High Quality Content by WIKIPEDIA articles! About 81 percent of total primary energy supply in Iceland is derived from domestically produced renewable energy sources. In 2007, geothermal energy provided about 66 percent of primary energy, the share of hydropower was 15 percent, and fossil fuels (mainly oil) 19 percent. The main use of geothermal energy is for space heating with the heat being distributed to buildings through extensive district-heating systems. About 85% of all houses in Iceland are heated with geothermal energy.