About 13 % of the world primary energy comes from renewable, with most of renewable energy coming from traditional biomass , like wood burning . Hydropower is the next largest renewable source, providing 2-3%, and modern technologies like geothermal, wind, solar, and marine energy together produce less than 1% of total world energy demand. The technical potential for their use is very large, exceeding all other readily available sources.
Renewable energy technologies are sometimes criticized for being unreliable or unsightly, yet the market is growing for many forms of renewable energy. Wind power has a worldwide installed capacity of 74,223 MW and is widely used in several European countries and the
While there are many large-scale renewable energy projects, renewable
technologies are also suited to small off-grid applications, sometimes in rural and remote areas, where energy is often crucial in human development.
Climate change concerns coupled with high oil prices , peak oil and increasing government support are driving increasing renewable energy legislation, incentives and commercialization. EU leaders reached agreement in principle in March that 20 percent of the bloc's energy should be produced from renewable fuels by 2020, as part of its drive to cut emissions of carbon dioxide, blamed in part for global warming . Investment capital flowing into renewable energy climbed from $80 billion in 2005 to a record $100 billion in 2006. Some very large corporations such as BP, GE, Sharp, and Shell are investing in the renewable energy sector.
Kinds of renewable energy
1. Biofuel (also called agrofuel) can be broadly defined as solid, liquid, or gas fuel consisting of, or derived from biomass . This article, however, is principally about biofuel in the form of liquid or gas transportation fuel derived from biomass. Biomass can also be used directly for heating or power. One type of biomass is wood, which is frequently used in industry, either by itself to create energy or with other combustible matter (such as coal ) to burn and create heat. (Wood d has been burned for millennia - as solids.)
Biofuel is considered a means of reducing greenhouse gas emissions and increasing energy security by providing an alternative to fossil fuels . However, In October 2007, Nobel Laureate Paul Crutzen published findings that the release of Nitrous Oxide (N2O) among the commonly used biofuels, such as biodisel from rapeseed and bioethanol from corn (maize), can contribute as much or more to global warming than fossil fuel savings do to global cooling . Crops with less N demand, such as grasses and woody coppice species have more favorable climate impacts.
Biofuels are used globally: biofuel industries are expanding in Europe, Asia and the
2. Biomass refers to living and recently dead biological material that can be used as fuel or for industrial production. Most commonly, biomass refers to plant matter grown for use as biofuel, but it also includes plant or animal matter used for production of fibers, chemicals or heat. Biomass may also include biodegradable wastes that can be burnt as fuel. It excludes organic material which has been transformed by geological processes into substances such as coal or petroleum .
Biomass is grown from several plants, including misconstrues , switch grass, hemp, corn,poplar, willow, sugarcane and oil palm. The particular plant used is usually not very important to the end products, but it does affect the processing of the raw material. Production of biomass is a growing industry as interest in sustainable fuel sources is growing.
Although fossil fuels have their origin in ancient biomass, they are not considered biomass by the generally accepted definition because they contain carbon that has been "out" of the carbon cycle for a very long time. Their combustion therefore disturbs the carbon dioxide content in the atmosphere.
Plastics from biomass, like some recently developed to dissolve in seawater, are made the same way as petroleum-based plastics, are actually cheaper to manufacture and meet or exceed most performance standards. But they lack the same water resistance or longevity as conventional plastics.
3. Geothermal power (from the greek words geo, meaning earth, and theme, meaning heat) is energy generated by heat stored beneath the Earth's surface. Prince Piero Ginori Conti tested the first geothermal generator on 4 July 1904, at the Larderello dry steam field in
4. Hydroelectricity is electricity produced by hydropower. It is a renewable source of energy, produces no waste, and does not produce carbon dioxide (CO2) which contributes to greenhouse gases. Hydroelectricity now supplies about 715,000 MWe or 19% of world electricity (16% in 2003), accounting for over 63% of the total electricity from renewable in 2005.
