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Wind energy As the sun heats up the Earth unevenly, winds are formed. The kinetic energy in the wind can be used to run wind turbines, some capable of producing 5 MW of power. The power output is a function of the cube of the wind speed, so such turbines generally require a wind in the range 5.5 m/s (20 km/h), and in practice relatively few land areas have significant prevailing winds. Luckily, offshore or at high altitudes, the winds are much more constant. There are now many thousands of wind turbines operating in various parts of the world, with utility companies having a total capacity of 59,322 MW"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) This number could also increase with higher altitude ground based or airborne wind turbines. Wind strengths vary and thus cannot guarantee continuous power. Some estimates suggest that 1,000 MW of 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 contributes to greenhouse gas mitigation because it removes energy directly from the atmosphere without producing net emissions of greenhouse gases such as carbon dioxide and methane. Water power Energy in water can be harnessed and used in the form of motive energy or temperature differences. 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: Hydroelectric power is probably not a major option for the future of energy production in the developed nations because most major sites within these nations with the potential for harnessing gravity in this way 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 so immensely that this risk of endangering local and non-local wildlife is great. 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 produce significant amounts of carbon dioxide and methane from rotting vegetation. In some cases they produce more of these greenhouse gases than power plants running on fossil fuels. 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 kill marine life. Dam failures, 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. Wave and tidal stream power schemes exist but require development capital. OTEC has not been field tested on a large scale. Solar energy
Geothermal energy Geothermal energy is energy obtained by tapping the heat of the earth itself, usually from kilometers deep into the Earth's crust. 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: 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". Biofuel Plants use photosynthesis to store solar energy in the form of chemical energy. Biofuel is any fuel that derives from biomass, including living organisms or their metabolic byproducts, such as cow manure. 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. Biomass, also known as biomatter, 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. 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. 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, sugarbeets, cane and grasses 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 kilometres of the country's 65,000 square kilometres 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. 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. 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. Biogas 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. Small scale energy sources There are many small scale energy sources that generally cannot be scaled up to industrial size. A short list: Criticism of renewable concept Some critics charge that renewable energy is an arbitrary definition with no bearing on how much an energy source pollutes, how dangerous it is, whether it takes up a large amount of land that could be left wild or farmed for food, whether the source of the renewable energy will last a very long time, or even whether a given energy source produces a net amount of energy. Supporters respond that most renewable energies are ultimately powered by the Sun, the Earth, or the Moon, so the underlying sources for these energies are expected to last for billions of years. Of course, this does not mean that renewable energy infrastructure, like hydroelectric dams, will last forever. Events like the shifting of riverbeds, or changing weather patterns could potentially alter or even halt the function of hydroelectric dams. While most renewable energy sources do not produce pollution directly, it is often produced indirectly or during construction. Some of the inputs required to produce renewable energy, such as the crops grown to create ethanol or biodiesel, require energy inputs. The exact amount of energy required to grow crops varies widely, since a number of modern farming methods can significantly reduce the amount of energy that must be used. It is also very tricky 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. 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. Batteries, while a source of power, are energy negative, since more energy is put into them during charging than can be taken out by discharging. They function solely as an energy storage or energy carrier mechanism. As much as 4/5 of the energy taken from a fuel is wasted in order to create electrical energy, due to inefficiencies, some of which it is not physically possible to improve. (Fossil fuel and nuclear power plants are rated in MWth and MWe, for instance; the thermal and electrical power outputs. The thermal output is always higher than the electrical output; much of the thermal energy is wasted.) Despite these inefficiencies, electrical energy is still generated, because it is more useful (powering a light or a computer) than the original energy sources that were used to create it. It is the high quality of this energy that would justify producing it even if it did take more energy than directly recovered from the final product. 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. Land usage Another problem with many renewable energy sources, particularly biomass and biofuels, is the large amount of land required to harvest energy, which otherwise could be left as wilderness. In general, renewables face inherent difficulty with their variable and diffuse nature (the exception being geothermal energy, which is however only accessible in exceptional locations). Since 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, this criticism must also take into consideration the land area required by 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, for example. Electrical power consumption in Western countries averages about 100 watts continuously per person (i.e. about 1 MWh per year). 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%. (about half the theoretical maximum efficiency for crystal silicon ). 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. Proximity to demand The geographic diversity of resources is also significant. Some countries and regions have significantly better resources than others in particular RE 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. 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 when the sky is not cloudy. 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. Fossil fuels Renewable energy sources are fundamentally different from fossil fuels, because the Sun, Earth, or Moon will 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 pollution as fossil fuel combustion. When the term renewable was introduced in the early 1970s, 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. 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. 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. 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. To handle this characteristic, a more balanced power supply may be obtained 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. 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. Also see renewable energy development. Aviation Kerosene, a non-renewable petroleum-based fuel, 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. 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 * or diesel. Given the proper equipment to prevent fuel gelling, a diesel-powered piston aircraft engine can be powered efficiently by biodiesel. 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 . 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. Accidents notwithstanding, and ignoring decommissioning issues, the relatively little direct pollution from nuclear power plants while productive is also often cited (see Sustainable energy). Nuclear has been referred to as "renewable" by the President of the United States George W. Bush and United Kingdom politician Lord David Sainsbury.. 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 , which provides support for renewable energy. Nuclear power production is promoted indirectly, by exclusion from this obligation. Historical usage of renewable energy Throughout history, various forms of renewable and non-renewable energies have been employed. See also | |||||||||||
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