Renewable energy

World renewable energy in 2005 (except 2004 data for items marked* or **). Enlarge image to read exclusions.

Renewable energy is energy derived from resources that are regenerative or for all practical purposes cannot be depleted. For this reason, renewable energy sources are fundamentally different from fossil fuels, and do not produce as many greenhouse gases and other pollutants as fossil fuel combustion.

Mankind's traditional uses of wind, water, and solar energy are widespread in developed and developing countries; but the mass production of electricity using renewable energy sources has become more commonplace recently, reflecting the major threats of climate change due to pollution, exhaustion of fossil fuels, and the environmental, social and political risks of fossil fuels and nuclear power.

Many countries and organizations promote renewable energies through tax incentives and subsidies.

Renewable energy use

Renewable energy flows involve natural phenomena such as sunlight, wind, tides and geothermal heat. Each of these sources has unique characteristics which influence how and where they are used.

Energy sources

The majority of renewable energy technologies are directly or indirectly powered by the Sun. The Earth-Atmosphere system is in equilibrium such that heat radiation into space is equal to incoming solar radiation, the resulting level of energy within the Earth-Atmosphere system can roughly be described as the Earth's "climate." The hydrosphere (water) absorbs a major fraction of the incoming radiation. Most radiation is absorbed at low latitudes around the equator, but this energy is dissipated around the globe in the form of winds and ocean currents. Wave motion may play a role in the process of transferring mechanical energy between the atmosphere and the ocean through wind stress . Solar energy is also responsible for the distribution of precipitation which is tapped by hydroelectric projects, and for the growth of plants used to create biofuels.

Wind power

Example of a traditional windmill

Main article: Wind power

Airflows can be used to run wind turbines and some are capable of producing 5 MW of power. Turbines with rated output of 1.5-3 MW have become the most common for commercial use. The power output of a turbine is a function of the cube of the wind speed, so as wind speed increases, power output increases dramatically. Areas where winds are stronger and more constant, such as offshore and high altitude sites, are preferred locations for wind farms.

Wind power is the fastest growing of the renewable energy technologies. Over the past decade, global installed maximum capacity increased from 2,500 MW in 1992 to just over 40,000 MW at the end of 2003, at an annual growth rate of near 30%. Due to the intermittency of wind resources, most deployed turbines in the EU produce electricity an average of 25% of their rated maximum power, (a load factor of 25%).[1], but under favourable wind regimes some reach 35% or higher. The load factor is generally higher in winter. It would mean that a typical 5 MW turbine in the EU would have an average output of 1.7 MW.

Globally, the long-term technical potential of wind energy is believed to be five times current production global energy consumption or 40 times current electricity demand. This could require large amounts of land to be utilized for wind turbines, particularly in areas of higher wind resources. Offshore resources experience mean wind speeds of ~90% greater than that of land, so offshore resources could contribute substantially more energy. This number could also increase with higher altitude ground-based or airborne wind turbines.

Wind strengths near the Earth's surface vary and thus cannot guarantee continuous power unless combined with other energy sources or storage systems. Some estimates suggest that 1,000 MW of conventional wind generation capacity can be relied on for just 333 MW of continuous power. While this might change as technology evolves, advocates have suggested incorporating wind power with other power sources, or the use of energy storage techniques, with this in mind. It is best used in the context of a system that has significant reserve capacity such as hydro, or reserve load, such as a desalination plant, to mitigate the economic effects of resource variability.

Wind power is renewable and produces no greenhouse gases during operation, such as carbon dioxide and methane.

Water power

Main article: Water power

Energy in water (in the form of motive energy or temperature differences) can be harnessed and used. Since water is about a thousand times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy.

