Renewable energy production is energy generated from natural resources—such as sunlight, wind, rain, tides, and geothermal heat—which are renewable (naturally replenished). Renewable energy technologies include solar power, wind power, hydroelectricity, micro hydro, biomass, and biofuels.
In 2006, about 18% of global final energy consumption came from renewables, with 13% coming from traditional biomass, such as wood-burning. Hydropower was the next largest renewable source, providing 3%, followed by hot water/heating, which contributed 1.3%. Modern technologies, such as geothermal, wind, solar, and ocean energy, together provided some 0.8% of final energy consumption. The technical potential for their use is very large, exceeding all other readily available sources.
Renewable energy technologies are sometimes criticized for being intermittent or unsightly, yet the market is growing for many forms of renewable energy. Wind power is growing at the rate of 30% annually, with a worldwide installed capacity of over 100 GW, and is widely used in several European countries and the United States. The manufacturing output of the photovoltaics industry reached more than 2,000 MW in 2006, and photovoltaic (PV) power stations are particularly popular in Germany. Solar thermal power stations operate in the US and Spain, and the largest of these is the 354 MW SEGS power plant in the Mojave Desert. The world's largest geothermal power installation is The Geysers in California, with a rated capacity of 750 MW. Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18% of that country's automotive fuel. Ethanol fuel is also widely available in the US.
While there are many large-scale renewable energy projects and production, renewable technologies are also suited to small off-grid applications, sometimes in rural and remote areas, where energy is often crucial in human development. Kenya has the world's highest household solar ownership rate with roughly 30,000 small (20–100 watt) solar power systems sold per year.
Climate change concerns coupled with high oil prices, peak oil, and increasing government support are driving increasing renewable energy legislation, incentives, and commercialization. European Union leaders reached an agreement in principle in March 2007 that 20% of their nations' energy should be produced from renewable fuels by 2020, as part of the drive to cut emissions of carbon dioxide, which are blamed in part for global warming. Investment capital flowing into renewable energy climbed from $80 billion in 2005 to a record $100 billion in 2006. This level of investment combined with continuing double-digit percentage increases each year has moved what once was considered alternative energy into the mainstream. Wind was the first to provide 1% of electricity, but solar is not far behind. Some very large corporations such as BP, General Electric, Sharp, and Royal Dutch Shell are investing in the renewable energy sector.
Contents |
Main Renewable Energy Technologies
The majority of renewable energy technologies are directly or indirectly powered by the sun. The Earth-Atmosphere system is in equilibrium such that heat radiation into space is equal to incoming solar radiation; the resulting level of energy within the Earth-Atmosphere system can roughly be described as the Earth's "climate." The hydrosphere (water) absorbs a major fraction of the incoming radiation. Most radiation is absorbed at low latitudes around the equator, but this energy is dissipated around the globe in the form of winds and ocean currents. Wave motion may play a role in the process of transferring mechanical energy between the atmosphere and the ocean through wind stress. Solar energy is also responsible for the distribution of precipitation, which is tapped by hydroelectric projects, and for the growth of plants used to create biofuels.
Renewable energy flows involve natural phenomena such as sunlight, wind, tides, and geothermal heat, as the International Energy Agency explains:
"Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources."
Each of these sources has unique characteristics that influence how and where that source is used:
- Wind power
- Water power
- Solar energy use
- Biofuel
- Biomass
- Biogas
- Geothermal power
Renewable Energy Commercialization
Costs
Renewable energy systems encompass a broad, diverse array of technologies, and the current status of these can vary considerably. Some technologies are already mature and economically competitive (e.g., geothermal and hydropower). Others need additional development to become competitive without subsidies. This can be helped by improvements to subcomponents, such as electric generators.
