Renewable energy

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Renewable energy is energy which can be replenished at the same rate it is used. Renewable energy sources contribute approximately 25% of human energy use worldwide. The prime source of renewable energy is solar radiation, i.e. sunlight. The Earth-Atmosphere system supports approximately 5.4 x 1024 joules per year in the solar radiation cycle (Sorensen, 2004).

Mankind's traditional uses of wind, water, and solar power are widespread in developed and developing countries; but the mass production of electricity using renewable energy sources has become more commonplace only 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 taxes and subsidies. Varying definitions of the term renewable energy have been adopted to define eligibility under these policies.

Contents

[edit] Renewable energy sources

Mass production of electricity from renewable energy flows requires technology that harnesses the power of 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.

[edit] Solar Renewable Energy

Energy sources
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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 (Sorensen, 2004). 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.


[edit] Wind power

Example of a traditional windmill
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Example of a traditional windmill
Main article: Wind power

Kinetic energy in airflows can be used to run wind turbines; some are capable of producing 5 MW of power, but the most cost-effective turbines are currently 500 kW - 1.5 MW in capacity (James + James 1999). The power output of a turbine is a function of the cube of the wind speed, so high-power output can be achieved as wind speed increases,[1] though turbines must shut off at extreme wind speeds to prevent damage. Areas where winds are stronger and more constant, such as offshore and high altitude sites, are preferred locations for wind farms.

Wind 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%,[2] (maximum capacity, in this case, does not count load factor). Due to the intermittency of wind resources, most deployed turbines in the EU produce electricity about 25% of the time, or have 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 5 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.[3] This number could also increase with higher altitude ground-based or airborne wind turbines.[4]

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.

[edit] 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 more dense 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 hydroelectric dams.
  • Tidal power captures energy from the tides in a vertical direction. Tides come in, raise water levels in a basin, and tides roll out. At low tide, the water must pass through a turbine to get out of the basin.
  • Tidal stream power captures a stream of water as it is pushed horizontally around the world by tides.
  • 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 no waves in the "shadow".
  • 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.
  • 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)

Hydroelectric power is 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. However, micro hydro may be an option for small-scale applications such as single farms, homes or small businesses.

Building a dam often involves flooding large areas of land, which can change 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.

The reservoir created for hydroelectric dams may initially produce significant amounts of carbon dioxide and methane from rotting vegetation. Once this vegetation is gone, no additional greenhouse gases are produced. In some cases they may produce more of these greenhouse gases than power plants running on fossil fuels[5]. They also affect water quality, creating large amounts of stagnant water without oxygen in the reservoir, and excessive air bubbles in the water downstream from the dam, both of which impact aquatic life.[6] 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.

Wave and tidal stream power demonstration projects exist, but large scale development requires additional capital.

OTEC has not been field-tested on a large scale.

[edit] Solar energy

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.
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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, wether it be from direct or indirect, the solar panels still collect energy. However, most fossil and renewable energy sources are ultimately derived from "solar energy," so some ascribe much broader meanings to the term.

Solar energy can be applied in many ways, including to:

The sun does not provide constant energy to any spot on the Earth, so its uninterrupted use on Earth requires a means for energy storage. This is typically accomplished by battery storage. However, battery storage implies energy losses. Some homeowners use a grid-connected solar system that feeds energy to the grid during the day and draw energy from the grid at night; this way no energy is expended for storage. Batteries provide direct current (DC), whereas most household appliances run off alternating current (AC). Conversion from DC to AC leads to some energy loss.

Advantages from solar energy sources include the inexhaustible supply of energy and zero emissions of greenhouse gas and air pollutants. Shortcomings include, depending on application:

  • Economic competitiveness with conventional energy conversion
  • Intermittency; it is not available at night or during heavy cloud cover.
  • For photovoltaics (solar-electric), the current generated is only of DC type, and must be converted if transmission over the standard AC grid is needed.

[edit] Biofuel

Main article: Biofuel

Biofuel is any fuel that derives from biomass, including living organisms or their metabolic byproducts, such as cow manure.

Plants use photosynthesis to grow and produce biomass. Other organisms may be grown to 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.

Biogas is a biofuel produced through the intermediary stage of anaerobic digestion. Biogas consists mainly (45–90%) biologically produced methane.

A drawback is that 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. However, the United States government passed legislation that requires the integration of 7.5 billion U.S. gallons (28,000,000 m³) of ethanol into the gasoline supply. Experts estimate that six billion dollars of investment will be created, along with 200,000 additional jobs in the United States.

Biomatter energy, under the right conditions, is considered to be renewable.

