Difference between revisions of "AY Honors/Renewable Energy/Answer Key"
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'''Renewable energy''' is energy from a source which can be managed so that it is not subject to [[depletion]] in a [[human timescale]] . Sources include the [[sun]]'s rays, wind, waves, rivers, tides, [[biomass]], and [[geothermal]]. Renewable energy does not include energy sources which are dependent upon [[limited resource]]s, such as [[fossil fuels]] and [[nuclear power|nuclear fission power]]. | '''Renewable energy''' is energy from a source which can be managed so that it is not subject to [[depletion]] in a [[human timescale]] . Sources include the [[sun]]'s rays, wind, waves, rivers, tides, [[biomass]], and [[geothermal]]. Renewable energy does not include energy sources which are dependent upon [[limited resource]]s, such as [[fossil fuels]] and [[nuclear power|nuclear fission power]]. | ||
| − | =General Information= | + | ==General Information== |
| + | |||
Most renewable forms of energy, other than geothermal, are in fact stored solar energy. Water power and wind power represent very short-term solar storage, while biomass represents slightly longer-term storage, but still on a very human time-scale, and so renewable within that human time-scale. Fossil fuels, on the other hand, while still stored solar energy, have taken millions of years to form, and so do not meet the definition of renewable. | Most renewable forms of energy, other than geothermal, are in fact stored solar energy. Water power and wind power represent very short-term solar storage, while biomass represents slightly longer-term storage, but still on a very human time-scale, and so renewable within that human time-scale. Fossil fuels, on the other hand, while still stored solar energy, have taken millions of years to form, and so do not meet the definition of renewable. | ||
Renewable energy resources may be used directly as energy sources, or used to create other forms of energy for use. Examples of direct use are [[solar oven]]s, geothermal [[heat pump]]s, and mechanical [[windmill]]s. Examples of indirect use in creating other energy sources are [[electricity generation]] through [[wind generator]]s or [[photovoltaic]] cells, or production of fuels such as [[ethanol]] from [[biomass]] (see [[alcohol as a fuel]]). | Renewable energy resources may be used directly as energy sources, or used to create other forms of energy for use. Examples of direct use are [[solar oven]]s, geothermal [[heat pump]]s, and mechanical [[windmill]]s. Examples of indirect use in creating other energy sources are [[electricity generation]] through [[wind generator]]s or [[photovoltaic]] cells, or production of fuels such as [[ethanol]] from [[biomass]] (see [[alcohol as a fuel]]). | ||
| − | =Pros and cons of renewable energy= | + | ==Pros and cons of renewable energy== |
| + | |||
Renewable energy sources are fundamentally different from fossil fuel or nuclear power plants because of their widespread occurrence and abundance - the [[sun]] will 'power' these 'powerplants' (meaning sunlight, the wind, flowing water, etc.) for the next 4 billion years. The primary advantage of many renewable energy sources are their lack of greenhouse gas and other emissions in comparison with fossil fuel combustion. Some renewable sources do not emit any additional [[carbon dioxide]] and do not introduce any new risks such as [[nuclear waste]]. In fact, one renewable energy source, wood, actively sequesters carbon dioxide while growing. | Renewable energy sources are fundamentally different from fossil fuel or nuclear power plants because of their widespread occurrence and abundance - the [[sun]] will 'power' these 'powerplants' (meaning sunlight, the wind, flowing water, etc.) for the next 4 billion years. The primary advantage of many renewable energy sources are their lack of greenhouse gas and other emissions in comparison with fossil fuel combustion. Some renewable sources do not emit any additional [[carbon dioxide]] and do not introduce any new risks such as [[nuclear waste]]. In fact, one renewable energy source, wood, actively sequesters carbon dioxide while growing. | ||
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If renewable and [[distributed generation]] were to become widespread, [[electric power transmission]] and [[electricity distribution]] systems would 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. This will require significant changes in the way that such networks are operated. In turn this may also require changes in the regulation which provides incentives to network operators in the way that they invest in their networks. | If renewable and [[distributed generation]] were to become widespread, [[electric power transmission]] and [[electricity distribution]] systems would 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. This will require significant changes in the way that such networks are operated. In turn this may also require changes in the regulation which provides incentives to network operators in the way that they invest in their networks. | ||
| − | =Renewable energy history= | + | ==Renewable energy history== |
| + | |||
The original energy source for all human activity was the [[sun]] via growing [[plant]]s. [[Solar power | Solar energy]]'s main human application throughout most of history has thus been in [[agriculture]] and [[forestry]], via photosynthesis. | The original energy source for all human activity was the [[sun]] via growing [[plant]]s. [[Solar power | Solar energy]]'s main human application throughout most of history has thus been in [[agriculture]] and [[forestry]], via photosynthesis. | ||
| − | ==Wood== | + | ===Wood=== |
| + | |||
[[Firewood]] was the earliest manipulated energy source in human history, being used as a thermal energy source through burning, and it is still important in this context today. Burning wood was important for both [[cooking]] and providing heat, enabling human presence in cold climates. Special types of wood cooking, [[drying (food)|food dehydration]] and [[smoke curing]], also enabled human societies to safely store perishable foodstuffs through the year. Eventually, it was discovered that partial combustion in the relative absence of oxygen could produce [[charcoal]], which provided a hotter and more compact and portable energy source. However, this was not a more efficient energy source, because it required a large input in wood to create the charcoal. | [[Firewood]] was the earliest manipulated energy source in human history, being used as a thermal energy source through burning, and it is still important in this context today. Burning wood was important for both [[cooking]] and providing heat, enabling human presence in cold climates. Special types of wood cooking, [[drying (food)|food dehydration]] and [[smoke curing]], also enabled human societies to safely store perishable foodstuffs through the year. Eventually, it was discovered that partial combustion in the relative absence of oxygen could produce [[charcoal]], which provided a hotter and more compact and portable energy source. However, this was not a more efficient energy source, because it required a large input in wood to create the charcoal. | ||
| − | ==Animal | + | ===Animal traction=== |
| + | |||
Motive power for vehicles and mechanical devices was originally produced through [[animal traction]]. Animals such as horses and oxen not only provided transportation but also powered mills. Animals are still extensively in use in many parts of the world for these purposes. | Motive power for vehicles and mechanical devices was originally produced through [[animal traction]]. Animals such as horses and oxen not only provided transportation but also powered mills. Animals are still extensively in use in many parts of the world for these purposes. | ||
| − | ==Water | + | ===Water power=== |
| + | |||
Animal power for mills was eventually supplanted by water power, the power of falling water in rivers, wherever it was exploitable. Direct use of water power for mechanical purposes is today fairly uncommon, but still in use. | Animal power for mills was eventually supplanted by water power, the power of falling water in rivers, wherever it was exploitable. Direct use of water power for mechanical purposes is today fairly uncommon, but still in use. | ||
Originally, water power through ([[hydroelectricity]]) was the most important source of electrical generation throughout society, and is still an important source today. Throughout most of the history of human technology, hydroelectricity has been the only renewable source of electricity generation significantly tapped for the generation of electricity. | Originally, water power through ([[hydroelectricity]]) was the most important source of electrical generation throughout society, and is still an important source today. Throughout most of the history of human technology, hydroelectricity has been the only renewable source of electricity generation significantly tapped for the generation of electricity. | ||
| − | ==Wind | + | ===Wind power=== |
| + | |||
Wind power has been used for several hundred years. It was originally used via large sail-blade windmills with slow-moving blades, such as those seen in the [[Netherlands]] and mentioned in [[Don Quixote]]. These large mills usually either pumped water or powered small mills. Newer windmills featured smaller, faster-turning, more compact units with more blades, such as those seen throughout the [[Great Plains]]. These were mostly used for pumping water from wells. Recent years have seen the rapid development of wind generation farms by mainstream power companies, using a new generation of large, high wind turbines with two or three immense and relatively slow-moving blades. | Wind power has been used for several hundred years. It was originally used via large sail-blade windmills with slow-moving blades, such as those seen in the [[Netherlands]] and mentioned in [[Don Quixote]]. These large mills usually either pumped water or powered small mills. Newer windmills featured smaller, faster-turning, more compact units with more blades, such as those seen throughout the [[Great Plains]]. These were mostly used for pumping water from wells. Recent years have seen the rapid development of wind generation farms by mainstream power companies, using a new generation of large, high wind turbines with two or three immense and relatively slow-moving blades. | ||
| − | ==Solar power== | + | ===Solar power=== |
| + | |||
Solar power as a direct energy source has been not been captured by mechanical systems until recent human history, but was captured as an energy source through architecture in certain societies for many centuries. Not until the twentieth century was direct solar input extensively explored via more carefully planned architecture (passive solar) or via heat capture in mechanical systems (active solar) or electrical conversion (photovoltaic). Increasingly today the sun is harnessed for heat and electricity. | Solar power as a direct energy source has been not been captured by mechanical systems until recent human history, but was captured as an energy source through architecture in certain societies for many centuries. Not until the twentieth century was direct solar input extensively explored via more carefully planned architecture (passive solar) or via heat capture in mechanical systems (active solar) or electrical conversion (photovoltaic). Increasingly today the sun is harnessed for heat and electricity. | ||
