After the 1973 oil crisis, the energy politics were determined to become less dependent on the import of petroleum. Since then, electricity has been generated mostly from hydropower and nuclear power. Sweden wants to be independent of petroleum use by 2020. The Three Mile Island accident (United States) prompted the Swedish parliament in 1980 after a referendum to decide that no further nuclear power plants should be built and that a nuclear power phase-out should be completed by 2010. , the use of renewables amounted to 26% of the energy supply in Sweden, most important being hydropower and biomass. In 2003, electricity from hydropower accounted for 53 TWh and 40% of the country's production of electricity with nuclear power delivering 65 TWh (49%). At the same time, the use of biofuels, peat etc. produced 13 TWh of electricity. Sweden is the highest ranked country in the Climate Change Performance Index.