Clever use of technology can save a lot of energy. The British government has set new rules for the way electricity is made, used and stored. New rules will make it easier for people to generate their own power with solar panels, store it in batteries and sell it to the National Grid. They will reduce costs for someone who allows their washing machine to be turned on by the internet to maximize use of cheap solar power on a sunny afternoon. They’ll also benefit a business that allows its air-conditioning to be turned down briefly to help balance a spell of peak energy demand. In this way, instead of predicting peak demand then building power stations to meet it, energy managers will be able to trade in Negawatts—negative, not used electricity.