| − | ==The renewable energy movement== | + | ===The renewable energy movement=== |
| + | |||
Renewable energy as an issue was virtually unheard-of before the middle of the twentieth century. There were experimentations with passive solar energy, including daylighting, in the early part of the twentieth century, but little beyond what had actually been practiced as a matter of course in some locales for hundreds of years. The renewable energy movement gained awareness, credence and strength with the great burgeoning of interest in environmental affairs in the mid-1900s, which in turn was largely due to [[Rachel Carson]]'s ?'Silent Spring'?. | Renewable energy as an issue was virtually unheard-of before the middle of the twentieth century. There were experimentations with passive solar energy, including daylighting, in the early part of the twentieth century, but little beyond what had actually been practiced as a matter of course in some locales for hundreds of years. The renewable energy movement gained awareness, credence and strength with the great burgeoning of interest in environmental affairs in the mid-1900s, which in turn was largely due to [[Rachel Carson]]'s ?'Silent Spring'?. | ||
The first US politician to focus significantly on solar energy was [[Jimmy Carter]], in response to the long term consequences of the [[1973 energy crisis]]. No president since has paid much attention to renewable energy. | The first US politician to focus significantly on solar energy was [[Jimmy Carter]], in response to the long term consequences of the [[1973 energy crisis]]. No president since has paid much attention to renewable energy. | ||
| − | =Renewable | + | ==Renewable energy today== |
| + | |||
Around 80% of energy requirements are focused around heating or cooling buildings and powering the vehicles that ensure mobility (cars, trains, airplanes). This is the core of society's energy requirements. However, most uses of renewable power focus on electricity generation. | Around 80% of energy requirements are focused around heating or cooling buildings and powering the vehicles that ensure mobility (cars, trains, airplanes). This is the core of society's energy requirements. However, most uses of renewable power focus on electricity generation. | ||
[[Geothermal exchange heat pump|Geothermal heat pumps]] (also called ground-source heat pumps) are a means of extracting heat in the winter or cold in the summer from the earth to heat or cool buildings. | [[Geothermal exchange heat pump|Geothermal heat pumps]] (also called ground-source heat pumps) are a means of extracting heat in the winter or cold in the summer from the earth to heat or cool buildings. | ||
| − | =Modern sources of renewable energy= | + | ==Modern sources of renewable energy== |
| + | |||
There are several types of renewable energy, including the following: | There are several types of renewable energy, including the following: | ||
* [[Solar power]]. | * [[Solar power]]. | ||
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* [[Biomatter]], including Biogas Energy. | * [[Biomatter]], including Biogas Energy. | ||
| − | ==Smaller-scale sources== | + | ===Smaller-scale sources=== |
| + | |||
Of course there are some smaller-scale applications as well: | Of course there are some smaller-scale applications as well: | ||
* [[piezoelectricity|Piezo electric]] crystals embedded in the sole of a shoe can yield a small amount of energy with each step. Vibration from [[internal combustion engine|engines]] can stimulate piezo electric crystals. | * [[piezoelectricity|Piezo electric]] crystals embedded in the sole of a shoe can yield a small amount of energy with each step. Vibration from [[internal combustion engine|engines]] can stimulate piezo electric crystals. | ||
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* Special [[antenna (electronics)|antennae]] can collect energy from stray radiowaves or even light ([[Electromagnetic radiation|EM radiation]]). | * Special [[antenna (electronics)|antennae]] can collect energy from stray radiowaves or even light ([[Electromagnetic radiation|EM radiation]]). | ||
| − | ==Renewables as solar energy== | + | ===Renewables as solar energy=== |
| + | |||
Most renewable energy sources can trace their roots to solar energy, with the exception of [[geothermal energy|geothermal]] and [[tidal power]]. For example, wind is caused by the sun heating the earth unevenly. Hot air is less dense, so it rises, causing cooler air to move in to replace it. Hydroelectric power can be ultimately traced to the sun too. When the [[sun]] evaporates water in the ocean, the vapor forms clouds which later fall on mountains as rain which is routed through turbines to generate electrity. The transformation goes from solar energy to potential energy to kinetic energy to electric energy. | Most renewable energy sources can trace their roots to solar energy, with the exception of [[geothermal energy|geothermal]] and [[tidal power]]. For example, wind is caused by the sun heating the earth unevenly. Hot air is less dense, so it rises, causing cooler air to move in to replace it. Hydroelectric power can be ultimately traced to the sun too. When the [[sun]] evaporates water in the ocean, the vapor forms clouds which later fall on mountains as rain which is routed through turbines to generate electrity. The transformation goes from solar energy to potential energy to kinetic energy to electric energy. | ||
| − | ==Solar energy per se== | + | ===Solar energy per se=== |
| + | |||
Since most renewable energy is "Solar Energy" this term is slightly confusing and used in two different ways: firstly as a synonym for "renewable energies" as a whole (like in the [[political slogan]] "Solar not nuclear") and secondly for the energy that is directly collected from solar radiation. In this section it is used in the latter category. | Since most renewable energy is "Solar Energy" this term is slightly confusing and used in two different ways: firstly as a synonym for "renewable energies" as a whole (like in the [[political slogan]] "Solar not nuclear") and secondly for the energy that is directly collected from solar radiation. In this section it is used in the latter category. | ||
There are actually two separate approaches to solar energy, termed [[active solar]] and [[passive solar]]. | There are actually two separate approaches to solar energy, termed [[active solar]] and [[passive solar]]. | ||
| − | ===Solar electrical energy=== | + | ====Solar electrical energy==== |
| + | |||
For electricity generation, ground-based solar power has serious limitations because of its diffuse and intermittent nature. First, ground-based solar input is interrupted by night and by cloud cover, which means that solar electric generation inevitably has a low capacity factor, typically less than 20%. Also, there is a low intensity of incoming radiation, and converting this to high grade electricity is still relatively inefficient (14% - 18%), though increased efficiency or lower production costs have been the subject of much research over several decades. | For electricity generation, ground-based solar power has serious limitations because of its diffuse and intermittent nature. First, ground-based solar input is interrupted by night and by cloud cover, which means that solar electric generation inevitably has a low capacity factor, typically less than 20%. Also, there is a low intensity of incoming radiation, and converting this to high grade electricity is still relatively inefficient (14% - 18%), though increased efficiency or lower production costs have been the subject of much research over several decades. | ||
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Alternatively, many individuals have installed small-scale PV arrays for domestic consumption. Some, particularly in isolated areas, are totally disconnected from the main power grid, and rely on a surplus of generation capacity combined with [[Battery (electricity)|batteries]] and/or a fossil fuel generator to cover periods when the cells are not operating. Others in more settled areas remain connected to the grid, using the grid to obtain electricity when solar cells are not providing power, and selling their surplus back to the grid. This works reasonably well in many climates, as the peak time for energy consumption is on hot, sunny days where air conditioners are running and solar cells produce their maximum power output. Many U.S. states have passed "net metering" laws, requiring electrical utilities to buy the locally-generated electricity for price comparable to that sold to the household. Photovoltaic generation is still considerably more expensive for the consumer than grid electricity unless the usage site is sufficiently isolated, in which case photovoltaics become the less expensive. | Alternatively, many individuals have installed small-scale PV arrays for domestic consumption. Some, particularly in isolated areas, are totally disconnected from the main power grid, and rely on a surplus of generation capacity combined with [[Battery (electricity)|batteries]] and/or a fossil fuel generator to cover periods when the cells are not operating. Others in more settled areas remain connected to the grid, using the grid to obtain electricity when solar cells are not providing power, and selling their surplus back to the grid. This works reasonably well in many climates, as the peak time for energy consumption is on hot, sunny days where air conditioners are running and solar cells produce their maximum power output. Many U.S. states have passed "net metering" laws, requiring electrical utilities to buy the locally-generated electricity for price comparable to that sold to the household. Photovoltaic generation is still considerably more expensive for the consumer than grid electricity unless the usage site is sufficiently isolated, in which case photovoltaics become the less expensive. | ||
| − | ===System problems with solar electric=== | + | ====System problems with solar electric==== |
| + | |||
Frequently renewable electricity sources are disadvantaged by regulation of the electricity supply industry which favors 'traditional' large-scale generators over smaller-scale and more distributed generating sources. If renewable and [[distributed generation]] were to become widespread, [[electric power transmission]] and [[electricity distribution]] systems would 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". 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. | Frequently renewable electricity sources are disadvantaged by regulation of the electricity supply industry which favors 'traditional' large-scale generators over smaller-scale and more distributed generating sources. If renewable and [[distributed generation]] were to become widespread, [[electric power transmission]] and [[electricity distribution]] systems would 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". 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. | ||
