Photovoltaic (PV) panels convert sunlight into electricity and come in a huge variety of shapes and sizes. They have no moving parts and last for many, many years, making them one of the ultimate sources of carbon and pollution free energy.
The most common systems are linked to the national grid but there are off-grid systems that store their energy in banks of batteries and even hybrid system which switch from grid to off-grid in the event of a power cut. In most domestic settings, it is unlikely a PV system will provide all your energy needs, but it will make a significant contribution.
When you turn on a light or pop the toast down in your toaster, the device will draw current from the nearest available source. If the sun is out, the electricity will come from the panels on your roof, if not, it will come from the grid as it has always done.
If you are out and the panels are generating more power than your house is consuming, it will travel back down the mains cable and be used by others on the grid. You'll be paid 3p extra for every kilowatt that you export in this way. Most electricity companies assume that you will export 50% of your electricity and will pay you accordingly. Occasionally, they will fit a meter to read how much you are putting back into the grid. Effectively, you'll become a small scale generator in your own right - you'll be paid for every kilowatt you generate, and then allowed to use it for nil cost or export it for an additional payment.
