Renewable energy

The 150 MW Andasol Solar Power Station is a commercial parabolic trough solar thermal power plant, located in Spain. The Andasol plant uses tanks of molten salt to store solar energy so that it can continue generating electricity even when the sun isn't shining.^[1]

Burbo Bank Offshore Wind Farm, at the entrance to the River Mersey in North West England.

In 2010 renewable energy accounted for 16.7% of total energy consumption. Biomass heat accounted for 11.4%, and hydropower 3.3%.

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Renewable energy is energy that comes from resources which are continually replenished such as sunlight, wind, rain, tides, waves and geothermal heat. About 16% of global final energy consumption comes from renewable resources, with 10% of all energy from traditional biomass, mainly used for heating, and 3.4% from hydroelectricity. New renewables (small hydro, modern biomass, wind, solar, geothermal, and biofuels) accounted for another 3% and are growing very rapidly.^[2] The share of renewables in electricity generation is around 19%, with 16% of electricity coming from hydroelectricity and 3% from new renewables.^[2]

The use of wind power is increasing at an annual rate of 20%, with a worldwide installed capacity of 238,000 megawatts (MW) at the end of 2011,^[3][4][5] and is widely used in Europe, Asia, and the United States.^[6] Since 2004, photovoltaics passed wind as the fastest growing energy source, and since 2007 has more than doubled every two years. At the end of 2011 the photovoltaic (PV) capacity worldwide was 67,000 MW, and PV power stations are popular in Germany and Italy.^[7] Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 MW SEGS power plant in the Mojave Desert.^[8] 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 sugarcane, and ethanol now provides 18% of the country's automotive fuel.^[9] Ethanol fuel is also widely available in the USA.

While many renewable energy projects are large-scale, renewable technologies are also suited to rural and remote areas, where energy is often crucial in human development.^[10] As of 2011, small solar PV systems provide electricity to a few million households, and micro-hydro configured into mini-grids serves many more. Over 44 million households use biogas made in household-scale digesters for lighting and/or cooking, and more than 166 million households rely on a new generation of more-efficient biomass cookstoves.^[11] United Nations' Secretary-General Ban Ki-moon has said that renewable energy has the ability to lift the poorest nations to new levels of prosperity.^[12]

Climate change concerns, coupled with high oil prices, peak oil, and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization.^[13] New government spending, regulation and policies helped the industry weather the global financial crisis better than many other sectors.^[14] According to a 2011 projection by the International Energy Agency, solar power generators may produce most of the world’s electricity within 50 years, dramatically reducing the emissions of greenhouse gases that harm the environment.^[15]

Overview

Global renewable power capacity excluding hydro^[16]

Renewable energy flows involve natural phenomena such as sunlight, wind, tides, plant growth, and geothermal heat, as the International Energy Agency explains:^[17]

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.

Renewable energy resources and significant opportunities for energy efficiency exist over wide geographical areas, in contrast to other energy sources, which are concentrated in a limited number of countries. Rapid deployment of renewable energy and energy efficiency, and technological diversification of energy sources, would result in significant energy security and economic benefits.^[18]

Renewable energy replaces conventional fuels in four distinct areas: electricity generation, hot water/space heating, motor fuels, and rural (off-grid) energy services:^[19]

• Power generation. Renewable energy provides 19% of electricity generation worldwide. Renewable power generators are spread across many countries, and wind power alone already provides a significant share of electricity in some areas: for example, 14% in the U.S. state of Iowa, 40% in the northern German state of Schleswig-Holstein, and 20% in Denmark. Some countries get most of their power from renewables, including Iceland (100%), Norway (98%), Brazil (86%), Austria (62%), New Zealand (65%), and Sweden (54%).^[20]

• Heating. Solar hot water makes an important contribution to renewable heat in many countries, most notably in China, which now has 70% of the global total (180 GWth). Most of these systems are installed on multi-family apartment buildings and meet a portion of the hot water needs of an estimated 50–60 million households in China. Worldwide, total installed solar water heating systems meet a portion of the water heating needs of over 70 million households. The use of biomass for heating continues to grow as well. In Sweden, national use of biomass energy has surpassed that of oil. Direct geothermal for heating is also growing rapidly.^[20]

• Transport fuels. Renewable biofuels have contributed to a significant decline in oil consumption in the United States since 2006.^[20] The 93 billion liters of biofuels produced worldwide in 2009 displaced the equivalent of an estimated 68 billion liters of gasoline, equal to about 5% of world gasoline production.^[20]

At the national level, at least 30 nations around the world already have renewable energy contributing more than 20% of energy supply. National renewable energy markets are projected to continue to grow strongly in the coming decade and beyond, and some 120 countries have various policy targets for longer-term shares of renewable energy, including a binding 20% by 2020 target for the European Union. Some countries have much higher long-term policy targets of up to 100% renewables. Outside of Europe, a diverse group of 20 or more other countries target renewable energy shares in the 2020–2030 time frame that range from 10% to 50%, including Algeria, China, Indonesia, Jamaica, Jordan, Madagascar, Mali, Mauritius, Samoa, Senegal, South Africa, Thailand, Turkey, Ukraine, and Vietnam.^[21]

