Buyers Guide Solar Pv Panels[1]

8/4/2019 Buyers Guide Solar Pv Panels[1]

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07 A buyer’s guide to solar electricity A buyer’s guide to solar electricity02 03

Energy from the sunThe sun provides an abundant, free source ofclean energy in the form of natural light andwarmth. It is possible to capture some of thisfree energy directly to convert sunlight intoelectricity using solar photovoltaic (PV) panels.If you’re thinking about installing solar PV togenerate electricity – this guide is for you.

How does solar PV work?Solar PV systems convert light into electricalpower using a thin layer of semi-conductingmaterial, usually silicon, encased between asheet of glass and a polymer resin. Theyrange in size from a few square centimetres,for example on calculators and watches to

systems of hundreds of square metres madefrom interconnected modules that form anarray. When exposed to daylight electronsin the semi-conducting material becomeenergised. These electrons are then ableto flow through the material generating adirect current (DC). The DC is carried throughwiring to an inverter which converts thecurrent to 240V alternating current (AC)so it can be connected to your home’smain electricity supply.

to an existing pitched roof or a tilted frameon a flat roof. In this arrangement the panelswill slightly protrude from the roof tiles butare still in keeping with the shape of thehouse. If you are replacing your roof you cannow buy solar PV integrated roof tiles andslates that can form part of the weatherproofmembrane or structure.

VersatilityAs solar PV is made up of modules, typicallyaround 1m x 1.5m, an array (the full solar PVinstallation) can be designed to accommodatevirtually any size and shape of roof. Solar PVcan also be mounted vertically and horizontallyallowing the system to form part of the walland roof structures in new properties althoughperformance will be reduced with these tilts.

Orientation and tiltYour roof should ideally face due south at apitched angle of between 30° and 50° fromthe horizontal to give the best overall annual

What does kWp andkWh mean?Solar electricity systems are given arating in kilowatts peak (kWp). This isessentially the rate at which it generatesenergy at peak performance for exampleat noon on a sunny day. The kWp of adomestic system will vary depending on howmuch a customer wants to spend andthe roof area available to accommodatethe panels.

The total amount of electricity the systemactually generates in a year is measuredin kilowatt hours (kWh). This will dependon the system’s orientation, shading andhow sunny your site is, as well as thesize of the system (in kWp) that youhave installed.

A typical domestic system is between1.5 to 3kWp. Each kWp should generatearound 800 to 850kWh per year if unshadedand perfectly south facing with a tilt ofaround 30-50°. A solar roof array wouldtypically generate 1200 to 2400kWh peryear depending on size.

By contrast an average home uses4000kWh of electricity per year on lightsand appliances. However, an energy efficienthome using A rated appliances and lightingcould conceivably use half this value.

Effortless integrationSolar PV can be easily incorporated into mosthouses. The most common option is to usestandard solar PV modules in a frame fixed

performance. Installations facing anywhereto the south of due east and due west arefeasible, although output will be reduced.Installation is not recommended on roofsfacing north.

This table shows the percentage variance in performance when orientation and tilt are adjustedaway from the optimum (100%).

To find out more callfree on 0800 512 012.

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90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90

0 87 88 90 91 92 92 93 93 93 93 93 93 92 92 91 90 89 87 86

10 84 87 90 92 94 95 95 96 96 97 97 96 95 94 93 91 89 87 84

20 82 85 90 93 94 96 97 98 99 99 98 97 96 95 93 91 88 84 81

30 78 83 87 91 93 96 97 98 99 100 98 97 96 95 93 89 85 81 78

40 75 79 84 87 92 94 95 96 96 96 96 95 94 92 90 86 82 77 7250 70 74 79 83 87 90 91 93 94 94 94 93 91 88 83 80 76 73 70

60 65 69 73 77 80 83 86 87 87 87 88 87 85 82 78 74 71 67 63

70 59 63 76 70 72 75 78 79 79 79 79 79 78 75 72 68 64 61 56

80 50 56 60 64 76 68 69 70 71 72 72 71 70 67 66 60 57 54 50

90 41 49 44 58 80 61 60 61 63 65 65 63 62 59 60 52 50 47 44

West

T I L T

d e g r e e s South East




Solar PV cell typesThere are several different types of solar PVwith different characteristics, costs and benefits.The main options for domestic use in theUK are:

Crystalline cellsThese are the most commonly manufacturedtype. There are performance variationsdepending on whether you opt for a‘monocrystalline’ cell (often the moreefficient of the two) or a mix of crystalsor ‘polycrystalline’ cells which have amarble-like appearance. Polycrystallinecells can be cheaper to produce.

