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Renewable Energy Portal - Selected articles

Article 1

Itumbiara dam on Paranaíba River in Brazil

Hydroelectricity is electricity generated by hydropower, i.e., the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy. Once a hydroelectric complex is constructed, the project produces no direct waste, and has a considerably lower output level of the greenhouse gas carbon dioxide (CO2) than fossil fuel powered energy plants. Worldwide, an installed capacity of 777 GWe supplied 2998 TWh of hydroelectricity in 2006. This was approximately 20% of the world's electricity, and accounted for about 88% of electricity from renewable sources.

Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. In this case the energy extracted from the water depends on the volume and on the difference in height between the source and the water's outflow. This height difference is called the head. The amount of potential energy in water is proportional to the head. To obtain very high head, water for a hydraulic turbine may be run through a large pipe called a penstock.


Article 2

Water enters the Arizona spillway during the 1983 floods

The Hoover Dam, once known as Boulder Dam, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the US states of Arizona and Nevada. It was constructed between 1931 and 1936, and was dedicated on September 30, 1935 by President Franklin Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over a hundred lives.

Hoover Dam impounds Lake Mead, and is located near Boulder City, Nevada, a municipality originally created for workers on the construction project, about 30 mi (48 km) south of Las Vegas, Nevada. The dam's generators provide power for public and private utilities in Nevada, Arizona and California. Hoover Dam is a major tourist attraction, and U.S. 93, a heavily travelled road, runs along its crest. In late 2010, traffic was rerouted onto a bypass and the dam roadway was limited to use by visitors.


Article 3

Wind turbine tower on a hilltop at Rochdale

Scout Moor Wind Farm is the second largest onshore wind farm in England. The wind farm, which was built for Peel Wind Power Ltd, produces electricity from 26 Nordex N80 wind turbines. It has a total nameplate capacity of 65 MW of electricity, providing 154,000 MW·h per year (average output 17.6 MWe, a capacity factor of 27%); enough to serve the average needs of 40,000 homes. The site occupies 1,347 acres (545 ha) of open moorland and is split between the Metropolitan Borough of Rochdale in northern Greater Manchester and the Borough of Rossendale in south-eastern Lancashire. The turbines are visible from as far away as south Manchester, 15–20 miles (24–32 km) away.

A protest group was formed to resist the proposed construction, and attracted support from the botanist and environmental campaigner David Bellamy. Despite the opposition, planning permission was granted in 2005 and construction began in 2007. Although work on the project was hampered by harsh weather, difficult terrain, and previous mining activity, the wind farm was officially opened on 25 September 2008, at a cost of £50 million.


Article 4

Mechanized harvesting of sugarcane in Piracicaba, São Paulo

The history of ethanol fuel in Brazil dates from the 1970s and relates to Brazil’s sugarcane based ethanol fuel program, which allowed the country to became the world's second largest producer of ethanol, and the world's largest exporter. Several important political and technological developments led Brazil to became the world leader in the sustainable use of bioethanol, a policy model for other countries, and allowed the country to achieve a landmark in ethanol consumption, when ethanol retail sales surpassed 50% market share of the gasoline-powered vehicle fleet in early 2008.

Ethyl alcohol or ethanol is obtained as a by-product of sugar mills producing sugar, and can be processed to produce alcoholic beverages, ethanol fuel or alcohol for industrial or antiseptic uses. The first use of sugarcane ethanol as fuel in Brazil dates back to the late twenties and early thirties of the twentieth century, with the introduction of the automobile in the country. After World War I some experimenting took place in Brazil's Northeast Region, and as early as 1919, the Governor of Pernambuco mandated all official vehicles to run on ethanol. The first ethanol fuel production plant went on line in 1927, the Usina Serra Grande Alagoas (USGA), located in the Northestern state of Alagoas, producing fuel with 75% ethanol and 25% ethyl ether. As other plants began producing ethanol fuel, two years later there were 500 cars running on this fuel in the country's Northeast Region.


Article 5

Mount Millar wind farm at sunset

Wind power has become a significant energy source within South Australia over the past decade. As of August 2014, there was an installed capacity of 1,473 MW, which accounts for 27 per cent of electricity production in the state. This represents around half of the nation's installed wind power capacity. The rapid growth of wind power in South Australia has enabled the state to achieve its target of sourcing 20% of electricity from renewable energy sources three years ahead of schedule.