| − | ===Solar thermal electric energy=== | + | ====Solar thermal electric energy==== |
| + | |||
The second method for utilizing solar energy is solar thermal. A solar thermal power plant has a system of [[mirror]]s to concentrate the sunlight on to an absorber, the resulting heat then being used to drive turbines. The concentrator is usually a long parabolic mirror trough oriented north-south, which tilts, tracking the Sun's path through the day. A black absorber tube is located at the focal point and converts the solar radiation to heat (about 400°C) which is transferred into a fluid such as synthetic oil. The oil can be used to heat buildings or water, or it can be used to drive a conventional turbine and generator. Several such installations in modules of 80 MW are now operating. Each module requires about 50 hectares of land and needs very precise engineering and control. These plants are supplemented by a gas-fired boiler which ensures full-time energy output. The gas generates about a quarter of the overall power output and keeps the system warm overnight. Over 800 MWe capacity worldwide has supplied about 80% of the total solar electricity to the mid-[[1990s]]. | The second method for utilizing solar energy is solar thermal. A solar thermal power plant has a system of [[mirror]]s to concentrate the sunlight on to an absorber, the resulting heat then being used to drive turbines. The concentrator is usually a long parabolic mirror trough oriented north-south, which tilts, tracking the Sun's path through the day. A black absorber tube is located at the focal point and converts the solar radiation to heat (about 400°C) which is transferred into a fluid such as synthetic oil. The oil can be used to heat buildings or water, or it can be used to drive a conventional turbine and generator. Several such installations in modules of 80 MW are now operating. Each module requires about 50 hectares of land and needs very precise engineering and control. These plants are supplemented by a gas-fired boiler which ensures full-time energy output. The gas generates about a quarter of the overall power output and keeps the system warm overnight. Over 800 MWe capacity worldwide has supplied about 80% of the total solar electricity to the mid-[[1990s]]. | ||
One proposal for a solar electrical plant is the [[solar tower]], in which a large area of land would be covered by a greenhouse made of something as simple as transparent foil, with a tall lightweight tower in the centre, which could also be composed largely of foil. The heated air would rush to and up the centre tower, spinning a turbine. A system of water pipes placed throughout the greenhouse would allow the capture of excess thermal energy, to be released throughout the night and thus providing 24-hour power production. A 200 MWe tower is proposed near [[Mildura, Australia]]. | One proposal for a solar electrical plant is the [[solar tower]], in which a large area of land would be covered by a greenhouse made of something as simple as transparent foil, with a tall lightweight tower in the centre, which could also be composed largely of foil. The heated air would rush to and up the centre tower, spinning a turbine. A system of water pipes placed throughout the greenhouse would allow the capture of excess thermal energy, to be released throughout the night and thus providing 24-hour power production. A 200 MWe tower is proposed near [[Mildura, Australia]]. | ||
| − | ===Solar thermal energy=== | + | ====Solar thermal energy==== |
| − | Solar energy need not be converted to electricity for use. Many of the world's energy needs are simply for heat | + | |
| + | Solar energy need not be converted to electricity for use. Many of the world's energy needs are simply for heat; space heating, water heating, process water heating, oven heating, and so forth. The main role of solar energy in the future may be that of direct heating. Much of society's energy need is for heat below 60°C (140°F) - e.g. in hot water systems. A lot more, particularly in industry, is for heat in the range 60 - 110°C. Together these may account for a significant proportion of primary energy use in industrialized nations. The first need can readily be supplied by solar power much of the time in some places, and the second application commercially is probably not far off. Such uses will diminish to some extent both the demand for electricity and the consumption of fossil fuels, particularly if coupled with [[energy conservation]] measures such as [[insulation]]. | ||
| + | |||
| + | =====Solar water heating===== | ||
| − | |||
Domestic solar hot water systems were once common in [[Florida]] until they were displaced by highly-advertized natural gas. Such systems are today common in the hotter areas of | Domestic solar hot water systems were once common in [[Florida]] until they were displaced by highly-advertized natural gas. Such systems are today common in the hotter areas of | ||
[[Australia]], and simply consist of a network of dark-colored pipes | [[Australia]], and simply consist of a network of dark-colored pipes | ||
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some remoter areas of Australia where electricity is expensive. | some remoter areas of Australia where electricity is expensive. | ||
| − | ====Solar heat pumps==== | + | =====Solar heat pumps===== |
| + | |||
With adequate insulation, [[heat pump]]s utilizing the conventional | With adequate insulation, [[heat pump]]s utilizing the conventional | ||
refrigeration cycle can be used to warm and cool buildings, with very | refrigeration cycle can be used to warm and cool buildings, with very | ||
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electrical energy. | electrical energy. | ||
| − | ====Solar ovens==== | + | =====Solar ovens===== |
| + | |||
Large scale solar thermal powerplants, as mentioned before, can be | Large scale solar thermal powerplants, as mentioned before, can be | ||
used to heat buildings, but on a smaller scale [[solar oven]]s can be | used to heat buildings, but on a smaller scale [[solar oven]]s can be | ||
| Line 118: | Line 139: | ||
pot which heats up as it would in a standard [[oven]]. | pot which heats up as it would in a standard [[oven]]. | ||
| + | ===Wind energy=== | ||
| − | |||
[[Wind generator|Wind turbines]] have been used for household electricity generation in conjunction with [[battery (electricity)|battery]] storage over many decades in remote areas. Generator units of more than 1 MWe are now functioning in several countries. The power output is a function of the cube of the wind speed, so such turbines require a wind in the range 3 to 25 | [[Wind generator|Wind turbines]] have been used for household electricity generation in conjunction with [[battery (electricity)|battery]] storage over many decades in remote areas. Generator units of more than 1 MWe are now functioning in several countries. The power output is a function of the cube of the wind speed, so such turbines require a wind in the range 3 to 25 | ||
m/s (11 - 90 km/h), and in practice relatively few | m/s (11 - 90 km/h), and in practice relatively few | ||
| Line 131: | Line 152: | ||
generation at the turn of the [[21st century]] and provides a complement to large-scale base-load power stations. [[Denmark]] generates over 10% of its electricity with wind[[turbine]]s, whereas windturbines account for 0.4% of the total electricity production on a global scale (ultimo [[2002]]). The most economical and practical size of commercial wind turbines seems to be around 600 kWe to 1 MWe, grouped into large wind farms. Most turbines operate at about 25% load factor over the course of a year, but some reach 35%. | generation at the turn of the [[21st century]] and provides a complement to large-scale base-load power stations. [[Denmark]] generates over 10% of its electricity with wind[[turbine]]s, whereas windturbines account for 0.4% of the total electricity production on a global scale (ultimo [[2002]]). The most economical and practical size of commercial wind turbines seems to be around 600 kWe to 1 MWe, grouped into large wind farms. Most turbines operate at about 25% load factor over the course of a year, but some reach 35%. | ||
| − | ==Geothermal | + | ==Geothermal energy== |
| + | |||
Where hot underground steam or water can be tapped and brought to the surface | 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 have | it may be used to generate electricity. Such [[geothermal power]] sources have | ||
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and using the steam thus produced for electricity generation. An Australian startup company, Geodynamics, proposes to build a commercial plant in the Cooper Basin region of [[South Australia]] using this technology by [[2004]]. | and using the steam thus produced for electricity generation. An Australian startup company, Geodynamics, proposes to build a commercial plant in the Cooper Basin region of [[South Australia]] using this technology by [[2004]]. | ||
| − | ==Water power== | + | ===Water power=== |
| + | |||
Energy inherent in water can be harnessed and used, in the forms of kinetic energy or temperature differences. | Energy inherent in water can be harnessed and used, in the forms of kinetic energy or temperature differences. | ||
| − | ===Electrokinetic energy=== | + | ====Electrokinetic energy==== |
| + | |||
This type of energy harnesses what happens to water when it is pumped through tiny channels. See [[electrokinetics]] (water). | This type of energy harnesses what happens to water when it is pumped through tiny channels. See [[electrokinetics]] (water). | ||
| − | ===Hydroelectric | + | ====Hydroelectric energy==== |
| − | [[Hydroelectric]] energy produces essentially no [[carbon dioxide]], in contrast to burning [[fossil fuel]]s or gas, and so is not a significant contributor to global warming. Hydroelectric power from potential energy of rivers, now supplies about 715,000 [[MWe]] or 19% of world electricity. Apart from a few countries with an abundance of it, hydro capacity is normally applied to peak-load demand, because it is so readily stopped and started. It is not a | + | |
| − | major option for the future in the developed countries because most major sites in these countries having potential for harnessing gravity in this way are either being exploited already or are unavailable for other reasons such as environmental considerations. | + | [[Hydroelectric]] energy produces essentially no [[carbon dioxide]], in contrast to burning [[fossil fuel]]s or gas, and so is not a significant contributor to global warming. Hydroelectric power from potential energy of rivers, now supplies about 715,000 [[MWe]] or 19% of world electricity. Apart from a few countries with an abundance of it, hydro capacity is normally applied to peak-load demand, because it is so readily stopped and started. It is not a major option for the future in the developed countries because most major sites in these countries having potential for harnessing gravity in this way are either being exploited already or are unavailable for other reasons such as environmental considerations. |
