Solar electricity: an introduction
Video courtesy of Explanimation.net - ready-made explainer videos
As the name suggests, solar panels use sunlight to generate electricity. The two key bits of equipment are the panels themselves (also known as modules) and an inverter. The modules generate the electricity. The inverter converts it from direct current (DC) to mains style electricity.
Solar panels are generally mounted on the roof, although they can also be installed on a frame on the ground. Solar electricity generation is supported via the government's feed-in tariff.
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.
You can use the solar PV potential calculator below to calculate 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.
Calculate your solar PV potential
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 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 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 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.
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.
What size / cost for solar PV panels?
The size of a 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 between 1,132kWh (in Sussex) and 714kWh (in Shetland) of power per year in the UK. Most domestic systems range between 1.5 and 4kWp.
The cost of photovoltaic systems has fallen rapidly since the feed-in tariff was introduced. A 1.5kW system will cost around £4,000. You should be able to get a 4kW installation for £6 - 8,000.
For anyone who installs with an eligibility date between 1 July 2015 and 30 September 2015, and has an energy performance certificate (EPC) of level D or above, the Feed-in tariff generation tariff is as follows:
4kW or less: 12.92 p per kWh
>4-10kW: 11.71 p / kWh
>10-50kW: 11.71 p / kWh
>50-100kW: 9.63 p / kWh
>100-150kW: 9.63 p / kWh
>150-250kW: 9.21 p/ kWh
>250kW and greater: 5.94 p / kWh
Stand alone: 4.44p / kWh
Tariff paid for 20 years. Export rate: 4.85p
If you have an EPC of E or below you will get 5.94 p per kWh.
Click here to download the full table of feed-in tariff rates backdated to the start of the scheme from the Ofgem website.
Feed-in tariff eligibility requirements
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 the stand-alone generation tariff which is significantly lower. 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.
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? And do they use specialist roofers?
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 are - and why they chose to supply that brand of panels and inverter.
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.
11. If they are giving you return on investment figures ask them how they reached this figure.
(with thanks to Stuart Houghton of Abacus Renewable Energy - watch his video tips for choosing a solar PV installer)
Maximising the benefit from solar PV
To get the best out of your solar generated electricity you want to use as much of it as possible. This is because the price you get for exporting it is about a quarter of the cost of buying in electricity from the grid.
Rule number one is to try and use appliances when the sun is shining and the modules are generating more than you are using in the house. These include washing machine, dishwasher, Hoover, kettle and oven. While you have to be present for some of these, you can put others on timer to run when the sun is forecast to be out and you're at work.
The simplest way of knowing whether your generating much electricity, is to look out of the window and see if the sun is shining. Or you could go and have a look at your generation meter. There are also a number of energy meters which also record your solar generation and tell you either in lights or numbers whether you are generating more electricity than you are using.
Another popular method is to divert excess solar electricity to your immersion to heat your water. This is something you can do manually if you are at home and watching the meter. Alternatively you can buy a solar switch device to do this for you automatically. There is a wide range of brands available. Market leaders include the ImmerSun and Optimersion. If your concern is about lowering carbon emissions rather than maximising return on investment, solar switches may not be for you.
The ultimate way of using more of your own electricity is to store it. However, this is currently prohibitively expensive for most people. There is a lot of work done on storage systems and it is expected to become more affordable in due course. The following systems are available or due to come on the market soon: SMA Smart Home, SunStore, PowerRouter and SolarMax P Battery.
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.
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.
More information on solar electricity
From the Blog
Feed-in tariffs - please see for more information our feed-in tariff page.YouGen responds to government consultation on solar Feed-in Tariffs Feed-in Tariffs Four Years On
Choosing your installer
DIY solar PV: is it a good idea? (Dec 2013)
Are solar panels from Ikea a good deal? (Oct 2013)
Your roof or site
How to get your ideal solar PV system (March 2014)
Solar panel performance
Coloured solar panels - worth it?
Maintenence & living with solar PVHow do I make the most of my solar panels?
How do I get the best out of my system? (Feb 2012)
More of your questions answeredFitting PV on a commercial premises: STA guide
Planning permission & permitted development
Solar PV and home sale pricesDoes your home's energy efficiency influence its price and salability?
Free solar (rent a roof schemes)
Storage / Using excess electricity on site
Combining solar PV with other technologies