Solar electricity: an introduction
Solar panels which generate electricity (known as solar PV) capture the sun's energy using photo voltaic cells. Even on a cloudy day, the cells can still generate electricity. which can be used to run household appliances and lighting.
How does solar PV 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.
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
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.
Find out more information on the Feed-in-Tariff.
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 keep hold of it using battery storage technology. A battery can store the solar energy that’s generated but not used at the time, so you can use it later on when your system isn’t generating.See our blog on choosing the right battery.
Planning permission for solar panels?
More information on solar electricity
From the Blog