| − | The chief advantage of hydrosystems is their capacity to handle seasonal (as well as daily) high peak loads. In practice the utilization of stored water is sometimes complicated by demands for | + | The chief advantage of hydrosystems is their capacity to handle seasonal (as well as daily) high peak loads. In practice the utilization of stored water is sometimes complicated by demands for irrigation which may occur out of phase with peak electrical demands. |
| − | irrigation which may occur out of phase with peak electrical demands. | + | |
| + | ====Tidal power==== | ||
| − | |||
Harnessing the tides in a bay or estuary has been achieved in | Harnessing the tides in a bay or estuary has been achieved in | ||
[[France]] (since [[1966]]) and [[Russia]], and could be achieved in | [[France]] (since [[1966]]) and [[Russia]], and could be achieved in | ||
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to have little potential, largely due to environmental constraints. | to have little potential, largely due to environmental constraints. | ||
| − | ===Tidal stream power=== | + | ====Tidal stream power==== |
| + | |||
A relatively new technology development, tidal stream generators draw energy from underwater currents in much the same way that wind generators are powered by the wind. The much higher density of water means that there is the potetial for a single generator to provide significant levels of power. Tidal stream technology is at the very early stages of development though and will require signifcantly more research before it becomes a significant contributor to electrical generation needs. | A relatively new technology development, tidal stream generators draw energy from underwater currents in much the same way that wind generators are powered by the wind. The much higher density of water means that there is the potetial for a single generator to provide significant levels of power. Tidal stream technology is at the very early stages of development though and will require signifcantly more research before it becomes a significant contributor to electrical generation needs. | ||
| − | ===Wave power=== | + | ====Wave power==== |
| + | |||
Harnessing power from wave motion is a possibility which might yield | Harnessing power from wave motion is a possibility which might yield | ||
much more energy than tides. The feasibility of this has been | much more energy than tides. The feasibility of this has been | ||
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Numerous practical problems have frustrated progress. | Numerous practical problems have frustrated progress. | ||
| − | ===OTEC=== | + | ====OTEC==== |
| + | |||
[[Ocean Thermal Energy Conversion]] is a relatively unproven technology, though it was first used by the French engineer [[Jacques Arsene d'Arsonval]] in [[1881]]. The difference in temperature between water near the surface and deeper water can be as much as 20°C. The warm water is used to make a liquid such as [[ammonia]] evaporate, causing it to expand. The expanding gas forces its way through turbines, after which it is condensed using the colder water and the cycle can begin again. | [[Ocean Thermal Energy Conversion]] is a relatively unproven technology, though it was first used by the French engineer [[Jacques Arsene d'Arsonval]] in [[1881]]. The difference in temperature between water near the surface and deeper water can be as much as 20°C. The warm water is used to make a liquid such as [[ammonia]] evaporate, causing it to expand. The expanding gas forces its way through turbines, after which it is condensed using the colder water and the cycle can begin again. | ||
| − | ==Biomass== | + | ===Biomass=== |
| + | |||
[[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]] (a byproduct of [[sugar cane]] cultivation) are burned in [[internal combustion engine]]s or [[boiler]]s. | [[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]] (a byproduct of [[sugar cane]] cultivation) are burned in [[internal combustion engine]]s or [[boiler]]s. | ||
| − | ===Liquid biofuel=== | + | ====Liquid biofuel==== |
| + | |||
Liquid biofuel is usually bioalcohols -like [[methanol]] and [[ethanol]]- or [[biodiesel]]. Biodiesel can be used in modern diesel vehicles with little or no modification and can be obtained from waste and crude vegetable and animal oil and fats ([[lipid]]s). In some areas [[maize|corn]], [[sugarbeet]]s, cane and grasses are grown specifically to produce [[ethanol]] (also known as alcohol) a liquid which can be used in [[internal combustion engine]]s and [[fuel cells]]. | Liquid biofuel is usually bioalcohols -like [[methanol]] and [[ethanol]]- or [[biodiesel]]. Biodiesel can be used in modern diesel vehicles with little or no modification and can be obtained from waste and crude vegetable and animal oil and fats ([[lipid]]s). In some areas [[maize|corn]], [[sugarbeet]]s, cane and grasses are grown specifically to produce [[ethanol]] (also known as alcohol) a liquid which can be used in [[internal combustion engine]]s and [[fuel cells]]. | ||
| − | ===Solid biomass=== | + | ====Solid biomass==== |
| + | |||
Direct use is usually in the form of combustible solids, either firewood 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. Plants partly use [[photosynthesis]] to store solar energy, water and [[CO2|CO]]<sub>2</sub>. [[Sugar cane]] residue, [[wheat]] chaff, [[maize|corn cobs]] and other plant matter can be, and is, burnt quite successfully. The process releases no net CO<sub>2</sub>. | Direct use is usually in the form of combustible solids, either firewood 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. Plants partly use [[photosynthesis]] to store solar energy, water and [[CO2|CO]]<sub>2</sub>. [[Sugar cane]] residue, [[wheat]] chaff, [[maize|corn cobs]] and other plant matter can be, and is, burnt quite successfully. The process releases no net CO<sub>2</sub>. | ||
| − | ===Biogas=== | + | ====Biogas==== |
| + | |||
Animal [[feces]] (manure) release [[methane]] under the influence of [[anaerobic bacteria]] which can also be used to generate electricity. See [[biogas]]. | Animal [[feces]] (manure) release [[methane]] under the influence of [[anaerobic bacteria]] which can also be used to generate electricity. See [[biogas]]. | ||
| − | =Renewable energy storage systems= | + | ==Renewable energy storage systems== |
| + | |||
One of the great problems with renewable energy, as mentioned above, is transporting it in time or space. Since most renewable energy sources are periodic, storage for off-generation times is important, and storage for powering transportation is also a critical issue. | One of the great problems with renewable energy, as mentioned above, is transporting it in time or space. Since most renewable energy sources are periodic, storage for off-generation times is important, and storage for powering transportation is also a critical issue. | ||
| − | ==Hydrogen fuel cells== | + | ===Hydrogen fuel cells=== |
| + | |||
[[Hydrogen]] as a fuel has been touted lately as a solution in our energy dilemmas. However, the idea that hydrogen is a renewable energy source is a misunderstanding. Hydrogen is not an energy source, but a portable energy storage method, because it must be manufactured by other energy sources in order to be used. However, as a storage medium, it may be a significant factor in using renewable energies. It is widely seen as a possible fuel for [[hydrogen car]]s, if certain problems can be overcome economically. It may be used in conventional [[internal combustion engine]]s, or in [[fuel cell]]s which convert chemical energy directly to electricity without flames, in the same way the human body burns fuel. Making hydrogen requires either reforming natural gas ([[methane]]) with steam, or, for a renewable and more ecologic source, ''the [[electrolysis]] of [[water]]'' into hydrogen and [[oxygen]]. The former process has [[carbon dioxide]] as a by-product, which exacerbates (or at least does not improve) [[greenhouse gas]] emissions relative to present technology. With electrolysis, the greenhouse burden depends on the source of the power, and both intermittent renewables and [[nuclear energy]] are considered here. | [[Hydrogen]] as a fuel has been touted lately as a solution in our energy dilemmas. However, the idea that hydrogen is a renewable energy source is a misunderstanding. Hydrogen is not an energy source, but a portable energy storage method, because it must be manufactured by other energy sources in order to be used. However, as a storage medium, it may be a significant factor in using renewable energies. It is widely seen as a possible fuel for [[hydrogen car]]s, if certain problems can be overcome economically. It may be used in conventional [[internal combustion engine]]s, or in [[fuel cell]]s which convert chemical energy directly to electricity without flames, in the same way the human body burns fuel. Making hydrogen requires either reforming natural gas ([[methane]]) with steam, or, for a renewable and more ecologic source, ''the [[electrolysis]] of [[water]]'' into hydrogen and [[oxygen]]. The former process has [[carbon dioxide]] as a by-product, which exacerbates (or at least does not improve) [[greenhouse gas]] emissions relative to present technology. With electrolysis, the greenhouse burden depends on the source of the power, and both intermittent renewables and [[nuclear energy]] are considered here. | ||
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About 50 kWh (1/144,000 J) is required to produce a kilogram of hydrogen by electrolysis, so the cost of the electricity clearly is crucial. | About 50 kWh (1/144,000 J) is required to produce a kilogram of hydrogen by electrolysis, so the cost of the electricity clearly is crucial. | ||
| − | ==Other renewable energy storage systems== | + | ===Other renewable energy storage systems=== |
| + | |||
Sun, wind, tides and waves cannot be controlled to provide directly either reliably continuous base-load power, because of their periodic natures, or peak-load power when it is needed. In practical terms, without proper energy storage methods these sources are therefore limited to some twenty percent of the capacity of an electricity grid, and cannot directly be applied as economic substitutes for fossil fuels or nuclear power, however important they may become in particular areas with favorable conditions. If there were some way that large amounts of electricity from intermittent producers such as solar and wind could be stored efficiently, the contribution of these technologies to supplying base-load energy demand would be much greater. | Sun, wind, tides and waves cannot be controlled to provide directly either reliably continuous base-load power, because of their periodic natures, or peak-load power when it is needed. In practical terms, without proper energy storage methods these sources are therefore limited to some twenty percent of the capacity of an electricity grid, and cannot directly be applied as economic substitutes for fossil fuels or nuclear power, however important they may become in particular areas with favorable conditions. If there were some way that large amounts of electricity from intermittent producers such as solar and wind could be stored efficiently, the contribution of these technologies to supplying base-load energy demand would be much greater. | ||
