(PV) Solar System

8/14/2019 (PV) Solar System...

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The Solar System ProjectReport (1)

Intro:

Its obviously that every single day the main sources of power are goingmore expensive than ever oil, gas, nuclear power etc, so the mainobjective nowadays is to find a good replacement for such a problem

PV Idea:

Photovoltaic cell (PV) is used to convert directly the solar radiation intoelectricity

-The PV cells are usually connected in series and parallel to construct aPV module-The PV modules once more are connected in series and parallel to form aPV 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 powerto appliances of different voltage forms (Dc or AC) such as the public

electricity grid, telecommunication stations on highways, houses orvillages appliances, and solar boot, etc

DC/DC Converter Module used to provide a regulated current and aregulated voltage with very small voltage ripples at the consumerterminals. It should provide high efficiency over the desired voltagerange, as well as consider the characteristics of the other differentmodules (MPP, power supply and battery controller. DSP-Kits are amicroprocessor unit. Its basic task is to control the DC/DC converter.

Electricity generation using photovoltaics (PV) represents an alternativesolution for clean energy source. Especially if the continuous increase ofthe oil prices and the escalation of the environmental problems arecontinued. Therefore, PV as renewable energy source with the energyefficient Light emitting diodes LED diodes are of high interest.


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PhotovoltaicCells Conversion

ElectricalEnergy OUTLight Energy IN

When the Sunlight hits then-type surface it will generateKind of -and + voltage which

We need to use in our devices

Its a simple example of how it workBut we need some more researchesFor that.So we will start from the beginning, whatWe 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. Themain power line (connected to the solar cells and battery) feeds into anumber of DC-DC power converters, which provides the necessary supplyvoltages for the electronics.


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Photovoltaic Panels cells are made upOf two thin layers usually made fromSilicon which is small amounts ofSubstances. The first layer is called the

P-type layer created by treatingSilicon with small amounts of Boron thatCauses a shortage of electrons anda positive charge. The second layer isCalled the n-type layer that is treated withPhosphorous creating a surplus of electronsAnd therefore a negative charge.The barrier between these two layers is calledThe p-n junction. When light energy is

Applied, the electrons are given enough energy toMove across this junction.

Explanation step by step:

Radiant energy passes through a glass cover and an anti-reflectivecoatingInside the cell itself we got a silicon sandwich, this is the working part ofthe 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 missingelectrons. So in general it has electron holes.The cell has a positive side and a negative side, just like a battery. Apermanent 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 anatom in the p-layer, it knocks an electron free. These electrons easilycross into the n-layer.Extra electrons accumulate in the n-layer. A metal wire attached to thislayer gives the electrons someplace to go. They enter a DC electricalcircuit.Electrons flow from the negative side of the cell, through the circuit, andrenter the cell at the positive side. As long as sunlight is corning in, theelectrical current will keep flowing.

The current delivers electrical energy to a load for instance.So for example:


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BatteryBatterySensors

DC-DC

Convertors

An Electrical

Device

If we use a light bulb, the current will give us the light we need, and if weput more efficient fluorescent bulb in our circuit, the same amount ofpower will give us five times more light.Any power we dont use can go towards reaching a battery. The battery

will push electrons through the circuit after the sun has set.


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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 Circuitand 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 fromthe cells to the circuit no need to use the battery, but we can't detectany sun light the same sensors will be in charge to turn on the batteriesto get the energy amount we need .

Project objectiveDesign and implementation of a controller with the following

specifications:- Over charge and Low charge protection of the battery.


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60-100 wattsLight bulb (energy hog because houseshave lots of lights, and it's easy to leavethem on when they're not being used)

Fans

100 watts Floor fan or box fan (high speed)

15-95 watts

Ceiling fan (Bigger fans and fasterspeeds use more energy. My 2004 42"Hampton Bay uses 24/28/42 watts onlow/med/high respectively, according to themanual. Progress Energysays on highspeed fans use 55/75/95 watts for36"/48"/52" models respectively.)

