Marstal Fjernvarme was established as a cooperative company in 1962. Marstal Fjernvarme is an example of a solar district heating plant on the island of Ærø, Denmark. The collectively-owned district heating network provides hot water to nearly all of the 2,200 inhabitants of the island town of Marstal. The company provides heat to Marstal from 100% renewables (50-55% of which comes from solar thermal collectors, 40% of the heat production comes from burning wood chips, 2-3% from a heat pump and the last residue up to 100% comes from burning bio-oil.). The aim of the project is to demonstrate a large scale innovative, cost-effective and technically 100% sustainable renewable energy system.