The table shows an overview of costs of various renewable energy technologies. For comparison with the prices in the table, electricity production from a conventional coal-fired plant costs about 4¢/kWh, though in some G8 nations the cost can be significantly higher at 7.88p (~15¢/kWh). Achieving further cost reductions as indicated in the table below requires further technology development, market deployment, an increase in production capacities to mass production levels, and the establishment of an emissions trading scheme and/or carbon tax which would attribute a cost to each unit of carbon emitted, thus reflecting the true cost of energy production by fossil fuels, which then could be used to lower the cost/kWh of these renewable energies.
| 2001 Energy Costs | Potential Future Energy Cost | |
| Electricity | ||
| Wind | 4–8 ¢/kWh | 3–10 ¢/kWh |
| Solar Photovoltaic | 25–160 ¢/kWh | 5–25 ¢/kWh |
| Solar Thermal | 12–34 ¢/kWh | 4–20 ¢/kWh |
| Large Hydropower | 2–10 ¢/kWh | 2–10 ¢/kWh |
| Small Hydropower | 2–12 ¢/kWh | 2–10 ¢/kWh |
| Geothermal | 2–10 ¢/kWh | 1–8 ¢/kWh |
| Biomass | 3–12 ¢/kWh | 4–10 ¢/kWh |
| Coal (comparison) | 4 ¢/kWh | |
| Heat | ||
| Geothermal Heat | 0.5–5 ¢/kWh | 0.5–5 ¢/kWh |
| Biomass—Heat | 1–6 ¢/kWh | 1–5 ¢/kWh |
| Low Temp Solar Hheat | 2–25 ¢/kWh | 2–10 ¢/kWh |
| All costs are in 2001 US$-cent per kilowatt-hour. | ||
| Source: World Energy Assessment, 2004 update | ||
Wind Power Market Increase
As of April 2008, worldwide wind farm capacity was 100,000 megawatts (MW), and wind power produced some 1.3% of global electricity consumption, accounting for approximately 18% of electricity use in Denmark, 9% in Spain, and 7% in Germany. The US is an important growth area, and latest American Wind Energy Association figures show that installed US wind power capacity has reached 18,302 MW, which is enough to serve 5 million average households.
Horse Hollow Wind Energy Center, in Texas, is the world's largest wind farm at 735.5 MW capacity. It consists of 291 GE Energy 1.5 MW wind turbines and 130 Siemens 2.3 MW wind turbines.
In the UK, a license to build the world's largest offshore wind farm, in the Thames estuary, has been granted. The London Array wind farm, 20 km off Kent and Essex, should eventually consist of 341 turbines, occupying an area of 230 km2. This is a £1.5 billion, 1,000 MW project, and it will power one third of London homes. The wind farm will produce an amount of energy that, if generated by conventional means, would result in 1.9 million tons of carbon dioxide emissions every year. It could also make up to 10% of the government's 2010 renewables target.
A proposed 4,000 MW facility, called the Pampa Wind Project, is to be located near Pampa, Texas.
New Generation of Solar Thermal Plants
Since 2004 there has been renewed interest in solar thermal power stations, and two plants were completed during 2006/2007: the 64 MW Nevada Solar One and the 11 MW PS10 solar power tower in Spain. Three 50 MW trough plants were under construction in Spain at the end of 2007 with 10 additional 50 MW plants planned. In the US, utilities in California and Florida have announced plans for (or contracted for) at least eight new projects totaling more than 2,000 MW.
In developing countries, three World Bank projects for integrated CSP/combined-cycle gas-turbine power plants in Egypt, Mexico, and Morocco were approved during 2006/2007.
There are several solar thermal power plants in the Mojave Desert that supply power to the electricity grid. Solar Energy Generating Systems (SEGS) is the name given to nine solar power plants in the Mojave Desert, which were built in the 1980s. These plants have a combined capacity of 354 MW, making them the largest solar power installation in the world.
The California Solar Initiative
As part of Governor Arnold Schwarzenegger's Million Solar Roofs Program, California has set a goal to create 3,000 MW of new, solar-produced electricity by 2017—moving the state toward a cleaner energy future and helping lower the cost of solar systems for consumers. This is a comprehensive $2.8 billion program.