Computers

140-330 watts Desktop Computer & 17" CRTmonitor

1-20 watts Desktop Computer & Monitor (insleep mode)

120 watts 17" CRT monitor

40 watts 17" LCD monitor

45 watts Laptop computer
http://www.progress-energy.com/custservice/carres/energytips/ceilingfans.asphttp://www.progress-energy.com/custservice/carres/energytips/ceilingfans.asphttp://www.progress-energy.com/custservice/carres/energytips/ceilingfans.asp


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Solar Cells

Solar cells are usually made from silicon, the same material used for

transistors and integrated circuits. The silicon is treated or "doped" sothat when light strikes it electrons are released, so generating anelectric current. There are three basic types of solar cell.Monocrystalline cells are cut from a single large crystal of silicon whilstpolycrystalline cells are made from a number of crystals. The third typeis 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, althoughamorphous panels are increasingly used in larger applications.They are made by depositing a thin film of silicon onto a sheetof another material such as steel. The panel is formed as onepiece and the individual cells are not as visible as in othertypes. The efficiency of amorphous solar panels is not as highas those made from individual solar cells, although this hasimproved over recent years to the point where they can be

seen as a practical alternative to panels made with crystallinecells.

Crystalline Solar Cells

Crystalline solar cells are wired in series to produce solarpanels. As each cell produces a voltage of between 0.5and 0.6 Volts, 36 cells are needed to produce an open-circuit voltage of about 20 Volts. This is sufficient to

charge a 12 Volt battery under most conditions. Althoughthe theoretical efficiency of monocrystalline cells isslightly higher than that of polycrystalline cells, there islittle practical difference in performance.


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Solar Power Batteries

In stand-alone systems, the power generated by the solar panels isusually used to charge a lead-acid battery. Other types of battery suchas nickel-cadmium batteries may be used, but the advantages of the lead-acid battery ensure that it is still the most popular choice. A battery iscomposed of individual cells; each cell in a lead-acid battery produces avoltage of about 2 Volts DC, so a 12 Volt battery needs 6 cells. Thecapacity of a battery is measured in Ampere-hoursor Amp-hours(Ah).

Battery Types

The number of times a battery can be discharged isknown as its cycle life, and this is what determines itssuitability for use with solar cells. Car batteries are themost common type of lead-acid battery, but will surviveonly 5 or 10 cycles so are unsuitable for our purposes.For solar applications a battery needs to be capable ofbeing discharged hundreds or even thousands of times.This type of battery is known as a deep-cyclebattery, and some of the

many different types are explained here.

Leisure Batteries

Leisure batteries or caravan batteries are usually thecheapest type of deep-cycle battery. They look similar to acar battery but have a different plate construction. Theircapacity is normally in the range of 60 to 120 Ah at 12Volts, making them most suitable for smaller systems. The

cycle life of leisure batteries is limited to a few hundred cycles, meaningthat they are most suitable for systems which will not be used every day,such as those in caravans or holiday homes.


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Traction Batteries

The term traction battery relates to all batteriesused to power electric vehicles. This can meananything from a mobility scooter to a fork-lifttruck, so encompasses capacities from 30 or 40 Ahto many hundreds. The smaller traction batteriesare usually 6 or 12 Volt units, where the largestare single 2 Volt cells. Traction batteries are ideal for solar powerapplications, as they are intended to be fully discharged and rechargeddaily. The larger traction batteries can withstand thousands of discharge

cycles. There are also batteries known as semi-traction batteries, whichcan be thought of as higher quality leisure batteries, exhibiting a greatercycle 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 tractionbatteries of hundreds of Amp-hours. The advantages

of sealed batteries are obvious; they need nomaintenance and are spill-proof. They do havedisadvantages however; they are more expensive than

other battery types, they require more accurate charging control and canhave a shorter life, especially at high temperatures. Sealed batteries aremost appropriate where the solar power system will need to operate forlong periods without maintenance.


