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A Buyer’s Guide

Photovoltaic Systems: A Buyer’s Guide

This guide is distributed for information purposes only and does not necessarily reflect the views of the Government of Canada or constitute an endorsement of any commercial productor person. Neither Canada nor its ministers, officers, employees or agents make any warrantywith respect to this guide or assumes any liability arising from this guide.

© Her Majesty the Queen in Right of Canada, 2002

Cat. No. M92-28/2001EISBN 0-662-31120-5

Aussi disponible en français sous le titre : Les systèmes photovoltaïques : Guide de l’acheteur

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Table of Contents

About This Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1. What Is a Solar Electric or Photovoltaic (PV) System? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3What Is PV? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3How Does It Work? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3The Three Types of PV Power Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2. What Photovoltaics Can Do for You . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7The Advantages of PV Power Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7The Limitations of PV Power Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3. Photovoltaics at Work in Canada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Cottages and Residences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Power for Remote Lodges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Mobile and Recreational Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Photovoltaics in Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15A PV System to Suit Your Particular Power Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4. Buying Your Photovoltaic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Be Prepared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Where to Find PV Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Choosing a Dealer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Making a Decision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5. Installing and Maintaining Your Photovoltaic System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Mounting the PV Array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Housing the Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

6. Estimating Your Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Step 1. Estimate Your Power and Energy Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Step 2. Make a Rough Evaluation of PV System Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

7. Sizing Worksheet Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Example 1. Summer Cabin Power System – The Smiths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Example 2. Year-Round Remote Residential Power System – The Wongs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

8. Technical Information on Photovoltaic System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35PV Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35The Electric Characteristics of PV Modules: The Current-Voltage (I-V) Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Other Components in PV Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Appendix A: Worksheet to Evaluate System Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Step 1. Estimate Your Power and Energy Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Step 2. Make a Rough Evaluation of PV System Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Appendix B: Typical Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Typical Power Ratings of Some Common Appliances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Appendix C: Energy-Efficient Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Comparison of Typical Lighting Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Learn More About Solar Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Reader Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

The information in the followingpages is for prospective buyers ofphotovoltaic (PV) systems for usein the following:

• remote cottages and residences;

• recreational and mobile applications;

• agricultural applications;

• remote lodges; and

• remote lighting applications.

The purpose of this guide is tohelp you determine whether a PVsystem is a suitable option for youin providing electrical power forone or more of the above uses. Itdescribes typical and innovativePV systems, provides examples ofsuccessful Canadian installationsand answers some of the ques-tions you should ask yourselfbefore approaching a PV dealer(as well as questions a dealershould be able to answer).

Each section of this guide isdivided into short, easy-to-readsubsections. This format allowsyou to browse by topic or readthe guide from cover to cover.Several forms are included to help you estimate your power and energy needs.

Once you have read this guide,you should know enough aboutPV systems to consult dealers and,with them, evaluate the best PVconfiguration to meet your needs– now and for the future. Thisguide provides only estimates andis not intended to replace thetechnical expertise required forthe detailed design and installa-tion of a PV system. Nowhereshould you construe that thisguide recommends or promotesany specific products.

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About this Guide

What Is PV?The term “photovoltaic,” com-monly referred to as PV, is derivedfrom a combination of “photo,”the Greek word for light, and“Volta,” the name of the Italianphysicist, Alessandro Volta, whoinvented the chemical battery in1800. The PV effect is the directconversion of solar energy intoelectricity. This process does notgenerate heat like solar domestichot water or solar pool heatingsystems do. It also differs fromthe process used in solar thermalpower plants, where concentratedsolar energy is used to producesteam that activates a turbineconnected to an electric genera-tor. PV power systems do nothave any moving parts. They are reliable, require little mainte-nance and generate no noise or pollutants. PV systems aremodular – the building blocks(modules) come in a wide rangeof power capabilities, from a fraction of a watt (e.g. solarwatches and pocket calculators)to more that 300 W. Modules can be connected to achieve the power that your applicationrequires. Some demonstration PV power plants have severalmegawatts of power, althoughmost installed PV systems aremuch smaller.

How Does It Work?PV cells are normally fabricatedusing special semiconductormaterials that allow electrons,which are energized when thematerial is exposed to sunlight,

to be freed from their atoms.Once freed, they can movethrough the material and carry anelectric current. The current flowsin one direction (like a battery),and thus the electricity generatedis termed direct current (DC).

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1. What Is a Solar Electric or Photovoltaic (PV) System?

▲A PV module converts sunlight directly into electricity.

▲For applications that require electricity during overcast periods, batteries ensurethat the PV system is autonomous.

The energy generated by PV modules can be used immediatelyor stored in batteries for later use. Normally, the excess energygenerated in autonomous PV systems during sunny periods isstored in batteries. The batteriesthen provide electricity at nightor when there is not enough solarradiation. For these applications,the number of watts in the arrayand the capacity of the batteriesare carefully sized to give opti-mum performance.

Some autonomous applications,such as water pumping, often have no need for batteries. Wateris pumped when the sun shinesand is stored directly in a reser-voir or a tank that is installed at a higher level for later use by gravity feed.

Other PV systems convert theelectricity into alternating current(AC), feed excess electricity intothe grid and draw out electricityat night or when the solar radia-tion is low. These systems arereferred to as grid-connected,grid-tied or net-metered.

The Three Typesof PV PowerSystemsThe three typical configurations ofPV power systems are autonomous,hybrid and grid-connected.Autonomous and hybrid powersystems are used in stand-aloneapplications. They are not con-nected to the main utility grid and are often used in remote areas.

AutonomousAutonomous systems rely exclu-sively on solar energy to meet aneed for electricity. As mentionedin the preceding, they may incorporate batteries – whichstore energy from the PV modulesduring the day – for use at night

or in periods of low solar radia-tion. Alternatively, they maypower the application entirely,with no need for batteries (e.g. water pumping). In general,autonomous PV systems are themost cost-effective source of electrical power. You may, however, decide to choose ahybrid PV system because of the environment in which it will operate or because you need a system that operates independently and reliably.

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▲Autonomous PV system without batteries.

▲Autonomous PV systemwith batteries.

▲Hybrid PV system.

Autonomous PV Systems Hybrid PV System

Generator

HybridHybrid systems, also used instand-alone systems, consist of PVmodules and a wind and/or fuel-fired generator. A hybrid system isa good option for larger systemsthat need a steady power supply,when there is not enough sun atcertain times of the year, or if youwant to lower your capital invest-ment in PV modules and storagebatteries.

Grid-ConnectedGrid-connected PV power systemsare part of the movement towarda decentralized electrical network.Power is generated closer towhere it is needed – not solely bycentral power stations and majorhydro stations. Over time, suchsystems will reduce the need toincrease the capacity of trans-portation and distribution lines.

A “grid-connected” system gener-ates its own electricity and feedsits excess power into the utilitygrid for later use. This does awaywith buying and maintaining abattery bank. You can still usebattery banks to provide backuppower when the grid goes down,but they are not required.

Smaller systems have a box – a small grid synchronous inverter– mounted on the back of eachpanel. Larger systems have onelarge inverter, which can handlemany panels (as in a stand-alonesystem). Both types convert DCpower output into AC power. Thenthey synchronize this output withthe grid to slow down the electri-cal meter. They can even turn themeter backward. If the PV outputis less than the load consumption,the meter slows down.

If PV output exceeds the loadconsumption, the meter turnsbackward, and a credit is accumu-lated. This credit can be drawnout of the utility when the sun is not shining. In essence, the grid

acts like a limitless battery bank.In most parts of Canada, permis-sion from the local utility isrequired in order to back feedpower into the grid.

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▲Water oxygenation compressors and water pumps are examples of PV systems that function with-out batteries. Photo courtesy ofEnvironergie Québec Inc.

▲Remote residences or cottages canhave access to electricity withoutextending the grid. Photo courtesy of Solener Inc.

▲Centralized and distributed grid-connected PV systems.

Grid-Connected PV Systems

A large portion of the cost of a grid-connected PV system ismanufacturing the PV modulesthemselves. Significant decreasesin manufacturing costs haveoccurred in recent years, with further decreases expected in thefuture. This kind of PV system isthus becoming more affordable.In some urban areas in warm cli-mates, the cost per kilowatt-hourof electricity from grid-connectedPV systems is competitive withthat of other electricity-generatingsystems. In areas with less solarradiation, the cost-effectiveness of this type of PV system is stillmarginal. But there is a potentialfor peak power savings in areaswhere air conditioning causes apower peak in the summer. Thereare also system savings where the PV modules can replace thetraditional roofing materials forbuildings or the cladding materialthat is normally used in buildingfaçades. These material savingsare making the costs per kilowatt-hour from grid-connected PVsystems increasingly competitive.

Decentralized small home systemsalso hold some potential for grid-connected PV systems, butthe costs will have to be reduced further in order to compete withthe low electricity rates now avail-able in most parts of Canada.Note, however, that PV electricityis “green” energy and, as such, isworth a premium. Even thoughthis value is subjective, it shouldbe expressed in numbers by thePV system’s designer. For exam-ple, how much is the avoidedpollution of conventional sourcesworth and how much is theavoided distribution cost worth?

To install a PV system, you mustpay the capital cost of the systemand amortize this cost over time.In contrast, where there is a utilitygrid, you pay for the electricityused and not a lump sum for thegenerating facility. The costs of the PV system may appear to be a burden because the electricitythat the system generates may costmore per kilowatt-hour than whata utility charges. But using a PVsystem may also be considered alifestyle choice, similar to choos-ing between a fuel-efficient car ora gas-guzzling sport utility vehicle.

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▲This house in Edmonton, Alberta, is equipped with a 2.3-kW system that is connected to the local power utility. About 2500 kWh are produced each year. The investment cost in 1995 was $28,000.

Perhaps you need reliable power in a location that is not connected to an electricalgrid. In this case, photovoltaicsmay be the best and most cost-effective solution. Manylocations in Canada that have adry continental climate have thesame number of daylight hoursas some Mediterranean countries. A photovoltaic (PV) system usedduring the summer in Canadacan take advantage of substantialdaily amounts of solar energy.Contrary to what many peoplethink, PV systems convert sunlight into electricity moreefficiently at lower temperatures.However, the winter months inCanada provide half the hours of sunlight as in summer. Muchof Canada experiences highwinds in the winter, which canmake a wind generator a logicaladdition to the system. Fuel-fired generators are then usedonly for backup.

Among other things, you can usePV energy to:

• supply power for lights,radios, televisions, pumps andother appliances in cottagesand residences;

• power electric fences, waterpumps and other devices inagricultural operations;

• run water-pumping and circu-lation systems in game fishingand aquaculture facilities;

• provide reliable electric powerfor wilderness lodges andhunting and fishing camps;

• recharge or maintain chargeof batteries for recreationalapplications such as recre-ational vehicles and sailboats;

• power portable devices such as laptop computers;

• power exterior lighting;

• provide reliable power for many commercial applications; and

• lower your monthly utility bills.

The Advantagesof PV PowerSystemsUsers of PV power systems appreciate their quiet, low-maintenance, pollution-free, safeand reliable operation, as well asthe degree of independence they provide. Why else should youconsider buying a PV system? If you are some distance from anelectrical grid, it may be cheaperto generate your own powerrather than pay to extend transmission lines from the grid. Diesel, gasoline or propane generators are the conventionalalternatives, but many peoplefind them noisy, polluting andcostly to run and maintain. It also makes little sense to turn ona 5-kW generator to power a few100-W light bulbs. PV systemsreduce the negative aspects ofgenerators by using them only as a backup.

