenance-free." They need to be regulated to a slightly lower voltage than flooded batteries or they will dry out and be ruined. Some controllers have a means to select the type of battery. Never use a controller that is not intended for your type of battery. Typical set points for 12 V lead-acid batteries at 77 F (25 C) (These are typical, presented here only for example.) High limit (flooded battery): 14.4 V High limit (sealed battery): 14.0 V Resume full charge: 13.0 V Low voltage disconnect: 10.8 V Reconnect: 12.5 V Temperature compensation for 12V battery: -.03 V per C deviation from standard 25 C Low Voltage Disconnect (LVD) The deep-cycle batteries used in renewable energy systems are designed to be discharged by about 80 percent. If they are discharged 100 percent, they are immediately damaged. Imagine a pot of water boiling on your kitchen stove. The moment it runs dry, the pot overheats. If you wait until the steaming stops, it is already too late! Similarly, if you wait until your lights look dim, some battery damage will have already occurred. Every time this happens, both the capacity and the life of the battery will be reduced by a small amount. If the battery sits in this overdischarged state for days or weeks at a time, it can be ruined quickly. The only way to prevent overdischarge when all else fails, is to disconnect loads (appliances, lights, etc.), and then to reconnect them only when the voltage has recovered due to some substantial charging. When overdischarge is approaching, a 12 volt battery drops below 11 volts (a 24 V battery drops below 22 V). A low voltage disconnect circuit will disconnect loads at that set point. It will reconnect the loads only when the battery voltage has substantially recovered due to the accumulation of some charge. A typical LVD reset point is 13 volts (26 V on a 24 V system). All modern inverters have LVD built in, even cheap pocket-sized ones. The inverter will turn off to protect itself and your loads as well as your battery. Normally, an inverter is connected directly to the batteries, not through the charge controller, because its current draw can be very high, and because it does not require external LVD. If you have any DC loads, you should have an LVD. Some charge controllers have one built in. You can also obtain a separate LVD device. Some LVD systems have a "mercy switch" to let you draw a minimal amount of energy, at least long enough to find the candles and matches! DC refrigerators have LVD built in. If you purchase a charge controller with built-in LVD, make sure that it has enough capacity to handle your DC loads. For example, let's say you need a charge controller to handle less than 10 amps of charge current, but you have a DC water pressurizing pump that draws 20 amps (for short periods) plus a 6 amp DC lighting load. A charge controller with a 30 amp LVD would be appropriate. Don't buy a 10 amp charge controller that has only a 10 or 15 amp load capacity! Overload Protection A circuit is overloaded when the current flowing in it is higher than it can safely handle. This can cause overheating and can even be a fire hazard. Overload can be caused by a fault (short circuit) in the wiring, or by a faulty appliance (like a frozen water pump). Some charge controllers have overload protection built in, usually with a push-button reset. Built-in overload protection can be useful, but most systems require additional protection in the form of fuses or circuit breakers. If you have a circuit with a wire size for which the safe

