Battery Maintenence and Solar panel System designing

8/9/2019 Battery Maintenence and Solar panel System designing

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Battery Tutorial

You have most likely heard the term K.I.S.S. (Keep It Simple, Stupid). I am going to attempt to explainhow lead acid batteries work and what they need without burying you with a bunch of needless technicaldata. Actually I have found that battery manufacturer's data will vary somewhat so I must generalize in

some cases.

The commercial use of the lead acid battery is over 100 years old. The same chemical principal is beingused to create energy that our Great, Great, Grandparents may have used.

If you can grasp the basics you will have fewer battery problems and will gain greater battery

performance, reliability, and longevity. I suggest you read the entire tutorial, however I have indexed allthe information for a quick read and easy reference.

A battery is like a piggy bank. If you keep taking out and putting nothing back you soon will have nothing.

Present day chassis battery power requirements are huge. Look at todays vehicle and all the electricaldevices that must be supplied. Electronics require a source of reliable power. Poor battery condition can

cause expensive electronic component failure. Did you know that the average auto has 11 pounds of wire

in the electrical system? Look at RVs and boats with all the electrical gadgets that require power. I can

remember when a trailer or motor home had a single 12-volt house battery. Today it is standard to have 2

or more house batteries powering inverters up to 4000 watts.

Average battery life has become shorter as energy requirements have increased. Life span depends onusage; 6 months to 48 months, yet only 30% of all batteries actually reach the 48-month mark.

A Few Basics

The Lead Acid battery is made up of plates, lead, and lead oxide (various other elements are used tochange density, hardness, porosity, etc.) with a 35% sulfuric acid and 65% water solution. This solution is

called electrolyte which causes a chemical reaction that produce electrons. When you test a battery with ahydrometer you are measuring the amount of sulfuric acid in the electrolyte. If your reading is low, that

means the chemistry that makes electrons is lacking. So where did the sulfur go? It is resting to thebattery plates and when you recharge the battery the sulfur returns to the electrolyte.

1.Safety

2. Battery types, Deep Cycle and Starting3. Wet Cell, Gel-Cell and Absorbed Glass Mat (AGM)4. CCA, CA, AH and RC; what's that all about?5. Battery Maintenance

6. Battery Testing7. Selecting and Buying a New Battery

8. Battery Life and Performance9. Battery Charging

10. Battery Do's

11. Battery Don'ts

1. We must think safety when we are working around and with batteries. Remove all jewelry. After all youdon't want to melt your watchband while you are wearing the watch. The hydrogen gas that batteriesmake when charging is very explosive. I have had 2 batteries blow up and drench me in sulfuric acid. That

is no fun. This is a good time to use those safety goggles that are hanging on the wall. Sulfuric Acid eats

up clothing and you may want to select Polyester clothing to wear, as it is naturally acid resistant. I justwear junk clothes, after all Polyester is so out of style. When doing electrical work on vehicles it is best todisconnect the ground cable. Just remember you are messing with corrosive acid, explosive gases and

100's amps of electrical current.

2.Basically there are two types of batteries; starting (cranking), and deep cycle (marine/golf cart).The starting battery (SLI starting lights ignition) is designed to deliver quick bursts of energy (such

as starting engines) and have agreater plate count. The plates will also be thinner and have somewhat

different material composition. The deep cycle battery has less instant energy but greater long-term


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energy delivery. Deep cycle batteries have thicker plates and can survive a number of discharge cycles.Starting batteries should not be used for deep cycle applications. The so-called Dual Purpose Battery is

only a compromise between the 2 types of batteries.

3. Wet Cell (flooded), Gel Cell,andAbsorbedGlass Mat (AGM) are various versions of the lead acid

battery. The wet cell comes in 2 styles; serviceable, and maintenance free. Both are filled with electrolyteand I prefer one that I can add water to and check the specific gravity of the electrolyte with a

hydrometer. The Gel Cell and the AGM batteries are specialty batteries that typically cost twice as muchas a premium wet cell. However they store very well and do not tend to sulfate or degrade as easily or aseasily as wet cell. There is little chance of a hydrogen gas explosion or corrosion when using these

batteries; these are the safest lead acid batteries you can use. Gel Cell and some AGM batteries mayrequire a special charging rate. I personally feel that careful consideration should be given to the AGMbattery technology for applications such as Marine, RV, Solar, Audio, Power Sports and Stand-By Power

just to name a few. If you don't use or operate your equipment daily; this can lead premature batteryfailure; or depend on top-notch battery performance then spend the extra money. Gel Cell batteries still

are being sold but the AGM batteries are replacing them in most applications. There is a little confusionabout AGM batteries because different manufactures call them different names; some of the popular onesare sealed regulated valve, dry cell, non spillable, and sealed lead acid batteries. In most cases AGM

batteries will give greater life span and greater cycle life than a wet cell battery.SPECIAL NOTE about Gel Batteries: It is very common for individuals to use the term GEL CELL when

referring to sealed, maintenance free batteries, much like one would use Kleenex when referring to facialtissue or "Xerox machine" when referring to a copy machine. Be very careful when specifying a batterycharger, many times we are told by customer they are requiring a charger for a Gel Cell battery and in fact

the battery is not a Gel Cell.

AGM: The Absorbed Glass Matt construction allows the electrolyte to be suspended in close proximity with

the plates active material. In theory, this enhances both the discharge and recharge efficiency. Actually,the AGM batteries are a variant of Sealed VRLA batteries. Popular usage high performance engine starting,

power sports, deep cycle, solar and storage battery. The AGM batteries we sell are typically good deepcycle batteries and they deliver best life performance if recharged before the battery drops below the 50percent discharge rate. If these AGM batteries are discharged to a rate of 100 percent the cycle life will be

300 plus cycles and this is true of most AGM batteries rated as deep cycle batteries.

GEL: The gel cell is similar to the AGM style because the electrolyte is suspended, but different becausetechnically the AGM battery is still considered to be a wet cell. The electrolyte in a GEL cell has a silica

additive that causes it to set up or stiffen. The recharge voltages on this type of cell are lower than the

other styles of lead acid battery. This is probably the most sensitive cell in terms of adverse reactions toover-voltage charging. Gel Batteries are best used in VERY DEEP cycle application and may last a bit longer

in hot weather applications. If the incorrect battery charger is used on a Gel Cell battery poor performanceand premature failure is certain.

4. CCA, CA,AHand RC what are these all about? Well these are the standards that most batterycompanies use to rate the output and capacity of a battery.

Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at 0 F for 30seconds and not drop below 7.2 volts. So a high CCA battery rating is good especially in cold weather.

CA is cranking amps measured at 32 degrees F. This rating is also called marine cranking amps(MCA). Hot

cranking amps (HCA) is seldom used any longer but is measured at 80 F.

Reserve Capacity (RC) is a very important rating. This is the number of minutes a fully charged battery at80 F will discharge 25 amps until the battery drops below 10.5 volts.

An amp hour (AH) is a rating usually found on deep cycle batteries. If a battery is rated at 100 amp hours

it should deliver 5 amps for 20 hours, 20 amps for 5 hours, etc.

5.Battery Maintenance is an important issue. The battery should be cleaned using a baking soda andwater mix; a couple of table spoons to a pint of water. Cable connection needs to be clean and tightened.

Many battery problems are caused by dirty and loose connections. A serviceable battery needs to have the

fluid level checked. Use only mineral free water. Distilled water is best. Don't overfill battery cells especially


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in warmer weather. The natural fluid expansion in hot weather will push excess electrolytes from thebattery. To prevent corrosion of cables on top post batteries use a small bead of silicon sealer at the

base of the post and place a felt battery washer over it. Coat the washer with high temperature grease or

petroleum jelly (Vaseline), then place cable on the post and tighten. Coat the exposed cable end with thegrease. Most folks don't know that just the gases from the battery condensing on metal parts cause most

corrosion.

6. Battery Testing can be done in more than one way. The most popular is measurement of specific gravityand battery voltage. To measure specific gravity buy a temperature compensating hydrometer andmeasure voltage, use a digital D.C. Voltmeter. A good digital load tester may be a good purchase if you

need to test batteries sealed batteries.

You must first have the battery fully charged. The surface charge must be removed before testing. If the

battery has been sitting at least several hours (I prefer at least 12 hours) you may begin testing. Toremove surface charge the battery must experience a load of 20 amps for 3 plus minutes. Turning on the

headlights (high beam) will do the trick. After turning off the lights you are ready to test the battery.

State of Charge Specific Gravity Voltage

12V6V

100% 1.265 12.7 6.3

*75% 1.225 12.4 6.2

50% 1.190 12.2 6.1

25% 1.155 12.0 6.0

Discharged 1.120 11.9 6.0

*Sulfation ofBatteries starts when specific gravity falls below 1.225 or voltage measures less than 12.4(12v Battery) or 6.2 (6 volt battery). Sulfation hardens the battery plates reducing and eventually

destroying the ability of the battery to generate Volts and Amps.

