Renewable energy (also called green energy) is energy made from renewable natural resources that are replenished on a human timescale. The most widely used renewable energy types are solar energy, wind power, and hydropower. Bioenergy and geothermal power are also significant in some countries. Some also consider nuclear power a renewable power source, although this is controversial, as nuclear energy requires mining uranium, a nonrenewable resource. Renewable energy installations can be large or small and are suited for both urban and rural areas. Renewable energy is often deployed together with further electrification. This has several benefits: electricity can move heat and vehicles efficiently and is clean at the point of consumption. Variable renewable energy sources are those that have a fluctuating nature, such as wind power and solar power. In contrast, controllable renewable energy sources include dammed hydroelectricity, bioenergy, or geothermal power.
Renewable energy systems have rapidly become more efficient and cheaper over the past 30 years. A large majority of worldwide newly installed electricity capacity is now renewable. Renewable energy sources, such as solar and wind power, have seen significant cost reductions over the past decade, making them more competitive with traditional fossil fuels. In most countries, photovoltaic solar or onshore wind are the cheapest new-build electricity. From 2011 to 2021, renewable energy grew from 20% to 28% of global electricity supply. Power from the sun and wind accounted for most of this increase, growing from a combined 2% to 10%. Use of fossil energy shrank from 68% to 62%. In 2022, renewables accounted for 30% of global electricity generation and are projected to reach over 42% by 2028. Many countries already have renewables contributing more than 20% of their total energy supply, with some generating over half or even all their electricity from renewable sources.
The main motivation to replace fossil fuels with renewable energy sources is to slow and eventually stop climate change, which is widely agreed to be caused mostly by greenhouse gas emissions. In general, renewable energy sources cause much lower emissions than fossil fuels. The International Energy Agency estimates that to achieve net zero emissions by 2050, 90% of global electricity generation will need to be produced from renewable sources. Renewables also cause much less air pollution than fossil fuels, improving public health, and are less noisy.
The deployment of renewable energy still faces obstacles, especially fossil fuel subsidies, lobbying by incumbent power providers, and local opposition to the use of land for renewable installations. Like all mining, the extraction of minerals required for many renewable energy technologies also results in environmental damage. In addition, although most renewable energy sources are sustainable, some are not. (Full article...)
Although San Francisco had sought Tuolumne River water as early as the 1890s, this project did not move forward until the disastrous earthquake and fire of 1906, which underscored the insufficiency of the existing water supply. The Hetch Hetchy Valley – then compared to Yosemite Valley for its scenic beauty – was chosen for its water quality and hydroelectric potential, but the location within the national park generated controversy. An act of Congress was required to circumvent federal protection of the Tuolumne River, with the reasoning that public land should be developed for the public benefit.
Construction of the dam started in 1919 and was finished in 1923, with the first water delivered in 1934 after numerous delays. From 1935 to 1938, the dam was raised to increase its capacity for water supply and power generation. The dam, aqueduct and appurtenant hydroelectric systems are collectively known as the Hetch Hetchy Project. Deriving from a largely wild and pristine area of the Sierra Nevada, the Hetch Hetchy supply is some of the cleanest municipal water in the US, requiring only primary filtration and disinfection. (Full article...)
"Perhaps because of its technical, economic, and thermodynamic advantages, a renewable power sector would have six benefits over one reliant on conventional power plants, including (1) lower negative externalities per kWh, (2) more stable and predictable fuel prices, (3) fewer greenhouse gas emissions, (4) less water use, (5) improved efficiency, and (6) greater local employment and revenue." – Benjamin K. Sovacool and Charmaine Watts. The Electricity Journal, May 2009, Vol. 22, Issue 4, p. 99.
"... renewable electricity technologies present policy makers with a superior alternative for minimising the risk of fuel interruptions and shortages, helping improve the fragile transmission network and reducing environmental harm. These smaller and more environmentally friendly generators cost less to construct, produce power in smaller increments and need not rely on continuous government subsidies. They generate little to no waste, have less greenhouse gas emissions per unit of electricity produced and do not contribute significantly to the risk of accidents." – Benjamin K. Sovacool, Journal of Contemporary Asia, 40(3), 2010, p. 371.
