It appears as though the crusade to determine the best alternative energy sources are seriously being looked into by lots of countries including most American cities. One validation is the signing of the Kyoto Treaty. The primary purpose of the concerned group and individuals is to decrease the greenhouse gases and pollutants.

These renewable energy sources have demonstrated to be of great aid in cutting down the amount of toxins, which are by-products of the consumption of energy. These sources also preserve most of the natural resources that people use as resources of energy. For example, after a solar panel converts the sun's rays into energy, the sun will still shine for someone else to use. What are the most popular sources of renewable energy? Here's a list to give you some basic information:

1. Solar Energy - Harnessing the sun's powerful energy is definitely not something new. Capturing the radiant light and heat from the sun has been practiced since ancient times. Since the rapid evolution of technology, we are now able to trap the sun's rays into solar cells. Since the 1950's solar cell technology has been advancing and has come quite a long way. The process turns the heat coming from the sun into electricity. Photovoltaic cells mounted on rooftops are used to heat water using the sun's rays. The water goes into a storage tank where the power is stored, ready for use. But you don't need all these scientific processes to be able to benefit from solar power. All you really have to do is open the windows and blinds on a nice sunny day to let the sunshine in.

To date, the main disadvantage of using this source is that it is limited. You cannot use it obviously on nighttime and during days when it is raining or even on cloudy days. This has been acted upon through solar power stations. But these are too expensive so there aren't too many of these stations around the globe.

2. Wind Energy - Another ancient source of power, wind energy has been harnessed by sailors, farmers and architects for many years, even documented as far back as 5,000 years ago. The energy coming from the wind supercharges the blades of the wind turbines. As this happens, electricity is produced through the use of an electrical generator. In the old days, windmills were created so that mechanical machinery could perform physical labor. This includes the pumping of water and crushing of grains that were essential in planting and farming.

Now there are large scale wind farms that produce electrical currents. The end products are then distributed to national electrical grids and small turbines owned by individuals to distribute electricity to far flung areas and homes. There are many advantages of this kind of power. The main one, of course, is that this doesn't produce any by-products that can be harmful to the environment. And we will never run out of this source of renewable energy. One of the main disadvantages of wind power is that it's never a constant speed or direction, so wind turbines have to be able to move with the direction of the wind.

3. Geothermal - Geothermal energy is energy obtained by tapping heat from the earth itself. Holes are drilled in certain regions, and the magma and radioactive decay that can be found underneath produce steam. This steam is purified and used to drive turbines. These turbines then become the power source for electric generators.

The downside to geothermal energy is the fact that it is expensive to build, and to ensure that no harmful by-products are going to be produced in the process, geothermal plants must be created accordingly. On the other hand, because the earth's crust continuously decays replenishing the heat, it is still a renewable source of energy.

4. Hydroelectricity - The use of hydroelectric power or even hydroelectricity dates back to Ancient Greece and China where they installed waterwheels in rapidly flowing rivers to turn millstones and other equipment. Hydroelectric plants today still use the same basic principles as the historical waterwheel, but with some variations. The difference is that we use the force of the water to push the turbine which in turn powers a generator thus generating electricity. The idea here is to make use of the kinetic energy of water. To make sure that there is a steady flow of power being produced, a dam has to be built to retain the water. If there is a need for more power, the gates of the dam are opened so water can be released.

There are issues with the use of hydroelectricity. Some claim that it poses a problem for fish and aquatic plants on both sides of the dam. Because the flow of water has been altered, the nutrient rich silt which helps crops grow could be affected.

5. Bio-Fuels - Bio-fuels are also a green energy source. They have been around for a very long time however just lately, people are beginning to take notice.During photosynthesis, plants grow and produce biomass. Also known as bio matter, biomass can be used directly as fuel or to produce bio-fuels. Agriculturally produced biomass fuels, such as bio-diesel, ethanol can be burned in internal combustion engines or boilers. Typically bio-fuel is burned to release its stored chemical energy. Liquid bio-fuel which is the one used in cars is a natural and renewable domestic fuel that can only be used for diesel engines. This can be made from vegetable oils mostly soy and corn. In fact diesel engines were originally created to run on vegetable oil! The nice thing about bio-fuels is that they contains no petroleum, and they are nontoxic and biodegradable.

By fueling up with bio-fuel, you decrease the pollutants in the air because it does not emit anything. Right now, it is the only fuel approved by the Environmental Protection Agency (EPA), passed every Heath-Effects Test of the Clean Air Act and meets the requirements of the California Air Resources Board (CARB).

Just by reading through the available alternative energy sources, you will be amazed at how nature works wonders. It is our responsibility to care for the environment around us and keep it clean for generations ahead of us.