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Solar Electricity

Solar electricity: an introduction

Solar photovoltaic (PV) technology on a small scale is familiar to most people in the UK. It is used to power calculators, road signs, toys and phone chargers. It takes light from the sun, and uses it to run the appliance. Solar PV panels for electricity generation work on the same principle, just at a larger scale.

Sunlight is all you need to get electricity from the panels. It is an unlimited resource that’s never going to stop shining (even though it doesn’t always feel like that in the UK). Although more electricity is produced on sunny days panels work well on overcast days too.

Is solar electricity suitable for my home?

Ideally a solar PV system should face between south east and south west, and be free of shade. For best performance they should be angled at 30 to 40 degrees – although you will still catch a reasonable level of sunlight at angles of 20 – 50 degrees.

Shade falling on the roof will reduce the performance. How much it affects it by depends on type of shading: close structures such as gable windows or chimney stacks can reduce output significantly as they will tend to throw shade on the panels for most of the day. Further away objects such as trees or a neighbouring house may not block the sun during summer, but create shade when the sun is lower in the sky in winter. There are several gizmos available to help installers predict the impact shading will have on estimated performance.

Click here for a tool that calculates how much potential your site has to generate electricity from PV.

Solar panels weigh quite a bit, so your roof must be strong enough to hold them. If you need to re-roof, you can do so using solar tiles. These are more expensive than panel systems, but if you are re-roofing anyway, it can be more cost-effective to re-roof with solar tiles than to use conventional tiles and put panels on top.

Solar PV systems are easy to install, need virtually no maintenance and are estimated to last 40 years. They are suitable for use in urban areas which wind or hydro systems don’t tend to be.

Find a solar PV installer.

What size / cost for solar PV panels?

Size of system will depend on which type of PV cell you choose, how good your site is, which part of the country you live in and how much electricity you want to generate. As a rule of thumb, a 1kWp system will generate an average of 850kWh of power in the UK. Most domestic systems are between 1.5 and 3 kWp.

The cost of photovoltaic systems has fallen rapidly since the feed-in tariff was introduced in April 2010 (although this is more to do with international market growth, than domestic). You should be able to get a 4kWp installation for around £10-11,000.

The Feed-in tariff generation tariff is:

4kW or less: 21p / kWh (retrofit & new build)
>4-10kW: 16.8p
>10-50kW: 15.2p
>50-150kW: 12.9p
>150-250kW: 12.9p
>250kW-5MW: 8.5p

These rates are under consultation until 23 December 2011.
Click the link to read more about what the changes mean for you.
NB: On 21 December 2012 the High Court ruled the government's consultation on changes to the solar PV FIT rates 'unlawful'. This has led to uncertainty over what rate will be payable to all installations made since 12 December 2012.

In addition you will receive 3.1p per kWh of electricity exported to the grid.

The rates are designed to give a 5% return on investment for a well-sited installation, except for the 4kW and below rate, which is intended to give a 4.5% return. However, many of the installers listed on YouGen are offering 8-11% returns on well-sited domestic scale installations.

It is likely that from April 2012, only buildings which meet new energy efficiency criteria, will be eligible for the feed-in tariff.

The payments are tax-free and index-linked, and will continue for a 25 year period. To qualify for this feed-in tariff you must use a MCS accredited installer and product.

The main grants scheme stopped with the introduction of the feed-in tariff, but to see if any grants are available in your area you can ring your local energy efficiency advice centre on 0800 512 012 or search the Energy Savings Trust database.

Find a solar PV installer.

Choosing a solar PV installer

1. Find out how long they've been in the business.

2. Ask if they will subcontract any of the work out, and if so, to who.

3. Are they qualified electricians?

4. Ask for recommendations from previous installations - either find them on YouGen, or ask for names and contact numbers of previous customers and follow them up.

5. Make sure the quotation is comprehensive - it should itemise all the equipment.

6. Get companies to give an estimate of how much the system will generate.

7. Ask for advice on the size of the system, don't be sold on a system on a standard size kit.

8. Ask what the benefits of the different modules is.

9. Get a really good feel for what the person's like. Talk to them and make sure you feel they really understand what they are talking about, and are an engineer, not just a salesman.