Load testing is yet another way of testing a battery. Load test removes amps from a battery much like

starting an engine would. A load tester can be purchased at most auto parts stores. Some batterycompanies label their battery with the amp load for testing. This number is usually 1/2 of the CCA rating.

For instance, a 500CCA battery would load test at 250 amps for 15 seconds. A load test can only beperformed if the battery is near or at full charge.

The results of your testing should be as follows:

Hydrometer readings should not vary more than .05 differences between cells.

Digital Voltmeters should read as the voltage is shown in this document. The sealed AGM and Gel-Cellbattery voltage (full charged) will be slightly higher in the 12.8 to 12.9 ranges. If you have voltage

readings in the 10.5 volts range on a charged battery, that indicates a shorted cell.

If you have a maintenance free wet cell, the only ways to test are voltmeter and load test. Most of themaintenance free batteries have a built in hydrometer that tells you the condition of 1 cell of 6. You mayget a good reading from 1 cell but have a problem with other cells in the battery.

When in doubt about battery testing, call the battery manufacturer. Many batteries sold today have a toll

free number to call for help.

7. Selecting a Battery - When buyinganew battery I suggest you purchase a battery with the greatest

reserve capacity or amp hour rating possible. Of course the physical size, cable hook up, and terminal typemust be a consideration. You may want to consider a Gel Cell or an Absorbed Glass Mat (AGM) rather thana Wet Cell if the application is in a harsher environment or the battery is not going to receive regular

maintenance and charging.

Be sure to purchase the correct type of battery for the job it must do. Remember an engine starting


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battery and deep cycle batteries are different. Freshness of a new battery is very important. The longer abattery sits and is not re-charged the more damaging sulfation build up there may be on the plates. Most

batteries have a date of manufacture code on them. The month is indicated by a letter 'A' being January

and a number '4' being 2004. C4 would tell us the battery was manufactured in March 2004. Rememberthe fresher the better. The letter "i" is not used because it can be confused with #1.

Battery warranties are figured in the favor of battery manufactures. Let's say you buy a 60-month

warranty battery and it lives 41 months. The warranty is pro-rated so when taking the months usedagainst the full retail price of the battery you end up paying about the same money as if you purchased thebattery at the sale price. This makes the manufacturer happy. What makes me happy is to exceed the

warranty. Let me assure you it can be done.

8.Batterylife andperformance - Average battery life has become shorter as energy requirements

have increased. Two phrases I hear most often are "my battery won'ttake a charge,andmy batterywon'tholda charge". Only 30% of batteries sold today reach the 48-month mark. In fact 80% of all

battery failure is related to sulfation build-up. This build up occurs when the sulfur molecules in theelectrolyte (battery acid) become so deeply discharged that they begin to coat the battery's lead plates.

Before long the plates become so coated that the battery dies. The causes of sulfation are numerous. Let

me list some for you.

y Batteries sit too long between charges. As little as 24 hours in hot weather and several days in cooler

weather.y Battery is stored without some type of energy input.

y "Deep cycling" an engine starting battery. Remember these batteries can't stand deep discharge.

y Undercharging of a battery, to charge a battery (lets say) to 90% of capacity will allow sulfation of thebattery using the 10% of battery chemistry not reactivated by the incomplete charging cycle.

y Heat of 100 plus F., increases internal discharge. As temperatures increase so does internal discharge. Anew fully charged battery left sitting 24 hours a day at 110 degrees F for 30 days would most likely not

start an engine.

y Low electrolyte level - battery plates exposed to air will immediately sulfate.

y Incorrect charging levels and settings. Most cheap battery chargers can do more harm than good. Seethe section on battery charging.

y Cold weather is also hard on the battery. The chemistry does not make the same amount of energy as awarm battery. A deeply discharged battery can freeze solid in sub zero weather.

y Parasitic drain is a load put on a battery with the key off. More info on parasitic drain will follow in thisdocument.

There are ways to greatly increase battery life and performance. All the products we sell are

targeted to improve performance and battery life.

An example: Let's say you have "toys"; an ATV, classic car, antique car, boat,Harley, etc.You mostlikely don't use these toys 365 days a year as you do your car. Many of these toys are seasonal so they are

stored. What happens to the batteries? Most batteries that supply energy to power our toys only last 2seasons. You must keep these batteries from sulfating or buy new ones. We sell products to prevent andreverse sulfation. The PulseTech products are patented electronic devices that reverse and prevent of

sulfation. Also Battery Equaliser a chemical battery additive has proven itself very effective in improvingbattery life and performance. Other devices such as Solar Trickle Chargers are a great option for battery

maintenance.

Parasitic drainis a load put on a battery with the key off. Most vehicles have clocks, engine management

computers, alarm systems, etc. In the case of a boat you may have an automatic bilge pump, radio, GPS,etc. These devices may all be operating without the engine running. You may have parasitic loads causedby a short in the electrical system. If you are always having dead battery problems most likely the parasitic

drain is excessive. The constant low or dead battery caused by excessive parasitic energy drain will

dramatically shorten battery life. If this is a problem you are having, check out the Priority Start and Marine

Priority Startto prevent dead batteries before they happen. This special computer switch will turn off


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your engine start battery before all the starting energy is drained. This technology will prevent you fromdeep cycling your starting battery.

9. Battery Charging - Remember you must put back the energy you use immediately. If you don't thebattery sulfates and that affects performance and longevity. The alternator is a battery charger. It works

well if the battery is not deeply discharged. The alternator tends to overcharge batteries that are very lowand the overcharge can damage batteries. In fact an engine starting battery on average has only about 10

deep cycles available when recharged by an alternator. Batteries like to be charged in a certain way,especially when they have been deeply discharged. This type of charging is called 3 step regulatedcharging. Please note that only special SMART CHARGERS using computer technology can perform 3 step

charging techniques. You don't find these types of chargers in parts stores and Wal-Marts. The first stepis bulk charging where up to 80% of the battery energy capacity is replaced by the charger at themaximum voltage and current amp rating of the charger. When the battery voltage reaches 14.4 volts this

begins theabsorption charge step. This is where the voltage is held at a constant 14.4 volts and thecurrent (amps) declines until the battery is 98% charged. Next comes the Float Step. This is a regulated

voltage of not more than 13.4 volts and usually less than 1 amp of current. This in time will bring thebattery to 100% charged or close to it. The float charge will not boil or heat batteries but will maintain thebatteries at 100% readiness and prevent cycling during long term inactivity. Some gel cell and AGM

batteries may require special settings or chargers.

10. Battery Do's

y Think Safety First.y Do read entire tutorial

y Do regular inspection and maintenance especially in hot weather.

y Do recharge batteries immediately after discharge.

y Do buy the highest RC reserve capacity or AH amp hour battery that will fit your configuration.

11. Battery Don'ts

y Don't forget safety first.

y Don't add new electrolyte (acid).

y Don't use unregulated high output battery chargers to charge batteries.

y Don't place your equipment and toys into storage without some type of device to keep the batterycharged.

y Don't disconnect battery cables while the engine is running (your battery acts as a filter).

y Don't put off recharging batteries.

y Don't add tap water as it may contain minerals that will contaminate the electrolyte.

y Don't discharge a battery any deeper than you possibly have to.

y Don't let a battery get hot to the touch and boil violently when charging.

y Don't mix size and types of batteries.

There are many points and details I have not written about but I wanted to keep this as short and simple

as possible. Further information can be found at the links below. If you are aware of sites with good

battery maintenance information please let me know.

Training Material - Balance of Systems


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Batteries: Preventing maintenance, charging and equalization

Batteries: Preventing maintenance, charging and equalization

1999 by Rolls Battery Engineering

Warning:

y

This advice does not apply to sealed batteries or any batteries other than flooded (wet) cell lead-acidbatteries. Equalization involves overcharging which can permanently damage sealed batteries.

y Equalization charging will produce an abnormal amount of gassing. Battery Gasses (Hydrogen andOxygen) are potentially explosive. Take extra precautions and keep unauthorized personel away from

batteries.

y Turn off sensitive loads during equalization. They will be exposed to higher than normal voltage. Mostinverters have a high voltage shutoff (see specifications for your inverter.)

This bulletin describes preventive maintenance and recommended charging procedures to maximize battery life.The leading cause of premature battery failure is improper charging and poor battery maintenance. Equalization is

very important in alternative energy applications and must be preformed correctly, but only as required.

Preventive Maintenance

When a battery is first received the cell acid levels should be checked and the battery should be put on charge.

After removing from charge the specific gravity readings of each cell should be recorded and kept for the life of thebattery.

All metal components attached to battery terminals, plus all nuts and bolts, should be coated with a thin layer ofpetroleum jelly (Vaseline) or other non-hardening sealant before assembly. This will stop the corrosive effects of

acid exposure.