When capital cost is an issue, orwhen photovoltaics alone are not enough to replace an existing generator, you can use a wind generator as part of a hybrid PVsystem, thus reducing the use ofthe generator. Such an intermit-tent charge system is more efficientthan a generator running continu-ously at low load. In addition tosaving fuel and lowering mainte-nance costs, you will increase thegenerator’s life span. Also, sincethe PV panels and battery banksare modular, you can expand thePV system gradually as your budget or needs increase.

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2. What Photovoltaics Can Do for You

The Limitationsof PV PowerSystemsIt is important to realize that PVpower systems are capital inten-sive from the buyer’s perspectiveand are expensive when com-pared with the low price of utilitypower in Canada. You shouldtherefore reserve the electricpower produced by PV modules,an inverter and a storage systemfor your most energy-efficientappliances, tools, lights, etc.

Although it is technically possi-ble, heating with photovoltaics isgenerally not recommended. Youcan easily and more efficientlycollect heat with a solar thermalsystem. A solar water heater gen-erates more hot water with lessinitial cost than any PV-poweredheater.1 Also, for cooking, it is

generally more cost-effective andconvenient to use a stove thatoperates on propane or naturalgas rather than solar electricity.Autonomous PV-powered homesand cottages often rely on woodcookstoves for cooking and spaceheating. Refrigerators are becom-ing more energy efficient, so thecost of operating them with PVpower is now feasible. Extremelyenergy-efficient refrigerators andfreezers are, unfortunately, stillexpensive, however, they can behad through PV dealers.

From an economic point of view,first consider investing in energy-efficient electric appliances, andthen size your PV system basedon actual consumption. Forexample, using compact fluores-cent lights will reduce yourelectrical consumption for lighting by 80 percent.

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1 For more information, obtain a free copy of Solar Water Heating Systems: A Buyer’s Guide from Natural Resources Canada. Call 1 800 387-2000 toll-free, or visit the Web site at http://www.canren.gc.ca.

The use of photovoltaic (PV) technology is increasing rapidlyin developed and developingcountries. Although the CanadianPV industry has also expandedsignificantly over the past decade,the use of photovoltaics inCanada is still relatively limited.This is partly because of Canada’slow utility rates, but the followingcommonly held myths are alsoresponsible:

Myth: “There is notenough sunlightin Canada.”

Myth: “Solar electrictechnology is notefficient in acold climate.”

Myth: “Photovoltaics is not a proventechnology.”

Myth: “PV systems aretoo expensive.”

Thousands of PV systems in myriad applications throughoutCanada and millions throughoutthe world today have debunkedthese myths. Although conditionsin Canada pose a special chal-lenge to the use of photovoltaics,an appropriately designed PV system can give you reliablepower to most remote sites. In the following pages, examples of actual, cost-effective PV installations across the countrywill demonstrate what photo-voltaics can do for you.

Cottages andResidencesIncreasingly, Canadian homeown-ers are using PV systems to powerlights and appliances in remotecottages and residences that arenot connected to a utility grid.Like these homeowners, you’llappreciate the quiet, low-mainte-nance, safe and pollution-freeoperation of a PV system, as wellas its versatility and reliability. In general, PV systems are cost-competitive for cottages andresidences that are more than several hundred metres from theelectricity grid. But they are notyet a cost-competitive alternativein locations that have direct accessto power from the grid.

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3. Photovoltaics at Work in Canada

Example 1. A TypicalAutonomous PV Application for a Remote Cottage

A cottage, located away from thepower grid, uses photovoltaics topower several fluorescent direct current (DC) lights, some halogenlights and a DC water pump, which supplies water to the resi-dents. A stove and a refrigerator run on propane fuel. No inverter isneeded, but one can be includedany time if alternating current (AC)loads are added.

The cottage is equipped witha PV system that consists of the following:

• two 75-W solar modules (150 W of photovoltaics);

• a 20-A (ampere) regulator;

• a load/fuse panel;

• a bank of batteries; and

• a second PV system that powers a small, exterior DC light with an 8-W panel and an independent battery.

The cottage is used primarily onweekends and during vacations,which explains the large batterycapacity compared with the totalarea of PV modules. This allowsmore energy to be available during two days of occupancy, and the PV modules recharge the batteries over the remaining fivedays of the week. This system has been functioning maintenance-free since 1997. ▲Photo courtesy of Cimat enr.

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Example 2. An Autonomous PV System Powers a SummerResidence on an Island on the St. Lawrence River nearMontréal, Quebec

Major power-line damages inQuebec have occurred twice in fiveyears, the most recent being thesevere ice storm of 1998. For oneof its customers that has an islandsummer cottage, Hydro-Québecdecided to provide a stand-alonePV system instead of maintaining a 200-m power line between theisland and the mainland.

The average amount of electricityneeded to run this cottage is 5.5 kWh/d (very low by Canadianstandards), mainly during the sum-mer. The load consists of lights,household appliances, power tools,water and pool pumps, an alarmsystem, etc. This load is expected to be 75 percent less during thewinter, when only exterior lightingand the alarm system are active.

Three possible solutions wereanalysed: the replacement of theoverhead power line, a submergedcable and renewable energy. Due

to Canadian Coast Guard regula-tions, the new overhead line wouldhave to be at least 10–15 m higherthan the one previously installed.And it would have been expensivefor Hydro-Québec to install a submerged cable, given the highlevels of polychlorinated biphenyls(PCBs) in sediments of theSt. Lawrence River. In November1997, Hydro-Québec decided toevaluate alternative options. A PVstand-alone system was preferredto a wind generator, due to thepotential for low winds in theMontréal region in the summer.

Finally, a solar-only PV system was chosen because the electricityneeds in the winter were about a quarter of those in the summer.This would avoid the trouble ofmaintaining a fuel-fired generator.The solar-only PV system consistsof the following:

• twelve 90-W PV modules, with atotal capacity of just over 1 kW in12 VDC (volt direct current);

• the existing Hydro-Québec poleused for the support structure;

• a separate, ventilated outbuildingprovided by the owner for thebatteries and system components(not always necessary);

• a 40-A solar controller;

• a 2.5-kW, 120-VAC (volt alternat-ing current) pure sine-waveinverter with a surge capacity of 8 kW; and

• a 1595-Ah (ampere-hour), 12-VDC battery bank.

The batteries offer seven-dayautonomy when the sun is notshining, based on the expecteddaily load. However, the home-owner knows about the need tomonitor the use of electricity whenovercast or rainy conditions areforecast. Therefore, a meter wasinstalled to provide instant infor-mation on the reserve capacityremaining in the battery bank(based on current load consump-tion) and on the charge rate fromthe PV array.

Hydro-Québec financed the instal-lation of the PV system, eventhough the cost of solar electricityproduced was more than 10 timesthe regular cost charged by theutility (about 60¢ per kWh versus6¢ per kWh). The savings on electric-line maintenance justify the cost. Hydro-Québec alsoplanned funds for replacing system components after their lifetime (e.g. 25 years for the PV modules).

After two seasons of use, bothHydro-Québec and the home-owner are satisfied with theperformance of the PV system. It can handle the heavy use of a washing machine, a toaster,lights, pumps, etc., during week-ends when all five bedrooms arefilled by up to all 16 members of the family.

Power forRemote LodgesOwners of remote fishing lodgesmay find that a properly designedPV hybrid system is economicallyattractive, be it PV-diesel, PV-windor a combination of the two. The

high cost of diesel generation atremote sites often prompts theowners to look for alternatives,namely, renewable energy tech-nologies. In many instances, aPV-diesel hybrid system provesattractive because it is cost-

effective, simple and reliable. During periods of little sunshine,the use of the diesel generator canbe reduced by drawing power froma bank of batteries and by runningthe generator only when the batteries are low.

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Example 3. A Solar-DieselHybrid System at TarryallResort, Catherine Lake (Near Keewatin), Ontario

Tarryall Resort operates from Aprilto October. The resort consists ofseven cottages and a main housethat can accommodate up to adozen people. The cottages areequipped with propane-poweredappliances and lighting. Electricityis used year-round in the mainlodge to power a full range ofappliances, including a clotheswasher, a large freezer, a waterpump, televisions, lights andpower tools.

The resort is located six kilometresfrom the electrical grid. In 1980the owners considered connectingto the utility grid, but the cost wasestimated at more than $80,000.

The owners instead decided toimprove the resort’s energy effi-ciency. They switched to moreefficient 12-V fluorescent lights,put a smaller motor in the water

pump, installed timers on the exte-rior lights and moved their freezeroutdoors in the winter. Using moreefficient lights, in particular, hashad a significant impact on dailyenergy consumption.

The resort’s electrical generatingsystem consisted of two diesel generators (a 7.5-kW main genera-tor running 24 hours a day and a 3.0-kW backup generator). Thehigh cost of diesel prompted theowners to investigate a solar-dieselhybrid system.

In 1986 the owners installed ahybrid system that included thefollowing:

• a 564-W PV array;

• a bank of 24 two-volt, deep-cycle batteries; and

• the existing 7.5-kW diesel generator.

The resort’s diesel consumptionhas been considerably reducedsince the PV-diesel hybrid systemwas installed. The generator isused once every three or four daysfor about 10 hours to recharge thebatteries. Previously, it had con-sumed fuel continuously, whilesupplying only about one quarterof its nominal capacity. The PVpanels contribute about 15 percentof the lodge’s energy require-ments. They also permit a gentletrickle charge of the batteries at

the end of the charging cycle,thereby extending battery life andincreasing the system’s efficiency.Because the diesel generator isused more efficiently in the hybridsystem configuration than it wouldbe on its own, it needs fewer oilchanges and less frequent majoroverhauls and repairs. Also, the lifespan of the generator is extended.During its first year alone, savingsin fuel and maintenance chargestotalled about $7,000.

Despite the high up-front cost($36,000 in 1986), the hybrid system paid for itself within six years. Tarryall’s owners arepleased with their PV system andparticularly enjoy the quiet, cleanoperation – a major improvementover the constant noise of a dieselgenerator. They have since addedfour PV modules, increasing thecapacity to 752 W. This furtherreduced the need for diesel-generated electricity. The originallead-acid batteries were still beingused in 2000, after 14 years of service. Tarryall’s owners were so satisfied with photovoltaics that they also equipped each of the seven cottages with anautonomous PV lighting kit (one module with one deep-cycle battery).

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Example 4. A Hybrid PVSystem at the Warden Stationon Huxley Island, GwaiiHaanas Marine ConservationArea National Park Reserve

Located in the Moresby Islandarchipelago in British Columbia,Huxley Island serves as a registra-tion office for visitors to GwaiiHaanas Marine Conservation AreaNational Park Reserve. Theseinclude scientists visiting the area,which is dedicated to environmen-tal conservation. The camp has a75-m2 building with a full kitchen,bunks for four people and an officeequipped with a satellite tele-phone, VHF radios and computers.To meet these electricity needs,park administrators chose a hybridstand-alone PV system. Its advan-tages over a continuously operatedgenerator include less enginemaintenance, a lower need forrefuelling and reduced noise.

A power system installed in 1996consists of the following:

• a 600-W solar array using eight 75-W modules;

• a 4.0-kW sine-wave inverter;

• a 38-kWh lead-acid battery bank; and

• a 5.0-kW gasoline generator.

To make installation easier, all electrical components were pre-assembled and wired on a 1.3-m2 board before shipment.The distributor also provided awaterproof aluminum outdoor cabinet for the batteries and power equipment. It was installeddirectly behind the living quarters.A state-of-charge battery displayand a remote control for theinverter and generator were

installed on an interior wall of thebuilding for the convenience ofpark staff.