The California Solar Initiative offers cash incentives on solar PV systems of up to $2.50 a watt. These incentives, combined with federal tax incentives, can cover up to 50% of the total cost of a solar panel system. There are many financial incentives to support the use of renewable energy in other US states.
Use of Ethanol for Transportation
Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18% of the country's automotive fuel. As a partial result, Brazil, which years ago had to import a large share of the petroleum needed for domestic consumption, recently reached complete self-sufficiency in oil.
Most cars on the road today in the US can run on blends of up to 10% ethanol, and motor vehicle manufacturers already produce vehicles designed to run on much higher ethanol blends. Ford, DaimlerChrysler, and GM are among the automobile companies that sell “flexible-fuel” cars, trucks, and minivans that can use gasoline and ethanol blends ranging from pure gasoline up to 85% ethanol (E85). By mid-2006, there were approximately six million E85-compatible vehicles on US roads. The challenge is to expand the market for biofuels beyond the farm states where they have been most popular to date. Flex-fuel vehicles are assisting in this transition because they allow drivers to choose different fuels based on price and availability. The Energy Policy Act of 2005, which calls for 7.5 billion gallons of biofuels to be used annually by 2012, will also help to expand the market.
Geothermal Energy Prospects
The Geysers is a geothermal power field located 72 miles (116 km) north of San Francisco, California. It is the largest geothermal development in the world, outputting over 750 MW.
By the end of 2005 worldwide use of geothermal energy for electricity had reached 9.3 GW, with an additional 28 GW used directly for heating. If heat recovered by ground source heat pumps is included, the nonelectric use of geothermal energy is estimated at more than 100 GWt (gigawatts of thermal power) and is used commercially in over 70 countries. During 2005 contracts were placed for an additional 0.5 GW of capacity in the US, while there were also plants under construction in 11 other countries.
Developing Country Markets
Renewable energy can be particularly suitable for developing countries. In rural and remote areas, transmission and distribution of energy generated from fossil fuels can be difficult and expensive. Producing renewable energy locally can offer a viable alternative.
Renewable energy projects in many developing countries have demonstrated that renewable energy can directly contribute to poverty alleviation by providing the energy needed for creating businesses and employment. Renewable energy technologies can also make indirect contributions to alleviating poverty by providing energy for cooking, space heating, and lighting. Renewable energy can also contribute to education, by providing electricity to schools.
Kenya is the world leader in the number of solar power systems installed per capita (but not the number of watts added). More than 30,000 very small solar panels, each producing 12 to 30 watts, are sold in Kenya annually. For an investment of as little as $100 for the panel and wiring, the PV system can be used to charge a car battery, which can then provide power to run a fluorescent lamp or a small television for a few hours a day. More Kenyans adopt solar power every year than make connections to the country’s electric grid.
Potential Future Utilization
Present renewable energy sources supply about 18% of current energy use, and there is much potential that could be exploited in the future. As the table below illustrates, the technical potential of renewable energy sources is more than 18 times current global primary energy use and several times higher than projected energy use in 2100.
Available renewable energy. The volumes of the cubes represent the amount of available geothermal, wind, and solar energy in TW, although only a small portion is recoverable. The small red cube shows the proportional global energy consumption.
| The Renewable Energy Resource Base (Exajoules [EJ] per year) | |||
| Current Use (2001) | Technical Potential | Theoretical Potential |
|
|---|---|---|---|
| Hydropower | 9 | 50 | 147 |
| Biomass Energy | 50 | >276 | 2,900 |
| Wind Energy | 0.12 | 640 | 6,000 |
| Solar Energy | 0.1 | >1,575 | 3,900,000 |
| Geothermal Energy | 0.6 | -- | -- |
| Ocean Energy | not estimated | not estimated | 7,400 |
| Total | 60 | >1,800 | >4,000,000 |
| Current use is in primary energy equivalent. For comparison, the global primary energy use was 402 EJ per year in 2001. Source: World Energy Assessment 2001 |
|||
There are many different ways to assess potentials. The theoretical potential indicates the amount of energy theoretically available for energy purposes, such as, in the case of solar energy, the amount of incoming radiation at the earth's surface. The technical potential is a more practical estimate of how much could be put to human use by considering conversion efficiencies of the available technology and available land area. To give an idea of the constraints, the estimate for solar energy assumes that 1% of the world's unused land surface is used for solar power.