Shape of roof areaSolar PV arrays are made up of modulesof about 1.5m2 which allows most availableroof shapes to be accommodated. TypicalUK installations are around 14m2 or 15m2.For example a 2.2kWp system could compriseof 12 panels taking up an area of 15m2 andwill generate roughly 1800kWh per annum.

ShadingAny shading on a single module will affectthe performance of the whole array as all themodules are connected. A system can toleratesome shading early or late in the day without

much reduction of overall output but it shouldnot be shaded between 10am and 4pm.Nearby trees, chimneys, TV aerials and ventpipes are all common causes of shading andshould be accounted for before anyinstallation.

Solar electricity doesn’t necessarily requiredirect sunlight and can still generate electricityon cloudy days. You will generate approximately1/3 of the energy on a cloudy day as on asunny day at the same time of year.

Hybrid cellsThese combine crystalline cells with anothercell type, thin film to give the best overallperformance and do not cost much more toproduce than conventional crystalline cells.

Comparison summary of different technologiesHybrid panels often cost more to buy than theother types. However, there are many otherfactors that also affect the total installed costof a system. A typical 2.2kWp system willcost around £12,500.

Seasonal performanceThe chart above shows a typical seasonalspread of energy generation for an averagesystem of 2.2kWp facing south. The wintermonths generate significantly less electricitycompared to the summer months.

Site locationThe amount of electricity generated by asolar PV system can also vary depending onwhere you live in the UK. Northern areasreceive slightly less energy from the sun overthe year. For example a 1kWp system will

generate less electricity in Northern Scotlandthan it would in Cornwall. However solarelectricity is still worth while in the northernparts of the UK as the differences aren’tsubstantial.

You can get an estimate of how much asystem will generate in your location (andhow much it will earn) using our CashbackCalculator visit energysavingtrust.org.uk/cashbackcalculator

Jan

Monthly energy generation in kWh

Feb March April May June July Aug Sep Oct Nov Dec

0

50

100

150

200

250

300

Energy generation by month – 2.2kWp system

Cell type Efficiencies* Approximate areaper kW(m2)

Monocrystalline 13-17% 6-8

Polycrystalline 11-15% 7-9

Hybrid 17%+ 5-6

*Theefciencyoasolarcellgivesanindicationohowmuchothesun’senergyisactuallyusedbythe systemperunitarea.Thehighertheefciency,thebetterthecellisatconvertingthesun’senergy.




MaintenanceVery little maintenance is required if a welldesigned solar PV system is installed properly.Modules that are tilted at 15° or more havethe additional benefit of being cleaned byrainfall to ensure optimal performance.

You can expect them to operate for 25 yearsor more before they need replacing, althoughthe inverter may need replacing over thelifetime of the panels. Once fitted, yourinstaller should leave written details of anymaintenance checks that you should carryout from time to time to ensure everything isworking properly. This should include detailsof the main inverter fault signals and key

trouble-shooting guidance. Ideally yourinstaller should demonstrate this to you atthe point of handover.

In areas that experience high levels of dustand grime such as city or industrial locationsyour solar PV array may need additionalcleaning from time to time as rainfall maynot be sufficient. Consult with your installerfor exact maintenance requirements beforeyou commit to installing a solar PV system.

Most of the above services will be required,so if they are excluded from your installer’squote, you will need to obtain separateestimates or make your own arrangements.It is important to bear this in mind whencomparing quotations.

Most domestic solar PV arrays are between1.5kWp and 3kWp. A typical 2.2kWp systemwill cost around £12,500.

Here is an example of what a typicaldomestic solar electricity system with aninstallation size of 2.2kWp could earn andsave you each year through the Feed-in Tariffs:

This assumes 50% of the electricity generatedis exported. The Feed-in Tariffs rates are indexlinked, so this income will hold its value overthe entire life of the system.

£ per year

Generation Tariff £770

Export Tariff £30Reduction in current electricity bills £120

Total savings and income generated £920

Basedonatarirateo41.3p/kWp,exportrateo3p/kWhandelectricitypriceo12.5p/kWh.TheFeed-inTarisarenotcurrentlyavailableinNorthernIreland.