Preventive maintenance involves, at a minimum, checking the cell electrolyte level for correct volume once amonth, and equalizing once every six months. The cells should be watered back to the original electrolyte level

which is 1/4 to 1/2" below the bottom of the vent well (tube inside the battery cell with slots on each side). Distilledor de-ionized water is preferred, but local water (not chlorinated) maybe acceptable if it is not "hard" or does not

contain high iron levels. Very clean rain water or melted snow can be used, if it is not collected or stored in metalcontainers.

A recommended preventive maintenance program can be summarized as follows:

1. Water each cell to original level as required

2. Equalize as required, or once every six months3. Record the specific gravity readings of each cell every three months.

Occasionally cleaning the battery terminals and case / cover is recommended. A weak solution of household

baking soda (sodium bicarbonate) and water can be used to neutralize any spilt or spattered acid (100 g per liter or4 Oz per pint). Make sure the vent caps a re securely tightened and no soda solution gets into the battery cells.

Good record keeping is important. Review of these records can help to determine the "health" of the battery and

can prove invaluable if system problems develop.

State of Charge and Charging

The truest measure of a battery's state of charge is the specific gravity of the battery acid. The following showsthe approximate state of charge at various specific gravities at 77F (25C). Temperature correction factor is -0.010

V per 10 F (-0.010 V per 5 C).

Charged Specific Gravity

100% 1.255 - 1.275


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75% 1.215 - 1.235

50% 1.200 - 1.180

25% 1.165 - 1.155

0% 1.130 - 1.110

Hydrometers can be difficult to use and at best accurate to +/-0.005 points. We recommend a three step charging

procedure. Recommended voltage settings are as follows:

(Volts per cell) 12V 24V 48V

Equalization 2.58 - 2.6715.5 - 16.0 31.0 - 32.0 61.9 - 64.1

Absorption 2.37 - 2.4514.2 - 14.7 28.4 - 29.4 56.9 - 58.8

Float 2.20 - 2.2313.2 - 13.4 26.4 - 26.8 52.8 - 53.5

EqualizationEqualization is required to mix the battery acid and bring every battery plate to an equal charge. Equalization

should only be performed when required or once every six months in a renewable energy system. Equalization is

required when the cell specific gravities vary from highest to lowest by 0.015 (1.245 - 1.260 at full charge).

After a season (several months) of generally low state of charge (SOC) or failure to reach full SOC frequently,

equalization will probably be required. After a season of abundent energy (long durations of full SOC) equalizationwill generally not be necessary.

The exact particulars (such as charging time and currents) are dependent on the charging system. However, the

point is to bring the batteries up to the equalization voltage and continue charging for 1-2 hours at a low current,

without excessive heat. The final or finishing charging current should be 3-7% (we recommend 5%) of the 20 hr

capacity in amps. If battery temperature exceeds 125F the battery shou ld be taken off of charge and allowed tocool before equalization is continued. When two consistent specific gravity readings are taken a half hour apart, the

battery is equalized.

It is recommended to water the battery cells before or half way through the equalizat ion. This is to assure the wateris completely mixed into the electrolyte. Do not fill higher than the recommended level, or overflow may result

during equalization because of excessive gassing.

Training Material - Balance of Systems


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Batteries: How to keep them alive for years and years

Lead-acid batteries are often considered to be the "weak link" in renewable energy systems. However, todays

renewable energy batteries are better than ever, and so are the devices that regulate and protect them. Battery failures

are rarely the fault of the batteries themselves! Follow these guidelines to avoid the vast majority of all batteryproblems.

Size a battery bank and PV array properlyA battery bank should be sized (as a minimum) to a capacity of 5 days of load. Energy use in most home powersystems increases over time, so consider sizing larger than that. Why? After 1 year of service, it is not advisable to

enlarge a battery bank by adding new batteries to it, because batteries' voltage response changes with age. Straycurrents flow, causing losses and failure to equalize. A PV array, if it is the primary energy source, should be sized to

produce (on average) 30% more energy than the load requires. This compensates for battery losses and for less-than-average charging conditions. Luckily, a PV array can be expanded at any time.

Buy high-quality batteries, selected for your needs

You get what you pay for! Good deep-cycle batteries can be expected to last for 5 to 15 years, and sometimes more.Cheap batteries can give you trouble in half that time. Buy from a reputable source.

Avoid multiple parallel strings

The ideal battery bank is the simplest, consisting of a single series of cells that are sized for the job. Higher capacitybatteries tend to have thicker plates, and therefore greater longevity. Having fewer cells will reduce the chance of

randomly occurring defects, and reduces maintenance. Suppose for example, that you require a 700 Amp -Hour bank.You can approximate that by using 3 parallel strings of golf-cart batteries (220 AH), or 2 strings of the larger L -16 stylebatteries (350 AH) or a single string of larger, industrial batteries.

Under no circumstances is it advisable to install more than three parallel battery strings. The resulting bank will tend to

lose its equalization, resulting in accellerated failure of any weak cells. Weak cells will be difficult to detect becausethey will "steal" from the surrounding cells, and the system will suffer as a whole and will cost you more in the long run.

Here are some precautions to take when wiring two or more strings of batteries in series-parallel. The goal is to

maintain all of the cells at an equal state of charge. Cells that tend to receive less charge are likely to fail prematurely.This can take years off of the effective life of the battery bank. A fraction of an ohm of added resistance in one batterystring can reduce the life of the entire string.

(1) Connect the two main cables to opposite corners of the battery bank, and maintain symmetry in wire size andlengths. This will help to distribute current evenly through the bank.

" (2) Arrange batteries to maintain even temperature distribution throughout the bank. Avoid uneven exposure to heat

sources. Leave at least 1/2 inch of air space around each battery, to promote even cooling.

(3) Apply a finish charge at least every 3 weeks (bring every cell to 100% charge).

Prevent corrosion

In flooded battery installations, corrosion of terminals and cables is an ugly nuisance that causes resistance and

potential hazards. Once corrosion gets hold, it is hard to stop. The good news -- it is easy to prevent! Apply a non-hardening sealant to all of the metal parts of the terminals before assembly. Completely coat the battery terminals, the

wire lugs, and the nuts and bolts individually. A sealant applied after assembly will not reach all around every junction.Voids will remain, acid spatter will enter, and corrosion will begin as soon as your installation is finished.

Special compounds are sold to protect terminals, but you can have perfectly good results using common petroleumjelly (Vaseline). It will not inhibit electrical contact. Apply a thin coating with your fingers, and it won't look sloppy. If wire

is exposed at a terminal lug, it should be sealed airtight, using either adhesive-lined heat-shrink tubing or submersiblerubber splice tape. You can also seal an end of stranded wire by warming it gently, and dipping it in the petroleum jelly

to liquify, and wick it into the wire.

It also helps to put the batteries over a floor drain, or in a space without a floor, so that they can be rinsed with watereasily. Washing the battery tops (about twice per year) will remove accumulated moisture (acid spatter) and dust. Thiswill further reduce corrosion, and will prevent stray currents from stealing energy. Batteries that we have protected bythese measures show very little corrosion, even after 10 years without terminal cleaning.

Moderate the temperature

Batteries lose approximately 25% of their capacity at a temperature of 30F (compared to a baseline of 77F). At


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higher temperatures, they deteriorate faster. Thus, it is desirable to protect them from temp erature extremes. If nothermally-stable structure is available, consider an earth-sheltered enclosure. Where low temperature cannot beavoided, get a larger battery bank to make up for the loss of capacity in the winter. Avoid direct radiant heat sourcesthat will cause some batteries to get warmer than others.

Use temperature compensation

When batteries are cold, they require an increase in the charge voltage limit, in order to reach full charge. When theyare warm, they require a reduction in the voltage limit in order to prevent overcharge. Temperature compensation is a

feature in many charge controllers and power centers, as well as in the back-up chargers in some inverters. To usethis feature, order the accessory temperature probe for each charging device, and attach it to any one of the batteries.

Use low-voltage disconnects

Discharging a battery to exhaustion will cause immediate, irreversable loss of capacity and life expectancy. Yoursystem should employ low voltage disconnect (LVD) in the load circuits. Most inverters have this feature, and so domany charge controllers and power centers. Don't depend on human behavior to prevent over-discharge. It can becaused easily by accident or by an irresponsible user. Again, most inverters have LVD built-in but if there are DC loads

on the system, please incorporate an LVD device.

Bring batteries to a full state-of-charge at least every 3 weeks.

Bring the batteries to a full state-of-charge (SOC) at least every 3 weeks. This reduces internal corrosion and

degradation, and helps to insure equalization, so that any weaker cells do not fall continually farther behind. A full SOCmay occur naturally during most of the year, but do not hesitate to run a generator when necessary, to bring thebatteries up. Information like this should be posted at the power center. For more details, refer to the in structions for

the inverter/charger and for the batteries.

How do you know when a battery is 100% charged?