The integrated power system iscompletely automated. The systemprovides the bulk of the power to the loads, with the generatoravailable for backup. In the eventof poor weather or excessive loads,the generator is programmed to start when the battery bankreaches 50 percent of its nominalcapacity. This way, the batteries are charged before a potentiallydamaging low-battery condition is reached.

▲Photo courtesy of Soltek Solar Energy Ltd.

Mobile andRecreationalApplications Chances are that you are alreadyrelying on PV technology to helpyou keep track of time, balanceyour budget or enliven your leisurehours. Many products such aswatches, calculators and toys havebeen PV-powered in an inexpen-sive, reliable and convenient wayfor many years. Equipped withtiny PV cells that produce powereven in dim lighting, these consumer products eliminate the need for costly batteries thatneed to be frequently replaced.

Nowadays, versatile PV powerpacks are also used to powerlarger consumer products. Theyare available in a range of sizes,from fractions of a watt to over100 W. Power packs can also behooked up in series or parallelconnections to serve variouspower needs. They can be used as either a direct power source or as a battery recharger. Theseconvenient PV systems powereverything from radios, cassetterecorders and cameras to lawnornaments, walkway lights andbatteries for sailboats and gliders.The clean and noiseless opera-tion of PV systems for many recreational applications is a significant benefit.

In recreational vehicles and electric-powered boats, PV panelscan help recharge batteries. Themain advantage of a PV system isthat it will, at the least, maintainthe state of charge of batteries onboard – even during extendedperiods of time when you are not using the equipment.

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▲ Many owners of recreational vehicles are already using PV technology. Photo courtesy of Rozon Batteries Inc.

People working in the field withportable computers appreciate the autonomy that PV offers. Photo courtesy of Midnight SunEnergy Ltd.

▲

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The Power SystemAs 5.5-W panels are common,the team needed at least twopanels, which provided extrapower to compensate for badweather or additional loads. ThePV system had the followingcharacteristics:

Main Advantages of the PV SystemPrimary lithium batteries are generally used for this kind ofexpedition. An estimated twenty10-Ah lithium batteries would havebeen needed, for a total cost of$6,000 and a weight of 12.5 kg.This alternative was rejected due to its cost and weight.

Another alternative would havebeen to carry a small gasoline generator. The smallest, lightestgenerator available was a 300-Wgenerator that weighed 18 kg.Apart from its weight, fuel wouldhave had to be carried and han-dled. Also, fumes and noise fromthe generator would be unpleas-ant, and starting the engine in

a cold environment would be difficult. The team rejected thisalternative as impractical.

PV energy represented the mosteconomical, reliable, practical and environmentally friendly way to generate electricity for such anexpedition – not to mention the lightest.

Example 5. Photovoltaics for a South Pole Expedition

Explorers Bernard Voyer and Thierry Petry were the first North Americans to reach the South Pole by ski unassisted. Each had to pull a 170-kg pulka (a toboggan-like sled) over an uneven surface of stratified ice swells. Sunlightwas available 24 hours a day during their expedition; however, the usablesunlight hours per day was between two and nine hours (or 5.5 hours perday on average).

Electricity NeedThe explorers used a PV system to power a satellite telephone under theextreme climatic conditions. This system also served as a backup for thelithium batteries for a video camera. The PV system was designed to powerthe following equipment:

Converted to Wh per day

• satellite telephone: 60 W (8 min/d) 60 W x 8/60 8 Wh/d

• portable computer: 42 W (15 min/d) 42 W x 15/60 10.5 Wh/d

• positioning system: 0.5 W (24 h/d) 0.5 W x 24 12 Wh/d

• video camera: 20 W (12 min/d) 20 W x 12/60 4 Wh/d

Average total daily demand: 34.5 Wh/d

As mentioned above, sunshine was usable for 5.5 hours a day on average, so the team needed 6.3-W worth of PV modules (34.5 Wh/d ÷ 5.5 h/d) daily.

▲Photo courtesy of Bernard VoyerExplorateur Inc.

• installed PV power: 2 x 5.5 W

• storage capacity: Lead-acid 12 V, 9 AhNickel-cadmium 12 V, 5 Ah

• total weight: 5 kg

The conditions of operation were as follows:• average temperature: -15°C to -33°C (December/January)

The system cost $600.

Photovoltaics in AgriculturePV systems are particularly wellsuited where a small amount ofenergy in remote locations isneeded for agricultural applica-tions, such as electric fencing,water pumping for irrigation orstock watering, pond aeration, etc.

Electric FencingPV-powered electric fencing ispopular in Canada’s westernprovinces, chiefly in northernpastures where land is open forcattle. Several cattle ranchers in northern Alberta and BritishColumbia have installed PV mod-ules to charge the batteries ofstandard electric fencing. Thesebatteries will never run down. PV-powered electric fencing notonly eliminates the cost andinconvenience of regular visits tocheck batteries, but also costs lessthan barbed wire fencing, whichis the other alternative to con-ventionally powered electricfencing. More and more ranchers and

farmers in Canada are findingthat PV systems, which can runall summer with no need for ser-vicing, are a practical alternativefor their remote fencing needs.

Water Pumping for StockWatering and IrrigationWater pumping is one of themost attractive uses for PV sys-tems. In agriculture, the demandfor water is greatest when the

weather is hot and dry, preciselywhen the most solar energy isavailable. Simple non-storagetypes of PV systems are ideal for many irrigation applicationswhere crops can do without waterwhen the sun is not shining. In situations where irrigation isneeded independent of weather,power stored in the form ofpumped water, rather than incostly storage batteries, makes PV-powered irrigation systemseconomically attractive.

Today, several million hectares of remote grazing land in Canadaare not being used because thecosts of pumping water for stockwatering by conventional meth-ods outweigh the grazing benefits.For many Canadian ranchers andfarmers, PV-powered pumpingsystems offer a cost-effective solution.

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▲PV-powered electric fencing savesboth time and money for ranchersand farmers. Photo courtesy of the Agricultural Technology Centre (formerly the Alberta FarmMachinery Research Centre).

▲Stock watering using a PV-powered waterpumping system from a pond to preventcontamination of the source. Photo courtesyof Sunmotor International.

A PV System to Suit YourParticular PowerRequirementsStandardized PV systems arebecoming more and more com-mon. However, many PV systemsin Canada are custom-designed totake into account the particularneeds of the user and the charac-teristics of the site. Therefore, youshould not necessarily expect tobuy such a system “off the shelf”as you would a diesel or gasolinegenerator. Rather, you will probably have to consult PVequipment suppliers for a systemthat is right for your needs.

The telecommunications industryand the Canadian Coast Guardused PV power systems early on for remote telecommunica-tions repeater stations, beaconsand navigational aid systems.Their expectations for reliability helped the PV industry developquality products and improvedesign tools.

Small PV lighting packages are available from dealers. For ski hills, lighthouses, isolatedstretches of highway and off-gridcommunities and businesses, PV-powered lighting provides a practical, affordable solution to remote lighting problems.

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▲A small PV module is used topower a trail indicator at night atMont-Tremblant, Quebec. Photocourtesy of TN conseil inc.

▲This PV-powered aquaculture facility ison an island off Canada’s west coast.

▲The limited powerneeds of remotemonitoring systemsare easily met bysmall PV systems.This exampleshows a gas wellhead.

Early Uses for PV in Commercial Applications

▲Due to the remotenessof repeater stations,telecommunicationshas been one of thefirst – and remainsone of the most popu-lar – applications for PV systems. Photo courtesy ofNorthwestel Inc.

▲The Canadian CoastGuard has been usingthousands of PV-powered buoys alongcoasts for many years.

Be PreparedBefore approaching a dealer, you should consider your powerrequirements and the type ofphotovoltaic (PV) system that willsuit your needs and your budget.

The following are typical questions that you should askyourself. Be prepared to supplythe following information as precisely and clearly as possible:

• What is the application?

• What needs to be powered?

• Are my loads as efficient aspossible?

• How much power (wattage)and/or energy (watt-hours per day) is required?

• What is the energy-usage pattern (e.g. hour per day,days per week, seasonal use)?

• Do I need battery storage?

• Do I want an autonomous,hybrid or grid-connected system?

• Do I want to start small andadd modules in the future?

A first step in any design or costevaluation is to assess your load:i.e. what do you expect the PVsystem to power? Section 6,“Estimating Your Needs” (page24) is intended to help you evalu-ate the options. A worksheet isprovided in Appendix A (page 40)to help you estimate and choose a suitable PV system. This work-sheet is intended to guide you inestimating your power and energyneeds, evaluating the PV arraysize and estimating the batterycapacity that you require.

Note that this exercise is optional.However, you should at least prepare a list of all appliances and other electrical equipmentthat the PV system might power and estimate their time of use (see Step 1 in the worksheet provided in Appendix A). Themore detailed and accurate the list, the easier the sizing of your PV system will be for you or your dealer.

Where to Find PV SystemsApart from some specific con-sumer products or special sales,PV power systems are just begin-ning to be widely available inhardware or department storechains. Dealers of recreationalvehicles, boats and electric fences may sometimes offer PVsolutions adapted to their prod-ucts. However, for most customapplications, you will need tofind a PV dealer. Generally, thisgives you the advantage of betterservice, since such dealers shouldhave a good understanding of the technology and can help youselect, size and design the systemthat best suits your needs. Thereare many distributors and dealersof PV systems in Canada, and the industry network is growing.Some of these companies special-ize in different types of systems,e.g. communications, homeenergy systems, consumer products, agricultural and unique design.

To find PV distributors or dealers,contact the Canadian SolarIndustries Association, NaturalResources Canada (see “LearnMore About Solar Energy” onpage 46) or consult the YellowPages™. You may also wish toobtain a referral from a satisfiedcustomer.

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4. Buying Your Photovoltaic System

Choosing a DealerA PV system should be designedfor the best efficiency and cost-effectiveness. It is wise to consulta professional at the design stage.Most dealers offer design and consultation services as well as PVmodules and “balance of system”components such as batteries and inverters. Some companiesconcentrate on industrial applica-tions; others specialize inresidential and commercial sys-tems. Make certain that the dealeryou select has proven experiencein designing and installing thetype of system you want. Ask to see some systems that havealready been installed, or talk to someone who has bought asystem that is similar to what you want.

A responsible dealer will ask you questions about your powerconsumption, lifestyle and needsbefore designing your PV system.If you cannot afford as many PVmodules as you would like butintend to add to the system later,make sure that the systemdesigner knows this.

The PV dealer should offer a warranty on parts and labour. The warranty for PV modules can now be as much as 25 years,depending on the type of mod-ules and manufacturers’ policies.Most modules will perform reliably for a longer period. Check which warranties thedealer offers on the other compo-nents (electrical and mechanical)and on the labour. Moreover,check on follow-up service avail-able from the dealer. In general,take the same sort of precautionswhen buying a PV system thatyou would when buying a newappliance.

Following is a list of items to consider in evaluating a dealer’sproduct and service. Use it whenchoosing a dealer.

• design/sales experience

• knowledge of energy efficiency

• area of expertise

• product quality

• product warranty

• installation service

• follow-up service

• price

Making aDecisionOf course, cost is always impor-tant in any purchase decision.The economics of PV systems are often quite site-specific. Ingeneral, conventional energysources tend to have low initialcapital costs but have high oper-ating and maintenance costs. Incomparison, PV systems havehigher initial capital costs buthave lower maintenance andoperating costs. Thus, to evaluatethe economics of a PV system,you must consider the total costs of competing alternatives –including capital costs, fuel costsand maintenance and operatingcosts over the life of the system.