The development of wind power capacity in South Australia has been encouraged by a number of factors. These include the Australian Government's Mandatory Renewable Energy Target, which require electricity retailers to source a proportion of energy from renewable sources, incentives from the South Australian Government including a supportive regulatory regime and a payroll tax rebate scheme for large scale renewable energy developments. Also the state's proximity to the Roaring forties means there are high quality wind resources for wind farms to exploit. In mid-2009, RenewablesSA was established by the South Australian Government to encourage further investment in renewable energy to the state.

The load factor (or capacity factor) for South Australian wind farms is usually in the range 32-38%. This means that a wind farm could typically produce between 32 and 38% of its nameplate capacity averaged over a year.


Article 6

The world's largest solar energy dish is located at the Ben-Gurion National Solar Energy Center

Solar power in Israel and the Israeli solar energy industry has a history that dates to the founding of the country. In the 1950s, Levi Yissar developed a solar water heater to help assuage an energy shortage in the new country. By 1967 around one in twenty households heated its water with the sun and 50,000 solar heaters had been sold. With the 1970s oil crisis, Harry Zvi Tabor, the father of Israel's solar industry, developed the prototype of the solar water heater now used in over 90% of Israeli homes. Israeli engineers are at the cutting edge of solar energy technology and its solar companies work on projects around the world.

Israeli innovation and research has advanced solar technology to a degree that it is almost cost-competitive with fossil fuels. Its abundant sun made the country a natural location for the promising technology. The high annual incident solar irradiance in the Negev Desert has spurred an internationally renowned solar research and development industry, with Harry Tabor and David Faiman of the National Solar Energy Center two of its more prominent members. At the end of 2008 a feed-in tariff scheme was approved, which immediately put in motion the building of many residential and commercial solar energy power station projects.


Article 7

Krafla geothermal power plant in Iceland.

Geothermal power (from the Greek roots geo, meaning earth, and thermos, meaning heat) is power extracted from heat stored in the earth. This geothermal energy originates from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. It has been used for bathing since Paleolithic times and for space heating since ancient Roman times, but is now better known for generating electricity. Worldwide, about 10,715 megawatts (MW) of geothermal power is online in 24 countries. An additional 28 gigawatts of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications.

Geothermal power is cost effective, reliable, sustainable, and environmentally friendly, 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.


Article 8

Krafla Geothermal Station

Domestically produced renewable energy in Iceland represents 85% of total primary energy supply. In 2011, geothermal energy provided about 65% of primary energy, the share of hydro power was 20%, and fossil fuels (mainly oil) 15%. The main use of geothermal energy is for space heating with the heat being distributed to buildings through extensive district-heating systems.

Renewable energy provides 100% of electricity production, with about 75% coming from hydropower and 25 percent from geothermal power. Most of the hydropower plants are owned by Landsvirkjun (the National Power Company) which is the main supplier of electricity in Iceland.


Article 9

Nellis Solar Power Plant in the United States, the largest photovoltaic power plant in North America.

Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available renewable energy on earth. Only a minuscule fraction of the available solar energy is used.

Solar powered electrical generation relies on heat engines and photovoltaics. Solar energy's uses are limited only by human ingenuity. A partial list of solar applications includes space heating and cooling through solar architecture, potable water via distillation and disinfection, daylighting, solar hot water, solar cooking, and high temperature process heat for industrial purposes. To harvest the solar energy, the most common way is to use solar panels.


Article 10

Panicum virgatum.jpg

Biofuelsliquid fuels derived from plant materials – are entering the market, driven by factors such as oil price spikes and the need for increased energy security. However, many of the biofuels that are currently being supplied have been criticised for their adverse impacts on the natural environment, food security, and land use.

The challenge is to support biofuel development, including the development of new cellulosic technologies, with responsible policies and economic instruments to help ensure that biofuel commercialization is sustainable. Responsible commercialization of biofuels represents an opportunity to enhance sustainable economic prospects in Africa, Latin America and Asia.

Biofuels offer the prospect of increased market competition and oil price moderation. A healthy supply of alternative energy sources will help to combat gasoline price spikes and reduce dependency on fossil fuels, especially in the transport sector. Using transportation fuels more efficiently is also an integral part of a sustainable transport strategy.


Article 11

Nellis AFB Solar panels.jpg

There are several solar power plants in the Mojave Desert which 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 megawatts (MW) making them the largest solar power installation in the world. Nevada Solar One is a solar thermal plant with a 64 MW generating capacity, located near Boulder City, Nevada. The Copper Mountain Solar Facility is a 48 MW photovoltaic power plant in Boulder City, Nevada. The Ivanpah Solar Power Facility is a 370 MW facility under construction which will consist of three separate solar thermal power plants. There are also plans to build other large solar plants in the Mojave Desert.

