Your Solar PV system is connected to the mains electricity grid and, because you can’t store electricity your panels generate, any electricity that you don’t use flows back into the grid for use by others.
As a producer of electricity, provided your system is installed by an MCS registered contractor, you’ll be therefore paid a Feed-In Tariff for the energy you don’t use. This is set at a flat rate of 50% of the capacity of the system – no matter how much of the electricity you generate you actually use.