In international public opinion surveys there is strong support for promoting renewable sources such as solar power and wind power, requiring utilities to use more renewable energy (even if this increases the cost), and providing tax incentives to encourage the development and use of such technologies. There is substantial optimism that renewable energy investments will pay off economically in the long term.^[22]

History

Prior to the development of coal in the mid 19th century, nearly all energy used was renewable. Almost without a doubt the oldest known use of renewable energy, in the form of traditional biomass to fuel fires, dates from 790,000 years ago. Use of biomass for fire did not become commonplace until many hundreds of thousands of years later, sometime between 200,000 and 400,000 years ago.^[23]

Probably the second oldest usage of renewable energy is harnessing the wind in order to drive ships over water. This practice can be traced back some 7000 years, to ships on the Nile.^[24]

Moving into the time of recorded history, the primary sources of traditional renewable energy were human labor, animal power, water power, wind, and firewood(traditional biomass). A graph of energy use in the United States up until 1900 shows oil and natural gas with about the same importance in 1900 as wind and solar played in 2010.

By 1873, concerns of running out of coal prompted experiments with using solar energy.^[25] Development of solar engines continued until the outbreak of World War I. The eventual importance of solar energy, though, was recognized in a 1911 Scientific American article: "in the far distant future, natural fuels having been exhausted [solar power] will remain as the only means of existence of the human race".^[26]

In the 1970s environmentalists promoted the development of renewable energy both as a replacement for the eventual depletion of oil, as well as for an escape from dependence on oil, and the first wind turbines appeared. Solar had long been used for heating and cooling, but solar panels were too costly to build solar farms until 1980.^[27] The theory of peak oil was published in 1956.^[28]

By 2008 renewable energy had ceased being an alternative, and more capacity of renewable energy was added than other sources in both the United States and in Europe.^[29]

Wind power

The National Renewable Energy Laboratory projects that the levelized cost of wind power will decline 25% from 2012 to 2030.^[30]

A wind farm located in Manjil, Iran.

Airflows can be used to run wind turbines. Modern utility-scale wind turbines range from around 600 kW to 5 MW of rated power, although turbines with rated output of 1.5–3 MW have become the most common for commercial use; the power available from the wind is a function of the cube of the wind speed, so as wind speed increases, power output increases dramatically up to the maximum output for the particular turbine.^[31] Areas where winds are stronger and more constant, such as offshore and high altitude sites, are preferred locations for wind farms. Typical capacity factors are 20-40%, with values at the upper end of the range in particularly favourable sites.^[32][33]

Globally, the long-term technical potential of wind energy is believed to be five times total current global energy production, or 40 times current electricity demand. This could require wind turbines to be installed over large areas, particularly in areas of higher wind resources. Offshore resources experience average wind speeds of ~90% greater than that of land, so offshore resources could contribute substantially more energy.^[34]

Hydropower

Grand Coulee Dam is a hydroelectric gravity dam on the Columbia River in the U.S. state of Washington. The dam supplies four power stations with an installed capacity of 6,809 MW and is the largest electric power-producing facility in the United States.

Energy in water can be harnessed and used. Since water is about 800 times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy. There are many forms of water energy:

• Hydroelectric energy is a term usually reserved for large-scale hydroelectric dams. Examples are the Grand Coulee Dam in Washington State and the Akosombo Dam in Ghana.
• Micro hydro systems are hydroelectric power installations that typically produce up to 100 kW of power. They are often used in water rich areas as a remote-area power supply (RAPS).
• Run-of-the-river hydroelectricity systems derive kinetic energy from rivers and oceans without the creation of a large reservoir.

Solar energy

Monocrystalline solar cell.

Solar energy applies energy from the sun in the form of solar radiation for heat or to generate electricity. Solar powered electricity generation uses either photovoltaics or heat engines (concentrated solar power). A partial list of other solar applications includes space heating and cooling through solar architecture, daylighting, solar hot water, solar cooking, and high temperature process heat for industrial purposes.

Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.

Biomass

A cogeneration plant in Metz, France. The station uses waste wood biomass as energy source, and provides electricity and heat for 30,000 dwellings.

