Renewable energy resources are natural resources which renew themselves as the result of the input of solar energy, and much less so because of energy generated by the Earth's core. The annual amount of solar energy the Earth's surface receives from the sun is the equivalent of 15,000 times the world's primary energy demand. Renewable energy resources include solar energy, wind energy, wave and tidal energy, hydroenergy, biomass energy and geothermal energy. They are renewable as long as their use is below or at the rate at which they replenish or renew themselves.
Renewable energy technologies like wind, solar and bioenergy can also help reduce the emissions of heat-trapping gases that are causing global warming, as well as reducing smog-forming pollution that fossil-fuel burning power plants emit.
These facts clearly indicate that the use of renewable energy resources is not only desirable but necessary. Their greater implementation has been limited in part by technological and financial drawbacks, but developments in renewable energy in the past several decades have led to significant cost reductions in these technologies. Some renewable forms of energy already cost no more than fossil fuels and virtually all cost less than nuclear power.
This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities. Agenda 21 recommends: formulating national action programmes to promote integrated development of energy saving and renewable energy technologies particularly for the use of solar, hydro, wind and biomass sources; support for developing countries in implementing national energy programmes in order to achieve widespread use of energy saving and renewable energy technologies, particularly the use of solar, wind, biomass and hydro sources.
Renewable generated electricity, notably produced via hydro, wind, solar, biomass and photovoltaic sources, has been rapidly increasing in the EU in recent years; 15-30% per year excluding large hydro since 1990. This trend is strongly expected to continue.
In the USA, consumption of energy from renewable sources, fell sharply in 2001, to the lowest level in more than 12 years, and accounting for only 6 percent of the energy consumed in the country. Much of the decline was attributed to to a drought that cut generation of hydroelectric power by 23 percent. Another factor is that solar equipment was being retired faster than new equipment was being built. This was despite an increase in the number of solar collectors for uses like warming swimming pools, and an increase in the use of photovoltaic cells, which generate electricity with sunlight. Biomass, including burning of wood or similar renewable products to produce energy and the use of alcohol fuels, declined nearly 2 percent. The use of wind power grew more than 3 percent. Of the renewables, biomass accounted for 50.4 percent of the total and hydroelectric for 41.9 percent. The remainder was from the sun, the wind and geothermal sources.
2. Clean electricity sources are available throughout United States. For example, Illinois has the technical potential to generate all of its current electricity needs from renewable power alone.