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Charge Controllers

Most solar power systems will need a charge controller. The purpose ofthis is to ensure that the battery is never overcharged, by divertingpower away from it once it is fully charged. Only if a very small solarpanel such as a battery saver is used to charge a large battery is itpossible to do without a controller. Most charge controllers alsoincorporate a low-voltage disconnect function, which prevents the batteryfrom being damaged by being completely discharged. It does this byswitching off any DC appliances when the battery voltage fallsdangerously low.

Controller Types

Solar charge controllers are specified by the systemvoltage they are designed to operate on and themaximum current they can handle. The system voltage isusually 12 or 24 Volts, or occasionally 48 Volts. Themaximum current is determined by the number and size of solar panelsused. 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. Thecontroller shown is available with ratings of 8, 12, 20 and 30 Amps, andautomatically 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 todisconnect the power from the appliances or loadswhen the battery voltage

falls dangerously low.


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Inverters

Many different types of inverter can be used in a solar power system.There are dedicated inverters for solar power available, but what'simportant 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 to230 Volts AC to power mains appliances. The right inverter will deliverenough power but will be no bigger than necessary, and will have the rightoutput waveform.

How it Works

Most people are familiar with the idea of atransformer. A transformer is a device that convertsone voltage into another, so why do we need aninverter? Well the problem with a transformer is thatit can only work with alternating current or AC. Thepower from the battery in a solar power system is direct currentor DC.Roughly, what an inverter does is to turn this DC into AC by rapidtransistorized switching, and then use a transformer to convert it to the

correct AC voltage. Depending on how this is done, the result can beeither a sine wave like the mains or a modified sine wave whichapproximates to the mains.

Inverter Types

Inverters come in many different sizes. Thesmallest and cheapest, like the one shown, are basicmodified sine wave devices designed to be plugged

into a lighter socket. The top end of the marketprovides inverters rated at many kilowatts, with asine wave output and additional features such as

generator control. As a rule, a smaller system will use a small inverter topower exceptional loads, whereas a larger system may have everythingpowered from the inverter. The choice of waveform is dependent on theloads; a modified sine wave inverter is likely to be cheaper and moreefficient, so a sine wave inverter would be chosen only if mains-qualitypower is specifically needed, for example for a high-quality sound system.


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UK's Heat map


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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 energysystem. To choose an inverter, you don't have to understand its inner workings, but you shouldknow some basic functions, capabilities, and limitations. This article gives you some of theinformation 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 insize 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 thestorage 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 thestandard 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 becauseit is more practical for long distance transmission.

An inverter converts DC to AC, and also changes the voltage. In other words, it is a poweradapter. It allows a battery-based system to run conventional appliances through conventionalhome wiring. There are ways to use DC directly, but for a modern lifestyle, you will need aninverter 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 (orother renewable) energy into a grid-connected home and to feed excess energy back into theutility grid. If such a system does not use batteries for backup storage, it is not independentfrom 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 smalluniverse of dynamic activity. A modern home inverter must cope with a wide range of loads, from asingle night light to the big surge required to start a well pump or a power tool. The batteryvoltage of a solar or wind system can vary as much as 35 percent (with varying state of charge andactivity).

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 batterybackup 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 theinverters that are available. Inverter manufacturers print everything you need to know on theirspecification sheets (commonly called "spec sheets"). Here is a list of the factors that you shouldconsider.

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 gridin some way? Electrical conventions and safety standards differ for various applications, so don't

improvise.

ELECTRICAL STANDARDS


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The DC input voltage must conform to that of the electrical system and battery bank. 12 volts isno 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 230volts at a frequency of 60 Hertz (cycles per second). In Europe, South America, and most otherplaces, it's 220 volts at 50 Hertz.

Safety Certification An inverter should be certified by an independent testing laboratory such asUL, ETL, CSA, etc., and be stamped accordingly. This is your assurance that it will be safe, willmeet the manufacturer's specifications, and will be approved in an electrical inspection. There aredifferent 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 surgerating. Continuous means the amount of power the inverter can handle for an indefinite period ofhours. When an inverter is rated at a certain number of watts, that number generally refers to itscontinuous rating.