Biomass (plant material) is a renewable energy source because the energy it contains comes from the sun. Through the process of photosynthesis, plants capture the sun's energy. When the plants are burnt, they release the sun's energy they contain. In this way, biomass functions as a sort of natural battery for storing solar energy. As long as biomass is produced sustainably, with only as much used as is grown, the battery will last indefinitely.^{[35][unreliable source?]} In general there are two main approaches to using plants for energy production: growing plants specifically for energy use (known as first and third-generation biomass), and using the residues (known as second-generation biomass) from plants that are used for other things. See biobased economy. The best approaches vary from region to region according to climate, soils and geography.^[35]

As of early 2012, 85 of 107 biomass plants operating in the U.S. had been cited by federal or state regulators for violating clean air or water laws over the past five years.^[36] The Energy Information Administration projected that by 2017, biomass is expected to be about twice as expensive as natural gas, slightly more expensive than nuclear power, and much less expensive than solar panels.^[37]

Biofuel

Brazil has bioethanol made from sugarcane available throughout the country. Shown a typical Petrobras gas station at São Paulo with dual fuel service, marked A for alcohol (ethanol) and G for gasoline.

Biofuels include a wide range of fuels which are derived from biomass. The term covers solid biomass, liquid fuels and various biogases.^[38] Liquid biofuels include bioalcohols, such as bioethanol, and oils, such as biodiesel. Gaseous biofuels include biogas, landfill gas and synthetic gas.

Bioethanol is an alcohol made by fermenting the sugar components of plant materials and it is made mostly from sugar and starch crops. With advanced technology being developed, cellulosic biomass, such as trees and grasses, are also used as feedstocks for ethanol production. Ethanol can be used as a fuel for vehicles in its pure form, but it is usually used as a gasoline additive to increase octane and improve vehicle emissions. Bioethanol is widely used in the USA and in Brazil. However, according to the European Environment Agency, biofuels do not address global warming concerns.^[39]

Biodiesel is made from vegetable oils, animal fats or recycled greases. Biodiesel can be used as a fuel for vehicles in its pure form, but it is usually used as a diesel additive to reduce levels of particulates, carbon monoxide, and hydrocarbons from diesel-powered vehicles. Biodiesel is produced from oils or fats using transesterification and is the most common biofuel in Europe.

Biofuels provided 2.7% of the world's transport fuel in 2010.^[40]

Geothermal energy

Steam rising from the Nesjavellir Geothermal Power Station in Iceland.

Geothermal energy is from thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. Earth's geothermal energy originates from the original formation of the planet (20%) and from radioactive decay of minerals (80%).^[41] The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface. The adjective geothermal originates from the Greek roots geo, meaning earth, and thermos, meaning heat.

The heat that is used for geothermal energy can be from deep within the Earth, all the way down to Earth’s core – 4,000 miles (6,400 km) down. At the core, temperatures may reach over 9,000 °F (5,000 °C). Heat conducts from the core to surrounding rock. Extremely high temperature and pressure cause some rock to melt, which is commonly known as magma. Magma convects upward since it is lighter than the solid rock. This magma then heats rock and water in the crust, sometimes up to 700 °F (371 °C).^[42]

From hot springs, geothermal energy has been used for bathing since Paleolithic times and for space heating since ancient Roman times, but it is now better known for electricity generation.

Renewable energy commercialization

Growth of renewables

Renewable power generation and capacity as a proportion of change in global power supply^[43]

Growth of wind power and photovoltaics

From the end of 2004, worldwide renewable energy capacity grew at rates of 10–60% annually for many technologies. For wind power and many other renewable technologies, growth accelerated in 2009 relative to the previous four years.^[19] More wind power capacity was added during 2009 than any other renewable technology. However, grid-connected PV increased the fastest of all renewables technologies, with a 60% annual average growth rate.^[19] In 2010, renewable power constituted about a third of the newly built power generation capacities.^[43] By 2014 the installed capacity of photovoltaics will likely exceed that of wind, but due to the lower capacity factor of solar, the energy generated from photovoltaics is not expected to exceed that of wind until 2015.

Projections vary, but scientists have advanced a plan to power 100% of the world's energy with wind, hydroelectric, and solar power by the year 2030.^[45][46]

According to a 2011 projection by the International Energy Agency, solar power generators may produce most of the world’s electricity within 50 years, dramatically reducing the emissions of greenhouse gases that harm the environment. Cedric Philibert, senior analyst in the renewable energy division at the IEA said: “Photovoltaic and solar-thermal plants may meet most of the world’s demand for electricity by 2060 -- and half of all energy needs -- with wind, hydropower and biomass plants supplying much of the remaining generation”. “Photovoltaic and concentrated solar power together can become the major source of electricity,” Philibert said.^[15]

Economic trends

Cost of photovoltaics in the EU

Cost of oil in 2012 US dollars (red)

All forms of energy are expensive, but as time progresses, renewable energy generally gets cheaper,^[47][48] while fossil fuels generally get more expensive. A 2011 IEA report said: "A portfolio of renewable energy technologies is becoming cost-competitive in an increasingly broad range of circumstances, in some cases providing investment opportunities without the need for specific economic support," and added that "cost reductions in critical technologies, such as wind and solar, are set to continue."^[49]

The International Solar Energy Society argues that renewable energy technologies and economics will continue to improve with time, and that they are "sufficiently advanced at present to allow for major penetrations of renewable energy into the mainstream energy and societal infrastructures".

