Renewable energy is somewhat of a catch all phrase. It refers not to one energy production method, but to many types that have one thing in common. They all use an energy resource that is freely available and does not run out per se. Let's take a look.

Solar Energy ? Solar energy is considered a renewable energy source because it uses the power of the sun to produce electricity and heat. Since the sun isn't going to burn out any time soon, it is a free power resource for the next four or five billion years.

Wind Power ? Wind power is actually a type of solar power. Wind is produced when the sun heats of different surface areas at different rates. The air over hotter surfaces rises and cooler air rushes in to fill the gap. This is wind. As long as the sun is shining, we will have wind. We can harness wind for electrical production through turbines. The wind turns the blades of the turbines, which crank a generator that puts out electricity. Wind power is currently the fastest growing renewable energy platform in the United States.

Hydropower ? Hydropower is electricity generated by damming a river. Turbines are built into the dam. Much like wind power, water flows down through the dam because of gravity and spins the turbine fans as it passes. This cranks a generator, which produces electricity. Hydropower currently accounts for 10 percent of the electricity production in the US, but is losing popularity as building dams is very expensive.

Biopower ? The great hope of President Bush, biopower is based on the idea of using organic material to produce fuel for cars, heating and so on. It is better than using fossil fuels, but has some serious disadvantages. Ethanol, for instance, can help replace gasoline, but it produces a ton of smog. Processing organic materials also takes nearly as much energy as it produces in the form of fuel and such. All and all, this is one of the weaker renewable energy resources.

Geothermal ? This renewable resource works by capturing the steaming water temperatures in the earth's crust. If temperatures reach 240 degrees, the inherent energy can be converted to electricity. Geothermal is a great idea with limited application. The problem? It is not readily available. In the United States, only California, Hawaii, Nevada and Utah can support geothermal plants.

Renewable energy is definitely the wave of the future. Sooner or later, we are going to have to convert to these energy platforms. With huge oil companies buying up solar and wind power companies, it looks like the future may be sooner than we think.