Image 10Concentrated solar panels are getting a power boost. Pacific Northwest National Laboratory (PNNL) will be testing a new concentrated solar power system – one that can help natural gas power plants reduce their fuel usage by up to 20 percent.[needs update] (from Solar energy)
Image 11Share of electricity production from wind, 2023 (from Wind power)
Image 13Museum Hydroelectric power plant "Under the Town" in Užice, Serbia, built in 1900 (from Hydroelectricity)
Image 14Installed geothermal energy capacity, 2022 (from Geothermal energy)
Image 15Global map of wind speed at 100 meters on land and around coasts. (from Wind power)
Image 16Hydro generation by country, 2021 (from Hydroelectricity)
Image 17The Hoover Dam in the United States is a large conventional dammed-hydro facility, with an installed capacity of 2,080 MW. (from Hydroelectricity)
Image 20A panoramic view of the United Kingdom's Whitelee Wind Farm with Lochgoin Reservoir in the foreground. (from Wind power)
Image 21The Warwick Castle water-powered generator house, used for the generation of electricity for the castle from 1894 until 1940 (from Hydroelectricity)
Image 22Greenhouses like these in the Westland municipality of the Netherlands grow vegetables, fruits and flowers. (from Solar energy)
Image 23Distribution of wind speed (red) and energy (blue) for all of 2002 at the Lee Ranch facility in Colorado. The histogram shows measured data, while the curve is the Rayleigh model distribution for the same average wind speed. (from Wind power)
Image 24Greenhouse gas emissions per energy source. Wind energy is one of the sources with the least greenhouse gas emissions. (from Wind power)
Image 25Merowe Dam in Sudan. Hydroelectric power stations that use dams submerge large areas of land due to the requirement of a reservoir. These changes to land color or albedo, alongside certain projects that concurrently submerge rainforests, can in these specific cases result in the global warming impact, or equivalent life-cycle greenhouse gases of hydroelectricity projects, to potentially exceed that of coal power stations. (from Hydroelectricity)
Image 33Geothermal power station in the Philippines (from Geothermal energy)
Image 34Acceptance of wind and solar facilities in one's community is stronger among U.S. Democrats (blue), while acceptance of nuclear power plants is stronger among U.S. Republicans (red). (from Wind power)
Image 36Cost development of solar PV modules per watt (from Solar energy)
Image 37Wind turbines such as these, in Cumbria, England, have been opposed for a number of reasons, including aesthetics, by some sectors of the population. (from Wind power)
Image 38Energy from wind, sunlight or other renewable energy is converted to potential energy for storage in devices such as electric batteries or higher-elevation water reservoirs. The stored potential energy is later converted to electricity that is added to the power grid, even when the original energy source is not available. (from Wind power)
Image 45A turbine blade convoy passing through Edenfield in the U.K. (2008). Even longer 2-piece blades are now manufactured, and then assembled on-site to reduce difficulties in transportation. (from Wind power)
Image 46Solar water heaters facing the Sun to maximize gain (from Solar energy)
Image 47Electricity generation at Ohaaki, New Zealand (from Geothermal energy)
Image 50The oldest known pool fed by a hot spring, built in the Qin dynasty in the 3rd century BCE (from Geothermal energy)
Image 51Onshore wind cost per kilowatt-hour between 1983 and 2017 (from Wind power)
Image 52Enhanced 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 (from Geothermal energy)
Image 54Seasonal cycle of capacity factors for wind and photovoltaics in Europe under idealized assumptions. The figure illustrates the balancing effects of wind and solar energy at the seasonal scale (Kaspar et al., 2019). (from Wind power)
![Image 10Concentrated solar panels are getting a power boost. Pacific Northwest National Laboratory (PNNL) will be testing a new concentrated solar power system – one that can help natural gas power plants reduce their fuel usage by up to 20 percent.[needs update] (from Solar energy)](/wiki/File:Photo_of_the_Week-_Boosting_Solar_Technology_(8722948189).jpg)
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