Hydroelectricity

Three Gorges Dam (left), Gezhouba Dam (right).

The Three Gorges Dam in Hubei, China, has the world's largest instantaneous generating capacity (22,500 MW), with the Itaipu Dam in Brazil/Paraguay in second place (14,000 MW). The Three Gorges Dam is operated jointly with the much smaller Gezhouba Dam (3,115 MW). As of 2012^[update], the total generating capacity of this two-dam complex is 25,615 MW. In 2008, this complex generated 97.9 TWh of electricity (80.8 TWh from the Three Gorges Dam and 17.1 TWh from the Gezhouba Dam), which is 3.4% more power in one year than the 94.7 TWh generated by Itaipu in 2008.

Wind power development

Wind power: worldwide installed capacity^[50]

Fenton Wind Farm at sunrise

Wind power is growing at over 20% annually, with a worldwide installed capacity of 238,000 MW at the end of 2011,^[3][4][5] and is widely used in Europe, Asia, and the United States.^[6][51] Several countries have achieved relatively high levels of wind power penetration, such as 21% of stationary electricity production in Denmark,^[52] 18% in Portugal,^[52] 16% in Spain,^[52] 14% in Ireland^[53] and 9% in Germany in 2010.^[40][52] As of 2011, 83 countries around the world are using wind power on a commercial basis.^[40]

As of 2012, the Alta Wind Energy Center (California, 1,020 MW) is the world's largest wind farm.^[55] As of February 2012, the Walney Wind Farm in the United Kingdom is the largest offshore wind farm in the world at 367 MW, followed by Thanet Offshore Wind Project (300 MW), also in the UK. The London Array (630 MW) is the largest project under construction. The United Kingdom is the world's leading generator of offshore wind power, followed by Denmark.^[56]

There are many large wind farms under construction and these include Anholt Offshore Wind Farm (400 MW), BARD Offshore 1 (400 MW), Clyde Wind Farm (548 MW), Fântânele-Cogealac Wind Farm (600 MW), Greater Gabbard wind farm (500 MW), Lincs Wind Farm (270 MW), London Array (1000 MW), Lower Snake River Wind Project (343 MW), Macarthur Wind Farm (420 MW), Shepherds Flat Wind Farm (845 MW), and the Sheringham Shoal (317 MW).

Solar thermal

Solar Towers from left: PS10, PS20.

Large solar thermal power stations include the 354 MW Solar Energy Generating Systems power plant in the USA, Solnova Solar Power Station (Spain, 150 MW), Andasol Solar Power Station (Spain, 100 MW), Nevada Solar One (USA, 64 MW), PS20 solar power plant (Spain, 20 MW), and the PS10 Solar Power Plant (Spain, 11 MW).

The Ivanpah Solar Power Facility is a 392 MW solar power facility which is under construction in south-eastern California.^[57] The Solana Generating Station is a 280 MW solar power plant which is under construction near Gila Bend, Arizona, about 70 miles (110 km) southwest of Phoenix. The Crescent Dunes Solar Energy Project is a 110 MW solar thermal power project currently under construction near Tonopah, about 190 miles (310 km) northwest of Las Vegas.^[58]

The solar thermal power industry is growing rapidly with 1.3 GW under construction in 2012 and more planned. Spain is the epicenter of solar thermal power development with 873 MW under construction, and a further 271 MW under development.^[59] In the United States, 5,600 MW of solar thermal power projects have been announced.^[60] In developing countries, three World Bank projects for integrated solar thermal/combined-cycle gas-turbine power plants in Egypt, Mexico, and Morocco have been approved.^[61]

Photovoltaic power stations

Nellis Solar Power Plant, 14 MW power plant installed 2007 in Nevada, USA.

Solar photovoltaic cells (PV) convert sunlight into electricity and photovoltaic production has been increasing by an average of more than 20% each year since 2002, making it a fast-growing energy technology.^[62][63] While wind is often cited as the fastest growing energy source, photovoltaics since 2007 has been increasing at twice the rate of wind - an average of 63.6%/year, due to the reduction in cost. At the end of 2011 the photovoltaic (PV) capacity world-wide was 67.4 GW, a 69.8% annual increase. Top capacity countries were, in GW: Germany 24.7, Italy 12.8, Japan 4.7, Spain 4.4, the USA 4.4, and China 3.1.^[7][64]

Many solar photovoltaic power stations have been built, mainly in Europe.^[65] As of May 2012, the largest photovoltaic (PV) power plants in the world are the Agua Caliente Solar Project (USA, 247 MW), Charanka Solar Park (India, 214 MW), Golmud Solar Park (China, 200 MW), Perovo Solar Park (Ukraine, 100 MW), Sarnia Photovoltaic Power Plant (Canada, 97 MW), Brandenburg-Briest Solarpark (Germany, 91 MW), Solarpark Finow Tower (Germany, 84.7 MW), Montalto di Castro Photovoltaic Power Station (Italy, 84.2 MW), and the Eggebek Solar Park (Germany, 83.6 MW).^[65]