There are many forms of water energy:

• Hydroelectric energy is a term usually reserved for large-scale hydroelectric dams.
• Micro hydro systems are hydroelectric power installations that typically produce up to 100 kW of power. They are often used in water rich areas as a Remote Area Power Supply (RAPS). There are many of these installations around the world, including several delivering around 50 kW in the Solomon Islands.
• Tidal power captures energy from the tides in a vertical direction. Tides come in, raise water levels in a basin, and tides roll out. Around low tide, the water in the basin is discharged through a turbine.
• Tidal stream power captures energy from the flow of tides, usually using underwater plant resembling a small wind turbine. Tidal stream power demonstration projects exist, but large scale development requires additional capital.
• Wave power uses the energy in waves. The waves will usually make large pontoons go up and down in the water, leaving an area with reduced wave height in the "shadow". Wave power demonstration projects exist, but large scale development requires additional capital.
• Ocean thermal energy conversion (OTEC) uses the temperature difference between the warmer surface of the ocean and the colder lower recesses. To this end, it employs a cyclic heat engine. OTEC has not been field-tested on a large scale.
• Deep lake water cooling, although not technically an energy generation method, can save a lot of energy in summer. It uses submerged pipes as a heat sink for climate control systems. Lake-bottom water is a year-round local constant of about 4 °C.
• Blue energy is the reverse of desalination. A difference in salt concentration exists between seawater and river water. This gradient can be utilized to generate electricity by separating positive and negative ions by ion-specific membranes. Brackish water is produced. This form of energy is in research; costs are not the issue, and tests on pollution of the membrane are in progress. At this moment it is predicted that if everything works out, 33% of the electricity needs in the Netherlands could be covered with this system.(2005)

Solar energy use

The solar panels (photovoltaic arrays) on this small yacht at sea can charge the 12 V batteries at up to 9 amperes in full, direct sunlight.

Main article: Solar power

In this context, "solar energy" refers to energy that is collected from sunlight. Solar energy can be applied in many ways, including to:

• Generate electricity using photovoltaic solar cells.
• Generate electricity using concentrated solar power.
• Generate electricity by heating trapped air which rotates turbines in a Solar updraft tower.
• Heat buildings, directly, through passive solar design.
• Heat foodstuffs, through solar ovens.
• Heat water or air for domestic hot water and space heating needs using solar-thermal panels.
• Heat and cool air through use of solar chimneys.

Biofuel

Main article: Biofuel

Plants use photosynthesis to grow and produce biomass. Also known as biomatter, biomass can be used directly as fuel or to produce liquid biofuel. Agriculturally produced biomass fuels, such as biodiesel, ethanol and bagasse (often a by-product of sugar cane cultivation) can be burned in internal combustion engines or boilers. Typically biofuel is burned to release its stored chemical energy. Research into more efficient methods of converting biofuels and other fuels into electricity utilizing fuel cells is an area of very active work.

Liquid biofuel

Liquid biofuel is usually bioalcohol such as ethanol, biodiesel and straight vegetable oil. Biodiesel can be used in modern diesel vehicles with little or no modification to the engine and can be made from waste and virgin vegetable and animal oil and fats (lipids). Virgin vegetable oils can be used in modified diesel engines. In fact the Diesel engine was originally designed to run on vegetable oil rather than fossil fuel. A major benefit of biodiesel is lower emissions. The use of biodiesel reduces emission of carbon monoxide and other hydrocarbons by 20 to 40 percent. In some areas corn, cornstalks, sugarbeets, sugar cane, and switchgrasses are grown specifically to produce ethanol (also known as alcohol) a liquid which can be used in internal combustion engines and fuel cells. Ethanol is being phased into the current energy infrastructure. E85 is a fuel composed of 85% ethanol and 15% gasoline that is sold to consumers.

In the future, there might be bio-synthetic liquid fuel available. It can be produced by the Fischer-Tropsch process, also called Biomass-To-Liquids (BTL).

Solid biomass

Direct use is usually in the form of combustible solids, either wood, the biogenic portion of municipal solid waste or combustible field crops. Field crops may be grown specifically for combustion or may be used for other purposes, and the processed plant waste then used for combustion. Most sorts of biomatter, including dried manure, can actually be burnt to heat water and to drive turbines.

Sugar cane residue, wheat chaff, corn cobs and other plant matter can be, and is, burnt quite successfully. The net Carbon Dioxide emissions that are added to the atmosphere by this process are only from the fossil fuel that is consumed to plant, fertilize, harvest and transport the biomass. Processes to grow perenials such as switchgrass, miscanthus, and willow, field pelletize and co-fire with coal for electricity generation are being studied and appear to be economically viable. [2] Co-firing this cellulosic biomass with coal to make electricity is more effective for reducing carbon dioxide emmissions to the atmosphere than using it to make ethanol.