carrying capacity (ampacity) is less than the overload limit of the controller, then you must protect that circuit with a fuse or breaker of a suitably lower amp rating. In any case, follow the manufacturer's requirements and the National Electrical Code for any external fuse or circuit breaker requirements. Displays and Metering Charge controllers include a variety of possible displays, ranging from a single red light to digital displays of voltage and current. These indicators are important and useful. Imagine driving across the country with no instrument panel in your car! A display system can indicate the flow of power into and out of the system, the approximate state of charge of your battery, and when various limits are reached. If you want complete and accurate monitoring however, spend about US$200 for a separate digital device that includes an amp-hour meter. It acts like an electronic accountant to keep track of the energy available in your battery. If you have a separate system monitor, then it is not important to have digital displays in the charge controller itself. Even the cheapest system should include a voltmeter as a bare minimum indicator of system function and status. Have It All with a Power Center If you are installing a system to power a modern home, then you will need safety shutoffs and interconnections to handle high current. The electrical hardware can be bulky, expensive and laborious to install. To make things economical and compact, obtain a ready-built "power center." It can include a charge controller with LVD and digital monitoring as options. This makes it easy for an electrician to tie in the major system components, and to meet the safety requirements of the National Electrical Code or your local authorities. Charge Controllers for Wind and Hydro A charge controller for a wind-electric or hydro-electric charging system must protect batteries from overcharge, just like a PV controller. However, a load must be kept on the generator at all times to prevent overspeed of the turbine. Instead of disconnecting the generator from the battery (like most PV controllers) it diverts excess energy to a special load that absorbs most of the power from the generator. That load is usually a heating element, which "burns off" excess energy as heat. If you can put the heat to good use, fine! Is It Working? How do you know if a controller is malfunctioning? Watch your voltmeter as the batteries reach full charge. Is the voltage reaching (but not exceeding) the appropriate set points for your type of battery? Use your ears and eyes-are the batteries bubbling severely? Is there a lot of moisture accumulation on the battery tops? These are signs of possible overcharge. Are you getting the capacity that you expect from your battery bank? If not, there may be a problem with your controller, and it may be damaging your batteries. Conclusion The control of battery charging is so important that most manufacturers of high quality batteries (with warranties of five years or longer) specify the requirements for voltage regulation, low voltage disconnect and temperature compensation. When these limits are not respected, it is common for batteries to fail after less than one quarter of their normal life expectancy, regardless of their quality or their cost. A good charge controller is not expensive in relation to the total cost of a power system. Nor is it very mysterious. I hope this article has given you the background that you need to make a good choice of controls for your power system.

More Information Photovoltaic modules are so reliable that we forget that things can go wrong! The real world imposes temperature extremes, lightning and static electricity, moisture and wind stresses, as well as imperfect manufacturing. Here are some suggestions for testing and troubleshooting. Selective shading test - If the array is in a parallel or series-parallel configuration, this trick will help you locate a fault without disconnecting any wiring. Find an object that is large enough to shade at least 4 cells. (A cowboy hat will do.) Shading just a few cells will drop the module's output to less than half. With the array connected andworking, monitor the current (or in the case of a nearby solar pump, just listen to it). Now, shade a portion of one module. You should see the current should drop noticeably (or the pump should slow down). If the current does NOT drop, then the module that you are shading is out of the circuit. Look for a fault in the wiring of that module, or of another module that is wired in series with it. Fading in the heat Occasionally somebody complains of reduced array output when the sun is hottest. Heat fade shows up most severely in battery systems. If the difference between the array voltage and the battery voltage approaches zero, then current flow can drop nearly to zero. This can also cause a solar pump to produce less than it should. The voltage of a PV module normally decreases with temperature rise. PV manufacturers document this by showing several lines on the IV curve (the graph of amps vs. volts), or by stating it in volts per degree of deviation from 25?C (77?F). Nominal "12 volt" PV modules are designed to sustain good current flow all the way to 17 or 18V at 25?C. This allows for voltage drop at higher temperatures. If heat fade is severe, it MAY be caused by weak PV modules or by any other weak links in the power chain, including undersized wiring, poor connections and controller losses. Here are some tests to isolate these factors. First, you can confirm heat fading by cooling the array with water while the system is operating. Monitor the current. Does it rise to normal? If so, you need to determine where the voltage drop is severe. Connect a voltmeter directly to the PV array (or it's combiner box). Disconnect the array from the controller, in order to read the open circuit voltage. If it is less than 18V (relative to a 12V configuration), then part or all of the PV array may be defective. The selective shading test (above) can help you locate weaker modules in an array. Next, reconnect the array to the system. Under good sunlight, test for voltage drop in the wiring by measuring the voltage at the array, and then again at the controller input. Note that voltage drop in wiring will increase in proportion to the current flow. Next, test for drop in the controller by measuring the voltage at its PV input, and then at its battery terminals. Remember, if the battery is fully charged, the controller SHOULD drop the voltage. If that is the case, you can bring down the battery voltage by turning loads on. When the battery is at less than 13.5V (relative to a 12V system), the controller should allow full current to flow. If voltage drop occurs at a single point (at a connector or within the controller) then concentrated heat will result. You may feel it, or see signs of heat damage. If voltage drop is evident at the loads (dimming lights, low voltage disconnection when batteries are not low) then check for corroded battery connections (see "Batteries: How to Keep Them Alive" in SunPaper 1, or at our website). Burnt terminals

