British Gas is giving customers 50% off their electricity bills during certain hours every week as a reward for making one small change to their energy usage.

The major energy supplier, which serves more than eight million homes in the UK, runs a rewards scheme that allows customers to halve their bill simply by shifting their electricity usage. The firm’s PeakSave scheme encourages households to use energy when there is less demand, or more renewable electricity available on the grid, in a bid to encourage greener energy use.

The scheme is open to all customers – no matter what tariff you’re on – and those who join can cut their electricity costs by 50% every Sunday between the hours of 11am and 4pm.

During the five-hour PeakSave event, customers can use as much electricity as needed – but it will be half the usual price. You don’t need to opt into each PeakSave event as British Gas will automatically include those who are signed up to the PeakSave scheme every Sunday.

British Gas said the scheme has saved more than £36 million off electricity bills since it begans, with more than 150 customers saving over £150 each.

PeakSave has also moved 40,000 MWh of electricity to off-peak times, helping the grid to run more efficiently, and it’s helped cut 2,939 of carbon emissions, which is the equivalent of taking 797 cars off the road for an entire year.

The supplier also runs separate PeakSave GreenFlex events too, which allow customers to get half-price electricity for one to two hour bursts by moving their electricity usage to times when there’s likely to be lots of renewable energy around.

These events require opting in and British Gas will notify customers when there is one coming up so they can choose whether to take part to save money.

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By using electricity during off-peak hours you can earn credit towards your electricity bill or meter and make big savings throughout the year.

It’s free to sign up to PeakSave online and British Gas will email you within seven to 10 days confirming if you’re eligible to take part.

British Gas said: “Demand for energy is typically lower on Sundays. So this is the perfect time for PeakSavers to make the most of half-price electricity and help make better use of cleaner, greener energy by moving your electricity use to off-peak times.

“And whatever tariff you’re on, you can take part. Just use as much electricity as you need from 11am to 4pm.”