For off-grid commercial opera-tions that have labour andmaintenance costs, PV systemscan often be economical. Forindividual homeowners, who usually do not count their own labour for operation andmaintenance as a cost of runninga generator, the initial cost of a PV system may appear to be high. However, for many homeand cottage owners, the non-economic benefits of PV systems – in particular, their reliability andquiet, non-polluting operation –far outweigh the extra costs.Especially in summer, owners ofPV systems appreciate that theycan enjoy the sounds and smellsof nature without interferencefrom their power system.

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Of course, the cost of a PV systemdepends on what it includes. Asimple autonomous system for acottage or cabin, suitable for pow-ering a few lights, a water pumpand radios (e.g. 40–100 W) cancost from $700 to $2,000. Larger,hybrid systems that are suitablefor year-round residences orlodges (200–1500 W) can costfrom $5,000 to $30,000.

In considering the economics ofPV systems, it is important torealize that the costs of these sys-tems are steadily declining. ThePV industry, like the computerindustry, is continually evolving.

Improvements in PV cells, batter-ies and other system componentsand in system design are resultingin lower prices for PV systems.

One of the most attractive fea-tures of PV systems is that theycome in modules. The PV compo-nent of a hybrid system can besized to suit your budget: as pricesdecline and/or your savingsincrease, you can add more PVpanels and decrease your relianceon the backup generator. If youdo not already have a generatorand are considering a solar-onlysystem for a cottage or sailboat,you can start with a small system

to power a few essential appliancesand upgrade it as your financesallow. Because PV systems last 25 years or more, they represent asolid investment. By the way, theprice for used panels is not muchless than that for new panelsbecause they remain in perfectcondition for years.

The following form will help you compare the advantages and disadvantages of an autonomousor hybrid PV system with conven-tional diesel, gasoline or propanealternatives.

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PV System – Purchase Decision Factors

Decision Factors Option A: Autonomous Option B: Hybrid PV Option C: PV System System Conventional System

(diesel, gasoline orpropane generator)

Capital Costs

Operating Costs

Maintenance Costs

Other Factors(e.g. noise, pollution, reliability, flexibility for expansion, refuelling needs, your time)

One major advantage of photo-voltaic (PV) systems is that they are relatively simple to install andmaintain. For large or complexsystems, PV companies usuallyhelp with installation and maintenance.

InstallationYour supplier should give you any relevant system documents.Carefully read all of the manufac-turer’s recommendations. As withany electrical system, safety isimportant. You must obtain anynecessary building and electricalpermits and ensure that the sys-tem is installed according to code.Qualified people should installthe system. If you have a grid-connected system, installationwill involve the local utility.

Wiring must be properly installedto avoid shocks, fires and otherhazards. The main considerationis the type and size of wire. Forexample, the array wiring must be suited for outdoor use and besized properly in order to carrythe peak current. As a result, youwill normally need larger wiresfor low-voltage systems (12 Vcompared with 120 V) to preventoverheating and voltage loss inthe wires. Consult a professionaldesigner or installer to select theproper wires. You will also needthe services of a professionalinstaller to:

• properly fuse the system for protection against shortcircuits in the wiring or appliances;

• ensure that the system isproperly grounded and pro-tected against lightning; and

• include switches between allcomponents of the systemthat need to be isolated forany reason.

Mounting the PV ArrayPV modules are designed to beinstalled outdoors without addi-tional protection. A mountingstructure must be constructed tosupport the modules in all weatherconditions. Many manufacturerssell support frames designed tohold their modules; you maydecide to build your own.

Factors to be considered in mount-ing the array include orientation,safety, structural integrity andlocal codes. The PV array shouldbe mounted so as to take fulladvantage of the sunlight. In thenorthern hemisphere, it shouldface south; true south is best, but a deviation of 15 degrees east orwest will not affect performancevery much. Very large installationscan be mounted to track the suneither automatically or manually(see “Technical Information onPhotovoltaic System Components”on page 35). In most cases, themounting is fixed at one angle (a right angle to the sun at noon),but can be adjusted according tothe season.

Select a site where the array will not be shaded at any pointduring the day. A shadow on thearray can substantially cut poweroutput. If possible, ask your neigh-bours if they plan to add trees orbuildings adjacent to your prop-erty. Easements and restrictivecovenants (for definitions, see the glossary on page 44) are two types of legal instruments. When used for solar applications,they provide certain guarantees to property owners about theiraccess to sunlight. If access tosunlight concerns you, such a written agreement may beworthwhile.

20

5. Installing and Maintaining Your Photovoltaic System

▲Array orientations showing suggested tilt angles for summer,spring and fall and winter use in southern Canada.

Summer

Springand Fall

Winter

45°

35°

60°

Depending on the array size andthe particulars of the site, the PVarray can be mounted on a roof, a pole or the ground. In general,the large surface areas of the mod-ules create high wind loads onthe mounting structure, so thestructure must be designedaccordingly. Due to these highwind loads, ground-mountedinstallations require proper foundations. For small, ground-mounted installations,

foundations can be posts sunkinto the ground to anchor thearray support frame. The supportframe itself may be made of metalor wood. Modules are mounted so that the bottom of the array isabove the highest depth of snowlikely to fall. Make sure that thereis no bottom lip on the array sothat snow can slide off freely.

You can use pole mounting forsmall systems (one to 12 modules)to ensure proper orientation or tolift them above potential sourcesof shade, such as buildings ortrees. The main advantages are nosnow buildup to shade the arrayand the potential to track the sun.

For many residences and cottages,roof mounting is an attractiveoption, particularly if the buildingis under construction. The mod-ules should be mounted a shortdistance above the pitched roofand tilted to the optimum angle.Since PV modules work betterwhen the ambient air tempera-ture is lower, the free circulationof air around them will improvetheir performance. Elevating thearray will also prevent thebuildup of moisture and debrisbehind the modules. This buildupcould rot the roof and deterioratethe electrical connections. For residences and cottages with achimney, the array should bemounted in such a way that shad-ing from the smoke is avoided.

Wherever you choose to mountthe array, unless shading is a con-cern, try to locate it as close aspossible to the battery bank or tothe load (if there are no batteries).This will lower wiring distancesand resultant power losses.

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▲Ensure that your PV array will notbe shaded by neighbouring trees orother sources of shade.

▲Ground- and roof-mounted PV arrays.

Is Magnetic South Truly South?

Using a compass to help you orient your PV array so that it facessouth means that you will be relying on magnetic south instead oftrue south. It is better to use true south. In some parts of Canada, thedeviation of true south from magnetic south can be large enough toaffect the performance of your PV array. If your array is fixed (i.e. itwill not be tracking the sun) and you are unfamiliar with the devia-tion of the compass needle from true south at your location, ask anexperienced local dealer or installer for assistance.

Housing theBatteriesYour choice of battery locationshould comply with the CanadianElectrical Code, whether youinstall the batteries inside or out-side. The location should also bedesigned to keep the batterieswarm (25°C is best), because theircapacity decreases at temperaturesbelow 25°C. This means that ifyou choose to locate your batter-ies in an unheated space, you willneed to insulate the area properly.You will also need greater batterycapacity to compensate for thelosses at lower temperatures.Make sure that your supplierknows about the planned locationof your batteries.

The batteries and other equip-ment should be accessible formaintenance and inspection, butsafety must also be considered.Batteries may give off hydrogengas during charging and can be a source of electric shock, so theroom or area where they arehoused should be properly ventedto the outside and kept locked.

In addition, other electrical components, which can also be asource of spark, should be keptseparately from the battery hous-ing. Do not locate batteries nearsources of heat or possible sourcesof open flame or spark. Finally,read all of the manufacturer’s recommendations and warningsabout the safe and proper use and handling of batteries.

Inside LocationsBatteries located inside the livingspace should be properly ventedto the outside. For small cottagesystems with, for example, two12-VDC (volt direct current) bat-teries, you need a vent that is atleast 2.5 cm (1 in.) in diameter.Keep batteries separate from theliving space by housing them inspecial battery cases (with ventila-tion to the outside). For summer

cottages, keep batteries full ofcharge to prevent freezing in the off-season.

Outside LocationsBatteries located outside of theliving space should be housed ina box or shed. In a very cold loca-tion, you can house the batteriesin a buried container for bettertemperature control. In all cases,batteries should be well protectedfrom the elements and be wellvented to the outside.

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▲Battery housed in a shed.

BatteryShed

Vent

Insulation

Battery

BatteryChargeController

HeatedBuilding

MaintenanceAn important advantage of PVsystems is that they require littlemaintenance. The arrays them-selves are durable and reliable andneed little attention. The follow-ing summarizes the principalmaintenance that your systemwill need, but you may wish toask your dealer for a maintenanceschedule that is adapted to yourparticular system and location.

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▲Unless you live in an extremelydusty area or have severe problemswith ice storms, you need to inspectthe wiring and general panel appear-ance only occasionally. If yoursystem has an adjustable mounting,you can carry out this routine main-tenance check at the same time asyou adjust the tilt angle of the array.When you adjust the angle of thearray for winter operation, snowloading is not a problem because the array is tilted steeply. If thearray becomes dusty, clean it with a mild soap or plain water and asoft cloth. Do not use solvents orstrong detergents.

▲Battery maintenance varies with the type used. Basic maintenanceincludes visually checking the elec-trolyte levels and regularly verifyingthe specific gravity of your batterieswith a hydrometer. Add distilledwater as necessary, and clean andtighten battery posts (only the latterare required for maintenance-freebatteries). Also, check for any leaksor physical damage to batteries.Follow battery and charge regulatorinstructions for annual equalizationcharges that help cure the batteriesfrom plate fouling due to corrosion.

▲Generator maintenance for hybridsystems is simpler and easier thanusing a generator to produce all your power. Change the oil as recommended (which will be less frequently than for a continuouslyoperating generator).

▲Keep track of any maintenance ormodification made to the system(date and action). This will help you remember when your last maintenance routine was carried out and may ease troubleshootingshould a problem occur.

To further investigate which kindof system will meet your powerneeds, this section will help youestimate your energy require-ments and then estimate thesystem size that your applicationwill require (a blank worksheet isprovided in Appendix A, page 40).Two examples have also beenworked out in the next section.Once you have followed thisprocess, you should be more comfortable discussing differentoptions with a dealer.

If you are involved in the designof power systems, a more detailedsizing and design guide calledPhotovoltaic Systems Design Manualis available from Natural ResourcesCanada (see “Learn More AboutSolar Energy” on page 46).

Step 1. EstimateYour Power andEnergy NeedsTo work out how much power andenergy you need, you must knowwhat loads you want to power,how much power they use (includ-ing stand-by consumption) andhow often they are used. For sin-gle-purpose applications, such aspowering a water pump, this isfairly simple to calculate. However,if you want a system that will runseveral appliances in your home or business, you must estimate theusage pattern of each load.

The more energy you need, thelarger and more expensive thesystem – especially if you want an autonomous one. Therefore,decrease your energy require-ments as much as possible. This

includes using energy-efficientappliances and using electricityonly for appliances that reallyrequire it. For example, it is notpractical to use a PV system topower an electric range or heatingsystem. Rather, meet your heatingand cooking needs with a morefitting energy source, such aswood or propane. A solar waterheater may also meet your hotwater needs (contact NaturalResources Canada for Solar WaterHeating Systems: A Buyer’s Guide2).

To estimate your power needs,first list all the loads you want to power, note whether they areAC or DC, and obtain their ratedwattage and the number of hoursper day they will be used (seeStep 1 of the worksheet inAppendix A).

If available, use the rating indicated on the label of theappliance or tool you need topower. Also use the typical valuesgiven in Appendices B (page 42)and C (page 43) for commonappliances and lighting.