[edit] Liquid biofuel

Liquid biofuel is usually bioalcohol such as ethanol and biodiesel and virgin vegetable oils. Biodiesel can be used in modern diesel vehicles with little or no modification to the engine and can be obtained 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 currently being sold to consumers.

The EU plans to add 5% bioethanol to Europe's petrol by 2010. For the UK alone the production would require 13,000 square kilometers of the country's 65,000 square kilometers of arable land assuming that no biofuels are created using waste produces from other agriculture. The supermarket chain Tesco has started adding the 5% bioethanol to the petrol it sells as of February 2006.

Thermal depolymerization (TDP) is an important new process for the reduction of complex organic materials including non oil based materials (for example waste products such as old tyres, offal, wood and plastic) into light crude oil, biogas and carbon solids. Light crude oil can be processed at an oil refinery to yield products such as kerosene, petroleum, diesel, plastics, etc.

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).[7]

[edit] 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. Whether this process releases net CO2 emissions is still up for debate in the scientific community.

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

[edit] Biogas

Main articles: Biogas and Anaerobic digestion

Many organic materials can release gases, due to metabolisation of organic matter by bacteria (anaerobic digestion, or fermentation). Landfills actually need to vent this gas (called landfill gas) to prevent dangerous explosions. Animal feces releases methane under the influence of anaerobic bacteria.

Also, under high pressure, high temperature, anaerobic conditions many organic materials such as wood can be gasified to produce gas. This is often found to be more efficient than direct burning. The gas can then be used to generate electricity and/or heat.

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 the existing gas grid.'

[edit] Non-Solar Renewable Energy

[edit] 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 create a power station, but after the station is created the energy is virtually free of cost due to the limited costs to run the station. Ultimately, this energy derives from the radioactive decay in the core of the Earth, which heats the Earth from the inside out. This energy can be used in three ways:

  • Geothermal electricity
  • Geothermal heating, through deep Earth pipes
  • Geothermal heating, through a heat pump.

Usually, the term 'geothermal' is reserved for thermal energy from within the Earth.

Geothermal electricity is created by pumping a fluid (oil or water) into the Earth, allowing it to evaporate and using the hot gases vented from the earth's crust to run turbines linked to electrical generators.

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.

Geothermal heat from the surface of the Earth can be used on most of the globe directly to heat and cool buildings with the use of Geothermal Systems. The temperature of the crust a few feet below the surface is buffered to a constant 7 to 14 °C (45 to 58 °F), so a liquid can be pre-heated or pre-cooled in underground pipelines, providing free cooling in the summer and, via a heat pump, heating in the winter. Other direct uses are in agriculture (greenhouses), aquaculture and industry.

Although geothermal sites are capable of providing heat for many decades, eventually specific locations cool down. Some interpret this as meaning a specific geothermal location can undergo depletion, and question whether geothermal energy is truly renewable.

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, and "Geoexchange".


[edit] Criticisms

Critics charge that some renewable energy sources may create pollution, be dangerous, take up large amounts of land, or be incapable of generating a large net amount of energy.

[edit] 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 of the inputs required to produce renewable energy, such as the crops grown to create ethanol or biodiesel fuels, may be grown using fuel and fertilizers derived from non-renewable energy sources.

[edit] Aesthetics and habitat hazards

Some people dislike the aesthetics of wind turbines or bring up nature conservation issues when it comes to large solar-electric installations outside of cities. 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.

Some renewable energy capture systems actually create environmental problems. For instance, older wind turbines can be hazardous to flying birds and hydroelectric dams create barriers for migrating fish. This latter example exists in the Pacific Northwest where salmon populations have been affected.

[edit] Land usage

Another issue with many renewable energy sources, particularly 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. Renewable sources like wind and solar power are variable or diffuse. Since these renewable energy sources are providing relatively low-intensity energy, the new kinds of "power plants" needed to convert the sources into usable energy need to be distributed over large areas. However, these sources 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.

[edit] Proximity to demand

The geographic diversity of resources is also significant. Some countries and regions have significantly better resources than others in particular renewable energy sectors. Some nations have significant resources at distance from the major population centers where electricity demand exists. Exploiting such resources on a large scale is likely to require considerable investment in transmission and distribution networks as well as in the technology itself.

In certain cases, for people that live in big houses, rooftop photovoltaic arrays may be attractive in that most of the power they produce is consumed in the structure on which they are mounted or in other nearby buildings.

[edit] Availability

One recurring criticism of renewable sources is their intermittent nature. Sunlight is available only during the day when the sun is well above the horizon. Wind energy is typically available much less than half the time. 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.