Years of temperature cycling will occasionally cause a screw to loosen, or metal to distort. This can be caused by poor workmanship and/or inferior materials. Add a touch of oxidation and corrosion, and you get electrical resistance. Now, keep the current flowing and you get even more heat. When you repair overheated connections, replace all metal parts that have been severely oxidized. In worst cases, an electric arc will jump a gap, melting metal and burning insulation to a char. Charred terminals on PV modules can be bypassed by soldering a wire directly to the metal strip that leads to the PV cells. Diode failures Most PV modules have bypass diodes in the junction boxes, to protect cells from overheating if there is a sustained partial shade on them. On rare occasions a diode will fail, usually as a result of lightning. Most often, it will short out and reduce the module's voltage drastically. (A shorted diode will read near-zero ohms in both directions.) If the module is in a 12V array, there is no need for the bypass diode so you can remove it. In a 24V array that is unlikely to experience sustained partial shading, you can remove it. In any other case, replace it with a silicon diode with an amps rating at or above the module's maximum current, and with a voltage rating of 400V or more.

Grounding Lightning and related static discharge is the number one cause of sudden, unexpected failures in PV systems. Lightning does not have to strike directly to cause damage to sensitive electronic equipment, such as inverters, controls, radios and entertainment equipment. It can be miles away and invisible, and still induce high voltage surges in wiring, especially in long lines. Fortunately, almost all cases of lightning damage can be prevented by proper system grounding. Owners of independent power systems do not have grounding supplied by the utility company, and often overlook it until it is too late. My own customers have reported damage to inverters, charge controllers, DC refrigerators, fluorescent light ballasts, TVs, pumps, and (rarely) photovoltaic panels. These damages cost many thousands of $, and ALL reports were from owner-installed systems that were NOT GROUNDED. GROUNDING means connecting part of your system structure and/or wiring electrically to the earth. During lightning storms, the clouds build up a static electric charge. This causes

accumulation of the opposite charge in objects on the ground. Objects that are INSULATED from the earth tend to accumulate the charge more strongly than the surrounding earth. If the potential difference (voltage) between sky and the object is great enough, lightning will jump the gap. Grounding your system does four things: (1) It drains off accumulated charges so that lightning is NOT HIGHLY ATTRACTED to your system. (2) If lightning does strike, or if a high charge does build up, your ground connection provides a safe path for discharge directly to the earth rather than through your wiring. (3) It reduces shock hazard from the higher voltage (AC) parts of your system, and (4) reduces electrical hum and radio caused by inverters, motors, fluorescent lights and other devices, and not least . . . GROUNDING IS REQUIRED by the NATIONAL ELECTRICAL CODE (NEC)(r). Photovoltaic systems are included in Article 690 of the Code. Low voltage systems are NOT exempt from grounding requirements or from the NEC. To achieve effective grounding FOLLOW THESE GUIDELINES: INSTALL A PROPER GROUNDING SYSTEM: Minimal grounding is provided by a copper-plated ground rod, usually 8 ft. long, driven into the earth. This is a minimum proceedure in an area where the ground is moist (electrically conductive). Where the ground may be dry, especially sandy, or where lightning may be particularly severe, more rods should be installed, at least 10 feet apart. Connect or "bond" all ground rods together via bare copper wire (#6 or larger, see the NEC) and bury the wire. Use only approved clamps to connect wire to rods. If your photovoltaic array is some distance from the house, drive ground rod(s) near it, and bury bare wire in the trench with the power lines. Metal water pipes that are buried in the ground are also good to ground to. Purchase connectors approved for the purpose, and connect ONLY to cold water pipes, NEVER to hot water or gas pipes. Beware of plastic fittings -- bypass them with copper wire. Iron well casings are super ground rods. Drill and tap a hole in the casing to get a good bolted connection. If you connect to more than one grounded object (the more the better) it is essential to electrically bond (wire) them to each other. Connections made in or near the ground are prone to corrosion, so use proper bronze or copper connectors. Your ground system is only as good as its weakest electrical connections. If your site is rocky and you cannot drive ground rods deeply, bury (as much as feasible) at least 150 feet of bare copper wire. Several pieces radiating outward is best. Try to bury them in areas that tend to be moist. If you are in a lightning-prone area, bury several hundred feet if you can. The idea is to make as much electrical contact with the earth as you can, over the broadest area feasible, preferably contacting moist soil. You can save money by purchasing used copper wire (not aluminum) from a scrap metal dealer, and stripping off the insulation (use copper "split bolts" or crimped splices to tie odd pieces together. If you need to run any power wiring over a distance of 30 feet or more, and are in a high-lightning, dry or rocky area, run the wires in metal conduit and bond the conduit to your grounding system. WHAT TO CONNECT TO YOUR GROUND SYSTEM: GROUND THE METALLIC FRAMEWORK of your PV array. (If your framework is wood, metalically bond the module frames together, and wire to ground.) Be sure to bolt your ground wires solidly to the metal so it will not come loose, and inspect it periodically. Also ground antenna masts and wind generator towers. GROUND THE NEGATIVE SIDE OF YOUR POWER SYSTEM, but FIRST make the following test for leakage to ground: Obtain a common "multi-tester". Set it on the highest "milliamp" scale. Place the negative probe on battery neg. and the positive probe on your ground system. No reading? Good. Now switch it down to the lowest milli- or microamp scale and try again. If you get only a few microamps, or zero, THEN GROUND YOUR BATTERY NEGATIVE. If you DID read