Insolation (solar radiation) in the Mojave Desert is among the best available in the United States, and some significant population centers are located in the area. This makes the Mojave Desert particularly suitable for solar power plants. These plants can generally be built in a few years because solar plants are built almost entirely with modular, readily available materials.


Article 12

Alternative Energies

Renewable energy commercialization involves the diffusion of three generations of renewable energy technologies dating back more than 100 years. First-generation technologies, which are already mature and economically competitive, include biomass, hydroelectricity, geothermal power and heat. Second-generation technologies are market-ready and are being deployed at the present time; they include solar heating, photovoltaics, wind power, solar thermal power stations, and modern forms of bioenergy. Third-generation technologies require continued R&D efforts in order to make large contributions on a global scale and include advanced biomass gasification, biorefinery technologies, hot-dry-rock geothermal power, and ocean energy.

There are some non-technical barriers to the widespread use of renewables, and it is often public policy and political leadership that drive the widespread acceptance of renewable energy technologies. Some 85 countries now have targets for their own renewable energy futures, and have enacted wide-ranging public policies to promote renewables. Climate change concerns are driving increasing growth in the renewable energy industries. Leading renewable energy companies include First Solar, Gamesa, GE Energy, Q-Cells, Sharp Solar, Siemens, SunOpta, Suntech, and Vestas.


Article 13

Calefon solar termosifonico compacto.jpg

Solar water heating (SWH) systems are a mature renewable energy technology which has been accepted in most countries for many years. SWH has been widely used in Israel, Australia, Japan, Austria and China.

In a "close-coupled" SWH system the storage tank is horizontally mounted immediately above the solar collectors on the roof. No pumping is required as the hot water naturally rises into the tank through thermosiphon flow. In a "pump-circulated" system the storage tank is ground or floor mounted and is below the level of the collectors; a circulating pump moves water or heat transfer fluid between the tank and the collectors.

SWH systems are designed to deliver the optimum amount of hot water for most of the year. However, in winter there sometimes may not be sufficient solar heat gain to deliver sufficient hot water. In this case a gas or electric booster is normally used to heat the water.


Article 14

Wind, wave and tide make up more than 80% of Scotland's renewable energy potential.

The natural resource base for renewable energy in Scotland is extraordinary by European, and even global standards. In addition to an existing installed capacity of 1.3 Gigawatts (GW) of hydro-electric schemes, Scotland has an estimated potential of 36.5 GW of wind and 7.5 GW of tidal power, 25% of the estimated total capacity for the European Union and up to 14 GW of wave power potential, 10% of EU capacity. The renewable electricity generating capacity may be 60 GW or more, considerably greater than the existing capacity from all Scottish fuel sources of 10.3 GW.

Much of this potential remains untapped, but continuing improvements in engineering are enabling more of the renewable resources to be utilised. Fears regarding "peak oil" and climate change have driven the subject high up the political agenda and are also encouraging the use of various biofuels. Although there is significant support from the public, private and community-led sectors, concerns about the effect of the technologies on the natural environment have been expressed.


Article 15

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

The Geysers is a complex of 22 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains 116 km (72 mi) north of San Francisco, California. The largest in the world, the Geysers has 1517 MW of active installed capacity with an average production factor of 63 % (955 MW).

Calpine Corporation operates and owns 19 of the 22 active plants in the Geysers and is currently the United States' largest producer of geothermal energy. Two other plants are owned jointly by the Northern California Power Agency and the City of Santa Clara's municipal Electric Utility (now called Silicon Valley Power). The Bottle Rock Power plant owned by the US Renewables Group has only recently been reopened. Another plant is under development by Ram Power, formerly Western Geopower, with operation set to begin in 2010.

Since the activities of one geothermal plant affects those nearby, the consolidation of plant ownership at The Geysers has been beneficial because the plants operate cooperatively instead of in their own short-term interest.


Article 16 A mandatory renewable energy target is a government legislated requirement on electricity retailers to source specific proportions of total electricity sales from renewable energy sources according to a fixed timeframe. The additional cost is distributed across most customers by increases in other tariffs. The cost of this measure is therefore not funded by government budgets, except for costs of establishing and monitoring the scheme and any audit and enforcement actions.

At least 66 countries, including 27 EU countries have renewable energy policy targets of some type. The EU baseline target is 20% by 2020. While the USA does not have a national RET, 29 of its states do. Similarly Canada has 9 state RETs but no national target. Targets are typically for shares of electricity production, but some are defined as by primary energy supply, installed capacity or otherwise. While some targets are based on 2010-12, many are now for 2020 which ties in with the IPCC suggested greenhouse gas emission cuts of 25 to 40% by Annex I countries by 2020, although some are for 2025.