| − | ===Pumped water storage=== | + | ====Pumped water storage==== |
| + | |||
Already in some places [[pumped storage hydroelectricity|pumped storage]] is used to even out the daily generating load by pumping water to a high storage dam during off-peak hours and weekends, using the excess base-load capacity from coal or nuclear sources. During peak hours this water can be used for hydroelectric generation. However, relatively few places have the scope for pumped storage dams close to where the power is needed. | Already in some places [[pumped storage hydroelectricity|pumped storage]] is used to even out the daily generating load by pumping water to a high storage dam during off-peak hours and weekends, using the excess base-load capacity from coal or nuclear sources. During peak hours this water can be used for hydroelectric generation. However, relatively few places have the scope for pumped storage dams close to where the power is needed. | ||
| − | ===Battery storage=== | + | ====Battery storage==== |
| + | |||
Many "off-the-grid" domestic systems rely on battery storage, but means of storing large amounts of electricity as such in giant batteries or by other means have not yet been put to general use. Batteries are generally expensive, have maintenance problems, and have limited lifespans. One possible technology for large-scale storage exists: large-scale flow batteries. | Many "off-the-grid" domestic systems rely on battery storage, but means of storing large amounts of electricity as such in giant batteries or by other means have not yet been put to general use. Batteries are generally expensive, have maintenance problems, and have limited lifespans. One possible technology for large-scale storage exists: large-scale flow batteries. | ||
| − | ===Electrical grid storage=== | + | ====Electrical grid storage==== |
| + | |||
One of the most important storage methods advocated by the renewable energy community is to rethink the whole way that we look at power supply, in its 24-hour, 7-day cycle, using peak load equipment simply to meet the daily peaks. Solar electric generation is a daylight process, whereas most homes have their peak energy requirements at night. Domestic solar generation can thus feed electricity into the grid during grid peaking times during the day, and domestic systems can then draw power from the grid during the night when overall grid loads are down. This results in using the power grid as a domestic energy storage system, and relies on ?'net metering'?, where electrical companies can only charge for the amount of electricity used in the home that is in excess of the electricity generated and fed back into the grid. Many states now have net metering laws. | One of the most important storage methods advocated by the renewable energy community is to rethink the whole way that we look at power supply, in its 24-hour, 7-day cycle, using peak load equipment simply to meet the daily peaks. Solar electric generation is a daylight process, whereas most homes have their peak energy requirements at night. Domestic solar generation can thus feed electricity into the grid during grid peaking times during the day, and domestic systems can then draw power from the grid during the night when overall grid loads are down. This results in using the power grid as a domestic energy storage system, and relies on ?'net metering'?, where electrical companies can only charge for the amount of electricity used in the home that is in excess of the electricity generated and fed back into the grid. Many states now have net metering laws. | ||
Today's peak-load equipment could also be used to some extent to provide infill capacity in a system relying heavily on renewables. The peak capacity would complement large-scale solar thermal and wind generation, providing power when they were unable to. Improved ability to predict the intermittent availability of wind enables better use of this resource. In Germany it is now possible to predict wind generation output with 90% certainty 24 hours ahead. This means that it is possible to deploy other plants more effectively so that the economic value of that wind contribution is greatly increased. | Today's peak-load equipment could also be used to some extent to provide infill capacity in a system relying heavily on renewables. The peak capacity would complement large-scale solar thermal and wind generation, providing power when they were unable to. Improved ability to predict the intermittent availability of wind enables better use of this resource. In Germany it is now possible to predict wind generation output with 90% certainty 24 hours ahead. This means that it is possible to deploy other plants more effectively so that the economic value of that wind contribution is greatly increased. | ||
| − | =Renewable energy use by nation= | + | ==Renewable energy use by nation== |
| + | |||
[[Iceland]] is a world leader in renewable energy due to its abundant hydro- and geothermal energy sources. Over 99% of the country's electricity is from renewable sources and most of its urban household heating is geothermal. [[Israel]] is also notable as much of its household hot water is heated by solar means. These countries' successes are at least partly based on their geographical advantages. | [[Iceland]] is a world leader in renewable energy due to its abundant hydro- and geothermal energy sources. Over 99% of the country's electricity is from renewable sources and most of its urban household heating is geothermal. [[Israel]] is also notable as much of its household hot water is heated by solar means. These countries' successes are at least partly based on their geographical advantages. | ||
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4.</td><td> [[China]]</td><td> [[Mexico]]</td><td> [[Denmark]]</td><td> [[India]]</td><td></tr><tr><td> | 4.</td><td> [[China]]</td><td> [[Mexico]]</td><td> [[Denmark]]</td><td> [[India]]</td><td></tr><tr><td> | ||
5.</td><td> [[Russia]]</td><td> [[Indonesia]]</td><td> India</td><td> [[Australia]] </tr></td> </table> | 5.</td><td> [[Russia]]</td><td> [[Indonesia]]</td><td> India</td><td> [[Australia]] </tr></td> </table> | ||
| − | |||
Share of the total power consumption in [[EU]]-countries that are renewable. | Share of the total power consumption in [[EU]]-countries that are renewable. | ||
| Line 245: | Line 282: | ||
Table from [http://europa.eu.int/abc/doc/off/bull/sv/9709/p106003.htm] | Table from [http://europa.eu.int/abc/doc/off/bull/sv/9709/p106003.htm] | ||
| − | =Renewable energy controversies= | + | ==Renewable energy controversies== |
| + | |||
As with anything, even renewable energy generates controversies. | As with anything, even renewable energy generates controversies. | ||
| − | ==Lack of motivation for funding== | + | ===Lack of motivation for funding=== |
| + | |||
Research and development in renewable energies has been severely hampered by only receiving a tiny fraction of energy R&D budgets, with conventional energy sources getting the lion's share. | Research and development in renewable energies has been severely hampered by only receiving a tiny fraction of energy R&D budgets, with conventional energy sources getting the lion's share. | ||
| − | ==Centralization versus decentralization== | + | ===Centralization versus decentralization=== |
| + | |||
Frequently renewable electricity sources will be disadvantaged by regulation of the electricity supply industry which favors 'traditional' large-scale generators over smaller-scale and more distributed generating sources. If renewable and [[distributed generation]] were to become widespread, [[electric power transmission]] and [[electricity distribution]] systems would 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". 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. | Frequently renewable electricity sources will be disadvantaged by regulation of the electricity supply industry which favors 'traditional' large-scale generators over smaller-scale and more distributed generating sources. If renewable and [[distributed generation]] were to become widespread, [[electric power transmission]] and [[electricity distribution]] systems would 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". 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. | ||
| − | ==The nuclear "renewable" claim== | + | ===The nuclear "renewable" claim=== |
| + | |||
Some nuclear advocates claim that [[nuclear energy]] should be regarded as renewable energy. | Some nuclear advocates claim that [[nuclear energy]] should be regarded as renewable energy. | ||
Arguments often put forward include: | Arguments often put forward include: | ||
| + | |||
*Nuclear energy does not contribute to [[global warming]]. | *Nuclear energy does not contribute to [[global warming]]. | ||
**Evaporative cooling has a minor effect by introducing additional water vapor into the atmosphere, along with the heat production of the process. However, both of these are insignificant compared to [[geothermal]] events such as [[volcano|volcanoes]]. | **Evaporative cooling has a minor effect by introducing additional water vapor into the atmosphere, along with the heat production of the process. However, both of these are insignificant compared to [[geothermal]] events such as [[volcano|volcanoes]]. | ||
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<!-- and [[tritium]], the latter bred from [[lithium]], ''Never heard of this.'' [[User:MrJones|Mr. Jones]] 16:21, 12 May 2004 (UTC) --> | <!-- and [[tritium]], the latter bred from [[lithium]], ''Never heard of this.'' [[User:MrJones|Mr. Jones]] 16:21, 12 May 2004 (UTC) --> | ||
| − | =References= | + | ==References== |
| + | |||
*[http://eia.doe.gov/ U.S. Energy Information Administration] provides lots of statistics and information on the industry. | *[http://eia.doe.gov/ U.S. Energy Information Administration] provides lots of statistics and information on the industry. | ||
*Boyle, G. (ed.), ''Renewable Energy: Power for a Sustainable Future''. Open University, UK, 1996. | *Boyle, G. (ed.), ''Renewable Energy: Power for a Sustainable Future''. Open University, UK, 1996. | ||
| + | |||
| + | [[Category:Environment]] | ||
| + | [[Category:Sustainability]] | ||
Revision as of 12:40, 2 June 2004
[[pl:Odnawialne %BCr%F3d%B3a energii]] es:energía renovablenl:Duurzame energiede:Regenerative Energie
Renewable energy is energy from a source which can be managed so that it is not subject to depletion in a human timescale . Sources include the sun's rays, wind, waves, rivers, tides, biomass, and geothermal. Renewable energy does not include energy sources which are dependent upon limited resources, such as fossil fuels and nuclear fission power.