The technical potentials generally do not include economic or other environmental constraints, and the potentials that could be realized at an economically competitive level under current conditions and in a short time frame are lower still.
Sustainable development and global warming groups propose a 100% Renewable Energy Source Supply, without fossil fuels and nuclear power. Scientists from the University of Kassel have been busy proving that Germany can power itself entirely by renewable energy.
Trends Favoring Renewables
The renewables market will boom when cost efficiency attains parity with other competing energy sources. The following trends are a few examples by which the renewables market is being helped to attain critical mass so that it can become more competitive with fossil fuels:
Renewable industry often needs government sponsorship to help generate enough momentum in the market. Many countries and states have implemented incentives—such as government tax subsidies, partial copayment schemes, and various rebates over purchase of renewables—to encourage consumers to shift to renewable energy sources. Government grants fund research in renewable technology to make the production cheaper and generation more efficient.
Loan programs are being developed to stimulate renewable-favoring market forces with attractive return rates, buffer initial deployment costs, and entice consumers to consider and purchase renewable technology. A famous example is the solar loan program sponsored by the United Nations Environment Program (UNEP), which is helping 100,000 people finance solar power systems in India. Success in India's solar program has led to similar projects in other parts of the developing world such as Tunisia, Morocco, Indonesia, and Mexico.
Carbon taxes and taxes for fossil fuel consumption and carbon taxes are being imposed, and the revenue earned can be channeled toward renewable energy development.
Also oil peak and world petroleum crisis and inflation are helping to promote renewables.
Many think tanks are warning that the world needs an urgency-driven concerted effort to create a competitive renewable energy infrastructure and market. The developed world can make more research investments to find better cost-efficient technologies, and manufacturing could be transferred to developing countries in order to use low-cost labor. The renewable energy market could increase fast enough to replace and initiate the decline of fossil fuel dominance, and the world could then avert the looming climate and peak oil crises.
Most importantly, renewables are gaining credence among private investors as having the potential to grow into the next big industry. Many companies and venture capitalists are investing in photovoltaic development and manufacturing. This trend is particularly visible in the Silicon Valley in California as well as in Europe and Japan.
Constraints and Opportunities
Critics suggest that some renewable energy applications may create pollution, be dangerous, take up large amounts of land, or be incapable of generating a large net amount of energy. Proponents advocate the use of "appropriate renewables," also known as soft energy technologies, as these have many advantages.
Availability and Reliability
There is no shortage of solar-derived energy on Earth. Indeed the storages and flows of energy on the planet are very large relative to human needs.
- The amount of solar energy intercepted by the Earth every minute is greater than the amount of energy the world uses in fossil fuels each year.
- Tropical oceans absorb 560 trillion gigajoules (GJ) of solar energy each year, equivalent to 1,600 times the world’s annual energy use.
- The energy in the winds that blow across the US each year could produce more than 16 billion GJ of electricity—more than one and one-half times the electricity consumed in the US in 2000.
- Annual photosynthesis by the vegetation in the US is 50 billion GJ, equivalent to nearly 60% of the nation’s annual fossil fuel use.
A criticism of some renewable sources is their variable nature. But renewable power sources can actually be integrated into the grid system quite well, as Amory Lovins explains:
Variable but forecastable renewables (wind and solar cells) are very reliable when integrated with each other, existing supplies and demand. For example, three German states were more than 30 percent wind-powered in 2007—and more than 100 percent in some months. Mostly renewable power generally needs less backup than utilities already bought to combat big coal and nuclear plants' intermittence.