There are also many large plants under construction. The Desert Sunlight Solar Farm is a 550 MW solar power plant under construction in Riverside County, California, that will use thin-film solar photovoltaic modules made by First Solar.^[66] The Topaz Solar Farm is a 550 MW photovoltaic power plant, being built in San Luis Obispo County, California.^[67] The Blythe Solar Power Project is a 500 MW photovoltaic station under construction in Riverside County, California. The California Valley Solar Ranch (CVSR) is a 250 MW solar photovoltaic power plant, which is being built by SunPower in the Carrizo Plain, northeast of California Valley.^[68] The 230 MW Antelope Valley Solar Ranch is a First Solar photovoltaic project which is under construction in the Antelope Valley area of the Western Mojave Desert, and due to be completed in 2013.^[69]

Many of these plants are integrated with agriculture and some use tracking systems that follow the sun's daily path across the sky to generate more electricity than fixed-mounted systems. There are no fuel costs or emissions during operation of the power stations.

However, when it comes to renewable energy systems and PV, it is not just large systems that matter. Building-integrated photovoltaics or "onsite" PV systems use existing land and structures and generate power close to where it is consumed.^[70]

Biofuel development

Biofuels provided 3% of the world's transport fuel in 2010.^[40] Mandates for blending biofuels exist in 31 countries at the national level and in 29 states/provinces.^[40] According to the International Energy Agency, biofuels have the potential to meet more than a quarter of world demand for transportation fuels by 2050.^[71]

Since the 1970s, Brazil has had an ethanol fuel program which has allowed the country to become the world's second largest producer of ethanol (after the United States) and the world's largest exporter.^[72] Brazil’s ethanol fuel program uses modern equipment and cheap sugarcane as feedstock, and the residual cane-waste (bagasse) is used to produce heat and power.^[73] There are no longer light vehicles in Brazil running on pure gasoline. By the end of 2008 there were 35,000 filling stations throughout Brazil with at least one ethanol pump.^[74]

Nearly all the gasoline sold in the United States today is mixed with 10% ethanol, a mix known as E10,^[75] and motor vehicle manufacturers already produce vehicles designed to run on much higher ethanol blends. Ford, Daimler AG, 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 6 million E85-compatible vehicles on U.S. roads.^[76] 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 US gallons (28,000,000 m³) of biofuels to be used annually by 2012, will also help to expand the market.^[76]

Geothermal development

The West Ford Flat power plant is one of 22 power plants at The Geysers.

Geothermal power is cost effective, reliable, sustainable, and environmentally friendly,^[77] but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation. Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit than those of fossil fuels. As a result, geothermal power has the potential to help mitigate global warming if widely deployed in place of fossil fuels.

The International Geothermal Association (IGA) has reported that 10,715 MW of geothermal power in 24 countries is online, which is expected to generate 67,246 GWh of electricity in 2010.^[78] This represents a 20% increase in geothermal power online capacity since 2005. IGA projects this will grow to 18,500 MW by 2015, due to the large number of projects presently under consideration, often in areas previously assumed to have little exploitable resource.^[78]

In 2010, the United States led the world in geothermal electricity production with 3,086 MW of installed capacity from 77 power plants;^[79] the largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California.^[80] The Philippines follows the US as the second highest producer of geothermal power in the world, with 1,904 MW of capacity online; geothermal power makes up approximately 18% of the country's electricity generation.^[79]

Developing countries

Solar cookers use sunlight as energy source for outdoor cooking.

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.^[81]

Technology advances are opening up a huge new market for solar power: the approximately 1.3 billion people around the world who don't have access to grid electricity. Even though they are typically very poor, these people have to pay far more for lighting than people in rich countries because they use inefficient kerosene lamps. Solar power costs half as much as lighting with kerosene.^[82] An estimated 3 million households get power from small solar PV systems.^[83] Kenya is the world leader in the number of solar power systems installed per capita. More than 30,000 very small solar panels, each producing 12 to 30 watts, are sold in Kenya annually.