[edit] Reliability

Current electrical power consumption in Western countries averages about 100 watts continuously per person (i.e. about 1 MWh per year). [citation needed] In cloudy Europe this would require about eight square meters of solar panels per person (a square 9 feet on a side), assuming a median solar conversion rate of 12.5%. [8] (about half the theoretical maximum efficiency for crystal silicon [9]). This assumes no technological energy efficiency gains or conservation measures.

If high reliability is required, systematic electrical generation requires overlapping sources or some means of storage on a reasonable scale. Available storage options include pumped-storage hydro systems, batteries, hydrogen fuel cells, etc. Initial investments in such energy storage systems can be high, although the costs can recovered in the long-term. Such solutions may be the only alternative where connection to a public grid would be impractical.

[edit] Longevity

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.

[edit] Energy Input versus Output

The exact amount of energy required to grow crops varies widely, and it is difficult to account for all energy inputs to biofuels. Opponents of corn ethanol production in the U.S. often quote the work 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.[citation needed]

A 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 an article in the 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.

According to information from the American Council for Ethanol, "ethanol has a 125 percent positive energy balance, compared to 85 percent for gasoline." As far as dealing with peak oil is concerned, this is an apples to oranges comparison, because gasoline comes as a portion of depletable crude oil, while ethanol is supposedly a sustainable alternative. If crude oil with a 10:1 energy balance is used to make gasoline with an 85% energy balance (simplifying to assume all energy is convertible into gasoline or waste heat), one gets 8.5 units of energy for every 1 they put into gasoline-powered oil wells and refineries. In this manner, ethanol proponents faced with these facts have come to argue that corn ethanol production may be a more efficient way of using crude oil than refining it. The issue of energy balance is important for any major energy source, but ultimately other factors come into play as well. Corn ethanol, for example, could not create energy independence for current markets because there is not enough arable land to provide equivalent ethanol as we use imported gasoline.

[edit] Issues

[edit] Fossil fuels

Main article: Fossil fuel

Renewable energy sources are fundamentally different from fossil fuels, because the Sun, Earth, or Moon power these 'power plants' (meaning sunlight, the wind, flowing water, etc.) for billions of years. They do not produce as many greenhouse gases and other pollutants as fossil fuel combustion.

When the term renewable was introduced in the early 1970s,[10] it was a generally held belief that the Earth's sources would be depleted within some 50 years:

The traditionally, though not universally, held Western (biogenic) theory postulates that fossil fuels are the altered remnants of ancient plant and animal life deposited in sedimentary rocks. They were formed millions of years ago and 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 consumption by humans. Because the current rate of consumption exceeds the rate of renewal (if, indeed, there is renewal of fossil fuels), the Earth will eventually run out of fossil fuels (see peak oil). Fossil fuels are therefore not considered a renewable energy source, but are often compared and contrasted with renewables in the context of future energy development.

Since then, large deposits of deep-Earth oil have been found, which has extended this timetable.

The coal industry in the US is publicly claiming coal is renewable energy because the coal was originally biomass.[citation needed] However, the biomass of fossil fuels was produced on the time scale of millions of years through a series of events and it is considered to be a deposit of energy, not an energy flow. 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.

In contrast, the Abiogenic petroleum origin theory states that petroleum (or crude oil) is primarily created from non-biological sources of hydrocarbons located deep in the Earth. This view was championed by Fred Hoyle in his book The Unity of the Universe.

Though it is possible to produce complex hydrocarbons artificially by using the Fischer-Tropsch process, this process does not generate net energy, and is not a solution to the energy problem; it is mainly useful for storing energy, and converting energy from alternative sources to provide power for equipment that can only use hydrocarbons. For instance, in a hypothetical world that used only electrical energy generated from renewables, jet fuel would still be needed because of its high energy density, and would be generated artificially by this process. The Fischer-Tropsch-process can use biomass, hydrogen and oxygen produced with renewable energy, as feedstocks.

[edit] 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 small scale, use of renewable energy that can often be produced "on the spot" 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. Hence, advocates of renewable energy believe electricity distribution systems will become smaller and easier to manage, rather than the opposite.

[edit] Load balancing and storage

A common criticism of renewable power is that generators such as wind turbines or solar arrays are liable to suffer variable output. In the case of solar power, this is a desirable characteristic as the increased output of solar arrays during sunny weather matches the increased power demand, e.g. for air conditioning. Variable output from renewable energy sources can be further balanced if the various renewable sources are interconnected and distributed. Indeed, distribution and redundancy are already features of existing electrical grids. The challenge of variable power supply may be further alleviated by energy storage. For example, pumped-storage hydroelectricity provides a popular energy storage mechanism. Also there are other means for energy storage.

[edit] 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[11] 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.[12]

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. Also see renewable energy development.

