Most houses in the UK are connected to the national grid which supplies the house with electricity. PV systems installed on these houses will also be connected to the grid. When they are producing more electricity than is needed the excess will be fed back into the grid, and when the demand is greater than the amount being produced they take electricity from it. This all happens automatically and the only difference you’ll notice is lower electricity bills.
A grid-connected solar installation will consist of the PV modules (or panels) connected to an inverter which feeds the electricity into your consumer unit (fuse box) for use within the house. (See parts of a solar PV system for more information.) The consumer unit will then have two inputs – one from the solar panels and one from the national grid. This allows you to take advantage of free electricity when your solar panels without losing your current supply.
Houses that do not have a connection to the grid can also benefit from solar electricity with an off-grid system. Instead of the being tied in to the grid, these systems will have a battery system which is charged when there is excess electricity being produced and used when not enough is being generated. An off-grid system will usually have other sources of electricity such as wind turbines or back-up generators to complement the solar panels and provide additional power, especially during the winter when output from the panels is lower.