Some Small Island Developing States (SIDS) are also turning to solar power to reduce their costs and increase their sustainability. Anguilla, for example, aims to obtain 15% of its energy from solar power so it is less reliant on expensive imported diesel. The Climate & Development Knowledge Network is helping the government gather all the information it needs to change the island’s legislation, so it can integrate renewables into its grid. Barbados, have also made good progress in switching to renewables, but many other SIDS are still at the early stages of planning how to integrate renewable energy into their grids. “For a small island we’re very far ahead,” said Beth Barry, Coordinator of the Anguilla Renewable Energy Office. "We’ve got an Energy Policy and a draft Climate Change policy and have been focussing efforts on the question of sustainable energy supply for several years now. As a result we have a lot of information we can share with other islands.”^[84]

Micro-hydro configured into mini-grids also provide power. Over 44 million households use biogas made in household-scale digesters for lighting and/or cooking, and more than 166 million households rely on a new generation of more-efficient biomass cookstoves.^[11] Clean liquid fuel sourced from renewable feedstocks are used for cooking and lighting in energy-poor areas of the developing world. Alcohol fuels (ethanol and methanol) can be produced sustainably from non-food sugary, starchy, and cellulostic feedstocks. Project Gaia, Inc. and CleanStar Mozambique are implementing clean cooking programs with liquid ethanol stoves in Ethiopia, Kenya, Nigeria and Mozambique.^[85]

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.^[86]

Industry and policy trends

Global New Investments in Renewable Energy^[87]

U.S. President Barack Obama's American Recovery and Reinvestment Act of 2009 includes more than $70 billion in direct spending and tax credits for clean energy and associated transportation programs. Clean Edge suggests that the commercialization of clean energy will help countries around the world pull out of the current economic malaise.^[14] Leading renewable energy companies include First Solar, Gamesa, GE Energy, Q-Cells, Sharp Solar, Siemens, SunOpta, Suntech Power, and Vestas.^[88]

The military has also focused on the use of renewable fuels for military vehicles. Unlike fossil fuels, renewable fuels can be produced in any country, creating a strategic advantage. The US military has already committed itself to have 50% of its energy consumption come from alternative sources.^[89]

The International Renewable Energy Agency (IRENA) is an intergovernmental organization for promoting the adoption of renewable energy worldwide. It aims to provide concrete policy advice and facilitate capacity building and technology transfer. IRENA was formed on January 26, 2009, by 75 countries signing the charter of IRENA.^[90] As of March 2010, IRENA has 143 member states who all are considered as founding members, of which 14 have also ratified the statute.^[91]

As of 2011, 119 countries have some form of national renewable energy policy target or renewable support policy. National targets now exist in at least 98 countries. There is also a wide range of policies at state/provincial and local levels.^[40]

United Nations' Secretary-General Ban Ki-moon has said that renewable energy has the ability to lift the poorest nations to new levels of prosperity.^[12] In October 2011, he "announced the creation of a high-level group to drum up support for energy access, energy efficiency and greater use of renewable energy. The group is to be co-chaired by Kandeh Yumkella, the chair of UN Energy and director general of the UN Industrial Development Organisation, and Charles Holliday, chairman of Bank of America".^[92]

100% renewable energy

Growth of wind and solar power

The incentive to use 100% renewable energy is created by global warming and ecological as well as economic concerns, post peak oil. The first country to propose 100% renewable energy was Iceland, in 1998.^[93] Proposals have been made for Japan in 2003,^[94] and for Australia in 2011.^[95] Norway and some other countries already obtain all of their electricity from renewable sources. Iceland proposed using hydrogen for transportation and its fishing fleet. Australia proposed biofuel for those elements of transportation not easily converted to electricity. The road map for the United States,^[96][97] commitment by Denmark,^[98] and Vision 2050 for Europe set a 2050 timeline for converting to 100% renewable energy,^[99] later reduced to 2040 in 2011.^[100] Zero Carbon Britain 2030 proposes eliminating carbon emissions in Britain by 2030 by transitioning to renewable energy.^[101]

It is estimated that the world will spend an extra $8 trillion over the next 25 years to prolong the use of non-renewable resources, a cost that would be eliminated by transitioning instead to 100% renewable energy.^[102] A 2009 study suggests that converting the entire world to 100% renewable energy by 2030 is both possible and affordable, but requires political support. It would require building many more wind turbines and solar power systems. Other changes involve use of electric cars and the development of enhanced transmission grids and storage.^{[103][104][105][106][107]}

The Fourth Revolution: Energy is a German documentary film released in 2010. It shows the vision of a global society, which lives in a world where the energy is produced 100% with renewable energies, showing a complete reconstruction of the economy, to reach this goal. In 2011, Hermann Scheer wrote the book The Energy Imperative: 100 Percent Renewable Now, published by Routledge.