Next, for each load, multiply the power rating (using actual or typical values) by the number of hours of estimated daily usageto obtain the total watt-hours of power needed per day. If con-sumption is already given inwatt-hours per day (or kilowatt-hours per year, as on EnerGuidelabels), you can skip columns Aand B in Step 1 of the worksheetand simply fill in column C usingthe watt-hours per day.

About Efficient Lighting

For lighting, consider AC or DC compact fluorescentlights instead of incandescentbulbs. They give four timesmore light per watt of elec-tricity and last 10 timeslonger. Consult a specializedsupplier for information onhigh-efficiency lighting foroutdoor applications.

24

6. Estimating Your Needs

60W ➜ 15W 10 � 1000h = 10 000h

▲Fluorescent lights use one quarter the energy of incandescent bulbs and last 10times longer.

2 For your copy of Solar Water Heating Systems: A Buyer’s Guide, call Natural Resources Canada at 1 800 387-2000 toll-free, or visit the Web siteat http://www.canren.gc.ca.

EnerGuide LabelsIf there is an EnerGuide label onyour appliance, you can use theelectrical consumption rating (inkilowatt-hours per year) given onthe label for your worksheet. Notethat the EnerGuide ratings forclothes washers and dishwashersinclude the electricity consumedin heating the water used in thoseappliances. These ratings are lessuseful to you if, as we recom-mend, you heat your water withsolar water heaters, propane orwood (instead of PV-generatedelectricity).

If you use the value on anEnerGuide label, convert the kilo-watt-hours per year (kWh/a) intowatt-hours per day (Wh/d) forinclusion in column C of theworksheet in Appendix A. Tomake this conversion, multiply by 1000 and then divide by 365.

Finally, fill in the subtotal(s), calculate the adjusted AC loads(for inverter losses) using 0.90 asyour initial conversion efficiency,and fill in the “total daily load”value at the bottom of the firstside of the worksheet.

Smaller, efficient appliances will require less PV equipment.Some PV dealers also carry high-efficiency appliances and lighting.

Always keep in mind that yourenergy requirement has a directimpact on the following:

• the area of PV modulesneeded to power the load or recharge the batteries;

• the capacity of the batteriesrequired to meet your needswithout running a generatorat night or on cloudy days;and

• the amount of fuel used by a generator or the size of awind generator.

Watch Out For“Phantom” Loads!

A growing number of elec-tronic appliances draw powereven when they are turnedoff. Examples are a TV or VCR that maintains programmemory, runs its clock andkeeps the remote-controlreceiver active. The stand-bypower required can appear tobe negligible, and it is oftennot even mentioned in appli-ance owner’s manuals. But itmay represent a substantialamount of energy becausepower is drawn 24 hours aday. For example, the stand-bypower for a remote-controlledportable TV may be as low as5 W, but it will still require120 Wh/d (5 W x 24 h). Thisrepresents the same amountof energy as using this TV (60 W) for two hours a day(120 Wh/d)!

25

▲EnerGuide labels provide energy consumption ratings (in kilowatt-hours per year) for major home appliances.

For example, using a 1650-W hairdryer for eight minutes draws thesame amount of energy as usingfive efficient lights (11 W each) for four hours: about the amountthat one 50-W PV module pro-duces in an average day.

Hair dryer: 1650 W x 8/60 = 220 Wh

Fluorescent lights: 5 x 11 W x 4 = 220 Wh

Step 2. Make aRough Evaluationof PV System Size2.1 Evaluate Which

Stand-Alone System Is More Suitable:Autonomous orHybrid

Stand-alone PV systems can beeither autonomous (with or with-out storage batteries), relying onlyon solar energy, or hybrid. Hybridsystems combine PV with one ormore other electrical generatingsources and normally includestorage batteries. Factors thatinfluence the type of systeminclude the following: total andpeak power requirements; whenpower is needed; required powerreliability; whether the applica-tion is seasonal or year-round;and whether the system will beeasily accessible or installed in a remote location.

Autonomous Systems

As the name suggests, autonomoussystems are self-sufficient and notbacked up by another generatingsource. They normally includebattery storage. Some applica-tions, such as irrigation, pumpingor greenhouse ventilation, requirepower only when the sun is shin-ing. Therefore, an autonomoussystem without storage would besuitable in such cases. In mostcases, however, power is neededwhether the sun is shining or not, so the system includes battery storage.

26

Power or Energy?The following two terms are used to characterize electricity usage:

• the power or “instantaneous power required”; and • the energy or “energy consumption over a period of time.”

Power

The power you need (the wattage) is the instantaneous intensity ofelectricity that is required to power the appliances you use. Themore appliances used at the same time, the more power required.Power is expressed in watts (W). A watt is a convenient SI unit inelectricity because it is simply the product of the current – inamperes (A) – and the voltage – in volts (V).

1 W = 1 A � 1 V

This simple formula indicates, for example, that a 12-W compactfluorescent light will require 1 A when connected to a 12-VDC (voltdirect current) power source.

Energy

Energy depends not only on the power required by your appliances,but also on how long and how often you use them. Energy isexpressed in watt-hours (Wh) for a given period of time (per day,month or year). It is defined as the power times the number ofhours the equipment is used over this time.

1 Wh = 1 W � 1 h

▲The autonomous PV system in Yoho National Park, British Columbia, supplieselectricity for the amphitheatre projector and recharges the batteries of a golf cartthat the staff uses to collect camping fees. Photo courtesy of Sovran Energy Inc.

In Canada, about twice as muchsunlight is available in summerthan in winter. To guaranteepower year-round using a solar-only system, a significantly larger(and hence more costly) array andbattery system is needed. Suchsystems are practical for applica-tions in remote, unattended sites,which are difficult and expensiveto visit, and where the capitalcosts are rapidly offset by avoid-ing costs for maintenance andfuelling visits. Thus, solar-onlysystems with storage are used forelectric fencing in remote areas,and in communications, markingand warning signs, monitoringsites and other situations wherereliability and low maintenanceare critical.

Autonomous systems are alsoappropriate for summer vacationproperties, sailboats and otherapplications where the period ofuse corresponds to the period ofgreatest available sunlight. If youconsider power a luxury insteadof a necessity and can tolerate theodd occasion when the systemcannot meet your loads, anautonomous system may be suitable at a reasonable price.However, if you want guaranteedpower on a year-round basis andcan easily access the site, somesort of hybrid system will likelybe more affordable.

27

2.2 2.2

CANADA

600KILOMETRES

400200200 0

2.8

2.8

3.3

3.3

3.3

3.9

3.94.4

4.4

4.4 4.4 4.4

4.4 4.4

5.0

5.0

5.6

5.6

2.2

CANADA

600KILOMETRES

400200200 0

2.8

1.7

0.6

POLAR NIGHT

2.8

1.1

2.2

2.8 2.2

0.6

1.1

1.7

2.2

2.8

1.7

1.7

POLAR NIGHT

▲Average daily number of peak sunlight hours in September (use for seasonal summer autonomous systems). Source: Environment Canada.

▲Average daily number of peak sunlight hours in December (use for year-round-operated autonomous systems). Source: Environment Canada.

Hybrid Systems

Hybrid systems use a combinationof PV and other power sources.Usually, hybrid systems use awind generator with a diesel,propane or gasoline generator asbackup. Hybrid systems may besuited for applications such as residences and commercial build-ings that are not connected to the grid. If you need more than2.5 kWh of energy per day year-round and already have a generator, or if you live in anarea that has poor sunlight forlong periods, a hybrid system isprobably a good choice.

Hybrid systems generally includebattery storage; the load drawspower from the batteries. Whenthere is enough sunshine, the PVarray keeps the batteries charged.If a wind generator is incorpo-rated, it charges the batteriesduring windy periods, which areoften when it is overcast or atnight. For this reason, wind andsolar equipment are a perfectcomplement to one another. The diesel or gasoline generator is needed only once in a while to charge the batteries duringextended overcast and calm

periods. The generator operates at nearly full capacity, and thisresults in a better generator dutycycle, more efficient fuel use,lower maintenance costs andlonger generator life. Applicationsthat involve both solar and windequipment often do not need a gas or diesel generator.

2.2 Estimate the Available Sunlight

Knowing the solar resources available is key to the design of an efficient and affordable PV system. The maps on page 27show the average daily values of peak sunlight hours that strikesouth-facing, fixed PV arrays in various parts of Canada inSeptember and December. These values assume that thearrays are tilted at right angles to the sun at noon. Alternatively,you can get weather and solarradiation values for selected sitesfrom Environment Canada’sMeteorological Service of Canadaor from RETScreen® Internationalsoftware (see “Learn More AboutSolar Energy” on page 46).Choose a value for your locationfrom either the September or

December map, and insert thisvalue under Step 2 of the work-sheet in Appendix A.

In the summer, September has the fewest hours of peak sunlight.Overall, December has the fewesthours of peak sunlight. To esti-mate the available sunlight designvalue for a seasonal (summer)autonomous system, use the values from the September map. To estimate the available sunlightdesign value for a year-roundautonomous system, use the values from the December map.

For a PV-diesel hybrid system, you may choose December values or average the two values(September and December). Thisis described in the case study on pages 33 and 34.

28

Parks Canada’s remote camp locatedin the far north on Ellesmere Island,Nunavut, is powered by a PV array(on a tracker) combined with a windgenerator and a gasoline generator.

▲

2.3 Estimate the Required PV Array Size

The next step is to size the PVarray. This takes into accountpower losses in battery charging(Effbat of 75 to 90 percent) and regulator efficiency (Effreg of 80 to 90 percent), especially if the controller does not include a

maximum power point tracker(MPPT) (see the glossary on page44). Typically, an MPPT is usedonly for medium to large systemswhen benefits related to energygains are greater than the cost ofthis feature. Additional losses dueto dust or snow accumulation onmodules are likely, but they are relatively low.

After you determine the array size (in watts), estimate the num-ber of modules required. To dothis, divide the array size by thepower rating of the module youintend to use in your installation(normally 20 W to 100 W).

29

Technical Note: Definition of Units Used to Describe a PV System and Some Orders of Magnitude

Full (peak) sunlight: 1000 W/m2 of energy density (about the intensity of the sun at noon on a brightsunny day)

1 hour of peak sunlight: 1000 Wh/m2, the equivalent of 1000 W/m2 during one hour (e.g. 2 h at 500 W/m2 or1 h at 600 W/m2 and 2 h at 200 W/m2)

100-W PV module: Power capacity of a PV module able to produce 100 W of electricity when maintainedat 25°C and exposed to full peak sunlight (1000 W/m2)

100 W (PV) exposed to 1 h of peak sunlight = 100 Wh of electricity

Rule of thumb: Typical annual radiation in Canada is 1500 h of peak sunlight (range of 1100–1700 h).100 W installed = potential of 150 kWh/a.

Due to system losses and other causes of inefficiency, the energy production of PV systems is often estimated as follows:

100 W installed ≈ 100 kWh/a

Power, Voltage and Current Ratings of Typical PV Modules

Module Rated Power (W) Nominal Voltage (V) Nominal Current (A)

Kyocera KC 120 120 16.9 7.1

Siemens SM100 100 17.0/34.0 5.9/2.95

Solarex SX-85 85 17.1 4.97

BP Solar BP-275 75 17 4.45

CANROM-65 65 16.5 4.2

Photowatt PWX500 50 17 2.8

UNI-SOLAR® US-21 21 21 1.27

Note: The above modules are examples of those available on the market. Each manufacturer provides a complete line of modulesthat have different sizes and power ratings. This list is not an endorsement of these products.

2.4 Estimate BatteryCapacity forAutonomous Systems

The size of battery you needdepends on whether you requireuninterrupted power and howmuch you are prepared to pay for that privilege. For a weekendcabin or cottage, you may notreally mind if the power fails occasionally during an extendedovercast period. On the otherhand, uninterrupted power may be a necessity for some applications.