The limited-time rating is a higher number of watts that it can handle for a defined period oftime, typically 10 or 20 minutes. The inverter specifications should define these ratings in relationto ambient temperature (the temperature of the surrounding atmosphere). When the invertergets too hot, it will shut off. This will happen more quickly in a hot atmosphere. The third level ofpower 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 toincrease their capacity. The most common scheme is to "stack" two inverters. A cable connectsthe 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; anythingelse 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 candeliver 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 harmonicdistortion (THD) lower than 6 percent should satisfy normal home requirements. Look for lessthan 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 plusor minus 5 percent or less. Peak voltage (Vp) regulation needs to be plus or minus 10 percent orless.

A "modified sine wave" inverter is less expensive, but it produces a distorted square waveformthat resembles the track of a pendulum being slammed back and forth by hammers. In truth, itisn't a sine wave at all. The misleading term "modified sine wave" was invented by advertisingpeople. Engineers prefer to call it "modified square wave."

The "modified sine wave" has detrimental effects on many electrical loads. It reduces the energyefficiency of motors and transformers by 10 to 20 percent. The wasted energy causes abnormalheat which reduces the reliability and longevity of motors and transformers and other devices,


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including some appliances and computers. The choppy waveform confuses some digital timingdevices.

About 5 percent of household appliances simply won't work on modified sine wave power at all. Abuzz will be heard from the speakers of nearly every audio device. An annoying buzz will also beemitted 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 mayoverheat and should not be used.

Modified sine wave inverters were tolerated in the 1980s, but since then, true sine wave invertershave become more efficient and more affordable. Some people compromise by using a modifiedwave inverter to run their larger power tools or other occasional heavy loads, and a small sine waveinverter to run their smaller, more frequent, and more sensitive loads. Modified wave inverters inrenewable 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 theefficiency is 90 percent, 10 percent of the power is lost in the inverter. The efficiency of aninverter varies with the load. Typically, it will be highest at about two thirds of the inverter'scapacity. 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. Underthese conditions, an inverter's efficiency may be around 50 percent or less. The full story is toldby 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 curveat 100 watts or so, not at zero!

Because the efficiency varies with load, don't assume that an inverter with 93 percent peakefficiency is better than one with 85 percent peak efficiency. If the 85 percent efficient unit ismore 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 lightningand static, and from surges that bounce back from motors under overload conditions. It must alsobe protected from overloads. Overloads can be caused by a faulty appliance, a wiring fault, orsimply too much load running at one time.

An inverter must include several sensing circuits to shut itself off if it cannot properly serve theload. It also needs to shut off if the DC supply voltage is too low, due to a low battery state-of-

charge or other weakness in the supply circuit. This protects the batteries from over-dischargedamage, as well as protecting the inverter and the loads. These protective measures are allstandard 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 inwell pumps, washing machines, refrigerators, power tools, etc. TVs and microwave ovens are alsoinductive 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 duringthe surge. This can cause a dimming of the lights in the house, and will sometimes crash acomputer.

Any weakness in the battery and cabling to the inverter will further limit its ability to start amotor. A battery bank that is undersized, in poor condition, or has corroded connections, can be a


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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 thesecables is many hundreds of amps at the instant of motor starting. Follow the inverter's instructionmanual when sizing the cables, or you'll cheat yourself. Coat battery connections with a protectivecoating 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 verylittle load (as in most residential situations), you want this to be as low as possible. Typical idlepower ranges from 15 watts to 50 watts for a home-size inverter. An inverter's spec sheet maydescribe the inverter's "idle current" in amps. To get watts, just multiply the amps times the DCvoltage 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) perkilowatt), and more expensive. It has the high surge capacity (four to eight times the continuouscapacity) needed to start large motors. Beware of the acoustical buzz that low switchingfrequency 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 thecontinuous capacity. It produces little or no audible noise. The idle power is generally higher. Ifthe inverter is oversized for motor starting, its idle power will be higher yet, and may beprohibitive. 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 theirloads and using two inverters. This adds a measure of redundancy. If one ever fails, the other onecan serve as backup.

