Bitcoin soaks up most of the hype heaped on cryptocurrencies, leaving its younger and smaller sibling Ethereum in the shadows. But Ethereum is anything but small. Its market capitalisation is roughly US $10 billion, and it has an equally whopping energy footprint. Ethereum mining consumes a quarter to half of what Bitcoin mining does, but that still means that for most of 2018 it was using roughly as much electricity as Iceland. Indeed, the typical Ethereum transaction gobbles more power than an average U.S. household uses in a day.