10. Make sure they look at the fuse box and look at the structure of the roof.

(with thanks to Stuart Houghton of Abacus Renewable Energy - watch his video tips for choosing a solar PV installer)

Planning permission for solar panels?

Solar panels are generally considered ‘permitted development’ in England and Wales as long as they do not protrude more than 200mm from the wall or above the roof slope; and are not higher than the highest part of the roof.

They are permitted in a conservation area as long as the panels are not installed on a wall that fronts a highway. However, if you live in a listed building you will have to apply for planning permission. Up-to-date advice is available on the government’s planning portal.

Stand alone solar is permitted development as long as it is less than 4m high, more than five meters from the boundary, and the surface area of the panels does not exceed nine square meters; or any dimension of its array does not exceed three meters. In a conservation area, it must not be nearer to the highway than it is to the dwelling. If it is in the grounds of a listed building you will need to apply for planning permission.

Click to see the full text of the most recent changes to permitted development.

For those of you living in Wales, from the beginning of September 2009, the Welsh Assembly Government announced new planning rules to encourage householders to install renewable energy equipment. A leaflet has been published to explain the changes - Domestic microgeneration permitted development: A guide for householders.

Find a solar PV installer.

How does solar electricity work?

Photovoltaic systems use cells, consisting of one or two layers of semi-conducting material, to convert solar radiation into electricity. The semi-conducting material is generally silicon, which is the second most abundant element on earth after oxygen.
light shines on the cell creating an electric field across the layers
this causes electrons to flow creating electricity
on its own each cell only creates a tiny bit of electricity, but when connected together to form panels, which are linked together to form a system, they create useful amounts
panels are mounted on the roof or on a frame
an inverter converts the direct current (DC) to alternating current (AC – or mains equivalent) electricity which is suitable for running appliances
grid connected systems can export electricity they don’t use to the grid, and import it from the grid when there is not enough sunlight
off-grid systems store excess electricity in a bank of batteries
off-grid systems can be used in conjunction with other sources of power such as biomass boilers, wind or hydro turbines.

Find a solar PV installer.

Which solar PV panels work best?

All types of solar PV system are measured according to their peak power rating which is measured in kWp (kilowatt peak). This is a guide to how much power the module produces under standard test conditions: it measures the power produced under 1kW per m2 of light. The more efficient the module, the smaller the array needed.

There are a number of different types of solar PV panels and the photovoltaic industry is developing fast, so it’s worth asking a few suppliers what they recommend.

Crystalline silicon technology is the most commonly used in the UK and the most efficient at converting sunlight into electricity. It consists of thin slices of silicon cut from a single crystal (monocrystalline) or from a block of crystals (polycrystalline). However, it is expensive to manufacture, so it costs more.

Monocrystalline performs most efficiently with modules typically converting 15 per cent of solar radiation into electrical energy, and with the best products reaching 21.5 per cent. The higher price reflects this. Polycrystalline silicon converts between 8 and 12 per cent of solar radiation into electricity.

Thin film technology involves depositing very thin layers of photosensitive materials onto a low-cost backing, such as glass, stainless steel or plastic. This technology is cheaper and more suitable for mass production. However, the efficiency rates are correspondingly lower. There is a range of types available:
Amorphous silicon (4-6 per cent efficient)
Cadmium telluride (7 per cent efficient)
Copper indium diselenide (9 per cent)

More discussion about the pros and cons of different types of solar PV panels is available in this blog: What types of solar panels are there?

How close to peak power a PV module performs will depend on the intensity of light shining on it. It also varies between makes of module. The PV-Compare project run by the University of Oxford’s Environmental Change Institute found that the number of kWh of electricity produced by a 1kWp PV array varies significantly, with the highest yielding modules producing nearly twice as much energy as the lowest yielding ones.

Research at the EC Joint Research Centre found that most of the panels they have tested continue to provide more than 92 per cent of the initial power after 20 years.

Find a solar PV installer.