Costs and savingsOn average (across cell types), solar PV costs£5,800 per kWp installed. When comparingquotes from installers do not simply focuson the suggested system capacity as thisis probably not the best way to compareperformance or cost effectiveness.When comparing prices ask the installerwhat is included. Some things are oftenexcluded from an initial estimate including:

• Scaffolding (if required).

• Removal of the existing roof and otherroofing works.

• Any internal work to install wiring.

• Connection agreement with the DistributionNetwork Operator (DNO).

• Allowance for lightning protection.

• Electrical connection work (this requires afully qualified electrician).

• A generation meter.

• Other display meters if required (i.e. handhelddisplay meter).

WarrantiesSystem warranties may vary: manufacturer’sperformance warranties on modern solar PVmodules typically last up to 25 years. Inverterwarranties are up to 5 years. Installers mayalso offer their own warranties so worthchecking. If the system is a part of otherroofing work check with your roofingcontractor that the solar PV installationdoes not affect the roof warranty.

How to find an installerLook for an installer or supplier certified byan independent body and signed up to anindustry code of practice.

The installer must be certified under theMicrogeneration Certification Scheme (MCS)or you will not be eligible for Feed-in Tariffspayments. You can find certified installers atmicrogenerationcertification.org

Speak to people in your area who have hadsolar PV systems installed and ask if theywould recommend their installer.




Check the time limits of any guarantees andwarranties and find out what they cover. Ask:

• About after – installation services offeredand what they cost.

• About warranties and guarantees - allinstallers should provide information aboutboth of these.

• For details of what the warranties coverand over what time periods. Who pays forthe labour if the product warranty is stillvalid but the installer warranty has expired?

Do not compare installers on cost alone; thecheapest may not be the most appropriate.

Ask:

• For details on available options such assize and efficiencies.

• About the technology types – the mostefficient types are often, but not always,more expensive.

• About independent testing carried out onsolar PV installations. The installer shouldbe willing to provide a copy of any testreports in full.

• For information on applicable regulations,including health and safety guidelines – forexample on safe roof access - and howthey will address them.

Check quotations for detail. Ask:

• About government incentives – the installerwill ensure that your system is eligible forFeed-in Tariffs payments.

• About payment options.

• About what is included.

• Are they a member of an Office of FairTrading or Local Trading Standardsorganisation scheme?

Use the checklist below to help you selectan installer.

Pick a installer with experience. Ask:

• How many years they have beeninstalling systems?

• How long they have been in business?Choose local where possible. Ask for a listof references and local installations andcheck them out.

If installers quote any professionalcredentials, such as MCS, REAL, Cityand Guilds.

• Ask for details so you can researchthem yourself.

• Check them out to make sure they are amember of a trade organisation such asRenewable Energy Association.

Get lots of information on system options andpotential problems so you can talkconfidently to installers. Ask:

• For recent manuals and brochures.

• For any background information on thetechnologies and systems available.

What to look for inan installerThe Energy Saving Trust recommends youuse an MCS certified installer.

You should get at least three quotes fromreputable installers and beware of heavyhanded sales techniques, such as pressure tosign on the day, high prices with large discounts for signing on the spot, or bogus monitoringscheme discounts. All installers or suppliersshould be able to provide a detailed breakdown of the specification and costs of theirproposed system. They should also be able to:

•Explain how they have calculated the size ofthe system to be appropriate for your needs.

• Supply clear, easy to understandinformation and operating instructions.

• Provide an estimate of how much electricitywill be generated by any proposed systems,and what this is as a proportion of yourannual use.

Check that the installers are members ofREAL Assurance Scheme. Members of thisscheme agree to abide by their ConsumerCode. The code covers issues such aspre-sales activity, contracts including depositsand payment schedules, completing the orderand after-sales activities. In particularmember companies must not use anyhigh-pressure selling techniques, including:

• Staying in your home for an unreasonablylong time.

• Offering you a high initial price followedby a discount.

•Offering you a discount for signing onthe day.

•Withholding price information from youuntil the end of the visit.

• Claiming that there is limited availabilityof a product.

For more information about the REALAssurance Scheme visit realassurance.org.uk

Call the Energy Saving Trust on

0800 512 012 for informationabout certified products andinstallers available in your area.

Buyers Guide Solar Pv Panels[1]

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