Renewable resources, whether they are material or energy, are natural resources which, due to natural characteristics or due to the production of man, are renewed over time (at a higher, or equal, renewal rate than the rate of consumption/use) and can be considered inexhaustible, or may be available for use by humans almost indefinitely. A renewable resource is also said to be “sustainable” if its rate of regeneration is equal to or higher than the rate of use.
As renewable resources are also an energy source, there is a wide range of different types of renewable energy sources such as wind, solar, hydropower, geothermal, biomass, and biofuels. Wind and hydroelectric power are the direct results of differential heating of the Earth’s surface which leads to air moving about (wind) and precipitation forming as the air is lifted. Solar energy is the direct conversion of sunlight using panels or collectors. Biomass energy is stored sunlight contained in plants. Other renewable energies that do not depend on sunlight are geothermal energy, which is a result of radioactive decay in the crust combined with the original heat of accreting the Earth, and tidal energy, which is a conversion of gravitational energy. It is useful to highlight how the forms of energy present on our planet (except nuclear energy, geothermal energy, and tidal energy) almost all originate from solar radiation, in fact:
- without the Sun there would be no wind, which is caused by the irregular heating of air masses, and with it wind energy;
- biomass energy can be considered chemically stored solar energy, through the process of chlorophyll photosynthesis;
- hydroelectric energy, which uses waterfalls, would not exist without the water cycle from evaporation to rain, triggered by the Sun;
- fossil fuels (coal, oil, and natural gas) derive from the sun’s energy stored in the biomass millions of years ago through the process of chlorophyll photosynthesis.
A non-renewable resource is a natural resource that is used up faster than it can be made by nature. It cannot be produced, grown, or generated on a scale which can sustain how quickly it is being consumed. Once it is used up, there is no more available for the future. Fossil fuels (such as coal, petroleum, and natural gas), types of nuclear power (uranium), and certain examples. Resources such as timber (when harvested sustainably) or metals (which can be recycled) are considered renewable resources. Non-renewable resources are also called exhaustible resources.