General Information
Most renewable forms of energy, other than geothermal, are in fact stored solar energy. Water power and wind power represent very short-term solar storage, while biomass represents slightly longer-term storage, but still on a very human time-scale, and so renewable within that human time-scale. Fossil fuels, on the other hand, while still stored solar energy, have taken millions of years to form, and so do not meet the definition of renewable.
Renewable energy resources may be used directly as energy sources, or used to create other forms of energy for use. Examples of direct use are solar ovens, geothermal heat pumps, and mechanical windmills. Examples of indirect use in creating other energy sources are electricity generation through wind generators or photovoltaic cells, or production of fuels such as ethanol from biomass (see alcohol as a fuel).
Pros and cons of renewable energy
Renewable energy sources are fundamentally different from fossil fuel or nuclear power plants because of their widespread occurrence and abundance - the sun will 'power' these 'powerplants' (meaning sunlight, the wind, flowing water, etc.) for the next 4 billion years. The primary advantage of many renewable energy sources are their lack of greenhouse gas and other emissions in comparison with fossil fuel combustion. Some renewable sources do not emit any additional carbon dioxide and do not introduce any new risks such as nuclear waste. In fact, one renewable energy source, wood, actively sequesters carbon dioxide while growing.
A visible disadvantage of renewables is their visual impact on local environments. 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. Some people try to utilize these renewable technologies in an efficient and aesthetically pleasing way: fixed solar collectors can double as noise barriers along highways, roof-tops are available already and could even be replaced totally by solar collectors, etc.
Some renewable energy capture systems entail unique environmental problems. For instance, wind turbines can be hazardous to flying birds, while hydroelectric dams can create barriers for migrating fish ? a serious problem in the Pacific Northwest that has decimated the numbers of many salmon populations.
Another inherent difficulty with renewables is their variable and diffuse nature (with the exception being geothermal energy, which is however only accessible where the earth's crust is thin, such as near hot springs and natural geysers). 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. To make the phrases 'low-intensity' and 'large area' easier to understand, note that in order to produce 1000 kWh of electricity per month (a typical per-month-per-capita consumption of electricity in Western countries), a home owner in cloudy Europe needs to use ten square meters of solar panels. Systematic electrical generation requires reliable overlapping sources or some means of storage on a reasonable scale (pumped-storage hydro systems, batteries, future hydrogen fuel cells, etc.). So, because of currently-expensive energy storage systems, a small stand-alone system is only economic in rare cases.
The geogrpahic 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 centres 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.
If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems would 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. This will require significant changes in the way that such networks are operated. In turn this may also require changes in the regulation which provides incentives to network operators in the way that they invest in their networks.
Renewable energy history
The original energy source for all human activity was the sun via growing plants. Solar energy's main human application throughout most of history has thus been in agriculture and forestry, via photosynthesis.
Wood
Firewood was the earliest manipulated energy source in human history, being used as a thermal energy source through burning, and it is still important in this context today. Burning wood was important for both cooking and providing heat, enabling human presence in cold climates. Special types of wood cooking, food dehydration and smoke curing, also enabled human societies to safely store perishable foodstuffs through the year. Eventually, it was discovered that partial combustion in the relative absence of oxygen could produce charcoal, which provided a hotter and more compact and portable energy source. However, this was not a more efficient energy source, because it required a large input in wood to create the charcoal.
Animal traction
Motive power for vehicles and mechanical devices was originally produced through animal traction. Animals such as horses and oxen not only provided transportation but also powered mills. Animals are still extensively in use in many parts of the world for these purposes.
Water power
Animal power for mills was eventually supplanted by water power, the power of falling water in rivers, wherever it was exploitable. Direct use of water power for mechanical purposes is today fairly uncommon, but still in use.
Originally, water power through (hydroelectricity) was the most important source of electrical generation throughout society, and is still an important source today. Throughout most of the history of human technology, hydroelectricity has been the only renewable source of electricity generation significantly tapped for the generation of electricity.
Wind power
Wind power has been used for several hundred years. It was originally used via large sail-blade windmills with slow-moving blades, such as those seen in the Netherlands and mentioned in Don Quixote. These large mills usually either pumped water or powered small mills. Newer windmills featured smaller, faster-turning, more compact units with more blades, such as those seen throughout the Great Plains. These were mostly used for pumping water from wells. Recent years have seen the rapid development of wind generation farms by mainstream power companies, using a new generation of large, high wind turbines with two or three immense and relatively slow-moving blades.
Solar power
Solar power as a direct energy source has been not been captured by mechanical systems until recent human history, but was captured as an energy source through architecture in certain societies for many centuries. Not until the twentieth century was direct solar input extensively explored via more carefully planned architecture (passive solar) or via heat capture in mechanical systems (active solar) or electrical conversion (photovoltaic). Increasingly today the sun is harnessed for heat and electricity.
The renewable energy movement
Renewable energy as an issue was virtually unheard-of before the middle of the twentieth century. There were experimentations with passive solar energy, including daylighting, in the early part of the twentieth century, but little beyond what had actually been practiced as a matter of course in some locales for hundreds of years. The renewable energy movement gained awareness, credence and strength with the great burgeoning of interest in environmental affairs in the mid-1900s, which in turn was largely due to Rachel Carson's ?'Silent Spring'?.
The first US politician to focus significantly on solar energy was Jimmy Carter, in response to the long term consequences of the 1973 energy crisis. No president since has paid much attention to renewable energy.
Renewable energy today
Around 80% of energy requirements are focused around heating or cooling buildings and powering the vehicles that ensure mobility (cars, trains, airplanes). This is the core of society's energy requirements. However, most uses of renewable power focus on electricity generation.
Geothermal heat pumps (also called ground-source heat pumps) are a means of extracting heat in the winter or cold in the summer from the earth to heat or cool buildings.
Modern sources of renewable energy
There are several types of renewable energy, including the following:
- Solar power.
- Wind power.
- Geothermal energy.
- Electrokinetic energy.
- Hydroelectricity.
- Biomatter, including Biogas Energy.
Smaller-scale sources
Of course there are some smaller-scale applications as well:
- Piezo electric crystals embedded in the sole of a shoe can yield a small amount of energy with each step. Vibration from engines can stimulate piezo electric crystals.
- Some watches are already powered by movement of the arm.
- Special antennae can collect energy from stray radiowaves or even light (EM radiation).
Renewables as solar energy
Most renewable energy sources can trace their roots to solar energy, with the exception of geothermal and tidal power. For example, wind is caused by the sun heating the earth unevenly. Hot air is less dense, so it rises, causing cooler air to move in to replace it. Hydroelectric power can be ultimately traced to the sun too. When the sun evaporates water in the ocean, the vapor forms clouds which later fall on mountains as rain which is routed through turbines to generate electrity. The transformation goes from solar energy to potential energy to kinetic energy to electric energy.
Solar energy per se
Since most renewable energy is "Solar Energy" this term is slightly confusing and used in two different ways: firstly as a synonym for "renewable energies" as a whole (like in the political slogan "Solar not nuclear") and secondly for the energy that is directly collected from solar radiation. In this section it is used in the latter category.
There are actually two separate approaches to solar energy, termed active solar and passive solar.
Solar electrical energy
For electricity generation, ground-based solar power has serious limitations because of its diffuse and intermittent nature. First, ground-based solar input is interrupted by night and by cloud cover, which means that solar electric generation inevitably has a low capacity factor, typically less than 20%. Also, there is a low intensity of incoming radiation, and converting this to high grade electricity is still relatively inefficient (14% - 18%), though increased efficiency or lower production costs have been the subject of much research over several decades.
Two methods of converting the Sun's radiant energy to electricity are the focus of attention. The better-known method uses sunlight acting on photovoltaic (PV) cells to produce electricity. This has many applications in satellites, small devices and lights, grid-free applications, earthbound signaling and communication equipment, such as remote area telecommunications equipment. Sales of solar PV modules are increasing strongly as their efficiency increases and price diminishes. But the high cost per unit of electricity still rules out most uses.
