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A renewable resource is a resource which is replaced naturally and can be used again.
Examples are: oxygen, fresh water, solar energy, timber, and biomass. They may become non-renewable resources if they are used faster than nature can replace them. For example, ground water may be removed from an aquifer faster than new water replacing it. Then wells or even streams can run dry. Timber (trees) are another example, it can take 25 years or more for a tree to grow big enough to be used for lumber or paper. So it is only a renewable resource if new trees grow up and replace them as fast as the older trees are cut.
Renewable resources may also include goods commodities such as wood, paper and leather.
Gasoline, coal, natural gas, diesel, plastics and other things that come from fossil fuels are non-renewable. They take millions of years to be made, and cannot be renewed in our lifetime or even a nation's lifetime (they are called fossil fuels because they are as old as fossils). Plastic can be recycled, and ways have been developed to make biodegradable plastic and biodiesel and other fuels from renewable resources such as corn, sugar cane, soybeans and canola.
A problem with fossil fuels is the pollution and global warming gases they produce. Renewable resources are usually much cleaner. But they can also cost more. New technology for renewable resources is helping to make them cheaper. And now even fossil fuels are becoming harder to find and more expensive. This combination means that renewable resources are making more sense than ever, and this is a growing field. From 2008 to 2012, the U.S. doubled renewable generation from wind, solar, and geothermal sources, and America is now home to some of the largest wind and solar farms in the world.
Types of renewable resources
Solar power is the technology of obtaining usable energy from the light of the sun. Solar energy has come into 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:
- Heat (hot water, building heat, solar cooking)
- Electricity generation (photovoltaics and solar thermal, Stirling and other heat engines)
- Desalination of seawater (taking the salt out so it can be used for drinking or growing crops).
Wind power is using the energy of wind to do something useful. Wind has been used since ancient times to move ships, and for hundreds of years to pump water or grind corn and grain into flour, now it is usually changed into electricity using wind turbines.
In 2008, worldwide wind farm capacity was 100,000 megawatts (MW), and wind power produced 1.3% of all the world's electricity. Wind makes about 19% of electricity use in Denmark, 9% in Spain and Portugal, and 6% in Germany and the Republic of Ireland. The United States is an important market for makers of wind mills, and it is rapidly growing. In 2007, the U.S. had enough windmills to produce 16,800 MW, enough for 4.5 million average households. In 2012 alone, the U.S. added 13,000 MWs, and in total could produce 60,000 MWs (60 gigawatts) a year.
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 turbines for providing electricity to a farm house or off-grid locations. Wind energy is common, renewable, usable in many places, clean, and works against the greenhouse effect if used to replace fossil-fuels.
But they have some problems. Some people do not like the tall towers that can be seen from far away, and close to houses they can make a flickering shadow and have a small amount of noise. Some of the early wind farms were built where birds migrated every year, and they had small, fast-spinning blades that often killed birds. Some people still think all wind farms do that, but newer wind turbines are much bigger, with slower-moving blades and do not have that problem.
Wind mills do not make power when the wind is stopped or just a light breeze, so back-up power is still needed, or electricity needs to be moved from a distant place where the wind is blowing. Another idea is to put the turbines on kites, and fly them very high where the wind is always blowing.
Hydropower is changing the energy of moving water into more useful forms. Even in ancient history hydropower was used for irrigating crops and milling of grain into flour, and later for textile manufacture (making cloth) and running sawmills to cut wood.
It was used in Ancient Rome for water powered mills, and in China and the rest of the Far East for "pot wheel" pumps that raised water into irrigation canals. In the 1830s, at the peak of building canals, hydropower was used to move barge traffic up and down steep hills using inclined plane railroads.
Direct mechanical power transmission meant that industries that used water power had to be near the water, particularly a waterfall. For example, during the late 1800's, many gristmills were built at Saint Anthony Falls, using the 50 foot (15 metre) drop in the Mississippi River. The mills helped Minneapolis grow.
Today the largest use of hydropower is for a dam that can use the falling water to make electricity. This electricity can be moved hundreds of miles through wires, so industry no longer needs to be very close to the water for power.
Geothermal energy uses the heat from deep underground to make electricity. It can be used to produce steam which goes up a pipe, which then pushes a turbine. It is best used in places where the Earth's crust is not real thick. In the United States, most of the western states have areas where this works. California makes the most geothermal energy. Iceland uses the most geothermal energy (per person) of any country in the world.
Once it is built, it is clean energy, but it requires deep wells. These areas often have volcanoes or earthquakes in the area, and sometimes adding or removing water deep underground might be enough to cause an earthquake. Some small earthquakes may have been caused this way.
Biomass includes sawdust and other leftover parts of trees or lumber. It can also be grease and food waste, straw, and plants grown for energy. Some of this is burned to make electricity, some is made into biogas,biofuel, like ethanol as a replacement for gasoline. Ethanol might be a big renewable resource in the future. It is already widely used in the United States and Brazil. In the U.S. it is made from corn, which uses about as much energy as it makes. But there could be ways to improve it.
- "Record Year for Wind". U.S. Dept. of Energy. http://energy.gov/articles/record-year-american-wind-industry. Retrieved 25 March 2013.
- Wind Power Continues Rapid Rise
- World Wind Energy Association (2008) Wind turbines generate more than 1 % of the global electricity
- New report: a complete analysis of the global offshore wind energy industry and its major players
- Installed U.S. Wind Power Capacity Surged 45% in 2007
- "Flying Wind Turbines". National Geographic. http://news.nationalgeographic.com/news/energy/2012/09/pictures/120924-flying-wind-turbines/. Retrieved 25 March 2013.
- "How Geothermal Energy Works". Union of Concerned Scientists. http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/how-geothermal-energy-works.html. Retrieved 25 March 2013.
- "Geothermal in Iceland". Iceland National Energy Authority. http://www.nea.is/geothermal. Retrieved 25 March 2013.
- "New Safeguards for Geothermal". NY Times. http://www.nytimes.com/2010/01/16/science/earth/16alta.html?ref=geothermalpower&_r=0. Retrieved 25 March 2013.