The "charged" indicator on most PV charge controllers means only that battery voltage is relatively high. The SOC may

be approaching full, but is not necessarily near 100% A voltmeter reading gets you closer, but it is not a certainindicator. It varies to much with current flow, temperature and time, to give a clear indication.

For flooded batteries, a hydrometer is the definitive indicating device, although not a convenient one. With it, you canmeasure every cell individually. Obtain one from a battery or automotive supplier. Even the cheapest hydrometer isfine. Rinse it after use, and keep it clean.

An amp-hour meter is the most informative and user-friendly way to monitor SOC. For sealed batteries, it is the ONLY

definitive method. See next paragraph.

Install a System Monitor

Would you drive a car with no dashboard? Metering is not just "bells and whistles". It is necessary to help you to readthe status of the sytem. Many charge controllers have indicator lights and readouts built-in. For a full-scale remotehome, consider the addition of a digital monitor, like Trace TM-500, Tri-Metric, E-Meter or Omni-Meter. These devices

monitor voltage and current, record amp-hours, and accurately display the state-of-charge of the battery bank. Theyalso record more detailed information that can be useful for troubleshooting. The monitor may be mounted in another

room or building, for handy viewing.

How to Read a Hydrometer

A hydrometer will help you to determine whether the battery bank is getting fully charged, and whether any individual

cells are falling behind. You should be aware that a hydrometer will give you false readings under the followingconditions.

(1) After adding water: For pure water to mix throughout the cell, it takes time and some bubbling during finish charge.

A hydrometer will show a greatly reduced reading until the fluid mixes.

(2) Low temperature: As battery temperature drops, the flu id becomes more dense. A temperature compensatinghydrometer is best. Otherwise, for every 10F below 70F, subtract 3.5 points from the reading.

(3) Time lag during recharge: As the battery recharges, the fluid becomes more dense down between the plates. The

hydrometer reads the fluid above the plates. You will get a delayed reading until the fluid is mixed by the movement ofbubbles during finish charge. The voltage will rise steadily, providing an indication that something is happening.

During discharge, you will get a true hydrometer reading because the fluid becomes less dense and will circulate to the

top. Any time a hydrometer indicates a fully charged cell, you KNOW it is fully charged.

WARNING


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Battery acid is hazardous. When working around batteries, wear safety glasses. Get a rugged plastic bottle to keepwith your service tools, and fill it with a sodium bicarbonate (baking soda) and water. Use it to neutralize accidentalsplash or spills and to clean normal acid spatter from battery tops. Finally, don't wear your favorite blue jeans!

Just add water.Note: This applies only to "flooded batteries", not to "sealed batteries". The plates of every cell in your battery bank

must be submerged at all times. Never add any fluid to a battery except distilled water, deionized water, or very cleanrainwater collected in plastic containers. Most batteries require addition of water every 6 to 12 months. There is no

need to fill them more frequently than needed to submerge the plates. Fill them only to the level recommended by themanufacturer, generally about an inch below the top, otherwise they may overflow during finish-charging.

Conclusion

Batteries are the heart of your power system. They may demand your attention occasionally, but your relationship withthem need not be a struggle. With a proper installation, a little understanding and some simple maintenance, your

batteries will live a long and healthy life.

Solar System Size

Step 1: Determine your daily Energy Budget

(Hours of use times watts e quals daily watt hours used)

AC ApplianceHours of Daily

Usage XAppliance Watts = Daily Watt Hours Used

1Microwave .5 600 3002Lights (x4) 6 40 2403Hair Dryer .75 750 5634Television 4 100 400

5Washing

Machine 1 375 375

Total Daily Watt Hrs. Used

Formula: Add Lines 1-5 >>> 1,878

Step 2 Determine Rough Battery Estimate

Multiply total daily watt hours used by number of

anticipated days of autonomy (days between charging,

usually beteen 1 to 5) to determine your Rough Battery

Estimate. Rough Battery Estimate

Formula: Total Daily Watt Hrs. Used x days

of autonomy >>>

5,634

Step 3: Determine Safe Battery size in Watts Hours

Multiply Rough Battery Estimate x 2, to determine safe

battery size in watt hours. (This allows for 50%

maximum battery discharge in normal operation and an

additional 50% in emergency situations.) Safe Battery Size in Watt Hrs.

Formula: Rough Battery Estimate x 2 >>> 11,268

Step 4: Determine Safe Battery Size inAmp Hours

Convert safe battery size to amp hours by dividingthe Safe Battery Size in Watt Hours by DC systemvoltage (i.e. 12, 24, 48 volts DC) Safe Battery Size in Amp Hrs.

Formula: Safe Battery Size in Watt Hours /

System Voltage >>> 470

Step 5: Determine Inverter Wattage

To properly determine inverter size add together theappliances that must/will run at the same time, from

column 2 (Appliance Watts listed above) and add 25%.

Then roundup to the next inverter wattage size. Properly sized inverter wattage

Formula: Add Total Appliance Watts + 25%

>>> 2,500

Solar Electricity

__________________

The process of converting light (photons) to electricity (voltage) is called the solar photovoltaic (PV) effect. Photovoltaic

solar cells convert sunlight directly into solar electricity.


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These solar cells are commonly used to power everything from calculators, watches and battery chargers to road signs a

security alarms.

PV solar energy cells are made of semi-conducting materials similar to those used in computer chips. When sunlight is

absorbed by these materials, solar energy releases energy from their atoms allowing the electrons to flow through the

material to produce electricity.

The basic PV building block is the photovoltaic cell. Referred to as a "cell", because it produces direct current (DC)

electricity like a battery, a PV cell converts energy from the sun directly into electricity. In practical applications ofphotovoltaic energy, groups of cells are unified to form a module (modules may be connected into an array).

There are 4 main components in most solar photovoltaic (PV) systems.

(1) The first is the solar array which is a collection the power producing cells. This converts the suns energy into DC

electricity.

(2) The second is the roof mounting structure consisting of aluminium or stainless steel components that are used to mo

the solar collector system onto the roof of the building. There are two major types; (1) roof integrated where the solar

energy panels replace the tile and become flush with the rest of the roof (2) on-top mounting where the solar panels sit

above existing roof tiles.

(3) A special solar energy inverter is then required to convert the DC (direct current) electricity into AC (alternating

current) electricity, which can be used by most home appliances or sold back to the grid.

(4) The final part is when the solar collector system is linked to your fuse box and an electric meter so you can tell how

much energy you have produced and how much unused energy you have sold back to the grid

Photovoltaic PV systems can be designed to sell any surplus energy back to electricity grid rather than store the energ

This overcomes many of the shortcomings of using batteries; including high cost, storage, limited useful lifespan and

environmentally unfriendly components.

In some remote areas, however, there may be no connection to the grid available making the use of batteries a necessity


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_____________________________________________________________________________P=Watt(power), E=Volt, I=Amp( P = I x E, I = P / E, E = P / I )1kw = 1000watts = 1.341hp1hp = 746 Watt = 3.6Amp = 0.75kw at 220VAC------------------------------------------------------? kw X 1000/12/8= ? Controller Size in Amps? Amps Controller /9.45 = ? Quantity of 165 Watt Panels? kw X 1000 /12 / 0.7 = ? / 75Ahr = Number of 75Ahr Batte ries you will use.? 75Ahr / 20hr = 3.75Ahr X ? Qty of Batteries = ? Amps Available over a 20 hour period.------------------------------------------------------(Rule of thump: One amp-hour is equal to one amp of power drawn for one hour of time).

Amp-hour capacity is generally given as the "20 hour rate" of the battery. Therefore, thenumber given as the amp-hour capacity for a deep cycle battery will be the number of amphours the battery can deliver over a 20 hour period at a constant draw. A 105 amp -hourbattery can deliver 5.25 amps constantly over a 20 hour period before it's voltage dropsbelow 10.5 volts, at which point the battery is discharged._____________________________________________________________________________..........Questions ??????? and Answers:_____________________________________________________________________________1 - For Example: if I need (5.5kw=5500Watts) per day or in 24 hrs = (5500) / (12) / (8) = 57.29thus needing a 60Amp Controller or 6pcs 10Amp controllers.-----2 - For Example: If I use a 60Amp Controller, how many what of the 165 Watt Solar Panels

will I need = (60Amp) / (9.45) = 6.34 or 6 or 7 panels (of a 165 Watt Panel size are needed(Note: the 165 Watt Panel is the Best size for all operation in the Middle Ea st)).-----3 - How many Batteries will I need for 5500Watts = (5500) / (12) / 0.7 = 462Ahr 12V Batteries75Ahr = 6.16 or 7 Batteries or Greater, (NEVER USE LESS).-----4 - What is the Battery Expected Discharge Rate and the Estimated Hourly Duration be forethe battery is depleted to below 10.5V?