AUTOMATIC ON/OFF

Inverter idling can be a substantial load on a small power system. Most inverters made for homepower systems have automatic load-sensing. The inverter puts out a brief pulse of power aboutevery second (more or less). When you switch on an AC load, it senses the current draw and turnsitself on. Manufacturers have various names for this feature, including "load demand," "sleepmode," "power saver," "autostart," and "standby."

Automatic on/off can make life awkward because a tiny load may not trigger the inverter to turnon or stay on. For example, a washing machine may pause between cycles, with only the timerrunning. The timer draws less than 10 watts. The inverter's turn-on "threshold" may be 10 or 15watts. The inverter shuts off and doesn't come back on until it sees an additional load from someother 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 havean always-on setting. With it, you can run your low-power night lights, your clocks, fax, answeringmachine and other tiny loads, without losing continuity. In that case, a good system designer willadd the inverter's idle power into the load calculation (24 hours a day). The cost of the powersystem 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 wheneverthey are plugged in. Some of them use power to do nothing at all. An example is a TV with aremote control. Its electric eye system is on day and night, watching for your signal to turn the


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screen on. Every appliance with an external wall-plug transformer uses power even when theappliance is turned off. These little demons are called "phantom loads" because their power drawis unexpected, unseen, and easily forgotten.

A similar concern is "idling loads." These are devices that must be on all the time in order tofunction when needed. These include smoke detectors, alarm systems, motion detector lights, fax

machines, and answering machines. Central heating systems have a transformer in theirthermostat circuit that stays on all the time. Cordless (rechargeable) appliances draw power evenafter their batteries reach a full charge. If in doubt, feel the device. If it's warm, that indicateswasted 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 (suchas switched plug-in strips or receptacles).* You can work around them by modifying certain equipment to shut off completely (centralheating 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 plusthe inverter's idle current.Be careful and honest if you contemplate avoiding all phantom and idling loads. You cannot alwaysanticipate 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 thatmay 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 supplyingsufficient data for sizing in relation to pumps.

In North America, most pumps (especially submersibles) run on 230 volts, while smaller appliancesand 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 morethan 1/2 HP. A water pump contractor will often supply a higher power pump than is needed for aresource-conserving household. You can request a smaller pump, or it may be feasible (andeconomical) to replace an existing pump with a smaller one. You can also consider one of a growingnumber 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 tobe occasions when the natural energy supply is insufficient. Some inverters have a built-in batterycharger that will recharge the battery bank whenever power is applied from an AC generator orfrom the utility grid (if the batteries are not already charged). This also means that an invertercan 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, insome cases, superior to those built into inverters. This is especially true in the case of lowswitching frequency inverters, which tend to require an oversized generator to produce the fullrated charge current.


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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, andother 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 beyondthe scope of this article). Be sure to get experienced advice on this, or you may be disappointedby the results.

QUALITY PAYS

A good inverter is an industrial quality device that is proven reliable, certified for safety, and canlast 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 futureexpansion of your needs.

YOUR FINAL CHOICE

Choosing an inverter is not a difficult task. Define where it is to be used. Define what type ofloads (appliances) you will be powering. Determine the maximum power the inverter will need tohandle. Is the quality of the power critical? Does size and weight matter? The inverter selectiontable 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 andcatalogs, 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 youmake 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 andprevent battery overcharge. Some controllers also prevent battery overdischarge, protect fromelectrical overload, and/or display battery status and the flow of power. Let's examine eachfunction individually.Blocking Reverse Current

Photovoltaic panels work by pumping current through your battery in one direction. At night, thepanels may pass a bit of current in the reverse direction, causing a slight discharge from thebattery. (Our term "battery" represents either a single battery or bank of batteries.) Thepotential 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 likea valve to control the current. It is called a "semiconductor" because it passes current only in onedirection. It prevents reverse current without any extra effort or cost.