Several experimental PV power plants mostly of 300 - 500 kW capacity are connected to electricity grids in Europe and the USA. Japan has 150 MWe installed. A large solar PV plant was planned for Crete. In 2001 the world total for PV electricity was less than 1000 MWe with Japan as the world's leading producer. Research continues into ways to make the actual solar collecting cells less expensive and more efficient. Other major research is investigating economic ways to store the energy which is collected from the Sun's rays during the day.
Alternatively, many individuals have installed small-scale PV arrays for domestic consumption. Some, particularly in isolated areas, are totally disconnected from the main power grid, and rely on a surplus of generation capacity combined with batteries and/or a fossil fuel generator to cover periods when the cells are not operating. Others in more settled areas remain connected to the grid, using the grid to obtain electricity when solar cells are not providing power, and selling their surplus back to the grid. This works reasonably well in many climates, as the peak time for energy consumption is on hot, sunny days where air conditioners are running and solar cells produce their maximum power output. Many U.S. states have passed "net metering" laws, requiring electrical utilities to buy the locally-generated electricity for price comparable to that sold to the household. Photovoltaic generation is still considerably more expensive for the consumer than grid electricity unless the usage site is sufficiently isolated, in which case photovoltaics become the less expensive.
System problems with solar electric
Frequently renewable electricity sources are disadvantaged by regulation of the electricity supply industry which favors 'traditional' large-scale generators over smaller-scale and more distributed generating sources. If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems would 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". 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.
Solar thermal electric energy
The second method for utilizing solar energy is solar thermal. A solar thermal power plant has a system of mirrors to concentrate the sunlight on to an absorber, the resulting heat then being used to drive turbines. The concentrator is usually a long parabolic mirror trough oriented north-south, which tilts, tracking the Sun's path through the day. A black absorber tube is located at the focal point and converts the solar radiation to heat (about 400°C) which is transferred into a fluid such as synthetic oil. The oil can be used to heat buildings or water, or it can be used to drive a conventional turbine and generator. Several such installations in modules of 80 MW are now operating. Each module requires about 50 hectares of land and needs very precise engineering and control. These plants are supplemented by a gas-fired boiler which ensures full-time energy output. The gas generates about a quarter of the overall power output and keeps the system warm overnight. Over 800 MWe capacity worldwide has supplied about 80% of the total solar electricity to the mid-1990s.
One proposal for a solar electrical plant is the solar tower, in which a large area of land would be covered by a greenhouse made of something as simple as transparent foil, with a tall lightweight tower in the centre, which could also be composed largely of foil. The heated air would rush to and up the centre tower, spinning a turbine. A system of water pipes placed throughout the greenhouse would allow the capture of excess thermal energy, to be released throughout the night and thus providing 24-hour power production. A 200 MWe tower is proposed near Mildura, Australia.
Solar thermal energy
Solar energy need not be converted to electricity for use. Many of the world's energy needs are simply for heat; space heating, water heating, process water heating, oven heating, and so forth. The main role of solar energy in the future may be that of direct heating. Much of society's energy need is for heat below 60°C (140°F) - e.g. in hot water systems. A lot more, particularly in industry, is for heat in the range 60 - 110°C. Together these may account for a significant proportion of primary energy use in industrialized nations. The first need can readily be supplied by solar power much of the time in some places, and the second application commercially is probably not far off. Such uses will diminish to some extent both the demand for electricity and the consumption of fossil fuels, particularly if coupled with energy conservation measures such as insulation.
Solar water heating
Domestic solar hot water systems were once common in Florida until they were displaced by highly-advertized natural gas. Such systems are today common in the hotter areas of Australia, and simply consist of a network of dark-colored pipes running beneath a window of heat-trapping glass. They typically have a backup electric or gas heating unit for cloudy days. Such systems can actually be justified purely on economic grounds, particularly in some remoter areas of Australia where electricity is expensive.
Solar heat pumps
With adequate insulation, heat pumps utilizing the conventional refrigeration cycle can be used to warm and cool buildings, with very little energy input other than energy needed to run a compressor. Eventually, up to ten percent of the total primary energy need in industrialized countries may be supplied by direct solar thermal techniques, and to some extent this will substitute for base-load electrical energy.
Solar ovens
Large scale solar thermal powerplants, as mentioned before, can be used to heat buildings, but on a smaller scale solar ovens can be used on sunny days. Such an oven or solar furnace uses mirrors or a large lens to focus the Sun's rays onto a baking tray or black pot which heats up as it would in a standard oven.
Wind energy
Wind turbines have been used for household electricity generation in conjunction with battery storage over many decades in remote areas. Generator units of more than 1 MWe are now functioning in several countries. The power output is a function of the cube of the wind speed, so such turbines require a wind in the range 3 to 25 m/s (11 - 90 km/h), and in practice relatively few land areas have significant prevailing winds. Like solar, wind power requires alternative power sources to cope with calmer periods.
There are now many thousands of wind turbines operating in various parts of the world, with utility companies having a total capacity of over 39,000 MWe of which Europe accounts for 75% (ultimo 2003). Additional windpower is generated by private windmills both on-grid and off-grid. Germany is the leading producer of wind generated electricity with over 14,600 MWe in 2003. In 2003 the U.S.A. produced over 6,300 Mwe of wind energy, second only to Germany.
New wind farms and offshore wind parks are being planned and built all over the world. This has been the most rapidly-growing means of electricity generation at the turn of the 21st century and provides a complement to large-scale base-load power stations. Denmark generates over 10% of its electricity with windturbines, whereas windturbines account for 0.4% of the total electricity production on a global scale (ultimo 2002). The most economical and practical size of commercial wind turbines seems to be around 600 kWe to 1 MWe, grouped into large wind farms. Most turbines operate at about 25% load factor over the course of a year, but some reach 35%.
Geothermal energy
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 have potential in certain parts of the world such as New Zealand, United States, 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 MWe geothermal power and heated 86% of all houses in the year 2000. Some 8000 MWe of capacity is operating over all.
There are also prospects in certain other areas for pumping water underground to very hot regions of the Earth's crust and using the steam thus produced for electricity generation. An Australian startup company, Geodynamics, proposes to build a commercial plant in the Cooper Basin region of South Australia using this technology by 2004.
Water power
Energy inherent in water can be harnessed and used, in the forms of kinetic energy or temperature differences.
Electrokinetic energy
This type of energy harnesses what happens to water when it is pumped through tiny channels. See electrokinetics (water).
Hydroelectric energy
Hydroelectric energy produces essentially no carbon dioxide, in contrast to burning fossil fuels or gas, and so is not a significant contributor to global warming. Hydroelectric power from potential energy of rivers, now supplies about 715,000 MWe or 19% of world electricity. Apart from a few countries with an abundance of it, hydro capacity is normally applied to peak-load demand, because it is so readily stopped and started. It is not a major option for the future in the developed countries because most major sites in these countries having potential for harnessing gravity in this way are either being exploited already or are unavailable for other reasons such as environmental considerations.
The chief advantage of hydrosystems is their capacity to handle seasonal (as well as daily) high peak loads. In practice the utilization of stored water is sometimes complicated by demands for irrigation which may occur out of phase with peak electrical demands.
Tidal power
Harnessing the tides in a bay or estuary has been achieved in France (since 1966) and Russia, and could be achieved in certain other areas where there is a large tidal range. The trapped water can be used to turn turbines as it is released through the tidal barrage in either direction. Worldwide this technology appears to have little potential, largely due to environmental constraints.
Tidal stream power
A relatively new technology development, tidal stream generators draw energy from underwater currents in much the same way that wind generators are powered by the wind. The much higher density of water means that there is the potetial for a single generator to provide significant levels of power. Tidal stream technology is at the very early stages of development though and will require signifcantly more research before it becomes a significant contributor to electrical generation needs.
Wave power
Harnessing power from wave motion is a possibility which might yield much more energy than tides. The feasibility of this has been investigated, particularly in the UK. Generators either coupled to floating devices or turned by air displaced by waves in a hollow concrete structure would produce electricity for delivery to shore. Numerous practical problems have frustrated progress.
OTEC
Ocean Thermal Energy Conversion is a relatively unproven technology, though it was first used by the French engineer Jacques Arsene d'Arsonval in 1881. The difference in temperature between water near the surface and deeper water can be as much as 20°C. The warm water is used to make a liquid such as ammonia evaporate, causing it to expand. The expanding gas forces its way through turbines, after which it is condensed using the colder water and the cycle can begin again.
Biomass
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 (a byproduct of sugar cane cultivation) are burned in internal combustion engines or boilers.
Liquid biofuel
Liquid biofuel is usually bioalcohols -like methanol and ethanol- or biodiesel. Biodiesel can be used in modern diesel vehicles with little or no modification and can be obtained from waste and crude vegetable and animal oil and fats (lipids). 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.