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If I must use 7pcs 75Ahr batteries in the solar panel system, as standard we always use 20hour rate depletion capacity for our calculation. Thus: 75Ahr / 20hr= 3.75Ahr then multiplyby 7 batteries: 3.75 X 7 = 26.25. Thus 7pcs 75Ahr amp-hour batteries can deliver 26.25 ampat 12V constantly over a 20 hour period before it's voltage drops below 10.5 volts, at whichpoint the battery is discharged.__________________________________________________________________ ___________1 - A 10Amp controller will give me how many watts total usage in 24 hrs = 10Amp X (8) X(12) = 960 Watts will be available in 24 hrs.-----2 - For Example, If I use a 10 Amp Controller, how many 165 Watt Solar Panel will I need =(10Amp) / (9.45Nominal Current) = 1.05 piece (of a 165 Watt Panel size is Needed).-----3 - How many Batteries will I need for 960Watts = (960) / (12) / 0.7 = 114Ahr 12V Batteries /75Ahr = 1.52 or 2 Batteries or Greater, (NEVER USE LESS).-----4 - What is the Battery Expected Discharge Rate and the Estimated Hourly Duration beforethe battery is depleted to below 10.5V?

If dual 75Ahr batteries are used in the solar panel system, as standard we always use 20hour rate depletion capacity for our calculation. Thus: 75 Ahr / 20hr= 3.75Ahr then multiplyby two batteries: 3.75 X 2 = 7.5. Thus a dual 75Ahr amp -hour batteries can deliver 7.5 ampat 12V constantly over a 20 hour period before it's voltage drops below 10.5 volts, at whichpoint the battery is discharged.

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Wind Power >

How to Size a Battery BankBattery bank sizing can be one of the more complex and important calculations in your systemdesign. If the battery bank is oversized, you risk not being able to keep it fully charged; if thebattery bank is sized too small, you won't be able to run your intended loads for as long as you'dplanned.written by Chris Brown


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Many renewable energy (RE) systems incorporate batteries.Batteries can be used in all types of

systems including:

y Photovoltaic or solar panelsy Wind Power Systems using Wind Turbines

y Hydroelectric generators

y Hybrid Renewable Energy Ststemsy Other DC power sources

The energy stored in the batteries can then be used directly to power DC loads or it can be

inverted to power AC loads. The batteries recommended for RE systems are deep cycle batteries.

To ensure you have enough reserve capacity to provide the electricity you need (without running

additional generators), invest the time to size your battery bank properly. Because of the various

conditions affecting battery bank sizing, this process may be one of the more challenging

calculations youll have to do when planning your RE system.

Before tackling the calculations, start by identifying a few key pieces of information:

y Watt-hours of electricity usage per day

y Number of Days of Autonomy

y Depth of Discharge limit

y Ambient temperature at battery bank

Electrical Usage

The first thing youll need to know is the amount of energy youll be consuming per day. Its worth

the time to do a careful evaluation of exactly what loads (appliances, electronics, etc.) you plan to

use and for what lengths of time. Keep track of this information on a loads list; youll refer to thislist often for sizing other components as well. Your final tally should be expressed in Watt-hours

(Wh) per day. If you know the kilowatt hours (kWh) per day just multiply that number by 1,000 to

determine the Watt-hours per day. (Example: 1.2 kWh = 1,200Wh)

Days of Autonomy

Next, you must determine the number of days of battery back-up that you want to have on hand.In other words, if you are unable to charge your batteries by any means, and you still need todraw power, you must provide this additional storage by increasing the size of your battery bank.For solar panel powered systems (PV), Days of Autonomy represents the number of cloudy days ina row that might occur and for which you intend to store energy. Consult a weather website, localmeteorologist or even long-term area residents.

If you conclude that you need more then five days of battery backup, you may want to explore

multiple sources of electricity generation or backup generator options (like a fossil-fueled

generator). If your primary electricity source is wind power, determine the number of days when

there is little or no wind. This information can be found in the data youve collected using your

data-logging anemometer.Hydroelectric turbine systems are unique because they usually operate

continuously, and therefore do not require extensive storage. If youre sizing a battery bank to be


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used in conjunction with an on-demand fuel-powered generator, the number of days of backup will

represent the number of days you wish to go without using your generator.

Depth of Discharge

Another factor to consider is the planned Depth of Discharge (DoD) of your battery bank.Floodedlead acid batteries (FLA),sealed AGM batteries and sealed gel batteries are all rated in terms of

charge cycles. A single cycle takes a battery from its fully charged state, through discharge (use),then back to full charge via recharging. The depth of discharge is the limit of energy withdrawal towhich you will subject the battery (or battery bank). DoD is expressed as a percent of total

capacity. The further you discharge a battery, the fewer cycles that battery will be capable of

completing. Simply stated, deeper discharge shortens battery life.

Battery Life based on Depth of Discharge

Its recommended that you never discharge a deep-cycle battery below 50% of its capacity;

however, many battery manufacturers recommend even shallower DoDs. For off-grid applications,

a 25% DoD will extend battery life significantly.On the other hand, if youre only using thebatteries occasionally, as a backup system, you can factor in a DoD of50% or perhaps more.

Temperature

Battery life and capacity are affected by temperature. Unlike PV modules, batteries perform best in

moderate temperatures. In fact, the temperature standard for most battery ratings is 77 F. Coldtemperatures tend to reduce battery capacity while high temperatures tend to shorten battery life.For this reason, people in colder climates will often find a place to keep their batteries indoorsrather then leaving them subject to outside temperatures. FLA batteries can be destroyed infreezing temperatures.While sealed batteries can operate in sub-freezing temperatures, theirreserve capacities will be reduced substantially. Identify the lowest temperatures that the batterieswill be exposed to and factor this into the calculation using the temperature table (below).

System Voltage

By this point, you will have identified your system voltage. This is typically 12V, 24V, or 48V.

Calculations

Once youve pinpointed all these variables, its time to calculate the size of your battery bank!Lets go through the steps below, using the following example system:

y A system load of6,000Watt-hours per day

y Three Days of Autonomy (back up) needed

y Planned Depth of Discharge (DoD): 40%


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y Battery bank ambient average low temperature 60 F.

y A 48V system

Step Process Example

1 Identify total daily use in Watt-hours (Wh) 6,000 Wh/day

2 Identify Days of Autonomy (backup days);

multiply Wh/day by this factor.

3 Days of Autonomy:

6,000 x 3 = 18,000 Wh

3 Identify Depth of Discharge (DoD) and convert

to a decimal value. Divide result of Step 2 by

this value.

40% DoD:

18,000 / 0.4 = 45,000 Wh

4 Derate battery bank for ambient temperature

effect. Select the multiplier corresponding to the

lowest average temperature your batteries will

be exposed to. Multiply result from Step 3 by

this factor. Result is minimum Wh capacityof

battery bank:

Temp. in [degrees] F. Factor

80+ 1.00

70 1.04

60 1.11

50 1.1940 1.30

30 1.40

20 1.59

60 F. = 1.11

45,000 x 1.11 = 49,950 Wh

5 Divide result from Step 4 by system voltage.

Result is the minimum Amp-hour (Ah)

capacityof your battery bank.

49,950 / 48 = 1,040 Ah

Selecting batteries to meet the Amp-hour capacity

Now that you know the Amp-hour (Ah) capacity that will give you the storage you need, you mayneed a little guidance in selecting specific batteries. Keep in mind that its best to keep the number

ofparallel strings of batteries to three or fewer. If you parallel more than three strings of batteries,you risk shortening battery life due to uneven charging1. The ideal battery bank has no parallelconnections but is comprised of one or more series-connected batteries. Though parallelconnections are not to be avoided at all cost, fewer such connections tends to reduce the chance ofcharging problems over time.


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When batteries are cabled together in series, the voltage is additive. For example, you can put two

12V, 100 Ah batteries in series for a 24V bank. The capacity of that bank would still be 100 Ah.

When batteries are connected in parallel, the voltage remains constant and the Ah capacity is

additive. In our example with the 12V, 100 Ah batteries, connecting them in parallel would result

in a 12V system with a capacity of200 Ah.

The batteries you select must meet both your system voltage requirements AND the Ah capacity

you calculated. In our example of the 48V system, we calculated that we needed 1,040 Ah to

produce 6,000Wh per day with 3 days of storage.More than one configuration of batteries can

meet this need. For example, you could have four 12V batteries in series, each with a capacity of

1,040 Ah or more.Or you could use eight 12V batteries wired in two parallel strings where each

battery had a 520 Ah capacity.Or you could use twelve 2V batteries in series, again with

appropriate Ah capacities. In any given case, there may be multiple solutions. Your choices will be

limited by battery availability and budget.

Building the bank: Amps, then Volts

To build your bank, try first to select a battery that is rated close to the Ah capacity you calculated

in Step 5 above. Ignore voltage for a moment. If you cant find one thats very close, look for one

that has a capacity either one-half or one-third your needed Ah figure. These fractions represent

the number of series strings of such batteries you would need, in parallel, to complete your bank

(1/2 = 2 strings, 1/3 = 3 strings).Once you find a candidate battery, divide your system voltage

by the batterys voltage. This will give you the number of such batteries you would need in each

series string.

