National Grid currently uses diesel generators to provide backup power to a substation for key activities such as cooling fans, pumps and lighting.

These backup generators are rarely used and have less than a 1% chance of operating per year.

However, on the rare occasion, that backup power is required, changing from diesel to low carbon alternatives could reduce carbon intensity by 90% and save more than 500,000 kilograms of carbon dioxide emissions, National Grid said.

Article source: https://www.energylivenews.com/2023/01/13/national-grid-completes-hydrogen-powered-substation-trial/