A natural resource is a renewable resource if it is replaced by natural processes at a rate comparable or faster than its rate of consumption by humans. Solar radiation, tides, winds and hydroelectricity are perpetual resources that are in no danger of a lack of long-term availability. Renewable resources may also mean commodities such as wood, paper, and leather, if harvesting is performed in a sustainable manner.
Some natural renewable resources such as geothermal power, fresh water, timber, and biomass must be carefully managed to avoid exceeding the world's capacity to replenish them. A life cycle assessment provides a systematic means of evaluating renewability.
The term has a connotation of sustainability of the natural environment. Gasoline, coal, natural gas, diesel, and other commodities derived from fossil fuels are non-renewable. Unlike fossil fuels, a renewable resource can have a sustainable yield.
Solar energy is the energy derived directly from the Sun. Along with nuclear energy, it is the most abundant source of energy on Earth. The fastest growing type of alternative energy, increasing at 50 percent a year, is the photovoltaic cell, which converts sunlight directly into electricity.  The Sun yearly delivers more than 10,000 times the energy that humans currently use. 
Wind power is derived from uneven heating of the Earth's surface from the Sun and the warm core. Most modern wind power is generated in the form of electricity by converting the rotation of turbine blades into electrical current by means of an electrical generator. In windmills (a much older technology) wind energy is used to turn mechanical machinery to do physical work, like crushing grain or pumping water.
Hydropower is energy derived from the movement of water in rivers and oceans (or other energy differentials), can likewise be used to generate electricity using turbines, or can be used mechanically to do useful work. It is a very common resource.
Geothermal power directly harnesses the natural flow of heat from the ground. The available energy from natural decay of radioactive elements in the Earth's crust and mantle is approximately equal to that of incoming solar energy.
Alcohol derived from corn, sugar cane, switchgrass, etc. is also a renewable source of energy. Similarly, oils from plants and seeds can be used as a substitute for non-renewable diesel. Methane is also considered as a renewable source of energy.
Techniques in agriculture which allow for minimal or controlled environmental damage qualify as sustainable agriculture. Products (foods, chemicals, biofuels, etc) from this type of agriculture may be considered "sustainable" when processing, logistics, etc. also have sustainable characteristics.
Water can be considered a renewable material (also non-renewable) when carefully controlled usage, treatment, and release are followed. If not, it would become a non-renewable resource at that location. For example, groundwater could be removed from an aquifer at a rate greater than the sustainable recharge. Removal of water from the pore spaces may cause permanent compaction (subsidence) that cannot be renewed.
A natural resource qualifies as a renewable resource if its stock (quantity) can increase over time.
Natural resources which qualify as renewable resources are, for example, oxygen, fresh water, solar energy, timber, and biomass. But they can become non-renewable resources if more of them is used than nature can reproduce in the same time at that place. For example ground water may be removed from an aquifer at a greater rate than that of new water flowing to that aquifer. Removal of water from the pore spaces may cause permanent compaction (subsidence) that cannot be reversed. Human consumption and use at sustainable levels primarily uses renewable resources versus non-renewable resources.
Renewable resources may also include goods commodities such as wood, paper and leather.
Gasoline, coal, natural gas, diesel and other commodities that come from fossil fuels are non-renewable. Some commodities, like plastics and diesel, are mostly made from fossil fuel but ways have been developed for biodegradable plastic and biodiesel made from renewable resources such as corn, soybeans and canola.
Solar power is the technology of obtaining usable energy from the light of the sun. Solar energy has been used in many traditional technologies for centuries and has come into widespread use where other power supplies are absent, such as in places far off from the national electrical grid and in space. Solar energy is currently used in a number of applications:
Wind power is the conversion of wind energy into more useful forms, usually electricity using wind turbines. As of April 2008, worldwide wind farm capacity was 100,000 megawatts (MW), and wind power produced some 1.3% of global electricity consumption, accounting for approximately 19% of electricity use in Denmark, 9% in Spain and Portugal, and 6% in Germany and the Republic of Ireland. United States is an important growth area and latest American Wind Energy Association figures show that installed U.S. wind power capacity has reached 16,800 MW, which is enough to serve 4.5 million average households.
Most modern wind power is generated in the form of electricity by converting the rotation of turbine blades into electrical current by means of an electrical generator. In windmills (a much older technology) wind energy is used to turn mechanical machinery to do physical work, like crushing grain or pumping water.
Wind power is used in large scale wind farms for national electrical grids as well as in small individual turbines for providing electricity to rural residences or grid-isolated locations. Wind energy is ample, renewable, widely distributed, clean, and works against the greenhouse effect if used to replace the use of fossil-fuel.
Hydropower is the conversion of the energy of moving water into more useful forms. Already in ancient history hydropower was used for irrigation and milling of grain and afterwards also for textile manufacture and the operation of sawmills.
The energy of moving water has been exploited for centuries; in Imperial Rome, water powered mills produced flour from grain, and in China and the rest of the Far East, hydraulically operated "pot wheel" pumps raised water into irrigation canals. In the 1830s, at the peak of the canal-building era, hydropower was used to transport barge traffic up and down steep hills using inclined plane railroads.
Direct mechanical power transmission made it necessary that industries that used hydropower had to be near the waterfall. For example, during the last half of the 19th century, many grist mills were built at Saint Anthony Falls, utilizing the 50 foot (15 metre) drop in the Mississippi River. The mills contributed to the growth of Minneapolis. Today the largest use of hydropower is for electric power generation, which allows low cost energy to be used at long distances from the watercourse.