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In some controllers, an electromagnetic coil opens and closes a mechanical switch. This is called arelay. (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 sizeof the battery), then you may not need a charge controller. This is a rare application. An exampleis 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. Adiode 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 tobe applied at the full rate, the battery voltage gets too high. Water separates into hydrogen andoxygen and bubbles out rapidly. (It looks like it's boiling so we sometimes call it that, although it'snot actually hot.) There is excessive loss of water, and a chance that the gasses can ignite andcause a small explosion. The battery will also degrade rapidly and may possibly overheat. Excessivevoltage 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 anincrease 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 orfully off. This is called "on/off control." Others reduce the current gradually. This is called "pulsewidth 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 holdthe voltage to a safe maximum for the battery to reach full charge. Then, it will drop the voltagelower, 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 afull charge but minimizes water loss and stress.

The voltages at which the controller changes the charge rate are called set points. Whendetermining the ideal set points, there is some compromise between charging quickly before thesun goes down, and mildly overcharging the battery. The determination of set points depends onthe anticipated patterns of usage, the type of battery, and to some extent, the experience andphilosophy of the system designer or operator. Some controllers have adjustable set points, whileothers do not.Control Set Points vs. Temperature

The ideal set points for charge control vary with a battery's temperature. Some controllers havea feature called "temperature compensation." When the controller senses a low batterytemperature, it will raise the set points. Otherwise when the battery is cold, it will reduce thecharge 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 placewhere the temperature is close to that of the batteries. Better controllers have a remotetemperature probe, on a small cable. The probe should be attached directly to a battery in orderto report its temperature to the controller.

An alternative to automatic temperature compensation is to manually adjust the set points (ifpossible) according to the seasons. It may be sufficient to do this only twice a year, in spring andfall.

Control Set Points vs. Battery Type

The ideal set points for charge controlling depend on the design of the battery. The vast majorityof 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.


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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 lowervoltage than flooded batteries or they will dry out and be ruined. Some controllers have a meansto select the type of battery. Never use a controller that is not intended for your type ofbattery.

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 VHigh limit (sealed battery): 14.0 VResume full charge: 13.0 VLow voltage disconnect: 10.8 VReconnect: 12.5 VTemperature compensation for 12V battery:-.03 V per C deviation from standard 25 CLow 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 apot of water boiling on your kitchen stove. The moment it runs dry, the pot overheats. If you waituntil 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 smallamount. If the battery sits in this overdischarged state for days or weeks at a time, it can beruined 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 substantialcharging. 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 loadsonly 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 toprotect itself and your loads as well as your battery. Normally, an inverter is connected directly tothe batteries, not through the charge controller, because its current draw can be very high, andbecause it does not require external LVD.

If you have any DC loads, you should have an LVD. Some charge controllers have one built in. Youcan also obtain a separate LVD device. Some LVD systems have a "mercy switch" to let you draw aminimal amount of energy, at least long enough to find the candles and matches! DC refrigeratorshave LVD built in.

If you purchase a charge controller with built-in LVD, make sure that it has enough capacity tohandle your DC loads. For example, let's say you need a charge controller to handle less than 10amps of charge current, but you have a DC water pressurizing pump that draws 20 amps (for shortperiods) plus a 6 amp DC lighting load. A charge controller with a 30 amp LVD would beappropriate. 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 cancause 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 haveoverload protection built in, usually with a push-button reset.

Built-in overload protection can be useful, but most systems require additional protection in theform of fuses or circuit breakers. If you have a circuit with a wire size for which the safe


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carrying capacity (ampacity) is less than the overload limit of the controller, then you mustprotect that circuit with a fuse or breaker of a suitably lower amp rating. In any case, follow themanufacturer's requirements and the National Electrical Code for any external fuse or circuitbreaker requirements.Displays and Metering

Charge controllers include a variety of possible displays, ranging from a single red light to digitaldisplays of voltage and current. These indicators are important and useful. Imagine driving acrossthe country with no instrument panel in your car! A display system can indicate the flow of powerinto and out of the system, the approximate state of charge of your battery, and when variouslimits are reached.