The total number of individual batteries you will need to complete your battery bank will be theproduct of the number of strings needed to meet your Ah requirement and the number of batteriesper string needed to meet your system voltage requirement.

Total # batteries in bank = (# series strings) X (# batteries per string)

You can then compare your candidate battery banks against price, size and availability. You may

want to talk with people who have used these batteries and learn what their experiences have

been, compare warranties and advertised features, and finally buy the batteries you feel are best

for you.

In any battery-based RE system, batteries are a major component investmentsecond in cost only

to the PV modules in most casesand they are a critical part of the system. Careful planning and

battery selection is vital to ensure that your battery bank meets your needs and provides many

hundreds or thousands of charge cycles. Take your time, run the numbers more than once, and

youll avoid the worst pitfalls of RE system design.

References:1A great article explaining the rationale behind this paralleled string limit is available in HomePower Magazine issue 114: Top Ten Battery Blunders .


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Batteries - Measuring State of ChargeAccurately knowing the state of charge of your batteries and keeping them properly charged canextend their life, keep your system running properly, and save you money.Voltage and State-of-Charge - a Cautionary Note

Please note that voltage is not the most accurate measure of state-of-charge. Voltage readingsfluctuate based on various prevailing conditions at the time of measurement. Use change of

voltage as an indicator of changing conditions or relative state-of-charge under similar conditions

over time. For more accurate state-of-charge readings, a shunt based monitoring system is

recommended.

Flooded Lead-Acid Batteries

Measuring the specific gravity (SG) of the battery electrolyte can provide the best measure of

the flooded lead-acidbatterys state of charge (SOC).Measuring voltage is one way to estimate the

state of charge of a battery; however voltage readings may vary depending upon whether the

battery is being charged, discharged or is at rest (open cell).Whether the battery is under load at

the time of the reading has little effect on the specific gravity of a tested cell. Additionally, specific

gravity is good for measuring overall battery bank health. By measuring the SG of each cell, you

can catch cell-to-cell or battery to battery differences that can result in untimely battery death.

Trojan Battery tips for Specific Gravity Testing (Flooded batteries only)

Source: Trojan Battery

1. Do not add water prior to testing.

2. Fill and drain the hydrometer 2-4 times before drawing a sample from the battery.

3. Have enough sample electrolyte in the hydrometer to completely support the float.4. Take a reading, record it and return the electrolyte to the cell.5. Check all cells in the battery, repeating the steps above.

6. Replace vent caps and wipe off any electrolyte that might have been spilled.7. Correct the readings to 80F:

Add 0.004 to readings for every 10 above 80F.Subtract 0.004 for every 10 below 80F.

8. Check the state of charge using the table provided by the manufacturer.The readings should be within the factory specification of1.277 +/- 0.007.

Examples of SG Readings as compared with SOC (Source: Rolls Battery)

% Charged Specific Gravity

100% 1.255 1.275

75% 1.215 1.235

50% 1.180 1.200


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25% 1.155 - 1.165

0% 1.110-1.130

Sealed Batteries

The state-of-charge of sealed batteries cannot be determined by looking at the specific gravity of

the electrolyte, since the batteries are, well, sealed! SOC can be determined by measuring the

voltage; this is most accurate when the battery has been removed from a load for at least 6 hours,

preferably 24 hours.Otherwise voltage values can fluctuate based on whether the battery is being

charged or discharged.Here is a chart from MK Battery showing different levels of charge for

flooded lead-acid and sealed batteries open circuit voltage.

Comparison of Battery State-of-Chart to Open Circuit Voltage for 12-VoltBatteries

% Charge FLA Gel AGM

100 12.70-12.60 12.95-12.85 12.90-12.80

75 12.40 12.65 12.60

50 12.20 12.35 12.30

25 12.00 12.00 12.00

0 11.80 11.80 11.80

Note: Divide values in half for 6-Volt batteries.

Source: MK Battery Manual

The time it takes to fully recharge a battery depends upon:

y Depth of dischargey Temperature

y Size and efficiency of charger

y Age and condition of battery

Locating and positioning your solar array


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Facing true south in an unobstructed location is extremely important to the proper functioning of asolar electric system

If your site is in the northern hemisphere you need to aim your solar modules to true south (the

reverse is true for locations in the southern hemisphere) to maximize your daily energy output. For

many locations there is quite a difference between magnetic south and true south, so please

consult a magnetic declination map before you setup your mount structure. Thesolar

modules should be tilted up from horizontal to get a better angle at the sun and help keep the

modules clean by shedding rain or snow. For best year round power output with the least amount

of maintenance, you should set the solar array facing true south at a tilt angle equal to your

latitude with respect to the horizontal position. If you plan to adjust your solar array tilt angle

seasonally, a good rule of thumb is:

y latitude minus 15 in the summer

y latitude in the spring/fall

y latitude plus 15 in the winter

Most mount structures are available with a seasonal adjustment of the tilt angle from horizontal to

65. To determine if your proposed array site will be shaded at any time of the day or year you

should consider using the Solar Pathfinder.

Solar Charge Controllers

Sizing a solar charge controller. You'll notice that solar charge controllers are specified by both

amperage and voltage. You will need a charge controller that matches the voltage of your solar

array and battery bank. (Usually 12, 24 or 48VDC) And you'll want to make sure the charge

controller has enough capacity to handle the current (in amps) from your solar array. The basic

formula for sizing a charge controller is to take the short circuit current (Isc) of the array, and

multiply it by 1.56. (What is short circuit current? Glossary of Alternative Energy Terms &Why

1.56? ) Be sure that the charge controller you select can handle at least that many amps.Please

protect this important part of your system with appropriate overcurrent protection before and after

the controller. (Enclosures, Electrical and Safety)

Continue reading about types of solar charge controllers and more!

Sub Categories

MPPT Solar Charge Controllers


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Pwm Type Solar Charge Contollers

Pwm Shunt Solar Charge Controllers

More info on Solar Charge Controllers

Charge controller types.Now that you know what size controller to look for, identify which type

of charge controller is right for your application: MPPT, PWM, and PWM shunt controllers. A PWM

(Pulse Width Modulated) charge controller is the traditional style. They are robust, inexpensive and

widely used in PV applications.PWM shunt controllers are used less often and mostly in

applications where electrical interference is an issue. The MPPT (Maximum Power Point Tracking)

charge controller is the shining star of today's PV systems. These controllers actually detect the

optimum operating voltage and amperage of the solar array and match that with thebattery bank.

The result is additional 15-30% more power out of your array versus a PWM controller. Although

the MPPT controller is more expensive than its PWM counterpart, it is generally worth the

investment for any solar electric system over 200 watts.

General Sizing Instructions

The design of any PV system requires certain basic calculations. First,

y Calculate the loads,

y Calculate the PV array current and array tilt angle, (depends on the solar energy received atthe site during the year)

y Calculate the battery size,

y Calculate the PV array size, and

y Determine if a PV/generator hybrid system should be used.

This method was first developed by experienced PC system designers and published in 1988

as "Stand-Alone Photovoltaic Systems - A Handbook of Recommended Design Practices". Theworksheets developed in this handbook can be completed to give the size of the PV array and batterythat are needed to produce and store the energy needed by the load. Other worksheets can be used todetermine the size of wires, fuses, switches, etc. (the BOS) required to install your system. The blank

worksheets in each section may be copied and saved.

Calculate the Load Design Current Battery Size PV Array Size Hybrid Needed??


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Use Worksheet #1 to calculate the power (current) requirements of the load

You must estimate the amount of power required by the load. This is done by listing each load and

making an estimate for how energy it will consume in a day. The worksheet calculations will yield thetotal daily load given in Amp-hours. If the load demand varies widely from month-to-month (or

season-to-season), you must fill out Worksheet #1 for each month. Usually the system size will be

dictated by the worst-case month&emdash;the month with the largest load and the lowest solarinsolation. Consider this month first.

Each box in the worksheet is numbered. The instructions below tell you how to fill in each box.

1 Load Description: List each load (i.e., fluorescent lamp, pump, radio). Enter the dc loads at the top

and the ac loads, if any, at the bottom part of the worksheet.

2 QTY: Enter the number of identical loads in the system.

3 Load Current (A): Enter an estimate of the current required by each load when operating. Use the

manufacturer's rated current, or measure the current.

4 Load Voltage (V): Enter the voltage of the load, i.e., 120 volt ac, 24 volt dc, etc. The operating

voltage is usually listed on the appliance.


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5A DC Load Power (W): Calculate and enter the power required by the dc load. Power equals the

product of voltage and current.

5B AC Load Power (W): Calculate and enter the power required by the ac load. Ignore the power

factor for this calculation.

