There are many sources of energy that are renewable and considered to be environmentally friendly and harness natural processes. These sources of energy provide an alternate "cleaner' source of energy, helping to negate the effects of certain forms of pollution. All of these power generation techniques can be described as renewable since they are not depleting any resource to create the energy. While there are many large-scale renewable energy projects and production, renewable technologies are also suited to small off-grid applications, sometimes in rural and remote areas, where energy is often crucial in human development.

Sources of energy are:

(i) Tidal energy.

(ii) Wave power.

(iii) Solar power.

(iv) Wind power.

(v) Hydroelectricity.

(vi) Radiant energy.

(vii) Geothermal power. 

(viii) Biomass.

(ix) Compressed Natural Gas.

(x) Nuclear power.

(a) Hydropower comes from moving water and ocean waves. Hydropower systems use the energy in flowing water for mechanical purposes or to produce electricity, Hydroelectric plants use the kinetic energy of moving water to spin the turbine generator.

(b) Biomass materials such as wood, agricultural crop wastes, fast- growing willow and switchgrass crops, animal wastes, and even garbage can be used as renewable sources of energy to generate heat and power. They also can be used as alternatives to petrochemicals in making plastics and other products. Today, biomass energy systems are very small-scale; some examples include ethanol in gasoline, and use of municipal waste to produce methane gas.

(c) Passive solar heating for buildings is a common application of renewable energy. A passive solar heating system collects energy from the sun. It uses this energy to heat a space directly, or to heat a fluid that later radiates heat to a space.

(d) Active solar systems--or photovoltaic systems--are another way of capturing the sun's energy. These systems use solar cells to directly produce electricity from solar radiation.

(e) At this time, photovoltaic systems are relatively expensive to build and maintain. They also require a back-up source of power, or batteries, to provide power when sunshine is inadequate. Because semiconductors contain toxic materials, the environmental impacts of manufacturing and disposing of solar cells and their batteries are also a concern.

(f) Solar thermal electricity is another variation on solar energy. These plants use a highly curved mirror to focus sunlight onto a pipe, concentrating the heat to boil water and create steam. That steam is then used to turn a turbine generator to make electricity.

(g) Wind power uses energy from the moving air to turn large blades on windmills. In the past the motion of the blades was used to grind flour or pump water, but now the blades turn turbines, which rotate generators in order to produce electricity.