In 2011, the refereed journal Energy Policy published two articles by Mark Z. Jacobson, a professor of engineering at Stanford University, and Mark A. Delucchi, about changing our energy supply mix and "Providing all global energy with wind, water, and solar power". The articles analyze the feasibility of providing worldwide energy for electric power, transportation, and heating/cooling from wind, water, and sunlight (WWS), which are safe clean options. In Part I, Jacobson and Delucchi discuss WWS energy system characteristics, aspects of energy demand, WWS resource availability, WWS devices needed, and material requirements.^[108] They estimate that 3,800,000 5 MW wind turbines, 5350 100 MW geothermal power plants, and 270 new 1300 MW hydroelectric power plants will be required. In terms of solar power, an additional 49,000 300 MW concentrating solar plants, 40,000 300 MW solar photovoltaic power plants, and 1.7 billion 3 kW rooftop photovoltaic systems will also be needed. Such an extensive WWS infrastructure could decrease world power demand by 30%.^[108] In Part II, Jacobson and Delucchi address variability of supply, system economics, and energy policy initiatives associated with a WWS system. The authors advocate producing all new energy with WWS by 2030 and replacing existing energy supply arrangements by 2050. Barriers to implementing the renewable energy plan are seen to be "primarily social and political, not technological or economic". Energy costs with a WWS system should be similar to today's energy costs.^[109]

The only sources available to provide a majority of the world's energy are, in order, solar, wind, and geothermal. Geothermal can be treated either as a non-renewable resource, where the heat in the first two miles of the Earth's mantle contains enough energy to supply all of the world's energy for 100,000 years, although only a small percentage of that is technically available, or as a renewable resource, where the heat used is that which is replenished each year. Due to the radiation in the Earth's mantle, this is sustainable for about 2 billion years, and can supply up to a majority of the energy used in 2010.^[110][111] Most of the energy available is from the Sun, and about 1% to 2% is converted to wind energy, and about 0.01% to plants. Each year the sun provides 160 times the total energy that is stored in fossil fuels.^[112]

A 2012 study by the University of Delaware for a 72 GW system considered 28 billion combinations of renewable energy and storage and found the most cost effective, for the PJM Interconnection, would use 17 GW of solar, 68 GW of offshore wind, and 115 GW of onshore wind, although at times as much as three times the demand would be provided. 0.1% of the time would require generation from other sources.^[113]

IRENEC is an annual conference on 100% renewable energy started in 2011 by EUROSOLAR Turkey. The 2013 conference is scheduled for June 27–29 in Istanbul.^[114][115]

Other technologies

Other renewable energy technologies are still under development, and include cellulosic ethanol, hot-dry-rock geothermal power, and ocean energy.^[116] These technologies are not yet widely demonstrated or have limited commercialization. Many are on the horizon and may have potential comparable to other renewable energy technologies, but still depend on attracting sufficient attention and research, development and demonstration (RD&D) funding.^[116]

Research

There are numerous organizations within the academic, federal, and commercial sectors conducting large scale advanced research in the field of renewable energy. This research spans several areas of focus across the renewable energy spectrum. Most of the research is targeted at improving efficiency and increasing overall energy yields.^[117] Multiple federally supported research organizations have focused on renewable energy in recent years. Two of the most prominent of these labs are Sandia National Laboratories and the National Renewable Energy Laboratory (NREL), both of which are funded by the United States Department of Energy and supported by various corporate partners.^[118] Sandia has a total budget of $2.4 billion^[119] while NREL has a budget of $375 million.^[120]

Cellulosic ethanol

Companies such as Iogen, POET, and Abengoa are building refineries that can process biomass and turn it into ethanol, while companies such as the Verenium Corporation, Novozymes, and Dyadic International are producing enzymes which could enable a cellulosic ethanol future. The shift from food crop feedstocks to waste residues and native grasses offers significant opportunities for a range of players, from farmers to biotechnology firms, and from project developers to investors.^[121]

Ocean energy

Ocean energy is a broad category currently encompassing: Marine current power, Osmotic power, Wave power, Tidal power, and Ocean thermal energy.

Wave Power

Systems to harvest utility-scale electrical power from ocean waves have recently been gaining momentum as a viable technology. The potential for this technology is considered promising, especially on west-facing coasts with latitudes between 40 and 60 degrees:^[124]

In the United Kingdom, for example, the Carbon Trust recently estimated the extent of the economically viable offshore resource at 55 TWh per year, about 14% of current national demand. Across Europe, the technologically achievable resource has been estimated to be at least 280 TWh per year. In 2003, the U.S. Electric Power Research Institute (EPRI) estimated the viable resource in the United States at 255 TWh per year (6% of demand).^[124]

Scotland is home to the European Marine Energy Centre the world's first testing facility for wave and tidal machines, located in the waters around the Orkney Islands. In 2012 at the wave test site, E.ON are testing a Pelamis Wave Energy Converter machine and Aquamarine Power are testing their near-shore Oyster device. Wave farm developments are planned in Scottish waters by E.ON, ScottishPower Renewables, SSE, Pelamis Wave Power, Aquamarine Power and Aegir Wave Power, a joint venture between Pelamis and Vattenfall.^[125]

In the U.S., Australia, as well as in Europe, full scale Wave power projects are underway or in planning by Ocean Power Technologies, as well as others, such as CETO.

