In order to understand the renewable energy it is necessary to distinguish between renewable and nonrenewable resources. So, the nonrenewable resources are those that could be exhausted within a short time as a result of our exploiting them. Nonrenewable energy sources are all the fossil fuels (coal, oil (petroleum), natural gas, shale oil, tar sands, etc.) uranium(nuclear energy), and some types of geothermal energy. It is likely that most forms of nonrenewable energy will get more expensive when they are near exhaustion.
As for the Renewable Resources, they can never be consumed to completion. We have only three sources: geothermal and tidal and solar in all its aspects: wind, hydroelectric power, ocean currents, ocean thermal gradients, and biomass, and direct use of solar radiation (sunlight). In these cases the time to exhaustion depends on the life of the sun itself. The rate at which we use solar energy does not affect its lifetime. Whatever solar energy source we put into use will continue to be available, or can be soon renewed. For example, firewood can be grown indefinitely, season after season, as long as water and plant nutrients are available.
In Contrast to the case of nonrenewables, renewable energy will tend to become less expensive as the scale of its use increases. In general, though, the more renewable energy we use, the cheaper it will be, and there will always be more for succeeding generations. As an old proverb says ” A penny saved is a penny earned” .
Because of concerns over resource depletion and environmental damage, the use of renewable energy presents an option that is often preferable to the use of nonrenewable. So, there is a substantial, both economic and environmental reason and motivation for breaking our dependence on the limited fossil fuel resources and switching more and more to renewable energy resources.
Bibliographical reference: Ristinen, Robert A., Kraushaar, Jack J. (1999) “Energy and the environment”.
New York, NY: John Wiley & Sons, Inc. pp. 25-27