From Rick Jefferys, Berkhamsted, Hertfordshire, UK
You are right to highlight the importance of heat storage as a way to use surplus renewable electricity. A big but under-appreciated resource on this front is the hot water tank. We have about 9 million in UK homes, typically supplied from a gas boiler, with a 3-kilowatt immersion heater backup (Leader, 20 July).
Adding an inexpensive Wi-Fi controller to each would enable utility control of 27 gigawatts of demand, 18 times the size of the largest pumped storage scheme in the UK. This would be a lot less expensive than hydrogen storage, yet could absorb most of our peak renewable production.