Tidal Power

The world's first commercial tidal stream generator was installed in 2007 in the narrows of Strangford Lough in Ireland. The 1.2 MW underwater tidal electricity generator, part of Northern Ireland's Environment & Renewable Energy Fund scheme, takes advantage of the fast tidal flow (up to 4 metres per second) in the lough. Although the generator is powerful enough to power a thousand homes, the turbine has minimal environmental impact, as it is almost entirely submerged, and the rotors pose no danger to wildlife as they turn quite slowly.^[126]

Ocean thermal energy

Ocean thermal energy conversion (OTEC) uses the temperature difference that exists between deep and shallow waters to run a heat engine.

Enhanced geothermal systems

Enhanced geothermal system 1:Reservoir 2:Pump house 3:Heat exchanger 4:Turbine hall 5:Production well 6:Injection well 7:Hot water to district heating 8:Porous sediments 9:Observation well 10:Crystalline bedrock

Enhanced geothermal systems are a new type of geothermal power technologies that do not require natural convective hydrothermal resources. The vast majority of geothermal energy within drilling reach is in dry and non-porous rock.^[127] EGS technologies "enhance" and/or create geothermal resources in this "hot dry rock (HDR)" through hydraulic stimulation.

EGS / HDR technologies, like hydrothermal geothermal, are expected to be baseload resources which produce power 24 hours a day like a fossil plant. Distinct from hydrothermal, HDR / EGS may be feasible anywhere in the world, depending on the economic limits of drill depth. Good locations are over deep granite covered by a thick (3–5 km) layer of insulating sediments which slow heat loss.^[128]

There are HDR and EGS systems currently being developed and tested in France, Australia, Japan, Germany, the U.S. and Switzerland. The largest EGS project in the world is a 25 megawatt demonstration plant currently being developed in the Cooper Basin, Australia. The Cooper Basin has the potential to generate 5,000–10,000 MW.

Experimental solar power

Concentrating photovoltaics in Catalonia, Spain

Concentrated photovoltaics (CPV) systems employ sunlight concentrated onto photovoltaic surfaces for the purpose of electricity generation. Thermoelectric, or "thermovoltaic" devices convert a temperature difference between dissimilar materials into an electric current.

Artificial photosynthesis

Artificial photosynthesis uses techniques include nanotechnology to store solar electromagnetic energy in chemical bonds by splitting water to produce hydrogen and then using carbon dioxide to make methanol.^[129] Researchers in this field are striving to design molecular mimics of photosynthesis that utilize a wider region of the solar spectrum, employ catalytic systems made from abundant, inexpensive materials that are robust, readily repaired, non-toxic, stable in a variety of environmental conditions and perform more efficiently allowing a greater proportion of photon energy to end up in the storage compounds, i.e., carbohydrates (rather than building and sustaining living cells). Relevant approaches utilize coordination chemistry, material science and modified bio-engineered, synthetic biomimetic and bio-inspired techniques, as well as nanosciences, to construct photo-semiconductors and solid state catalysts for water oxidation, plus hydrogen evolution catalysts based on enzymes.^[130]

Renewable energy debate

Renewable electricity production, from sources such as wind power and solar power, is sometimes criticized for being variable or intermittent. However, the International Energy Agency has stated that deployment of renewable technologies usually increases the diversity of electricity sources and, through local generation, contributes to the flexibility of the system and its resistance to central shocks.^[131]

There have been "not in my back yard" (NIMBY) concerns relating to the visual and other impacts of some wind farms, with local residents sometimes fighting or blocking construction.^[132] In the USA, the Massachusetts Cape Wind project was delayed for years partly because of aesthetic concerns. However, residents in other areas have been more positive. According to a town councilor, the overwhelming majority of locals believe that the Ardrossan Wind Farm in Scotland has enhanced the area.^[133]

A recent UK Government document states that “projects are generally more likely to succeed if they have broad public support and the consent of local communities. This means giving communities both a say and a stake” ^[134]. In countries such as Germany and Denmark many renewable projects are owned by communities, particularly through cooperative structures, and contribute significantly to overall levels of renewable energy deployment ^{[135] [136]}. In recent years, new online crowdfunding platforms have provided additional mechanisms for broader participation in, and support for, renewable energy by allowing anyone to invest even small amounts and benefit from the returns. Examples include Abundance Generation in the UK ^[137] and Solar Mosaic in the USA.

The market for renewable energy technologies has continued to grow. Climate change concerns, coupled with high oil prices, peak oil, and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization.^[13] New government spending, regulation and policies helped the industry weather the 2009 economic crisis better than many other sectors.^[14]

See also

	Renewable energy portal
	Energy portal
	Sustainable development portal
	Ecology portal

• International Renewable Energy Agency
• Lists about renewable energy
• Outline of solar energy
• Sustainable energy

References

Bibliography

External links

• The dictionary definition of renewable energy at Wiktionary
• Media related to Renewable energy at Wikimedia Commons

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