The challenge of variable power supply may be readily alleviated by energy storage. Available storage options include pumped-storage hydro systems, batteries, hydrogen fuel cells, and thermal mass. Initial investments in such energy storage systems may be high, although the costs can be recovered over the life of the system.
Lovins goes on to say that the unreliability of renewable energy is a myth, while the unreliability of nuclear energy is real. Of all US nuclear plants built, 21% were abandoned and 27% have failed at least once. Successful reactors must close for refueling every 17 months for 39 days. And when shut in response to grid failure, they can't quickly restart. This is simply not the case for wind farms, for example.
Wave energy and some other renewables are continuously available. A wave energy scheme installed in Australia generates electricity with an 80% availability factor.
Aesthetics
Both solar and wind generating stations have been criticized from an aesthetic point of view. However, methods and opportunities exist to deploy these renewable technologies efficiently and unobtrusively: Fixed solar collectors can double as noise barriers along highways, and extensive roadway, parking lot, and roof-top area is currently available; amorphous photovoltaic cells can also be used to tint windows and produce energy. Advocates of renewable energy also argue that current infrastructure is less aesthetically pleasing than alternatives, but sited further from the view of most critics.
Environmental and Social Considerations
While most renewable energy sources do not produce pollution directly, the materials, industrial processes, and construction equipment used to create them may generate waste and pollution. Some renewable energy systems actually create environmental problems. For instance, older wind turbines can be hazardous to flying birds.
Land Area Required
Another environmental issue, particularly with biomass and biofuels, is the large amount of land required to harvest energy—land which otherwise could be used for other purposes or left as undeveloped land. However, it should be pointed out that these fuels may reduce the need for harvesting nonrenewable energy sources, such as vast strip-mined areas and slag mountains for coal, safety zones around nuclear plants, and hundreds of square miles being strip-mined for oil sands. These responses, however, do not account for the extremely high biodiversity and endemism of land used for ethanol crops, particularly sugar cane.
In the US, crops grown for biofuels are the most land- and water-intensive of the renewable energy sources. In 2005, about 12% of the nation’s corn crop (covering 11 million acres (45,000 km2) of farmland) was used to produce four billion gallons of ethanol—which equates to about 2% of annual US gasoline consumption. For biofuels to make a much larger contribution to the energy economy, the industry will have to accelerate the development of new feedstocks, agricultural practices, and technologies that are more land and water efficient. Already, the efficiency of biofuels production has increased significantly and there are new methods to boost biofuel production.
Hydroelectric Dams
The major advantage of hydroelectric systems is the elimination of the cost of fuel. Other advantages include longer life than fuel-fired generation, low operating costs, and the provision of facilities for water sports. Operation of pumped-storage plants improves the daily load factor of the generation system. Overall, hydroelectric power can be far less expensive than electricity generated from fossil fuels or nuclear energy, and areas with abundant hydroelectric power attract industry.
However, there are several major disadvantages of hydroelectric systems. These include dislocation of people living where the reservoirs are planned, release of significant amounts of carbon dioxide at construction and flooding of the reservoir, disruption of aquatic ecosystems and birdlife, adverse impacts on the river environment, potential risks of sabotage and terrorism, and in rare cases catastrophic failure of the dam wall.
Hydroelectric power is now more difficult to site in developed nations because most major sites within these nations are either already being exploited or may be unavailable for other reasons such as environmental considerations.
Wind Farms
A wind farm, when installed on agricultural land, has one of the lowest environmental impacts of all energy sources:
- It occupies less land area per kWh of electricity generated than any other energy conversion system, apart from roof-top solar energy, and is compatible with grazing and crops.
- It generates the energy used in its construction in just 3 months of operation, yet its operational lifetime is 20–25 years.