Although large hydroelectric installations generate most of the world's hydroelectricity, small hydro schemes are particularly popular in
At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine. Pumped storage schemes currently provide the only commercially important means of large-scale grid energy storage and improve the daily load factor of the generation system. Hydroelectric plants with no reservoir capacity are called run-of-the-river plants, since it is not then possible to store water. A tidal power plant makes use of the daily rise and fall of water due to tides; such sources are highly predictable, and if conditions permit construction of barrages and reservoirs, can also be dispatch able to generate power during high demand periods. Less common types of hydro schemes use water's kinetic energy or undimmed sources such as undershot waterwheels, the relatively recent field of hydrokinetics.
A simple formula for approximating electric power production at a hydroelectric plant is: P = hrk, where P is Power in watts, h is height in meters, r is flow rate in cubic meters per second, and k is a conversion factor of 7500 watts (assuming an efficiency factor of about 76.5 percent and acceleration due to gravity of 9.81 m/s2, and fresh water with a density of 1000 kg per cubic meter. Efficiency is often higher with larger modern turbines and may be lower with very old or small installations due to proportionately higher friction losses). Annual electric energy production depends on the available water supply. In some installations the water flow rate can vary by a factor of 10:1 over the course of a year.
5. Solar energy is energy from the Sun. This energy drives the climate and weather and supports virtually all life on Earth. Heat and light from the sun, sexy along with solar-based resources such as wind and wave power, hydroelectricity and biomass, account for most of the available flow of renewable energy.
Solar energy technologies harness the sun's energy for practical ends. These technologies date from the time of the early Greeks, Native Americans and Chinese, who warmed their buildings by orienting them toward the sun. Modern solar technologies provide heating, lighting, electricity and even flight.
Solar power is used synonymously with solar energy or more specifically to refer to the conversion of sunlight into electricity . This can be done either through the photovoltaic effect or by heating a transfer fluid to produce steam to run a generator. Solar photovoltaic provide 0.04% of the world's energy usage.
6. Tidal power, sometimes called tidal energy, is a form of hydropower that exploits the movement of water caused by tidal currents or the rise and fall in sea levels due to the tides.
Although not yet widely used, tidal power has potential for future electricity generation and is more predictable than wind energy and solar power. In
7. Wave power refers to the energy of ocean surface waves and the capture of that energy to do useful work - including electricity generation, desalination, and the pumping of water (into reservoirs). Wave power is a form of renewable energy. Though often co-mingled, wave power is distinct from the diurnal flux of tidal power and the steady gyre ofnocean currents. Wave power generation is not a widely employed technology, and no commercial wave farm has yet been established.
On December 18, 2007, Pacific Gas and Electric Company announced its support for plans to build America's first commercial wave power plant off the coast of
Plans to install three 750 kW Pelamis devices at the
The north and south temperate zones have the best sites for capturing wave power. The prevailing waterlines these zones blow strongest in winter.
8. Wind power is the conversion of wind energy into useful form, such as electricity, using wind turbines. In windmills, wind energy is directly used to crush grain or to pump water. At the end of 2006, worldwide capacity of wind-powered generators was 73.9 gig watts . Although wind currently produces just over 1% of world-wide electricity use, it accounts for approximately 20% of electricity production in Denmark , 9% in Spain, and 7% in Germany Globally, wind power generation more than quadrupled between 2000 and 2006.
Wind power is produced in large scale wind farms connected to electrical grids, as well as in individual turbines for providing electricity to isolated locations.
Wind energy is plentiful, renewable, widely distributed, clean, and reduces greenhouse gas emissions when it displaces fossil-fuel-derived electricity. The intermittency of wind seldom creates insurmountable problems when using wind power to supply up to roughly 10% of total electrical demand (low to moderate penetration), but it presents challenges that are not yet fully solved when wind is to be used for a larger fraction of demand.
