Renewable energy sources which are naturally replenished on a human timescale such as sunlight, wind, rain, tides, waves and geothermal heat. Renewable energy sources include the sun, wind, water, geothermal energy and biomass.
Ever since 1973 oil crises, many countries have justifiably maintained an abiding interest in renewable energy sources and as a result many renewable energy programs were developed. Since then, research and development in the field were more promising and reliable. Main advantage of renewable energy is that its main ingredient is renewable and it plays crucial role in meeting environmental standards by combating global warming and other threats. At the current rate of energy consumption, the limited reserves of coal, oil, and gas may last only for 197, 40, and 56 years respectively.
Our forests on the other hand are declining due to many reasons and recent studies show that firewood demand is not the only reason for forest degradation, though it contributes significantly. Environmental health of our planet is degrading and it is losing its ecological balance. Climate change, ozone depletion, acid rain, global warming, loss of biodiversity are some of the threats to be tackled if planet earth has to survive for long time. Energy issues are the focus of all these threats and therefore it needs special attention. Renewable energy sources promise to meet all the challenges, so as to attain the sustainable development.
The principle types of renewable energies available today are:
Geo thermal energy
All the above renewable could make a major contribution to meet the present energy needs.
Energy from sun. The sun gives out 3.7 × 10^26 watt of power in to space, out of which the earth intercepted is equivalent to1.7 × 10^17 watt. Solar energy emitted by sun within three minutes is equal to the world energy consumption during a year. Photovoltaic (PV) panels use silicon cells, which transform solar radiation into direct current. The energy is used simultaneously (for example to pump water) or is stored in batteries to provide electricity. Solar energy can also be used to cook food by trapping and concentrating the sun's heat in a cooker, and to heat water or to generate steam which, in turn, can be utilized for mechanical applications. This is usually done by flat plate collectors which are exposing a large thin surface, containing a liquid, to the sun. The sun's heat can be intensified with lenses and mirrors and stored in salts and stones. Solar energy is still not viable on economic front to many developing countries therefore its use is promoted by various agencies. The World Bank has a program to install home lighting system in 200,000 homes to Indonesia. Of the 200 million Indonesian, 60 million people still rely on kerosene for lighting.
Hydropower is a well-established technology, which has been producing firm power at competitive price for about a century. It is the principal source of electric power in some 30 countries, and provides about one fifth of the world's annual electrical supply. Its power stations include some of the largest artificial structures in the
world. The dams, which are constructed during the process, are considered as most vulnerable because much
Renewable energy sources include the sun, wind, water, geothermal energy and biomass.These renewable sources are all natural occurring elements. If these sources are utilized properly we can able to produce energy in large scale without disturbing earth’s nature and not making pollution.