Article 17

View of the Three Gorges Dam on the Yangtze River, China

The Three Gorges Dam is a hydroelectric dam that spans the Yangtze River by the town of Sandouping, located in the Yiling District of Yichang, in Hubei province, China. The Three Gorges Dam is the world’s largest capacity hydroelectric power station with a total generating capacity of 18,200 MW.

The dam body was completed in 2006. Except for a ship lift, the originally planned components of the project were completed on October 30, 2008, when the 26th turbine in the shore plant began commercial operation. Each turbine has a capacity of 700  MW. Six additional turbines in the underground power plant are not expected to become fully operational until 2012. Coupling the dam's thirty-two main turbines with two smaller generators (50 MW each) to power the plant itself, the total electric generating capacity of the dam will eventually reach 22,500 MW.

As well as producing electricity, the dam increases the Yangtze River's shipping capacity, and reduces the potential for floods downstream by providing flood storage space. The Chinese government regards the project as a historic engineering, social and economic success, with the design of state-of-the-art large turbines, and a move toward limiting greenhouse gas emissions. However, the dam flooded archaeological and cultural sites and displaced some 1.3 million people, and is causing significant ecological changes, including an increased risk of landslides. The dam has been a controversial topic both in China and abroad.


Article 18

Tidal mill at Olhão, Portugal

A tide mill is a specialist type of water mill driven by tidal rise and fall. A dam with a sluice is created across a suitable tidal inlet, or a section of river estuary is made into a reservoir. As the tide comes in, it enters the mill pond through a one way gate, and this gate closes automatically when the tide begins to fall. When the tide is low enough, the stored water can be released to turn a water wheel.

Tide mills are usually situated in river estuaries, away from the effects of waves but close enough to the sea to have a reasonable tidal range. These mills have existed since the Middle Ages, and some may go back to the Roman period.

A modern version of a tide mill is the electricity generating tidal barrage.


Article 19

Sayano–Shushenskaya Dam, Russia

Renewable energy in Russia mainly consists of hydroelectric energy. The country is the fifth largest producer of renewable energy in the world, although it is 56th when hydroelectric energy is not taken into account. Only 179 TWh of Russia's energy production comes from renewable energy sources, out of a total economically feasible potential of 1823 TWh. Only 16% of Russia's electricity is generated from hydropower, and less than 1% is generated from all other renewable energy sources combined. Roughly 68% of Russia's electricity is generated from thermal power and 16% from nuclear power. The abundance of fossil fuels in the Soviet Union and the Russian Federation has resulted in little development of the renewable energy sector. There are currently plans to expand the share of renewable energy in Russia's energy output, plans strongly encouraged by the Russian government. Russian President Dmitry Medvedev has called for renewable energy to have a larger share of Russia's energy output, and has taken steps to promote the development of renewable energy in Russia since 2008.


Article 20

Grand Coulee Dam on the Columbia River in the U.S. state of Washington

Grand Coulee Dam is a gravity dam on the Columbia River in the U.S. state of Washington built to produce hydroelectric power and provide irrigation. It was constructed between 1933 and 1942, originally with two power plants. A third power station was completed in 1974 to increase its energy production. It is the largest electric power-producing facility in the United States and one of the largest concrete structures in the world.

Power from the dam fueled the growing industries of the Northwest United States during World War II. Between 1967 and 1974, the Third Powerplant was constructed. The decision to construct the additional facility was influenced by growing energy demand, regulated river flows stipulated in the Columbia River Treaty with Canada and competition with the Soviet Union. Through a series of upgrades and the installation of pump-generators, the dam now supplies four power stations with an installed capacity of 6,809 MW. As the center-piece of the Columbia Basin Project, the dam's reservoir supplies water for the irrigation of 671,000 acres (2,700 km2).


Article 21

Growth of wind and solar power

The incentive to use 100% renewable energy has been created by global warming and other ecological as well as economic concerns. Renewable energy use has grown much faster than anyone anticipated. The Intergovernmental Panel on Climate Change has said that there are few fundamental technological limits to integrating a portfolio of renewable energy technologies to meet most of total global energy demand. Mark Z. Jacobson says producing all new energy with wind power, solar power, and hydropower by 2030 is feasible and existing energy supply arrangements could be replaced by 2050. Barriers to implementing the renewable energy plan are seen to be "primarily social and political, not technological or economic". Jacobson says that energy costs with a wind, solar, water system should be similar to today's energy costs. Critics of the "100% renewable energy" approach include Vaclav Smil and James E. Hansen.


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