An earthship is a sustainable house. All its energy needs are met by small-scale hydro, wind and solar power. The water is filtered rainwater and the heating is stored when the sun shines and slowly released by the walls when it is cold. The front of the (south-facing) house is a greenhouse with tomatoes growing in it. The earthship even takes care of its own sewage treatment.
This is an experiment in Scotland. As a house like this has never been built here before, it remains to be seen whether it will be warm enough to live in during winter.