- Greenhouse gas emissions and air pollution produced by its construction are tiny and declining. There are no emissions or pollution produced by its operation.
- In substituting for base-load coal power, wind power produces a net decrease in greenhouse gas emissions and air pollution, and a net increase in biodiversity.
- Modern wind turbines are almost silent and rotate so slowly (in terms of revolutions per minute) that they are rarely a hazard to birds.
Studies of birds and offshore wind farms in Europe have found that there are very few bird collisions. Several offshore wind sites in Europe have been in areas heavily used by seabirds. Improvements in wind turbine design, including a much slower rate of rotation of the blades and a smooth tower base instead of perchable lattice towers, have helped reduce bird mortality at wind farms around the world. However, older, smaller wind turbines may be hazardous to flying birds. By contrast, birds are severely impacted by fossil fuel energy; for example, they can die from exposure to oil spills or from mercury poising, and they can suffer habitat loss due to acid rain and mountaintop removal coal mining.
Longevity Issues
Though a source of renewable energy may last for billions of years, renewable energy infrastructure, like hydroelectric dams, will not last forever, and must be removed and replaced at some point. Events like the shifting of riverbeds or changing weather patterns could potentially alter or even halt the function of hydroelectric dams, lowering the amount of time they are available to generate electricity.
Although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down. It is likely that in these locations, the system was designed too large for the site, since there is only so much energy that can be stored and replenished in a given volume of earth. Some interpret this as meaning a specific geothermal location can undergo depletion.
Biofuels Production
All biomass needs to go through some of these steps: It needs to be grown, collected, dried, fermented, and burned. All of these steps require resources and an infrastructure.
Some studies contend that ethanol is "energy negative," meaning that it takes more energy to produce than is contained in the final product. However, a large number of recent studies, including a 2006 article in the journal Science, offer the opinion that fuels like ethanol are energy positive. Furthermore, fossil fuels also require significant energy inputs that have seldom been accounted for in the past.
Additionally, ethanol is not the only product created during production, and the energy content of the by-products must also be considered. Corn is typically 66% starch, and the remaining 33% is not fermented. This unfermented component is called distillers grain; it is high in fats and proteins and makes good animal feed. In Brazil, where sugar cane is used, the yield is higher, and conversion to ethanol is somewhat more energy efficient than corn. Recent developments with cellulosic ethanol production may improve yields even further.
According to the International Energy Agency, new biofuels technologies being developed today, notably cellulosic ethanol, could allow biofuels to play a much bigger role in the future than previously thought. Cellulosic ethanol can be made from plant matter composed primarily of inedible cellulose fibers that form the stems and branches of most plants. Crop residues (such as corn stalks, wheat straw, and rice straw), wood waste, and municipal solid waste are potential sources of cellulosic biomass. Dedicated energy crops, such as switchgrass, are also promising cellulose sources that can be sustainably produced in many regions of the US.
The ethanol and biodiesel production industries also create jobs in plant construction, operations, and maintenance, mostly in rural communities. According to the Renewable Fuels Association, the ethanol industry created almost 154,000 US jobs in 2005 alone, boosting household income by $5.7 billion. It also contributed about $3.5 billion in tax revenues at the local, state, and federal levels.
Diversification
The US electric power industry now relies on large, central power stations including coal, natural gas, nuclear, and hydropower plants that together generate more than 95% of the nation’s electricity. Over the next few decades uses of renewable energy could help to diversify the nation’s bulk power supply. Already, appropriate renewable resources (which excludes large hydropower) produce 12% of northern California’s electricity.
Although most of today’s electricity comes from large, central-station power plants, new technologies offer a range of options for generating electricity nearer to where it is needed, saving on the cost of transmitting and distributing power and improving the overall efficiency and reliability of the system.
Improving energy efficiency represents the most immediate and often the most cost-effective way to reduce oil dependence, improve energy security, and reduce the health and environmental impact of the energy system. By reducing the total energy requirements of the economy, improved energy efficiency could make increased reliance on renewable energy sources more practical and affordable.