For most applications, a good ruleof thumb is to provide enoughbattery storage to supply power

during three to five overcast days. (Battery capacity for hybridsystems is usually enough foronly one or two days). A batteryshould not be completely dis-charged, so as not to shorten itslife. Thus the available capacity of a battery is less than the name-plate rating. A “maximum depthof discharge” factor is alreadyincluded in the equation in theworksheet (see Step 2 in AppendixA on page 41). It ensures that the battery charge never dropsbelow 50 percent of full charge.This value depends on the type of battery you select. Consultyour dealer.

Use the blank worksheet to helpsize your stand-alone PV system.Now that you have estimated the size of the PV array and theamount of battery storage yourequire, you are in a position toapproach a dealer. Discuss costsand make decisions on what isbest for your particular situation.

30

Technical Note: Battery Capacity Rating

Watts may be expressed in Wh (volts x amps). Likewise, energy may beexpressed in Ah (amperes x hours) at a given voltage. This is often usedin the battery industry to express battery capacity. For example, a batterywith 960 Wh of capacity is generally referred to as a 12-V, 80-Ah battery(12V x 80 Ah = 960 Wh).

Wh = V � Ah

In the following examples, two hypothetical casestudies show how the worksheets can be used. TheSmiths, for example, are interested in PV power for aremote vacation cabin. The Wongs, meanwhile, wanta system that will provide reliable power year-roundfor their home and business. Both families are inter-ested in renewable energy and want to know if a PVsystem would be appropriate for them.

Example 1. Summer CabinPower System – The SmithsThe Smiths own a small vacation cabin where theyspend most summer weekends and holidays, as well as the occasional weekend in the winter. The cabin hasno electricity or running water and is far from the grid.After several years of filling oil lamps and hauling water,the Smiths would like to enjoy the benefits of electricity.However, the cabin is their escape from the noise and

pollution of the city, and they would prefer a quiet,non-polluting power source. They are particularly interested in a PV system because it is durable andrequires low maintenance.

The Smiths’ main priority is to keep costs at a mini-mum, and they are willing to sacrifice power availabilityto do this. After all, they do not have power now, andthe thought of the odd blackout does not bother them.They have a propane-powered refrigerator, and they are willing to switch to fluorescent lighting and makedo with a minimum of appliances to keep their powerneeds low. For their needs, a system that is small, solar-only and is stand-alone appears to be a good solution.

Working through the worksheet, the Smiths find thatroughly a 120-W (watt) system and about 211 Ah(ampere-hours) of batteries could meet their needs at a price they can afford.

31

7. Sizing Worksheet Examples

Worksheet: The Smiths (Summer Cabin)

Step 1. Estimate Your Power and Energy Needs (watt-hours per day)AC or DC (A) Rated Wattage (B) Hours (C) Watt-Hours Per Day

(check one) (actual or Used (A) x (B)Appliance Load AC DC typical values) Per Day AC DC

Kitchen lights (2) ✓ (12 V) 15 1 h (x 2) = 2 30

Bedroom lights (2) ✓ (12 V) 15 1 h (x 2) = 2 30Living-room lights (2) ✓ (12 V) 15 4 h (x 2) = 8 120

Water pump ✓ (12 V) 90 1 h 90

Stereo ✓ (12 V) 6 4 h 24

TV (black and white) ✓ (12 V) 20 3 h 60

Subtotal: AC: N/A Wh/d DC: 354 Wh/d

Adjust AC loads for inverter losses: AC load = 0 Wh/d: 0 Effdc ac 0.90

Total daily load: DC loads + adjusted AC loads = 354 Wh/d

DC to AC inverter efficiency (Effdc ac) ranges from 80 to 95 percent (0.80 to 0.95). To help you with your first calculation, 0.90 has been inserted in italics. Adjust the efficiency figure, if necessary, once you have chosen theinverter for your system and have read the manufacturer’s ratings.

The Smiths do not need an inverter because all their loads are 12 VDC (volt direct current). They can add one atany time.

32

Worksheet: The Smiths (Summer Cabin)

Step 2. Make a Rough Evaluation of PV-System Size

2.1. Evaluate Which Stand-Alone System Is More Suitable: Autonomous or Hybrid

This summer cottage will be equipped with an autonomous PV system.

2.2. Estimate the Available Sunlight

Sunlight: 3.9 h/d (Consult maps on page 27 or see “Learn More About Solar Energy” on page 46.)

2.3. Estimate the Required PV Array Size (W)

Array size (W) = Total daily load (Wh/d) Peak sunlight hours x 0.77*

= 354 Wh/d 3.9 h/d x 0.77

= 118 W**

* The factor 0.77 assumes a 90-percent battery charge regulator efficiency and an 85-percent battery efficiency.

** Based on rated power output of PV modules if an MPPT controller is used (see the glossary on page 44). If an MPPTcontroller is not used, further losses should be accounted for, resulting in an increased power capacity of 15–25 percent. Consult your dealer.

2.4. Estimate the Required Battery Capacity (ampere-hours)

Nominal voltage of battery: (Vbat): 12 VDC(typically 12, 24 or 48 volts)

Number of days of battery storage needed (a good rule of thumb is three days for an autonomous system): 3 d

Battery capacity (Ah):

Total daily load (Wh/d) x days of storageBattery voltage (Vbat) x 0.42***

= 354 Wh/d x 3 d12 V x 0.42

= 211 Ah at 12 V

*** The factor 0.42 assumes an 85-percent battery efficiencyand a 50-percent maximum depth of discharge. If the battery is used at temperatures lower than 25°C, its capacity (ampere-hours) will decrease. Consult your PV system supplier.

■■ Autonomous

• seasonal use (summer mainly)

• year-round operation with low energy requirements (< 1 kWh/d)or low requirements for power availability

• limited/expensive access to the site

• maintenance is an issue

■■ Hybrid

• year-round operation and energy requirements > 2.5 kWh/dor higher latitudes

• already have a generator

• very high requirements for power availability

✓

Example 2. Year-RoundRemote Residential Power System – The WongsThe Wongs are a young couple who have been livingbeside a small lake for several years, away from theelectric grid. They run a small handicrafts business,manufacturing woven goods. The Wongs use apropane generator to provide power for their homeand studio. But they have grown tired of constant noiseand pollution, increasingly high fuel bills and frequentmaintenance requirements. Their electrical consump-tion is low despite many loads because the fridge and

stove run on propane. (Running large loads on propanegreatly reduces the up-front cost of a PV system.)

After filling out the worksheet, the Wongs find thatmeeting their needs with an autonomous system wouldbe too expensive. They figure that they can currentlyafford only a small fraction of the PV panels required,but they may be able to add more panels in a fewyears. In the meantime, they decide to combine theirexisting propane generator with PV panels to make ahybrid PV system that offers the potential to reduce the aggravation and costs linked with using a genera-tor. Based on their current resources, this appears to be their best option. Knowing this, they are now in abetter position to talk to a PV dealer about the type of system they want.

Worksheet: The Wongs (Year-Round Residence)

Step 1. Estimate Your Power and Energy Needs (watt-hours per day)AC or DC (A) Rated Wattage (B) Hours (C) Watt-Hours Per Day

(check one) (actual or Used (A) x (B)Appliance Load AC DC typical values) Per Day AC DC

Fluorescent:Kitchen lights (2) ✓ 15 3h x 2 lights 90Living-room lights (2) ✓ 15 5 (x 2) 150Bedroom lights (2) ✓ 11 2 (x 2) 44Basement, bathroom and hall lights (4) ✓ 15 1 (x 4) 60

Freezer (very efficient) ✓ 600Water pump ✓ (12 V) 90 2 180Outdoor lights (2) ✓ 15 8 (x 2) 240Clothes washer (front load) ✓ 160 1 (1 load) 160Furnace fan ✓ 250 4 1000Workshop lights (4) ✓ 15 7 (x 4) 420Radio (in workshop) ✓ 5 7 35Colour TV (no remote control) ✓ (12 V) 60 3 180Vacuum cleaner ✓ 800 0.25 200Intermittent loads ✓ 1000 (estimate) 1 1000

(e.g. coffee-maker, iron, small power tools, block heater, etc.)

Subtotal: AC: 3999 Wh/d DC: 360 Wh/d

DC to AC inverter efficiency (Effdc ac) ranges from 80 to 95 percent (0.80 to 0.95). To help you with your first calculation, 0.90 has been inserted in italics. Adjust the efficiency figure, if necessary, once you have chosen theinverter for your system and have read the manufacturer’s ratings.

Adjust AC loads for inverter losses: AC load = 3999 Wh/d: 4443 Effdc ac 0.90

Total daily load: DC loads + adjusted AC loads = 4803 Wh/d

33

34

Worksheet: The Wongs (Year-Round Residence)

Step 2. Make a Rough Evaluation of PV-System Size

2.1. Evaluate Which Stand-Alone System Is More Suitable: Autonomous or Hybrid

This summer cottage will be equipped with a hybrid PV system.

2.2. Estimate the Available Sunlight

Sunlight: 3.4 h/d (consult the maps on page 27 orsee “Learn More About Solar Energy” on page 46.)

2.3. Estimate the Required PV Array Size (W)

Array size (W) = Total daily load (Wh/d) Peak sunlight hours x 0.77*

= 4803 Wh/d 3.4 h/d x 0.77

= 1835 W**

* The factor 0.77 assumes a 90-percent battery charge regulator efficiency and an 85-percent battery efficiency.

** Based on rated power output of PV modules if an MPPT controller is used (see the glossary on page 44). If an MPPTcontroller is not used, further losses should be accounted for, resulting in a required power capacity increase of 15–25 percent. Consult your dealer.

2.4. Estimate the Required Battery Capacity (ampere-hours)

Nominal voltage of battery: (Vbat): 24 VDC(typically 12, 24 or 48 volts)

Number of days of battery storage needed (a good rule of thumb is two days for a hybrid system): 2 d

Battery capacity (Ah):

Total daily load (Wh/d) x days of storageBattery voltage (Vbat) x 0.42***

= 4803 Wh/d x 2 d24 V x 0.42

= 953 Ah at 24 V

*** The factor 0.42 assumes an 85-percent battery efficiencyand a 50-percent maximum depth of discharge. If the battery is used at temperatures lower than 25°C, its capacity (ampere-hours) will decrease. Consult your PV system supplier.

■■ Autonomous

• seasonal use (summer mainly)

• year-round operation with low energy requirements (< 1 kWh/d)orlow requirements for power availability

• limited/expensive access to the site

• maintenance is an issue

■■ Hybrid

• year-round operation and energy requirements > 2.5 kWh/dorhigher latitudes

• already have a generator

• very high requirements for power availability

✓

PV TechnologyThe most common photovoltaic(PV) cell material is silicon. It is one of the most abundant elements on earth: sand from the beach is an oxide of silicon.The first commercial PV cells were monocrystalline silicon.Other manufacturing techniquesresulted in polycrystalline silicon cells. A monocrystalline cell is made of a single crystal; a polycrystalline cell containsmany crystals. Commercial polycrystalline cells are onlyslightly less efficient thanmonocrystalline cells and are,therefore, widely used becausetheir cost-performance ratio is similar.

The development of thin-filmtechnologies reduces costs furtherby decreasing the amount ofmaterial needed to make a cell.Amorphous silicon modulesrequire only a thin layer of siliconand can be mass produced. New

production techniques led to themanufacture of “multi-junction”amorphous cells, which containtwo or three layers of semicon-ductor. Because of the lowerefficiency, modules that are physically larger are needed inorder to generate a given amountof power.