Solid biomass can also be gasified, and used as described in the next section.

Biogas

Main articles: Biogas and Anaerobic digestion

Biogas can easily be produced from current waste streams, such as: paper production, sugar production, sewage, animal waste and so forth. These various waste streams have to be slurried together and allowed to naturally ferment, producing methane gas. This can be done by converting current sewage plants into biogas plants. When a biogas plant has extracted all the methane it can, the remains are sometimes better suitable as fertilizer than the original biomass.

Alternatively biogas can be produced via advanced waste processing systems such as mechanical biological treatment. These systems recover the recyclable elements of household waste and process the biodegradable fraction in anaerobic digesters.

Renewable natural gas is a biogas which has been upgraded to a quality similar to natural gas. By upgrading the quality to that of natural gas, it becomes possible to distribute the gas to the mass market via gas grid.

Geothermal energy

Main article: Geothermal energy

Geothermal energy is energy obtained by tapping the heat of the earth itself, usually from kilometers deep into the Earth's crust. It is expensive to build a power station but operating costs are low resulting in low energy costs for suitable sites. Ultimately, this energy derives from the radioactive decay in the core of the Earth, which heats the Earth from the inside out.

File:Bjarnarflag Geothermal Station.jpg

Bjarnarflag Geothermal Station in northeast Iceland

Three types of power plants are used to generate power from geothermal energy: dry steam, flash, and binary. Dry steam plants take steam out of fractures in the ground and use it to directly drive a turbine that spins a generator. Flash plants take hot water, usually at temperatures over 200°C, out of the ground, and allows it to boil as it rises to the surface then separates the steam phase in steam/water separators and then runs the steam through a turbine. In binary plants, the hot water flows through heat exchangers, boiling an organic fluid that spins the turbine. The condensed steam and remaining geothermal fluid from all three types of plants are injected back into the hot rock to pick up more heat. This is why geothermal energy is viewed as sustainable. The heat of the earth is so vast that there is no way to remove more than a small fraction even if most of the world's energy needs came from geothermal sources.

The geothermal energy from the core of the Earth is closer to the surface in some areas than in others. Where hot underground steam or water can be tapped and brought to the surface it may be used to generate electricity. Such geothermal power sources exist in certain geologically unstable parts of the world such as Iceland, New Zealand, United States, the Philippines and Italy. The two most prominent areas for this in the United States are in the Yellowstone basin and in northern California. Iceland produced 170 MW geothermal power and heated 86% of all houses in the year 2000 through geothermal energy. Some 8000 MW of capacity is operational in total.

By the end of 2005 worldwide use of geothermal energy for electricity had reached 9.3 GWs, with an additional 28 GW used directly for heating [3]. If heat recovered by ground source heat pumps is included, the non-electric use of geothermal energy is estimated at more than 100 GWt (gigawatts of thermal power) and is used commercially in over 70 countries [4]. During 2005 contracts were placed for an additional 0.5 GW of capacity in the United States, while there were also plants under construction in 11 other countries [5].

Small scale geothermal heating can also be used to directly heat buildings: there are many names for this technology including "Ground Source Heat Pump" technology, Earth Energy and "Geoexchange".

Renewable energy commercialization

Wind power market strengthens

The Global Wind Energy Council (GWEC) has released its annual figures for 2006. These figures, which include wind energy developments in more than 70 countries around the world, show that 2006 saw the installation of 15,197 megawatts (MW), taking the total installed wind energy capacity to 74,223 MW, up from 59,091 MW in 2005. [6]

Despite constraints facing supply chains for wind turbines, the annual market for wind continued to increase at the rate of 32% following the 2005 record year, in which the market grew by 41%. This development shows that the global wind energy industry is responding fast to the challenge of manufacturing at the required level, and manages to deliver sustained growth. [7]

In terms of economic value, the wind energy sector has now become firmly installed as one of the important players in the energy markets, with the total value of new generating equipment installed in 2006 reaching €18 billion, or US$23 billion. [8]

