A twentieth-century technology is photovoltaics, which turns sunlight directly into electricity. Wind power is another ancient energy source that has moved into the modern era. Advanced aerodynamics research has developed wind turbines that can produce electricity at a lower cost than power from polluting coal plants. Geothermal energy taps into the heat under the earth's crust to boil water. The hot water is then used to drive electric turbines and heat buildings.
Hydroelectric power uses the force of moving water to produce electricity.
Hydropower is one of the main suppliers of electricity in the world, but most often in the form of large dams that disrupt habitats and displace people. Coal is the largest source of fuel for electricity production, and also the largest source of environmental harm. Coal provides 54 percent of the US electricity supply. Oil is used primarily for transportation fuels, but also for power production, heat and as a feedstock for chemicals. The US imports over half of the oil we use, more than ever before.