Solid biomass
Direct use is usually in the form of combustible solids, either firewood 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. Plants partly use photosynthesis to store solar energy, water and CO2. Sugar cane residue, wheat chaff, corn cobs and other plant matter can be, and is, burnt quite successfully. The process releases no net CO2.
Biogas
Animal feces (manure) release methane under the influence of anaerobic bacteria which can also be used to generate electricity. See biogas.
Renewable energy storage systems
One of the great problems with renewable energy, as mentioned above, is transporting it in time or space. Since most renewable energy sources are periodic, storage for off-generation times is important, and storage for powering transportation is also a critical issue.
Hydrogen fuel cells
Hydrogen as a fuel has been touted lately as a solution in our energy dilemmas. However, the idea that hydrogen is a renewable energy source is a misunderstanding. Hydrogen is not an energy source, but a portable energy storage method, because it must be manufactured by other energy sources in order to be used. However, as a storage medium, it may be a significant factor in using renewable energies. It is widely seen as a possible fuel for hydrogen cars, if certain problems can be overcome economically. It may be used in conventional internal combustion engines, or in fuel cells which convert chemical energy directly to electricity without flames, in the same way the human body burns fuel. Making hydrogen requires either reforming natural gas (methane) with steam, or, for a renewable and more ecologic source, the electrolysis of water into hydrogen and oxygen. The former process has carbon dioxide as a by-product, which exacerbates (or at least does not improve) greenhouse gas emissions relative to present technology. With electrolysis, the greenhouse burden depends on the source of the power, and both intermittent renewables and nuclear energy are considered here.
With intermittent renewables such as solar and wind, matching the output to grid demand is very difficult, and beyond about 20% of the total supply, apparently impossible. But if these sources are used for electricity to make hydrogen, then they can be utilized fully whenever they are available, opportunistically. Broadly speaking it does not matter when they cut in or out, the hydrogen is simply stored and used as required.
Nuclear advocates note that using nuclear power to manufacture hydrogen would help solve plant inefficiencies. Here the plant would be run continuously at full capacity, with perhaps all the output being supplied to the grid in peak periods and any not needed to meet civil demand being used to make hydrogen at other times. This would mean far better efficiency for the nuclear power plants.
About 50 kWh (1/144,000 J) is required to produce a kilogram of hydrogen by electrolysis, so the cost of the electricity clearly is crucial.
Other renewable energy storage systems
Sun, wind, tides and waves cannot be controlled to provide directly either reliably continuous base-load power, because of their periodic natures, or peak-load power when it is needed. In practical terms, without proper energy storage methods these sources are therefore limited to some twenty percent of the capacity of an electricity grid, and cannot directly be applied as economic substitutes for fossil fuels or nuclear power, however important they may become in particular areas with favorable conditions. If there were some way that large amounts of electricity from intermittent producers such as solar and wind could be stored efficiently, the contribution of these technologies to supplying base-load energy demand would be much greater.
Pumped water storage
Already in some places pumped storage is used to even out the daily generating load by pumping water to a high storage dam during off-peak hours and weekends, using the excess base-load capacity from coal or nuclear sources. During peak hours this water can be used for hydroelectric generation. However, relatively few places have the scope for pumped storage dams close to where the power is needed.
Battery storage
Many "off-the-grid" domestic systems rely on battery storage, but means of storing large amounts of electricity as such in giant batteries or by other means have not yet been put to general use. Batteries are generally expensive, have maintenance problems, and have limited lifespans. One possible technology for large-scale storage exists: large-scale flow batteries.
Electrical grid storage
One of the most important storage methods advocated by the renewable energy community is to rethink the whole way that we look at power supply, in its 24-hour, 7-day cycle, using peak load equipment simply to meet the daily peaks. Solar electric generation is a daylight process, whereas most homes have their peak energy requirements at night. Domestic solar generation can thus feed electricity into the grid during grid peaking times during the day, and domestic systems can then draw power from the grid during the night when overall grid loads are down. This results in using the power grid as a domestic energy storage system, and relies on ?'net metering'?, where electrical companies can only charge for the amount of electricity used in the home that is in excess of the electricity generated and fed back into the grid. Many states now have net metering laws.
Today's peak-load equipment could also be used to some extent to provide infill capacity in a system relying heavily on renewables. The peak capacity would complement large-scale solar thermal and wind generation, providing power when they were unable to. Improved ability to predict the intermittent availability of wind enables better use of this resource. In Germany it is now possible to predict wind generation output with 90% certainty 24 hours ahead. This means that it is possible to deploy other plants more effectively so that the economic value of that wind contribution is greatly increased.
Renewable energy use by nation
Iceland is a world leader in renewable energy due to its abundant hydro- and geothermal energy sources. Over 99% of the country's electricity is from renewable sources and most of its urban household heating is geothermal. Israel is also notable as much of its household hot water is heated by solar means. These countries' successes are at least partly based on their geographical advantages.
| Hydro | Geothermal | Wind | PV Solar | ||
| 1. | Canada | U.S. | Germany | Japan | |
| 2. | U.S. | Philippines | U.S. | Germany | |
| 3. | Brazil | Italy | Spain | U.S. | |
| 4. | China | Mexico | Denmark | India | |
| 5. | Russia | Indonesia | India | Australia |
Share of the total power consumption in EU-countries that are renewable.
| 1985 | 1990 | 1991 | 1992 | 1993 | 1994 | |
| EUR-15 | 5,61 | 5,13 | 4,92 | 5,16 | 5,28 | 5,37 |
| Belgium | 1,04 | 1,01 | 1,01 | 0,96 | 0,84 | 0,80 |
| Denmark | 4,48 | 6,32 | 6,38 | 6,80 | 7,03 | 6,49 |
| Germany | 2,09 | 2,06 | 1,61 | 1,73 | 1,75 | 1,79 |
| Greece | 8,77 | 7,14 | 7,63 | 7,13 | 7,33 | 7,16 |
| Spain | 8,83 | 6,70 | 6,56 | 5,73 | 6,49 | 6,50 |
| France | 7,24 | 6,34 | 6,75 | 7,54 | 7,32 | 7,98 |
| Ireland | 1,75 | 1,65 | 1,68 | 1,59 | 1,59 | 1,63 |
| Italy | 5,60 | 4,64 | 5,16 | 5,19 | 5,34 | 5,50 |
| Luxembourg | 1,28 | 1,21 | 1,14 | 1,26 | 1,21 | 1,34 |
| The Netherlands | 1,36 | 1,35 | 1,35 | 1,37 | 1,38 | 1,43 |
| Austria | 24,23 | 22,81 | 20,99 | 23,39 | 24,23 | 23,71 |
| Portugal | 25,07 | 17,45 | 17,03 | 13,88 | 15,98 | 16,61 |
| Finland | 18,29 | 16,71 | 17,02 | 18,10 | 18,48 | 18,28 |
| Sweden | 24,36 | 24,86 | 22,98 | 26,53 | 27,31 | 24,04 |
| United Kingdom | 0,47 | 0,49 | 0,48 | 0,56 | 0,54 | 0,65 |
Table from [1]
Renewable energy controversies
As with anything, even renewable energy generates controversies.
Lack of motivation for funding
Research and development in renewable energies has been severely hampered by only receiving a tiny fraction of energy R&D budgets, with conventional energy sources getting the lion's share.
Centralization versus decentralization
Frequently renewable electricity sources will be disadvantaged by regulation of the electricity supply industry which favors 'traditional' large-scale generators over smaller-scale and more distributed generating sources. If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems would 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". 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.
The nuclear "renewable" claim
Some nuclear advocates claim that nuclear energy should be regarded as renewable energy.
Arguments often put forward include:
- Nuclear energy does not contribute to global warming.
- Evaporative cooling has a minor effect by introducing additional water vapor into the atmosphere, along with the heat production of the process. However, both of these are insignificant compared to geothermal events such as volcanoes.
- Fast breeder reactors can produce more fuel than they consume.
- Uranium and thorium, being radioactive, are not resources that are essential in the long-term in the way that, say, oil is.
- Nuclear waste, since it will eventually become less radioactive than the original ore bodies, is not a long-term problem.
This claim is rejected by most renewable energy advocates, primarily because of concerns over pollution caused by failure to store the waste material correctly, and the dangers involved in operation of plants (see Chernobyl and Selafield).
That
- nuclear power uses a depleting resource (uranium or thorium)
- the half-life of uranium 238 is 4.5 billion years
- the decay of the waste to a safe level may take three thousand years or longer (depending on the technology used)
are widely accepted arguments that fission power cannot be included in such a classification.
Similar arguments have been applied against proposed nuclear fusion power stations using deuterium as fuel. However, the expected by-products are entirely different to those of nuclear fission, so they need to be re-examined somewhat.
References
- U.S. Energy Information Administration provides lots of statistics and information on the industry.
- Boyle, G. (ed.), Renewable Energy: Power for a Sustainable Future. Open University, UK, 1996.