6 Daily Duty Cycle (hrs/day): Enter the average amount of time per day the load will be used. (Enterfractions of hours in decimal form, i.e., 1 hour, 15 minutes would be entered as 1.25.)

7 Weekly Duty Cycle (days/wk): Enter the average number of days each week the load will be used.

8 Power Conversion Efficiency (decimal): This factor accounts for power loss in systems using

power conditioning components (converters or inverters). If the appliance requires ac power or dc

power at a voltage other than your system voltage, you should enter the conversion efficiency of thedevice. If you do not have the actual efficiency of the converter being used, use the default values

given below for initial sizing.

Power Conversion Efficiency Default

DC to AC 0.85DC to DC 0.9

9 Nominal System Voltage (V): Enter the desired system voltage. The system voltage is normally thevoltage required by the largest loads. Common values are 12 or 24 volts dc and 120 volts ac.

10 Amp-Hour Load (Ah/day): Calculate the average energy requirement per day in ampere-hours by

performing the calculations as indicated by the mathematical symbols across the page.

11 Total DC and AC Load Power (W): Enter the individual ac and/or dc loads.

11A Total dc load in Watts.

11B Total ac load in Watts.

12 Total Ampere-Hour Load (Ah/day): Calculate the daily average system load in ampere-hours.

13 Total DC Load Power (W): Enter value from Block 11A.

14 Total AC Load Power (W): Enter value from Block 11B.

15 Nominal System Voltage (V): Enter value from Block 9.

16 Peak Current Draw (A): Calculate the maximum current required if all the loads are operating

simultaneously. This value is used for sizing fuses, wiring, etc.

17 Total Ampere-Hour Load (Ah/day): Enter value from Block 12.

18 Wire EfficiencyFactor (decimal) (1 - wire loss): Enter the decimal fraction accounting for loss

due to wiring and switchgear. This factor can vary from 0.95 to 0.99. Wire size should be chosen to

keep wire loss in any single circuit to less than 3 percent (>0.97).


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Wire Efficiency Factor Default Value = 0.98

19 Battery Efficiency Factor (decimal): Enter the battery efficiency which is equal to ampere-hoursout divided by ampere-hours in. Use manufacturer's data for specific battery. Assume constant voltage

operation.

Battery Efficiency Factor Default Value = 0.90

20 Corrected Amp-Hour Load (Ah/day): Calculate the energy required to meet the average daily

load plus losses.

Use Worksheet #2 with estimates of the solar energy available at (or near) your site to determine the

Design Current and the optimum tilt angle for your PV array. An array set at the same angle as the

latitude of the site will receive the maximum annual solar radiation. If the load demand is high in the

winter (northern hemisphere), set the array tilt at latitude plus 15. For a predominant summer load,set the array tilt angle at latitude minus 15. Calculate the design current for all three tilt angles if theload demand varies widely throughout the year. Completing the calculation on the worksheet will

yield the optimum tilt angle for your array. The numbered instructions correspond to the numbers in

the boxes in the worksheet. The worksheet may be copied and saved.


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21 System Location/Insolation Location: Enter the latitude and longitude of the system site and the

location of the insolation data used. See Appendix A.

22A, B, & C Corrected Load (Ah/day): See Block 20 Worksheet #1. Enter the corrected load for

each month for each tilt angle.

23A, B, & C Peak Sun (hrs/day): Enter the average number of hours each day when insolation was1,000 watts per square meter. Enter the value for each month for each tilt angle. Weather data for

selected sites is given in Appendix A.

NOTE: Peak sun hours are equal to the average kilowatt-hours/m2-day.

1 kwh/m2 =Langley/85.93 =316.96 Btu/ft2

= 3.6 MJ/m2.

24A, B, & C Design Current (A): Calculate the current required to meet the system load.

NOTE: The recommended tilt angle for the array is selected by first determining the

largest design current for each of the three tilt angles; then selecting the smallest of

those three values.


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25A + 26A Peak Sun (hrs/day) and Design Current (A): Select and enter the largest monthly

design current and corresponding peak sun hours from columns 24A, 24B, and 24C.

27 & 28 Peak Sun (hrs/day) and Design Current (A): Select and enter the smallest of the three

design currents and the corresponding peak sun hours from 25A, B, or C and 26A, B, or C.

Use Worksheet #3 to calculate the size of the battery needed for the PV system. This will dependlargely on the value you select for storage days. This value depends on many factors such as siteaccessibility, type of batteries selected, and variability of the load. For more information see the

discussion onbatteries.

29 Corrected Amp-Hour Load (Ah/day): Enter value from Block 20 Worksheet #1.

30 Storage Days: Choose and enter the consecutive number of days the battery subsystem is requiredto meet the load with no energy production by the array. System availability is defined as critical (99

percent available) or non critical (95 percent available) and directly affects the number of storagedays. Use the chart below to find the recommended number of storage days if no better estimate can

be made.

31 Maximum Depth of Discharge (decimal): Enter the maximum discharge allowed for the battery.

This depends on size and type of battery. Consult the battery manufacturer or use default values

below.

Maximum Depth of Discharge

Battery Type Default Value


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Lead Acid Shallow Cycle 0.25

Lead Acid Deep Cycle 0.75

Nickel Cadmium 0.9

32 Derate for Temperature (decimal): Enter a factor that derates the battery capacity for cold

operating temperatures. Ask the battery manufacturer for this information. If no better information isavailable derate a lead acid battery's capacity one percent for each degree Celsius below 20C

operating temperature.

Temperature Correction Factor Default = 0.90

33 Required Battery Capacity (Ah): Calculate the battery capacity required to meet the daily load

for the required number of days.

NOTE: Select a battery for your system and record the specifications in the battery

information block.

34 Capacity of Selected Battery (Ah): Enter the manufacturer's rating of battery storage capacity inampere-hours. Batteries are normally rated at optimum test conditions; 20C, and discharge rates of

C/20 or lower.

35 Batteries in Parallel: Calculate the number of parallel connected batteries required to provide the

storage capacity.

36 Nominal System Voltage (V): Enter the value from Block 9, Worksheet #1.

37 Nominal Battery Voltage (V): Enter the rated voltage of the selected battery, i.e., 2, 6, or 12 volts.

38 Batteries in Series: Calculate the number of series connected batteries required to provide thesystem voltage.

39 Batteries in Parallel: Enter the value from Block 35.

40 Total Batteries: Calculate the total number of batteries in the system.

41 Batteries in Parallel: Enter the value from Block 35.

42 Capacity of Selected Battery (Ah): Enter the value from Block 34.

43 System Battery Capacity (Ah): Calculate the battery system storage capacity.

44 Maximum Depth of Discharge (decimal): Enter the value from Block 31.

45 Usable Battery Capacity (Ah): This is the amount of ampere-hours that can safely be used from

the installed batteries.


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Use Worksheet #4 to calculate the size of the photovoltaic array. This should be large enough to

provide energy to the load during the Design Month and to fully recharge the batteries during periodsof sunny weather. For information on PV modules clickhere. The blank worksheet may be copied and

saved.

46 Design Current (A): Enter the value from Block 28, Worksheet #2.

47 Module Derate Factor (decimal): Enter a factor to adjust module current from standard operating

conditions (SOC) of 1,000 w/m2 and 45C temperature to field conditions, i.e., dust accumulations,

mismatch loss between modules, degradation over time, etc.) Ask the module distributor or use thedefault values below.

Module Derate Factor Default Value

Module Type Default Value

Single or Polycrystalline Silicon 0.90

Amorphous Silicon 0.70

48 Derated Design Current (A): Calculate the minimum array current necessary to supply the

average daily load at the chosen site.


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NOTE: Select a PV module and record the specifications in the module information

block. Be sure to determine the module voltage when it is operating at the highest

temperatures expected for your site.

49 Rated Module Current (A): Enter the rated module operating current at 1,000 w/m2 and 45C

operating temperature as given by the manufacturer.

50 Modules in Parallel: Calculate the number of parallel connected modules required to provide the

array current.

51 Nominal Battery Voltage (V): Enter the value from Block 37 Worksheet #3.

52 Batteries in Series: Enter the value from Block 38 Worksheet #3.

53 Voltage Required to Charge Batteries (V): Calculate the minimum voltage required to charge

the batteries.

54 Voltage at Highest Module Temperature (V): Enter this value from the manufacturer's

specifications.

55 Modules in Series: Calculate the number of series connected modules required to produce the

system voltage. You must not round down. Round up or select another module with a higher

operating voltage.

56 Modules in Parallel: Enter the value from Block 50.

57 Total Modules: Calculate the total number of modules in the array.

58 Modules in Parallel: Enter value from Block 50.

59 Rated Module Current (A): Enter the module current when operating at 1,000 w/m2 and 45Ctemperature.

60 Rated Array Current (A): Calculate the rated array current when operating at 1,000 w/m2 and

45C temperature.

