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 thatâ€™s never going to stop shining (even though it doesnâ€™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 â€“ although you will still catch a reasonable level of sunlight at angles of 20 â€“ 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 donâ€™t tend to be.
The energy efficiency requirement
New energy efficiency requirements for the feed-in tariff (FiT) for solar PV start on 1 April 2012. As a result, the full FITs rate is only available for buildings which have an Energy Performance Certificate of band D or above. Currently just under half the UK housing stock meets this criteria.
The installation of solar panels is, in itself,
an energy efficiency measure and will bring some properties that are
currently band E to band D. However, don't assume that is the case. The
EPC algorithms are complicated, and the only way to be sure is to run
the data through the software. Don't go ahead on a 'guesstimate' from a domestic energy assessor (DEA) or your installer.
Installations that don't meet the
criteria, will get a significantly lower level of generation tariff: 9p
per kW instead of 21p per kW for systems of 4kW or less, so you may need to take additional energy efficiency measures to get up to the required standard. You must send the EPC certificate to your FiT supplier when you register for the tariff. They will not change the FIT rate retrospectively if you achieve band D at a later date.
Some homes are unlikely to reach D without significant investment. There will be exemptions for buildings that cannot get an EPC, but they are expected to be few and far between.
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 Â£6 - 8,000.
For anyone who installs with an eligibility date between 1 July and 31 March 2014 and has an energy performance certificate (EPC) of level D or above, the Feed-in tariff generation tariff is (figures in brackets for 1 January to 30 March 2014 where it is different):
4kW or less: 14.90p per kWh
>4-10kW: 13.50p / kWh
>10-50kW: 12.57p / kWh
>50-100kW: 11.1p (10.71p) / kWh
>100-150kW: 11.1p (10.71p) / kWh
>150-250kW: 10.62p (10.25p)/ kWh
>250kW-5MW: 6.85p (6.61p) / kWh
Stand alone: 6.85 (6.61p) / kWh
Tariff paid for 20 years. Export rate: 4.64p
Click here to download the full table of feed-in tariff rates backdated to the start of the scheme from the Ofgem website. Click here for the table of installations from 1 February 2013 to 31 March 2014)
Calculate your solar PV potential
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 â€˜permitted developmentâ€™ 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 governmentâ€™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.
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 â€“ or mains equivalent) electricity which is suitable for running appliances
- grid connected systems can export electricity they donâ€™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.
Which solar PV panels work best?
Sadly, there isn't a simple answer to this question. It depends on a whole range of criteria, including what your motivation for installing the panels is. These include: panel efficiency, performance (ideally measured in outdoor trials), long-term degradation, the strength of the company that makes them, warranties and price. For more detail on this click here.
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 itâ€™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 used to be seen as the more efficient panel. However, as the market has developed the efficiency rates have become more similar with a typical efficiency level of around 15%. Click the link to read more about the importance of efficiency in choosing a solar panel.
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, but the efficiency rates are correspondingly lower.
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 Oxfordâ€™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.
The BRE National Solar Centre which was founded in 2013 intends to test performance of solar PV panels.
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.
This is mostly important because you want the warranty to be worth more than the paper it's written on when you're buying a product that has a 30 year lifetime. For more about solar PV and brands click here.
More information on solar electricity
From the Blog
Feed-in tariffs - please see for more information our feed-in tariff page.
Choosing your installer
Your roof or site
Solar panel performance
Maintenence & living with solar PV
More of your questions answered
Planning permission & permitted development
Solar PV and home sale prices
Free solar (rent a roof schemes)
Using excess electricity on site / Storage
Combining solar PV with other technologies