Independent (UK): Michael Rea, 64, and his wife Dot retired to the Shetland island of Unst in 2001 and now live in a zero-carbon house. In the past year, the couple have lived near off-grid, with heating costs of just 50p a day for their 180sq m home in the most northerly part of the British Isles “We had always wanted to live in a truly sustainable way and we decided that we wanted to put a lot of energy-efficient technology into the house. “At that point we weren’t actually considering …