Hundreds of Asda supermarket stores will help power the UK’s electricity system this winter by using their fridges as a virtual battery pack for the energy grid. Britain’s third-largest supermarket chain has signed up 300 stores and 18 distribution depots to schemes which can earn the grocery giant extra revenue while helping to balance the electricity grid. Under the long-term deal with National Grid the supermarket’s nationwide networks of freezer aisles and storage fridges will make up a 13-megawatt power source – enough energy to power about 8,500 homes. Asda has also signed up to a trial which could mean its fridges are called on at only 10 minutes’ notice to act as a safety net if there is an unexpected power station outage. National Grid pays out about £1bn worth of contracts through its energy capacity market. Most are awarded to power plants so they are ready to ramp up their generation but they can also be given to companies which can cut their electricity use to help reduce overall demand on the grid. The supermarket is working with Flexitricity, a specialist Edinburgh-based energy firm, which uses technology to aggregate the energy potential of companies across the country. Flexitricity hopes that by creating a virtual battery across its portfolio of clients it can bid for National Grid contracts which would earn the companies extra revenue while cutting carbon emissions.