These companies are Octopus Energy, OVO Energy, British Gas, ad E.On. The scheme the companies have agreed to is designed to encourage customers to switch the time they use electricity to off-peak hours on some days when supply is tight.
Most customers use electricty at similar times, with a particularly big spike in the evenings when people return from work, start cooking, or switch the TV on.
The scheme was decided on by the National Grid, and the energy companies have either signed up to its scheme, or have created their own.
OVO Energy, for example, has announced the launch of Power Move. The trial rewards customers up to £100 in total for moving non-essential energy use to times when the grid is greener and less congested.