How does a geothermal power station work and how does it compare with a fossil fuelled power station?

A geothermal power plant works by pumping a material that transfers heat energy well through pipes drilled deep into the earth's crust. As the material (usually water in geothermal furnaces in private citizens' homes) is pumped through these pipes, it equilibrates with the temperature of the surrounding earth. During the hot months, the water is hotter at the surface than the earth, so the water carries heat into the earth where it is absorbed and the water cools. During the cold months, the earth is hotter, so the water is cold when it enters the earth and picks up heat to carry back to the surface. In the power plant, the heat differential causes a turbine to rotate, which then generates power.

In contrast, a fossil fuel power plant works exclusively by burning fuel (coal, natural gas, etc.). This heat is used to boil water into steam, which is then used to turn a turbine to generate power.