Other thin-film technologies have been developed – such as cadmium telluride and copperindium diselenide – and are beginning to appear on the market.

35

8. Technical Information on Photovoltaic System Components

▲Monocrystalline, polycrystalline and flexible amorphous silicon cells.Photos courtesy of Siemens SolarIndustries, Photowatt InternationalS.A. and United Solar SystemsCorp., respectively.

36

The ElectricCharacteristics of PV Modules:The Current-Voltage (I-V) Curve The PV module can be operatedat any combination of currentand voltage found on its “I-Vcurve.” But in reality it operatesat only one combination at agiven time. This favoured combi-nation is chosen not by themodules, but rather by the elec-tric characteristics of the circuitthat is connected to the modules.

The voltage that occurs when current is zero is known as theopen-circuit voltage (Voc). Onthe other hand, the current whenthe voltage is zero is referred to as the short-circuit current (Isc).While current and voltage are attheir highest under short-circuitand open-circuit conditions,respectively, the power at thesepoints is zero. In practice, a system operates at a combinationof current and voltage at which a reasonable amount of power isproduced. The best point is themaximum power point (MPP).Corresponding voltage and current are called Vp (nominalvoltage) and Ip (nominal current), respectively. This point of operation (MPP) is used todefine the nominal rating andefficiency of a module.

You should find all of these electric characteristics (Voc, Isc,MPP, Vp, Ip) on the label of agood-quality PV module (notethat the Vp and Ip values are alsocalled nominal or rated voltageand current). Do not expect to get the rated power from yourinstalled system – it is impossiblefor a fixed system to operate atthe highest power point at alltimes. Temperature variationsalone will change the amount of power your system generates.

Model

Manufacturer XYZ

Made in WZC

Performance at 1999 W/m2 solar irradiance and 25°C cell temperature

Max. power

Max. syst. open circuit voltage

Fire rating

Short circuit current

Open circuit voltage

Series fuse

Rated current

Rated voltage

Field wiring

copper only, 14 A WG min. insulated for 75°C min.

Serial numberABC

48 Wp

600 V

Class C

3.35 A

19.8 V

3.02 A

15.9 V

5 A

123456789

▲Typical information found on a PV module label.

▲ Important points that characterize a PV module.

Maximum PowerPoint Pmax = Ip x Vp

I = Isc

Ip

Vp

Voc

Current(I)

Voltage(V)

37

OtherComponents in PV SystemsBatteriesMost off-grid PV systems use batteries to store power for useduring periods of low or no sunlight. Certain specializedapplications (e.g. some pumpingand ventilation systems and cal-culators) do not require storagebecause power is needed onlyduring periods of light. Somepumping applications usepumped water as the storagemedium rather than electricity.However, most PV systems inCanada use batteries.

Your choice of battery size andtype is an important design consideration, particularly for systems that have no backuppower source. The batteries alonecan represent 25 to 50 percent oftotal system cost, so it is essentialto select the right type. You canuse different types of rechargeablebatteries, depending on the sys-tem’s requirements. Batteries witha long expected life have higherinitial costs but should cost lessin the long run. Several batterieson the market are designed foruse with renewable energy sys-tems, such as PV and windsystems. Deep-discharge marine,golf cart or recreational vehicle(RV) batteries may also be suitableand are generally more affordableup front. An experienced PVdealer can advise on what type of battery is best for your needs.

Most PV systems use lead-acidbatteries such as deep-dischargelead-calcium or lead-antimonybatteries. Do not use car batteriesas they are not designed forrepeated deep discharges. Nickel-cadmium (Ni-Cd) batteries arerarely used in residential applica-tions. Although they can bedeeply discharged many timeswithout harm and are lessaffected by temperature changesthan lead-acid batteries, Ni-Cdbatteries are more expensive andvery expensive to recycle. As aresult, their use is primarilyrestricted to applications wheretheir increased reliability and low maintenance are worth the premium price.

Battery storage capacity is gener-ally rated in ampere-hours (Ah).This is the amount of current thata battery will deliver over a givennumber of hours at its normalvoltage and at a temperature of25°C. The rated capacity of anybattery drops with temperature.The size of battery you require isdetermined by the total antici-pated drain on the battery. Youcan calculate this if you know thefollowing information: the volt-age of the battery, the wattage ofthe load, the length of time theload is operated and the ambienttemperature of the batteries.

For example, to run a 25-W bulbfor eight hours from a 12-V batterythat is maintained at 25°C, youwould need a battery with a capac-ity of at least 16.7 Ah (200 Wh at 12 V). If the battery must operate at temperatures as low as

Technical Note: Selecting Batteries for PV Systems – Points to Consider

• voltage and current characteristics;

• storage capacity is quoted ata certain discharge rate. If the discharge rate (the rate atwhich power is being drawnout) is less than what themanufacturer quotes, the battery’s capacity is greater.The opposite is also true;

• maximum depth of discharge (different for each type of battery);

• operating temperature rangeand how temperature affectsperformance;

• battery lifetime: the numberof times the battery can becharged and dischargedbefore it has to be replaced.This number depends on thedepth of discharge of cycle.The less discharged the bat-tery is at each cycle, themore cycles it can sustain;

• maintenance requirements:some batteries are almostmaintenance-free;

• energy density: the amountof usable energy a batterycan produce over a giventime relative to its weightand volume;

• cost; and

• warranty.

0°C, then at least a 20-Ah batterywould be required for the sameload. But in practice, to protectthe battery against acceleratedaging, a larger capacity is used toavoid a complete discharge. Fordeep discharge batteries, do notuse more than 80 percent of their nominal capacity. Also, carbatteries start to be damaged ifdischarged more than 20 percentof their nominal capacity; there-fore, they are not well suited forthis type of application.

In the sizing worksheet examplesin Section 7 (Step 2.4), an averagevalue of 50 percent was chosenfor the depths of discharge (theportion of battery nominal capacity used) so that the recom-mended sizes for the examplesabove would be 40 to 50 Ah,depending on the temperature at which the battery is operated.

PV battery systems are usuallydesigned to provide several daysof storage in the absence of sunlight. In cases where longerovercast periods are anticipated,such as in the Far North, it is usu-ally wiser to use a hybrid systemrather than trying to provideenough battery storage. In thisand many other cases, your mostpractical approach may be to usea combination of backup powerand batteries.

Power-ConditioningEquipmentPower-conditioning equipmentmodifies the power from the PVarray to make it more usable. Two power-conditioning devices –inverters and battery charge regulators – are described in the following.

Inverters

PV cells generate direct current(DC), and batteries store electric-ity as DC, but most commonappliances require alternating current (AC). In cases where youneed AC power, an inverter isused to change low-voltage DC(12, 24, 32, 36, 48, 96, 120) tohigher voltage AC (120 or 240).Some power is lost in the conver-sion as inverters are, on average,about 80- to 95-percent efficient.AC wiring, components andappliances are more available andgenerally less expensive than sim-ilar DC products. Consequently,inverters are convenient for many systems.

Inverters cover a wide range ofpower capacity, and the typeneeded depends on the applica-tion. Light-duty inverters

(100–1000 W) are suitable forsmall systems (e.g. power forlights). They are available with12- or 24-volt direct current(VDC) input voltages and 120-volt alternating current (VAC) output. Larger inverters(1000–4000 W) are available,mainly with 12, 24 and 48 VDCinput and 120 or 240 VAC output.For high-start power surges (e.g. from large electric motors),heavy-duty inverters are needed.

Low-cost inverters produce amodified square wave, whichis not as good as utility power.Roughly a dozen electrical loadsdo not run well on this type ofinverter. Your dealer can help you overcome most of these loadproblems by choosing properappliances, tools, etc. Sine-waveinverters generally produce powerthat is similar to the quality ofutility power.

Some PV modules even comewith built-in inverters. Such mod-ules are called AC modules. Youcan build up a complete AC sys-tem, AC module by AC module,increasing the capacity with eachaddition. (These inverters are usedonly for grid-connected systems.)

Many of today’s inverters alsocome equipped with the follow-ing features:

1) Metering: a display to provide volts input/output,frequency output, voltage and frequency of a fuel-firedgenerator.

2) Fuel-fired generator start capability: Extra relays areprovided to auto-start a gener-ator if the batteries reach aprogrammed state of low

38

Perc

ent

of

25°C

Dis

char

ge

Cap

acit

y D

eliv

ered

Discharge Temperature (°C)

120

110

100

90

80

70

60

50

40

30-30 -20 -10 0 10 20 30 40

▲Operating batteries at temperaturesbelow 25°C implies that you willneed more nominal capacity. (Thiswill vary, according to the type ofbatteries and rate of dischargeapplied.)

capacity. Some can even beprogrammed to keep the gen-erator from starting duringthe night (to avoid the noise),unless the batteries reach asecond programmed low, inwhich case the generator willstart regardless.

3) Grid-connected capability:The inverter can convert the DC output from the array to AC power that can be synchronized with the grid (utility). This featuremakes it possible to reduce or even eliminate monthlyutility bills.

4) Charging capability:Inverters can draw powerfrom either the grid or a fuel-fired generator to chargethe battery bank while, at the same time, continuing topass that power through tothe electrical loads in yourhouse. Some inverters varythe charge rate and voltage to certain types of batteries andtheir current temperature.

5) Stacking: Some inverters canbe linked together, either toproduce twice the output orto produce power that is outof phase from inverter toinverter in order to produce240-VAC power.

Battery Charge Regulators

Battery charge regulators controlthe amount of current enteringthe battery and protect it fromovercharging and from com-pletely discharging. They can alsomeasure battery voltage to detectthe state of charge. Regulatorsrange from 2 to 300 A for voltagesfrom 12 to 48 volts DC.

Different types of controllersexist: the on-off and the pulse-width modulation controls arethe most common types. Moresophisticated controllers are more efficient, but you and yourdealer should evaluate whethertheir performance justifies theinvestment. For example, somecontrollers include a maximumpower point tracker (MPPT) feature. It allows a PV module or array to work at its highestpower point depending on solarintensity, even if the battery isrecharged at a constant voltage.This feature provides about10 percent more power in thesummer and roughly 30 percentmore in the winter. These gainsare generally higher for panelswith high voltage peak (Vp) values.

PV TrackersThe sun “tracks” across the skyevery day. To get maximum out-put from your PV array, a trackercan be a cost-effective feature.The main issue is economics.Does the increased output from areduced number of tracked panelsoutweigh the cost of the extrapanels bought for a fixed array?Generally speaking, the larger thearray, the more cost-effective thetracker. Remember, a fixed arraymust be mounted on a structure,so the true cost of a tracker is thedifference between its cost andthe cost of a fixed array mountingstructure.

Trackers are usually mounted 3 m (10 ft.) off the ground, avoiding the need to drill througha roof. Less snow and ice accumu-lates out in the open and off theground, compared with a roof.Ask your dealer to explain the

pros and cons of manual andautomatic trackers that are currently on the market.

When considering the use of atracker, remember that it will notsignificantly increase the perfor-mance of the PV system duringthe winter in Canada. The use ofa tracker is more cost-effective forapplications operating from thespring to the fall, especially thoselocated at higher-latitude sites.

Because automatic trackers makethe system more complex, theyare rarely used for applicationswhere no one is present forextended periods of time, such as telecommunications.

39

40

This worksheet will help you get arough estimate of the size of yourPV system. For this level ofdesign, you need only choose anominal battery voltage and col-lect the information on theavailable hours of peak sunlightin your area. The results that youwill obtain below are only esti-mates and do not replace the

technical design and expertiserequired for a proper system. Ifyou wish to undertake such atechnical design, consider order-ing Photovoltaic Systems DesignManual from Natural ResourcesCanada (for contact information,see “Learn More About SolarEnergy” on page 46).