Other Issues
Sustainability
Renewable energy sources are generally sustainable in the sense that they cannot "run out" as well as in the sense that their environmental and social impacts are generally more benign than those of fossil. However, both biomass and geothermal energy require wise management if they are to be used in a sustainable manner. For all of the other renewables, almost any realistic rate of use would be unlikely to approach their rate of replenishment by nature.
Transmission
If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems might no longer be the main distributors of electrical energy but would operate to balance the electricity needs of local communities. Those with surplus energy would sell to areas needing "top ups." That is, network operation would require a shift from "passive management"—where generators are hooked up and the system is operated to get electricity "downstream" to the consumer — to 'active management," wherein generators are spread across a network and inputs and outputs need to be constantly monitored to ensure proper balancing occurs within the system. Some governments and regulators are moving to address this problem, though much remains to be done. One potential solution is the increased use of active management of electricity transmission and distribution networks. This will require significant changes in the way that such networks are operated.
However, on a smaller scale, use of renewable energy produced on-site reduces burdens on electricity distribution systems. Current systems, while rarely economically efficient, have shown that an average household with an appropriately sized solar panel array and energy storage system needs electricity from outside sources for only a few hours per week. Advocates of renewable energy and the soft energy path believe that by matching electricity supply to end-use needs, we can make electricity systems smaller and easier to manage, rather than the opposite.
Market Development of Renewable Heat Energy
Renewable heat is the generation of heat from renewable sources. Much current discussion on renewable energy focuses on the generation of electrical energy, despite the fact that many colder countries consume more energy for heating than as electricity. In 2005 the UK consumed 354 TWh of electric power, but had a heat requirement of 907 TWh, the majority of which (81%) was met using gas. The residential sector alone consumed a massive 550 TWh of energy for heating, mainly in the form of gas. Almost half of the final energy consumed in the UK (49%) was in the form of heat.
Renewable electric power is becoming cheap and convenient enough to place it, in many cases, within reach of the average consumer. By contrast, the market for renewable heat is mostly inaccessible to domestic consumers due to inconvenience of supply, and high capital costs. Heating accounts for a large proportion of energy consumption, and yet a universally accessible market for renewable heat is yet to emerge. Solutions such as geothermal heat pumps may be more widely applicable, but may not be economical in all cases.
Controversy over Nuclear Power as a Renewable Energy Source
In 1983, physicist Bernard Cohen proposed that uranium is effectively inexhaustible, and could therefore be considered a renewable source of energy. He claims that fast breeder reactors, fueled by naturally replenished uranium extracted from seawater, could supply energy at least as long as the sun's expected remaining lifespan of five billion years. Nuclear energy has also been referred to as "renewable" by politicians like George W. Bush, Charlie Crist, and David Sainsbury. In England and Wales there is a Non-Fossil Fuel Obligation, which provides support for renewable energy. Nuclear power production was also subsidized by this obligation from 1990 until 2002.
Inclusion under the "renewable energy" classification could render nuclear power projects eligible for development aid under various jurisdictions. However, it is has not been established that nuclear energy is inexhaustible, and debate continues over issues such as peak uranium and uranium depletion. No legislative body has yet included nuclear energy under any legal definition of "renewable energy sources" for provision of development support. Similarly, statutory and scientific definitions of renewable energies usually exclude nuclear energy. Commonly sourced definitions of renewable energy sources often omit or explicitly exclude nuclear energy sources as examples. Nuclear fission is generally not regarded as renewable, as indicated by the US Departmentof energy on the website "What Is Energy?"
There are also environmental concerns regarding nuclear power, including the dangerous environmental hazards of nuclear waste and concerns that development of new plants cannot happen quickly enough to reduce CO2 emissions, such that nuclear energy is neither efficient nor effective in cutting CO2 emissions.