Thousands of householders are installing solar-powered “smart meters” that promise to cut household bills by £250 a year. The development comes as state payouts for renewable energy produced in homes fall sharply. The devices track when rooftop solar panels produce excess energy and divert it to a water heater. The hot water can be used later, saving on gas and electricity bills. Any gadget that claims to improve the return on solar panels will come as welcome news to home owners who could see subsidies cut by 87pc as part of a government reform to the “feed-in tariff”. If you bought solar panels today the Government would pay a feed-in-tariff rate of 13p per kilowatt hour (kWh). But from January this rate will drop to less than 2p.