The countries with the highest total installed capacity are Germany (20,621 MW), Spain (11,615 MW), the USA (11,603 MW), India (6,270 MW) and Denmark (3,136). Thirteen countries around the world can now be counted among those with over 1000 MW of wind capacity, with France and Canada reaching this threshold in 2006. [9]

In terms of new installed capacity in 2006, the US continued to lead with 2,454 MW, followed by Germany (2,233 MW), India (1,840 MW), Spain (1,587 MW), China (1,347 MW) and France (810 MW). This development shows that new players such as France and China are gaining ground. [10]

EPA uses onsite renewable technologies

To promote energy efficiency and environmentally sensitive energy generation, EPA facilities in the United States are using renewable energy technologies to supplement or replace a large portion of their energy requirements at the following facilities:

• Ada, Oklahoma (geothermal heat pump)
• Ann Arbor, Michigan (fuel cell)
• Chicago, Illinois, Regional Office (photovoltaic array)
• Corvallis, Oregon (photovoltaic array)
• Edison, New Jersey (solar water heating)
• Gulf Breeze, Florida (solar lighting)
• Golden, Colorado (wind power and transpired solar collector)
• Manchester, Washington (wind power)
• Research Triangle Park, North Carolina (photovoltaic solar panels and street lights) [11]

Wave farms expand

Portugal claims the world's first commercial wave farm, the Aguçadora Wave Park near Póvoa de Varzim, established in 2006. The farm will initially use three Pelmis P-750 machines generating 2.25 MW. [12][13] Initial costs are put at 8.5 million euro. Subject to successful operation, a further 70 million euro is likely to be invested before 2009 on a further 28 machines to generate 525 MW.[14]

Funding for a wave farm in Scotland was announced on February 20, 2007, at a cost of over 4 million pounds, as part of a £13 million funding packages for marine power in Scotland. The farm will be the world's largest with a capacity of 3MW generated by four Pelamis machines.[15]

New generation of solar thermal plants

Construction has begun on the largest solar thermal power plant to be built in 15 years, in Boulder City, Nevada.

The 64MW Nevada Solar One power plant will generate enough power to meet the electricity needs of about 40,000 households and follows in the steps of the 354MW solar thermal power plants located in California’s Mojave Desert. While California’s solar plants have generated billions of kilowatt hours of electricity for the past two decades, the Nevada Solar One plant will use new technologies to capture even more energy from the sun. [16]

High energy prices have triggered increased interest in renewable energy technologies. In his State of the Union address early in 2006, President Bush said the United States needs to reduce its "addiction" to oil and called for more investment in solar and other renewable energy technologies. [17]

The California Solar Initiative

As part of Governor Arnold Schwarzenegger's Million Solar Roofs Program, California has set a goal to create 3,000 megawatts of new, solar-produced electricity by 2017 - moving the state toward a cleaner energy future and helping lower the cost of solar systems for consumers. [18]

The California Solar Initiative offers cash incentives on solar systems of up to $2.50 a watt. These incentives, combined with federal tax incentives, can cover up to 50 percent of the total cost of a solar system. [19]

Criticisms and responses

Critics suggest that some renewable energy applications may create pollution, be dangerous, take up large amounts of land, or be incapable of generating a large net amount of energy. Proponents advocate the use of "appropriate renewables", also known as soft energy technologies, as these have many advantages.

Availability

There is no shortage of solar-derived energy on Earth. Indeed the storages and flows of energy on the planet are very large relative to human needs.

• The amount of solar energy intercepted by the Earth every minute is greater than the amount of energy the world uses in fossil fuels each year.
• Tropical oceans absorb 560 trillion gigajoules (GJ) of solar energy each year, equivalent to 1,600 times the world’s annual energy use.
• The energy in the winds that blow across the United States each year could produce more than 16 billion GJ of electricity—more than one and one-half times the electricity consumed in the United States in 2000.
• Annual photosynthesis by the vegetation in the United States is 50 billion GJ, equivalent to nearly 60% of the nation’s annual fossil fuel use.