Note: Figures in the equationsbelow must be expressed as fractions, not percentages. For example, an efficiency of 90 percent should be written as 0.90 in your calculations.

Appendix A: Worksheet to Evaluate System Size

Worksheet

Step 1. Estimate Your Power and Energy Needs (watt-hours per day)AC or DC (A) Rated Wattage (B) Hours (C) Watt-Hours Per Day

(check one) (actual or Used (A) x (B)Appliance Load AC DC typical values) Per Day AC DC

Subtotal: AC: Wh/d DC: Wh/d

Adjust AC loads for inverter losses: AC load = Wh/d: Effdc ac 0.90

Total daily load: DC loads + adjusted AC loads = ________ Wh/d

DC to AC inverter efficiency (Effdc ac) ranges from 80 to 95 percent (0.80 to 0.95). To help you with your first calculation, 0.90 has been inserted in italics. Adjust the efficiency value, if necessary, once you have chosen theinverter for your system and have read the manufacturer’s ratings.

41

Worksheet

Step 2. Make a Rough Evaluation of PV System Size

2.1. Evaluate Which Stand-Alone System Is More Suitable: Autonomous or Hybrid

■■ Autonomous

• seasonal use (summer mainly)

• year-round operation with low energy requirements (< 1 kWh/d)orlow requirements for power availability

• limited/expensive access to the site

• maintenance is an issue

■■ Hybrid

• year-round operation and energy requirements > 2.5 kWh/dorhigher latitudes

• already have a generator

• very high requirements for power availability

2.2. Estimate the Available Sunlight

Sunlight: h/d (consult the maps on page 27 orsee “Learn More About Solar Energy” on page 46.)

2.3. Estimate the Required PV Array Size (W)

Array size (W) = Total daily load (Wh/d) Peak sunlight hours x 0.77*

= Wh/dh/d x 0.77

= W**

* The factor 0.77 assumes a 90-percent battery charge regulator efficiency and an 85-percent battery efficiency.

** Based on rated power output of PV modules if an MPPT controller is used (see the glossary on page 44). If an MPPTcontroller is not used, further losses should be accounted for, resulting in a required power capacity increase of 15–25 percent. Consult your dealer.

2.4. Estimate the Required Battery Capacity (ampere-hours)

Nominal voltage of battery: (Vbat): ____ VDC(typically 12, 24 or 48 volts)

Number of days of battery storage needed (a good rule of thumb is two days for a hybrid system and three days for an autonomous system): _____ days

Battery capacity (Ah):Total daily load (Wh/d) x days of storage

Battery voltage (Vbat) x 0.42***

= Wh/d x days ____ V x 0.42

= _______ Ah

*** The factor 0.42 assumes an 85-percent battery efficiencyand a 50-percent maximum depth of discharge. If the battery is used at temperatures lower than 25°C, its capacity (ampere-hours) will decrease. Consult your PV system supplier.

Typical Power Ratings of Some Common Appliances

42

Appendix B: Typical Loads

Power Rating (watt)

12-V DC loads

Auto stereo 6CB radio:

Receive 4Transmit 6

Digital clock (LED) 2Coffee-maker 140Drill (3/8 inch) 144Lighting:

Incandescent 25Compact fluorescent 4–20Four-foot type (double-ended) 40

Portable TV:Black and white 20Colour 60

Vent fan (15-cm blade) 24Water pump 50–300Hair dryer 400

Power Rating (watt)

120-V AC loads

Block heater 600Clock 2Clothes washer, excluding hot water 300–500Front-loading washer 160Coffee-maker 900Dishwasher, excluding hot water 1300Drill (3/8 inch) 300Fan, portable 115Furnace fan motor (varies greatly) 350Hair dryer 1000–1500Curling iron 25Iron 1000Lighting:

Incandescent 25–100Compact fluorescent 4–20Four-foot type (double-ended) 40

Microwave oven 600–1500Personal computer:

Desk model 250Laser printer (while printing/standby) 600/30Laptop in use 25Laptop charger 100 (max.)

Radio 5Saw 400–1000Radio-telephone (transmitting/idle) 96/12Single-side band radio (idle) 4Stereo 30TV (19 inches):

Black and white (in use) 60Colour (in use/standby with remote control) 100/5Remote control (standby) 5

Toaster 1100Vacuum cleaner 200–1400VCR (on/standby) 30/5Water pump (1/2-hp jet) 1000

Note: These are typical values only. For exact numbers, consult product literature or supplier.

About Electric Motors

Power is often expressed in horsepower (hp) formotors. This refers to the mechanical power outputof the motor. If you have information on currentand voltage, always use this information ratherthan converting hp into watts. A watt (W) is the SI unit for power (1 hp ≈ 746 W). However, this maydiffer from the actual electric power requirements,due to the power factor of a motor in AC or othersources of inefficiency found in any motor. If you intend to power a standard AC motor with a PV system, you can use the following formula to estimate your electric power requirement: 1 hp (mechanical output) ≈ 1 kW (electrical input).

Comparison of Typical Lighting Systems

43

Appendix C: Energy-Efficient Lighting

Incandescent Bulbs

Watts Lumens25 22040 49560 85575 1170

100 1680

CompactFluorescent Lights (CFLs) with Magnetic Ballast

Watts Lumens5 2207 4009 550

13 86018 116026 1700CFLs with

Electronic Ballast

Watts Lumens15 90018 110020 120025 1750

▲Source: Energy-Efficient Lighting Products for Your Home(Natural Resources Canada’s pulication)

Ampere-hour (Ah)A current of one ampere runningfor one hour.

Autonomous systemA stand-alone photovoltaic (PV)system that has no backup gener-ating source and relies only onsolar energy to meet the needs ofthe load. May or may not includestorage batteries.

Balance of systemThe parts of a PV system otherthan the PV array and batteries.This may include switches, con-trols, meters, power-conditioningequipment, trackers and a sup-porting structure for the PV array.

EasementAn oral or written legal agreementdefining an interest in exclusive,common or bipartisan use of pri-vate property or air/space abovethat property. A common form ofeasement is the concept of “rightof way,” as when an electric util-ity has the right of way to extendelectrical transmission lines across private property. See also“Restrictive covenant.”

Horsepower (hp)An imperial system unit of powerequivalent to 746 W.

Hybrid PV systemA PV system that includes othersources of electricity generation,such as a wind or diesel generator.

Kilowatt (kW)One thousand watts.

Kilowatt-hour (kWh)One kilowatt acting over one hour.

LoadAnything in an electrical circuitwhich, when the circuit is turnedon, draws power from that circuit (lights, appliances, tools,pumps, etc.).

LumenA metric measurement of therate at which light is emittedfrom a source.

Maximum power pointtracker (MPPT)Charge controller that continu-ously tracks the maximum powerpoint (MPP) of a PV module orarray, thus increasing its effi-ciency. The MPP is the point on a current-voltage (I-V) curvewhere a PV device produces maximum power.

Open-circuit voltageThe voltage across a PV cell in full sunlight when there is no current flowing; the highest possible voltage.

Parallel connectionA method of interconnecting twoor more devices that generate oruse electricity, such that the volt-age produced, or required, is notincreased, but the current is thesum of the two. Opposite of“series connection” (see entry).

Photovoltaic (PV) arrayAn interconnected system of PVmodules that function as a singleelectricity-producing unit. Themodules are assembled as a discrete structure with a commonsupport or mounting. In smallersystems, an array can consist of two modules plus a support structure or mounting.

Photovoltaic (PV) cellA device that converts lightdirectly into electricity. The building block of a PV module.

Photovoltaic (PV) moduleA number of PV cells electricallyinterconnected (in either series orparallel) and mounted together,usually in a sealed unit of conve-nient size to make shipping,handling and assembly intoarrays easier.

Photovoltaic (PV) systemA complete set of components forconverting sunlight into electric-ity by the PV process, includingthe array and balance of systemcomponents.

Power-conditioningequipmentElectrical equipment used to con-vert power from a PV array into aform suitable for subsequent use.A collective term for inverter,converter, battery charge regula-tor and blocking diode.

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Glossary

Restrictive covenantA specialized type of easementthat can be used to protect accessto sunlight or wind flow for solaror wind energy applications. Seealso “Easement.”

Series connectionA method of interconnectingdevices that generate or use elec-tricity so that the voltage, but not the current, is additive.Opposite of “parallel connection”(see entry).

Short circuit currentThe current flowing freely from a PV cell through an external circuit that has no load or resistance; the highest currentpossible.

Stand-alone (PV system)A photovoltaic system not con-nected to a main electric grid.May be solar-only or hybrid. Mayor may not have storage batteries,but most stand-alone systemsrequire batteries or some otherform of storage (e.g. water reservoir for pumping).

Stand-off mountingTechnique for mounting a PV array on a sloped roof thatinvolves mounting the modules a short distance above the pitchedroof and tilting them to the best angle.

TelemetryThe remote measurement of any physical quantity usinginstruments that convert the measurement into a transmit-table signal.

Watt-hour (Wh)A quantity of energy. One watt-hour of electricity is consumedwhen one watt of power is used for one hour.

45

Natural Resources CanadaRenewable and Electrical

Energy Division Energy Resources Branch580 Booth Street, 17th FloorOttawa ON K1A 0E4Fax: (613) 995-0087Web site:http://www.nrcan.gc.ca/redi

or

Natural Resources CanadaCANMET Energy Diversification

Research Laboratory1615 Lionel Boulet BoulevardPO Box 4800Varennes QC J3X 1S6Fax: (450) 652-5177Web site:http://cedrl.mets.nrcan.gc.ca

Canadian Solar IndustriesAssociation (CanSIA)

2415 Holly Lane, Suite 250Ottawa ON K1V 7P2Tel.: (613) 736-9077Fax: (613) 736-8938Web site: http://www.cansia.ca

Énergie Solaire Québec460, rue Sainte-Catherine Ouest,

Bureau 701Montréal QC H3B 1A7Tel.: (514) 392-0095Fax: (514) 392-0952Web site: http://www.esq.qc.ca

To order more copies of this pub-lication or others on renewableenergy and energy efficiency, call1 800 387-2000 toll-free. You canalso obtain a copy of this publica-tion by visiting Natural ResourcesCanada’s (NRCan’s) CanadianRenewable Energy Network(CanREN) Web site athttp://www.canren.gc.ca.

Free Software to Help You in Your DecisionAbout Medium and Large ProjectsRenewable energy technologies –such as photovoltaic systems,wind farms, solar ventilation air- heating or solar water-heating systems – can be a smart invest-ment. RETScreen® Internationaljust made it easier. RETScreen®

International is a standardized,renewable energy project analysissoftware program that will help you determine whether aphotovoltaic system is a goodinvestment for you. The softwareuses Microsoft® Excel spreadsheetsand comes with a comprehensiveuser’s manual and supportingdatabases to help your evaluation.You can download the softwareand user manual free of charge from the Web site athttp://retscreen.gc.ca, or callNRCan at (450) 652-4621 or faxyour request to (450) 652-5177.

Weather and SolarRadiation DataMonthly climate data and1961–1990 normals are availableon CD-ROM. To order your copy, visit Environment Canada’s Web site athttp://www.msc-smc.ec.gc.ca/climate/products_services/climate_products/climate_data_e.cfm.

Some data is available directly on-line athttp://www.msc-smc.ec.gc.ca/climate/climate_normals/index_e.cfm.

You can also find some of that data in the RETScreen®

International software previously mentioned.

46

Learn More About Solar Energy

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