If you want complete and accurate monitoring however, spend about US$200 for a separatedigital device that includes an amp-hour meter. It acts like an electronic accountant to keep trackof the energy available in your battery. If you have a separate system monitor, then it is notimportant to have digital displays in the charge controller itself. Even the cheapest system shouldinclude 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 andinterconnections to handle high current. The electrical hardware can be bulky, expensive andlaborious 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 easyfor an electrician to tie in the major system components, and to meet the safety requirements ofthe 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 batteriesfrom overcharge, just like a PV controller. However, a load must be kept on the generator at alltimes 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 ofthe power from the generator. That load is usually a heating element, which "burns off" excessenergy 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 reachfull charge. Is the voltage reaching (but not exceeding) the appropriate set points for your typeof battery? Use your ears and eyes-are the batteries bubbling severely? Is there a lot ofmoisture accumulation on the battery tops? These are signs of possible overcharge. Are yougetting 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, lowvoltage disconnect and temperature compensation. When these limits are not respected, it iscommon 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 itvery mysterious. I hope this article has given you the background that you need to make a goodchoice of controls for your power system.


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More Information

Photovoltaic modules are so reliable that we forget that things can go wrong! The real worldimposes temperature extremes, lightning and static electricity, moisture and wind stresses, aswell 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 willhelp you locate a fault without disconnecting any wiring. Find an object that is large enough toshade at least 4 cells. (A cowboy hat will do.) Shading just a few cells will drop the module'soutput to less than half. With the array connected andworking, monitor the current (or in the caseof 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 thatmodule, 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 fadeshows up most severely in battery systems. If the difference between the array voltage and thebattery voltage approaches zero, then current flow can drop nearly to zero. This can also cause asolar pump to produce less than it should.

The voltage of a PV module normally decreases with temperature rise. PV manufacturers documentthis by showing several lines on the IV curve (the graph of amps vs. volts), or by stating it in voltsper degree of deviation from 25?C (77?F). Nominal "12 volt" PV modules are designed to sustaingood current flow all the way to 17 or 18V at 25?C. This allows for voltage drop at highertemperatures. If heat fade is severe, it MAY be caused by weak PV modules or by any other weaklinks in the power chain, including undersized wiring, poor connections and controller losses. Hereare 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 dropis severe. Connect a voltmeter directly to the PV array (or it's combiner box). Disconnect thearray from the controller, in order to read the open circuit voltage. If it is less than 18V (relativeto a 12V configuration), then part or all of the PV array may be defective. The selective shadingtest (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 wiringby measuring the voltage at the array, and then again at the controller input. Note that voltagedrop in wiring will increase in proportion to the current flow. Next, test for drop in the controllerby measuring the voltage at its PV input, and then at its battery terminals. Remember, if thebattery is fully charged, the controller SHOULD drop the voltage. If that is the case, you canbring 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 concentratedheat will result. You may feel it, or see signs of heat damage. If voltage drop is evident at theloads (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 ourwebsite).

Burnt terminals


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Years of temperature cycling will occasionally cause a screw to loosen, or metal to distort. Thiscan be caused by poor workmanship and/or inferior materials. Add a touch of oxidation andcorrosion, and you get electrical resistance. Now, keep the current flowing and you get even moreheat. When you repair overheated connections, replace all metal parts that have been severelyoxidized. In worst cases, an electric arc will jump a gap, melting metal and burning insulation to achar. Charred terminals on PV modules can be bypassed by soldering a wire directly to the metalstrip that leads to the PV cells.

Diode failures

Most PV modules have bypass diodes in the junction boxes, to protect cells from overheating ifthere is a sustained partial shade on them. On rare occasions a diode will fail, usually as a result oflightning. Most often, it will short out and reduce the module's voltage drastically. (A shorteddiode will read near-zero ohms in both directions.) If the module is in a 12V array, there is noneed for the bypass diode so you can remove it. In a 24V array that is unlikely to experiencesustained partial shading, you can remove it. In any other case, replace it with a silicon diode withan amps rating at or above the module's maximum current, and with a voltage rating of 400V ormore.

