Nuclear Power Most of the world's electricity is generated by either thermal or hydroelectric power plants. Thermal power plants use fuel to boil water which makes steam. The steam turns turbines that generate electricity. Hydroelectric power plants use the great force of rushing water from a dam or a waterfall to turn the turbines. The majority of thermal power plants burn fossil fuels because thermal power plants are cheaper to maintain and have to meet less of the governments requirements compared to nuclear power plants. Fossil fuels are coal and oil. The downfall of using fossil fuels is that they are limited.