Hydro-electric power stations require water to flow over turbines and so locations are a big limiting factor. They do not pollute, however, lakes created behind the dams built, so that the water level is enough to turn the turbines, will destroy whatever is on the land behind the dam by submerging it.

Wind turbine power(windmills, ect) are clean sources of fuel, however, their power generation is completely dependent on the wind. On a calm day, they are generating almost no power. Cost to build is the biggest turnoff to them.

Geothermal energy is rather costly, and functions best at places where the earth is hot near the surface, such as near hotsprings, though it will work just about anywhere.

Solar power is an energy source that is expensive but very clean, using the sun to provide power. Some require solar cells to use this energy. Some places have made large solar towers surrounded by mirrors to focus the sun’s light on one point of the tower, greatly increasing the heat in the tower, and using that heat to produce energy.

Nuclear fission power(Current nuclear power plants use this) require a fissiable energy source, such as uranium, which is not easlily accessable. No pollution, though a chance of a meltdown exists, even though higher safety standards and technology have minimized these odds. Safely storing/desposing of depleted uranium is still a controversial issue as spent cores will still be radioactive 10000 years after they are used up.

Nuclear Fusion is an energy source, though one still better left to science fiction writers for the near future. Tremendous amounts of energy is required for even the smallest amount of fusion to occur. While fusion produces an inexhaustable supply of energy, and massive amounts of it(such as the sun), however, current technologies require far more energy to produce fusion than the energy that fusion releases.