61 Module Short Circuit Current (A) : Enter module short circuit current when operating at 1,000

w/m2 and 45C temperature.

62 Array Short Circuit Current (A): Calculate the array short circuit current when operating at

1000 w/m2

and 45C temperature.

63 Modules in Series: Use the value from Block 55.

64 Rated Module Voltage (V): Enter module voltage when operating at 1,000 w/m2 and 45C

temperature.

65 Array Rate Voltage (V): Calculate array voltage when operating at 1,000 w/m2 and 45C

temperature.

66 Open Circuit Module Voltage (V): Enter module open circuit voltage when operating at 1,000

w/m2 and 45C temperature.


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67 Array Open Circuit Voltage (V): Calculate array open circuit voltage when operating at 1,000

w/m2

and 45C temperature.

NOTE: In some applications you may wish to know the highest voltages that might be

produced by the array. This will occur when the array is operating at its lowest

temperature. Use manufacturer's data to determine module voltage for the coldest

temperatures expected.

Use Worksheet #5 to determine if your application would be a candidate for a hybrid power system.

This type of system uses more than one power generator and may be the cost-effective alternative for

specific systems. Completing this worksheet will give an indication of whether a hybrid power system

should be considered for this application. This blank worksheet may be copied and saved.

68 Total Amp-Hour Load (Ah): Enter the value from Block 20 Worksheet #1.

69 Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1.

70 Watt-Hour Load (Wh/day): Calculate the average daily load power of the system.


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71 Conversion Factor: Multiplying by this factor converts watt-hours per day to kilowatt hours per

year.

72 Annual Kilowatt-Hour Load (KWH/YEAR): Calculate the average annual load power. This

value is helpful if a hybrid system is required.

73 Derated Design Current (A): Enter the value from Block 48 Worksheet #4.

74 Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1.

75 Design Array Power (W): Calculate the average daily power required by the load.

76 Watt-Hour Load (Wh/day): Enter the value from Block 70.

77 Array to Load Ratio (decimal): Calculate the factor used to determine if a hybrid design should

be considered.

78 Hybrid Indicator: Plot a point on the graph using values from Blocks 76 and 77.

NOTE: If the hybrid indicator suggests a hybrid system, complete the hybrid

worksheets, HY#1 and HY#2. Compare life cycle cost analyses of both designs andmake a decision as to which would be the optimum system.

Otherwise: Use the Component Specification Worksheets to complete the design

Top of page

Designing a hybrid power system is not a simple matter. You are considering at least two independentpower sources that must be controlled and synchronized. Most controllers for hybrid systems are

custom-designed. Still this should not discourage you from completing the Hybrid worksheets. Thisexercise will help you learn about your application and cost-effective methods of providing energy.


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Use Hybrid Worksheet #1 HY to calculate the Battery Capacity, Generator Size, and Percent

Contribution of the PV Array and Generator. The blank worksheet may be copied and saved.

1Y Corrected Amp-Hour Load (Ah/day): Enter value from Block 20 Worksheet #1.

2Y Storage Days for Hybrid System: Enter the number of days of storage for the hybrid system.

This value is usually smaller than for a stand-alone system because the generator is available forbackup.

Days of Storage Default for Hybrid System = 3 Days

3Y Maximum Depth of Discharge (decimal): Enter the value from Block 31 Worksheet #3 if thesame battery will be used. If another battery is selected, use the manufacturer's specifications to select

a safe depth of discharge.

4Y Derate for Temperature (decimal): Enter the value from Block 32 Worksheet #3 if the same

battery will be used.

Allowance for Temperature Derate of Battery = 0.90

5Y Hybrid Battery Capacity (Ah): Calculate the required hybrid battery capacity.

6Y Peak Current Demand (A): Enter the value from Block 16 Worksheet #1.

7Y Battery Discharge Time (HOURS): Calculate the battery discharge factor&emdash;this is thenumber of hours the battery can supply the peak current to the load. This factor should be greater than


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5 to prevent damage to the batteries. If less than 5, increase the number of storage days and

recalculate 1Y through 7Y.

8Y Hybrid Battery Capacity (Ah): Enter the value from Block 5Y.

9Y Battery Charge Time (HOURS): Enter the minimum time that will be used to charge the battery.

Determine the maximum charging current that should be used for the chosen battery from themanufacturer's specifications.

Charge Time Default Value = 5

10Y Maximum Battery Charge Rate (A): Calculate the maximum battery charge rate.

11Y Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1.

12Y Nominal Charging Power (W): Calculate the charging power required.

13Y Efficiency of Battery Charger (decimal): Determine and enter the battery charger efficiency.

See manufacturers' specifications

Battery Charger Efficiency Default Value = 0.80

14Y Generator Derate (decimal): Generator power output should be derated for high altitudeoperation because the thinner air reduces combustion efficiency. Ask your generator supplier what

derate factor should be used. If no other information is available, use a default of 3 percent per 1000feet of elevation above sea level for gasoline, diesel, and propane fueled generators. Use 5 percent fornatural gas generators. For example, a 5000 Watt diesel generator operating at 9000 feet elevation

should be considered as a 3650 Watt generator.

[5000 * (1 - 9 * 0.03)] = 3650

15Y Generator Size (W): Calculate the generator size to the nearest whole number.

16Y Hybrid Array to Load Ratio (HAL): Determine the split between generator and PV power

using the graph provided on the next page. Start with the HAL factor calculated in Block77, Worksheet #5and determine the amount of load provided by the PV array. In most cases this will

indicate a high percentage of PV power and therefore a high initial cost for the system. Systemdesigners adjust the HAL to change the PV array size depending on the application and the budgetavailable. The percentage of the load provided by PV power, and thus the initial cost, increase as you

move up the curve. The shape of this curve will change slightly with weather patterns. For areas with

long periods of inclement weather, the slope of the curve will decrease, indicating a smaller PV array

for a given HAL value.

17Y Load Provided by Array (decimal): Enter the number selected from the left axis of the graph

that corresponds to the HAL ratio chosen.

18Y Load Provided by PV Array (decimal): Enter the value from Block 17Y.

19Y Load Provided by Generator (decimal): Calculate the percentage of load provided by the

generator.


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20Y Annual Kilowatt-Hour Load (kWh/yr): Enter value from Block 72 Worksheet #5.

21Y Annual Generator Output (kWh): Calculate the annual generator output.

22Y Annual Generator Output (kWh): Enter the value from Block 21Y.

23Y Conversion Factor: This factor converts kilowatt-hours to watt-hours.

24Y Nominal Charging Power (W): Enter the value from Block 12Y.

25Y Annual Generator Run Time (hr): Calculate the time the generator will run in a typical year.

26Y Oil Change Interval (hrs): Select and enter number of operating hours between oil changes for

your generator. Some typical intervals are given in the following table along with suggested intervals

for more thorough cleaning and maintenance and engine rebuild.

Generator Maintenance Interval Default Values - Hours

Oil Change Engine Tune-up Rebuild Engine

Gasoline Engine (3600 rpm) 50 300 5,000

Gasoline Engine (1800 rpm) 100 300 5,000

Diesel 400 1,200 7,200

27Y Services Per Year (number): Calculate the recommended number of service calls per year.

Use Hybrid Worksheet #2 HY to calculate the number of PV modules and batteries for your hybrid

system. These will differ from the calculation you made using Worksheets 3 and 4. The blank

worksheet may be copied and saved.


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28Y Hybrid Array to Load Ratio: Enter the value from Block 16Y Worksheet #1HY.

29Y Watt-Hour Load (Wh/day): Enter the value from Block 70 Worksheet #5.

30Y Hybrid Array Power (W): Calculate the hybrid array power.

31Y Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1.

32Y Rated Module Current (A): Enter the value from Block 59 Worksheet #4.

33Y Modules in Parallel: Calculate the number of modules connected in parallel required to provide

the array current. Rounding down will mean more generator operating time.

34Y Nominal System Voltage (V): Enter the value from Block 31Y Worksheet #1HY.

35Y Nominal Module Voltage (V): Enter the nominal module voltage from Block 64 Worksheet #4.

36Y Modules in Series: Calculate the number of series connected modules required to produce the

system voltage.

37Y Modules in Parallel: Enter the value from Block 33Y.

38Y Total Modules: Calculate the total number of modules required.

39Y Hybrid Battery Capacity (Ah): Enter the value from Block 5Y Worksheet #1HY.


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40Y Capacity of Selected Battery (Ah): Enter the rated capacity for the selected battery from

manufacturers' specifications.

41Y Hybrid Batteries in Parallel: Calculate the number of parallel connected batteries required to

provide the storage capacity.

42Y Nominal System Voltage (V): Enter the value from Block 31Y Worksheet #1HY.

43Y Nominal Battery Voltage (V): Enter the nominal battery voltage from Block 37 Worksheet #3.

44Y Batteries in Series: Calculate the number of series connected batteries required t

Battery Maintenence and Solar panel System designing

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