Yet a recurring criticism of renewable sources is their intermittent nature. But a variety of renewable sources in combination can overcome this problem. As Amory Lovins explains:

"Stormy weather, bad for direct solar collection, is generally good for windmills and small hydropower plants; dry, sunny weather, bad for hydropower, is ideal for photovoltaics. [20]

The challenge of variable power supply may be further alleviated by energy storage. Available storage options include pumped-storage hydro systems, batteries, hydrogen fuel cells, and thermal mass. Initial investments in such energy storage systems can be high, although the costs can be recovered over the life of the system.

Wave energy is continuously available, although wave intensity varies by season. A wave energy scheme installed in Australia generates electricity with an 80% availability factor.

Reliability

Renewable energy sources are often dismissed as unreliable. Yet a diversity of renewable sources, each serving fewer and nearer users, would also greatly restrict the area blacked out if a grid connecting them failed. And when renewable energy sources do fail, they generally fail for shorter periods than do large power plants. [21]

Our complex, interdependent systems for the production and delivery of energy are vulnerable to simple but devastating acts of sabotage. More efficient, diverse, dispersed, renewable energy systems can make major failures impossible. [22]

Storage of energy from renewable energy systems can also contribute to improved reliability.

Aesthetics

Some people dislike the aesthetics of large solar-electric installations outside cities. However, methods and opportunities exist to deploy these renewable technologies in an efficient and aesthetically pleasing way: fixed solar collectors can double as noise barriers along highways; tremendous roadway, parking lot, and roof-top area is available already (and rooftops could even be replaced totally by solar collectors); amorphous photovoltaic cells can be used to tint windows and produce energy, etc.

Environmental impacts

While most renewable energy sources do not produce pollution directly, the materials, industrial processes, and construction equipment used to create them may generate waste and pollution. Some renewable energy systems actually create environmental problems. For instance, older wind turbines can be hazardous to flying birds.

Another environmental issue, particularly with biomass and biofuels, is the large amount of land required to harvest energy, which otherwise could be used for other purposes or left as undeveloped land. However, it should be pointed out that these fuels may reduce the need for harvesting non-renewable energy sources, such as vast strip-mined areas and slag mountains for coal, safety zones around nuclear plants, and hundreds of square miles being strip-mined for oil sands.

Hydroelectric Dams

Building a dam often involves flooding large areas of land, which can change water quality and habitats immensely, with risks to wildlife. For example, since damming and redirecting the waters of the Platte River in Nebraska for agricultural and energy use, many native and migratory birds such as the Piping Plover and Sandhill Crane have become increasingly endangered.

Hydroelectric dams can have a significant impact on aquatic life. For example, dams may create barriers for migrating fish, as has occurred in the Pacific Northwest where salmon populations have been affected. Large-scale hydroelectric dams, such as the Aswan Dam and the Three Gorges Dam, have created environmental problems both upstream and downstream. Hydroelectric power is now difficult to site in developed nations because most major sites within these nations are either already being exploited or are unavailable for other reasons such as environmental considerations.

The reservoir created for hydroelectric dams may initially produce significant amounts of carbon dioxide and methane from rotting vegetation. In some cases they may produce more of these greenhouse gases than power plants running on fossil fuels. [23] However, once this vegetation is gone, no additional greenhouse gases are produced.

Failures of large dams, while rare, are potentially serious — the Banqiao Dam failure in China killed 171,000 people and left millions homeless, many more than the death toll from the Chernobyl disaster. Though the dams can be built stronger, at greater cost, they are still prone to sabotage and terrorism. Smaller dams and micro hydro facilities are less vulnerable to these threats.

The chief advantage of hydroelectric dams is their ability to handle seasonal (as well as daily) high peak loads. When the electricity demands drop, the dam simply stores more water. Some electricity generators use water dams to store excess energy (often during the night), by using the electricity to pump water up into a basin. Electricity can be generated when demand increases. In practice the utilization of stored water in river dams is sometimes complicated by demands for irrigation which may occur out of phase with peak electrical demands.

Hydroelectric power can be far less expensive than electricity generated from fossil fuel or nuclear energy. Areas with abundant hydroelectric power attract industry.

