Referát: Geothermal energy, geothermal power plants

Most countries throughout the world use oil, gas and coal as their principal sources of energy. The use of these fossil fuels to produce energy, however, is source of controversy.
On the one hand, fossil fuels are relatively abundant (of late years their is less and less) and are cheap sources of energy.
On the other hand, the burning of fossil fuels to produce energy is the principal cause of acid rain and global warming.
In order to reduce the environmental damage caused by the burning of fossil fuels, scientists and engineers have developing alternative energy sources.