In 1974, the United States Department of Energy established the National Renewable Energy Laboratory (NREL), however, it did not go into use until 1977. Since 1977, NREL has been investigating and putting money into the research and development of a variety of different renewable energy sources.

The list of renewable energy options has only grown in recent years, and according to renewableenergyworld.com, there are at least seven different types of renewable energy. These include: solar power, wind power, geothermal, bio-energy, hydro-power, ocean power, and hydrogen fuel cells.

The top three sources of renewable energy according to an article from About Environment includes: solar energy, wind energy, and hydro-power.

Solar energy harnesses the natural and abundant power of the sun with solar panels. However, the problem with solar energy is the expense of the solar panels. A single solar system that can power a small to medium sized home can cost upwards of $25,000.

Wind energy also harnesses natural energy of wind. This energy source is very ineffective in areas where wind is scarce. Also, wind turbines, the windmills that capture and convert the wind energy into useful electricity are less expensive than solar panels, however, are still on the upward slant which costs as much as $1,200 for a 600-watt tower.

Moving water is the source that generates hydro-power. On its largest scale, hydro-power is showcased in dams. The largest concrete dam in the United States today is the Hoover dam standing at 726 feet tall. Dams are large concrete blockages in rivers that allow small amounts of water through to turn turbines within the dams; these turbines turn and convert the energy of the flowing water into electricity, much like the system of wind turbines collecting their energy.

According to a poll taken by the Program on International Policy Attitude at the University of Maryland, 66 percent of people polled were in favor of the national government requiring utilities to use more renewable energy sources.

These energy sources are all cleaner than fossil fuels. Although they each have their downsides, the continued research of these fuels may help to reduce pollution throughout the world.

Connor Sample is Variety Editor for The Spartan Speaks