Quite a large proportion of its energy requirements will be supplied by geothermal sources.
From
wikipedia...
About 85 percent of total primary energy supply in Iceland is derived from domestically produced renewable energy sources.
In 2011, geothermal energy provided about 65 percent of primary energy, the share of hydropower was 20 percent, and the share of fossil fuels (mainly oil products for the transport sector) was 15 percent. In 2013, Iceland also became a producer of wind energy.
So natural nuclear energy from Mother Earth herself!