Longevity issues

Though a source of renewable energy may last for billions of years, renewable energy infrastructure, like hydroelectric dams, will not last forever, and must be removed and replaced at some point. Events like the shifting of riverbeds, or changing weather patterns could potentially alter or even halt the function of hydroelectric dams, lowering the amount of time they are available to generate electricity.

Although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down. It is likely that in these locations, the system was designed too large for the site, since there is only so much energy that can be stored and replenished in a given volume of earth. Some interpret this as meaning a specific geothermal location can undergo depletion, and question whether geothermal energy is truly renewable. The government of Iceland states It should be stressed that the geothermal resource is not strictly renewable in the same sense as the hydro resource. It estimates that Iceland's geothermal energy could provide 1700 MW for over 100 years, compared to the current production of 140 MW.

Net energy balance

All biomass needs to go through some of these steps: it needs to be grown, collected, dried, fermented and burned. All of these steps require resources and an infrastructure.

Opponents of corn ethanol production in the U.S. often quote the 2005 paper of David Pimentel, a retired Entomologist, and Tadeusz Patzek, a Geological Engineer from Berkeley. Both have been exceptionally critical of ethanol and other biofuels. Their studies contend that ethanol, and biofuels in general, are "energy negative", meaning they take more energy to produce than is contained in the final product.

A 2006 report by the U.S. Department Agriculture compared the methodologies used by a number of researchers on this subject and found that the majority of researchers think the energy balance for ethanol is positive. In fact, a large number of recent studies, including a 2006 article in the prestigious journal Science offer the consensus opinion that fuels like ethanol are energy positive. Furthermore, it should be pointed out that fossil fuels also require significant energy inputs which have seldom been accounted for in the past.

Other issues

Fossil fuels

Main article: Fossil fuel

The established, though not universally held, Western (biogenic) theory is that fossil fuels are the altered remnants of ancient plant and animal life, deposited in sedimentary rocks millions of years ago, which have rested underground, mostly dormant, since that time. Although this process may continue today, it is extremely slow and produces a negligible amount of these resources compared to the rate of consumption by humans. Therefore, the Earth will eventually run out of fossil fuels (see peak oil). Fossil fuels are therefore not considered a renewable energy source, and are often contrasted with renewables in the context of future energy development.

The coal industry in the US is publicly claiming that coal is a renewable energy source because coal was originally biomass. Some scientists hold the view that the formation of fossil fuels was a one-time event, made possible by unique conditions during the Devonian period, such as increased oxygen levels and huge swamps.

Transmission

If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems might no longer be the main distributors of electrical energy but would operate to balance the electricity needs of local communities. Those with surplus energy would sell to areas needing "top ups". That is, network operation would require a shift from 'passive management' — where generators are hooked up and the system is operated to get electricity 'downstream' to the consumer — to 'active management', wherein generators are spread across a network and inputs and outputs need to be constantly monitored to ensure proper balancing occurs within the system. Some Governments and regulators are moving to address this, though much remains to be done. One potential solution is the increased use of active management of electricity transmission and distribution networks. This will require significant changes in the way that such networks are operated.

However, on a smaller scale, use of renewable energy that can often be produced "onsite" lowers the requirements electricity distribution systems have to fulfill. Current systems, while rarely economically efficient, have proven an average household with a solar panel array and energy storage system of the right size needs electricity from outside sources for only a few hours every week. By matching electicity supply to end-use needs in this way, advocates of renewable energy and the soft energy path believe electricity systems will become smaller and easier to manage, rather than the opposite (see Soft energy technology).

Market development of renewable heat energy

Renewable heat is an application of renewable energy, namely the generation of heat from renewable sources. In some cases, contemporary discussion on renewable energy focuses on the generation of electrical, rather than heat energy. This is despite the fact that many colder countries consume more energy for heating than as electricity. On an annual basis the United Kingdom consumes 350 TWh of electric power, and 840 TWh of gas and other fuels for heating. The residential sector alone consumes a massive 550 TWh of energy for heating, mainly in the form of gas.

