The first district heating systems were developed in the first energy crisis post-WWI, and the energy crises of the 1970s pushed for further geothermal resource development and the generation of electricity from geothermal sources. In 2009, the National Energy Authority reported that Icelanders have saved ISK 880 billion (USD 7.2 billion) through geothermal heating since 1970, assuming a two percent real yield. Today, around 90% of Iceland’s substantial heating needs are met with geothermal resources.