Grounding

Lightning and related static discharge is the number one cause of sudden, unexpected failures inPV systems. Lightning does not have to strike directly to cause damage to sensitive electronicequipment, such as inverters, controls, radios and entertainment equipment. It can be miles awayand 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 ofindependent power systems do not have grounding supplied by the utility company, and oftenoverlook 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 manythousands 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 theearth. During lightning storms, the clouds build up a static electric charge. This causes


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accumulation of the opposite charge in objects on the ground. Objects that are INSULATED fromthe earth tend to accumulate the charge more strongly than the surrounding earth. If thepotential difference (voltage) between sky and the object is great enough, lightning will jump thegap.

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 doesbuild up, your ground connection provides a safe path for discharge directly to the earth ratherthan through your wiring. (3) It reduces shock hazard from the higher voltage (AC) parts of yoursystem, and (4) reduces electrical hum and radio caused by inverters, motors, fluorescent lightsand other devices, and not least . . .

GROUNDING IS REQUIRED by the NATIONAL ELECTRICAL CODE (NEC)(r). Photovoltaicsystems are included in Article 690 of the Code. Low voltage systems are NOT exempt fromgrounding 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 theearth. 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 togethervia bare copper wire (#6 or larger, see the NEC) and bury the wire. Use only approved clamps toconnect wire to rods. If your photovoltaic array is some distance from the house, drive groundrod(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 connectorsapproved 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 superground rods. Drill and tap a hole in the casing to get a good bolted connection. If you connect tomore 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 properbronze or copper connectors. Your ground system is only as good as its weakest electricalconnections.

If your site is rocky and you cannot drive ground rods deeply, bury (as much as feasible) at least150 feet of bare copper wire. Several pieces radiating outward is best. Try to bury them in areasthat 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 areafeasible, preferably contacting moist soil.

You can save money by purchasing used copper wire (not aluminum) from a scrap metal dealer, andstripping 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, metalicallybond the module frames together, and wire to ground.) Be sure to bolt your ground wires solidly tothe metal so it will not come loose, and inspect it periodically. Also ground antenna masts and windgenerator towers.

GROUND THE NEGATIVE SIDE OF YOUR POWER SYSTEM, but FIRST make the following testfor 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. Noreading? Good. Now switch it down to the lowest milli- or microamp scale and try again. If you getonly a few microamps, or zero, THEN GROUND YOUR BATTERY NEGATIVE. If you DID read


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leakage to ground, check your system for something on the positive side that may be contactingearth somehow. (If you read a few microamps to ground, it is probably your meter detecting radiostation signals.)

Connect your DC negative to ground ONLY IN ONE PLACE, at a negative battery connection orother 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 inthe manner conventional for all AC systems. This protects from shock hazard as well as lightningdamage.

PV ARRAY WIRING should be done with minimum lengths of wire, tucked into the metalframework, then run through metal conduit. Positive and negative wires should be run togetherwherever possible, rather than being some distance apart. This will minimize induction of lightningsurges. Bury long outdoor wire runs instead of running them overhead. Place them in groundedmetal conduit if you feel you need maximum protection.

SURGE PROTECTION DEVICES bypass the high voltages induced by lightning. They arerecommended for additional protection in lightning-prone areas or where good grounding is notfeasible (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, socontact your PV dealer.

SAFETY FIRST!!! If you are uncertain of your ability to wire your system properly, HIRE ANELECTRICIAN!

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 theeffect of shadows. It delivers maximum power in the smallest module size saving weight andspace. It is supplied with all the necessary cable (5m), connectors and detailed installationinstructions.


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The 8Ah (STS01208) Charge controller (sold separately) should be used with this kit to protectthe battery from being overcharged and to prevent reverse current drain.

Specifications

Power: 120wattsPeak Output: 7.93A @ 17.2VApprox. watt-hours/day** 840Approx. amp-hours/day** 55.1Dimensions: 1483x671x35mmWeight: 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

Documents

(PV) Solar System