leakage to ground, check your system for something on the positive side that may be contacting earth somehow. (If you read a few microamps to ground, it is probably your meter detecting radio station signals.) Connect your DC negative to ground ONLY IN ONE PLACE, at a negative battery connection or other main negative junction nearby (at a disconnect switch or inverter, for instance. Do NOT ground negative at the array or at any other points. GROUND YOUR AC GENERATOR AND INVERTER FRAMES, and AC neutral wires and conduits in the manner conventional for all AC systems. This protects from shock hazard as well as lightning damage. PV ARRAY WIRING should be done with minimum lengths of wire, tucked into the metal framework, then run through metal conduit. Positive and negative wires should be run together wherever possible, rather than being some distance apart. This will minimize induction of lightning surges. Bury long outdoor wire runs instead of running them overhead. Place them in grounded metal conduit if you feel you need maximum protection. SURGE PROTECTION DEVICES bypass the high voltages induced by lightning. They are recommended for additional protection in lightning-prone areas or where good grounding is not feasible (such as on a dry rocky mountain top), especially if long lines are being run to an array, pump, antenna, or between buildings. Surge protectors must be special for low voltage systems, so contact your PV dealer. SAFETY FIRST!!! If you are uncertain of your ability to wire your system properly, HIRE AN ELECTRICIAN!

120W Solar Panel Kit

• • • •

£699.99

High efficiency crystalline cell for “all weather” charging Perfect for TV operation, 240v appliances* and for permanent fitting Water resistant, robust construction for outdoor use. 20 year cell warranty and 10 year module warranty

The 120W panel provides much higher power demands and includes bypass diodes to minimise the effect of shadows. It delivers maximum power in the smallest module size saving weight and space. It is supplied with all the necessary cable (5m), connectors and detailed installation instructions.

The 8Ah (STS01208) Charge controller (sold separately) should be used with this kit to protect the battery from being overcharged and to prevent reverse current drain. Specifications Power: 120watts Peak Output: 7.93A @ 17.2V Approx. watt-hours/day** 840 Approx. amp-hours/day** 55.1 Dimensions: 1483x671x35mm Weight: 11.5kg * An inverter is required to power or charge 240V appliances – not included ** Based on 7 hours of average daily peak sunlight hours Price £699.99 VAT included Reference