[edit] Aviation

Kerosene, a petroleum-based fuel currently sourced from non-renewable sources, is currently considered to be the only fuel practical and economic for commercial jet-engine aviation. Although hydrogen has a high energy density, it has very high volume even in liquid form so the need for huge fuel tanks or heavy fuel-cell stacks makes it impractical for aircraft. 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 [2] or diesel. Given the proper equipment to prevent fuel gelling, a diesel-powered piston aircraft engine can be powered efficiently by biodiesel.

[edit] Nuclear power

Main article: Nuclear power

Because nuclear power is not renewed from an external energy source, it does not meet the conventional definition of renewable energy. 'Renewable', as a term in modern usage, was coined during the energy crisis of the 1970s and was clearly meant to exclude nuclear power [13]. Inclusion of nuclear power under the "renewable energy" umbrella may render nuclear power projects eligible for development aid under various jurisdictions. Arguments in favor of including nuclear power under renewable energy title are based on the potentially large amount of raw materials that may become available to fuel nuclear fission. 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, remarking that this should qualify it as a renewable resource. [citation needed]

Nuclear has been referred to as "renewable" by the President of the United States George W. Bush and United Kingdom businessman Lord David Sainsbury.[14][15] The U.S. federal government has traditionally acted as vocal support and significant subsidizer of the nuclear power industry.

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 by-and-large exclude nuclear energy.

In England and Wales there is a Non-Fossil Fuel Obligation [16], which provides support for renewable energy. Nuclear power production is promoted indirectly, by exclusion from this obligation.

[edit] Nuclear Power Issues

Many are concerned about nuclear and radiation accidents and nuclear power plant decommissioning. There is also concern regarding disposal and storage of the waste produced by nuclear reactors. Many existing on-site nuclear waste storage facilities near reactors are currently full or almost full. Proposals to relocate all U.S. nuclear waste to a single location, such as Yucca Mountain, have met with vigorous local opposition. Debate centers primarily on two issues: whether a single large storage facility would be safer than many small ones, and if so, where it should be placed

[edit] 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

[edit] External links

 Wikimedia Commons has media related to:

[edit] References

  1. ^ http://www.ewea.org/fileadmin/ewea_documents/documents/publications/WETF/Facts_Summary.pdf EWEA Executive summary (URL accessed January 30, 2006
  2. ^ http://www.ewea.org/fileadmin/ewea_documents/documents/publications/WETF/Facts_Summary.pdf EWEA Executive summary (URL accessed January 30, 2006)
  3. ^ "Offshore stations experience mean wind speeds at 80 m that are ~90% greater than over land on average. Evaluation of global wind power
    "Overall, the researchers calculated winds at 80 meters [300 feet] traveled over the ocean at approximately 8.6 meters per second and at nearly 4.5 meters per second over land [20 and 10 miles per hour, respectively]." Global Wind Map Shows Best Wind Farm Locations (URL accessed January 30, 2006)
  4. ^ "High-altitude winds could provide a potentially enormous renewable energy source, and scientists like Roberts believe flying windmills could put an end to dependence on fossil fuels. At 15,000 feet, winds are strong and constant. On the ground, wind is often unreliable — the biggest problem for ground-based wind turbines." Windmills in the Sky (URL accessed January 30, 2006)
  5. ^ Hydroelectric power's dirty secret revealed — New Scientist
  6. ^ How Hydroelectric Energy Works
  7. ^ Status And Perspectives of Biomass-To-Liquid Fuels in the European Union
  8. ^ AE photovoltaic efficiency (URL accessed July 24, 2006)
  9. ^ Solar Electricity and Solar Cells in Theory and Practice (URL accessed July 24, 2006)
  10. ^ Etymology of the word "renew" — "Renewable is recorded from 1727; in ref. to energy sources, it is attested from 1971."
  11. ^ Department of Trade and Industry report UK Energy in Brief July 2005 (URL accessed Mar 18, 2006)
  12. ^ Department of Trade and Industry, 2005 study on Renewable Heat (URL accessed Mar 18, 2006)
  13. ^ History of Support for Renewable Energy in Germany
  14. ^ Bush: 'Nuclear Power Safe, Clean, Renewable' — NewsMax.com
  15. ^ Minister declares nuclear 'renewable' — UK Times
  16. ^ DTI Non-Fossil Fuel Obligation
Energy Development and Use   Edit
Energy development | Environmental concerns with electricity generation | Future energy development | Inertial fusion power plant | Hydrogen storage | Hydrogen station | Hydrogen economy | Hubbert peak theory | Renewable energy | Hypermodernity | Technological singularity | Air engine | Liquid nitrogen economy | Flywheel energy storage
Sustainability and Development of Energy   Edit
Conversion | Development and Use | Sustainable Energy | Conservation | Transportation
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