Scotsman: If you travel to Unst in Shetland you may come across a worldwide eco-phenomenon – a self-built zero-carbon house has been built on this remote, windy island. It has been designed, constructed and powered to minimise its impact on the environment. Even the food eaten by its residents is considered. The story of the zero-carbon house is being followed by thousands of people, some of them very influential. It is the brainchild and retirement project of an English couple, Michael …