Renewable electric power is becoming cheap and convenient enough to place it, in many cases, within reach of the average consumer. By contrast, the market for renewable heat is mostly inaccessible to domestic consumers due to inconvenience of supply, and high capital costs. Heating accounts for a large proportion of energy consumption, however a universally accessible market for renewable heat is yet to emerge. Solutions such as geothermal heat pumps may be more widely applicable, but may not be economical in all cases. Also see renewable energy development.

Aviation applications

Kerosene, a petroleum-based fuel currently sourced from non-renewable sources, is considered to be the only fuel practical and economic for commercial jet-engine aviation. However, kerosene can now be manufactured from the light crude oil that is the output of the Thermal depolymerization of renewable feedstocks. Biodiesel, another candidate aviation fuel, is problematic due its tendency to freeze more readily than kerosene.

Smaller piston-engined aircraft are mainly fueled by aviation grade gasoline (avgas) but are increasingly being fueled by ethanol [24] or diesel. Given the proper equipment to prevent fuel gelling, a diesel-powered piston aircraft engine can be powered efficiently by biodiesel.

Nuclear power

Main article: Nuclear power

'Renewable energy', as a term in modern usage, was invented just before the energy crisis of 1973. More recent arguments in favor of classifying nuclear power as renewable are based largely on the potential amount of raw materials that may become available for nuclear fission and its low environmental impact. In 1983, the physicist Bernard Cohen calculated the useful lifetime of nuclear power in the billions of years — longer than the life of the sun itself (which ultimately powers other renewables), remarking that this should qualify it as a renewable resource, too. Nuclear energy has also been referred to as "renewable" by the President of the United States George W. Bush and David Sainsbury, former Parliamentary Under-Secretary of State for the House of Lords.

Inclusion of nuclear power under the "renewable energy" classification could render nuclear power projects eligible for development aid under various jurisdictions. However, no legislative body has yet included nuclear energy under any legal definition of "renewable energy sources" for provision of development support (see: Renewable energy development). Similarly, statutory and scientific definitions of renewable energies usually exclude nuclear energy. In England and Wales there is a Non-Fossil Fuel Obligation, which provides support for renewable energy. Nuclear power production was also subsidised by this obligation from 1990 until 2002.

See also

For renewable energy use in current societies, see Renewable energy development.

For a discussion of future options, see Future energy development.

For involving your city, see Energie-Cités

• List of energy topics
• Biodiesel
• Biofuel
• Biomass
• Non food crops
• Biobutanol from Clostridium acetobutylicum
• Energy conservation
• Ethanol fuel in Brazil
• Ethanol fuel
• Hydrogen economy
• Hydrogen station
• Oil phase-out in Sweden
• Peak Oil
• Renewable energy development
• Low-carbon economy
• Mitigation of global warming
• Mechanical Biological Treatment
• Renewable energy in the European Union
• Renewable energy in Germany
• Renewable energy in Scotland
• Soft energy path
• Soft energy technologies
• Solar chimney
• Straight vegetable oil
• Sustainable energy
• Thermal depolymerization
• Tidal power
• Vegetable oil economy
• Wave Power
• Wind power
• Energy: world resources and consumption

External links

• Global wind energy markets continue to boom
• EPA uses onsite renewable technologies
• Orkney to get "biggest" wave farm
• Largest solar power plant in a generation to be built in Nevada
• Solar thermal power plants
• American Energy: The Renewable Path to Energy Security - Easy to read, downloadable report on the potential for renewable energy to become cost-competitive with fossil fuels in the U.S.
• EU Sustainable Energy Week (EUSEW).
• ESRU University of Strathclyde, Scotland — Library of MSc Theses on broad ranging renewable energy research topics
• Atlas of Renewable Energy (in English, French & German)
• Surface meteorology and Solar Energy — a renewable energy resource for data and images
• The British Library — finding information on the renewable energy industry
• reegle Information Gateway for Renewable Energy and Energy Efficiency
• Database of State Incentives for Renewable Energy — Summary of U.S. federal and state renewable energy programs
• Energie-Cités, The association of European local authorities promoting local sustainable energy policy
• (http://www.hkc22.com/renewableenergy.html) The worldwide markets and developments for renewable energies worldwide to 2015
• Renewable Energy Directory A categorized visual directory of renewable energy websites.