In Denmark by 1900, there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 (MW). The largest machines were on 24-meter (79 ft) towers with four-bladed 23-meter (75 ft) diameter rotors. By 1908 there were 72 wind-driven electric generators operating in the United States from 5 kW to 25 kW. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, mostly for water-pumping.[9]
“Trump’s Keystone XL Tar Sands Oil Pipeline Promise, Unkept and Undone” • The federal judge for the District of Montana who overturned permit for the Keystone XL pipeline issued an order that all but guarantees the project will die another death by a thousand cuts. He ordered a complete do-over on economic and environmental impacts. [CleanTechnica]
List of onshore wind farms List of onshore wind farms in the United Kingdom List of offshore wind farms in the United Kingdom List of offshore wind farms in the United States Lists of offshore wind farms by country Lists of offshore wind farms by water area Lists of wind farms by country List of wind farms in Australia List of wind farms in Canada List of wind farms in Iran List of wind farms in New Zealand List of wind farms in Romania List of wind farms in Sweden List of wind farms in the United States List of wind turbine manufacturers

DOE selected six companies for its 2007 Green Power Supplier Awards, including Constellation NewEnergy; 3Degrees; Sterling Planet; SunEdison; Pacific Power and Rocky Mountain Power; and Silicon Valley Power. The combined green power provided by those six winners equals more than 5 billion kilowatt-hours per year, which is enough to power nearly 465,000 average U.S. households. In 2014, Arcadia Power made RECS available to homes and businesses in all 50 states, allowing consumers to use "100% green power" as defined by the EPA's Green Power Partnership.[86][87]


Second-generation technologies include solar heating and cooling, wind power, modern forms of bioenergy and solar photovoltaics. These are now entering markets as a result of research, development and demonstration (RD&D) investments since the 1980s. The initial investment was prompted by energy security concerns linked to the oil crises (1973 and 1979) of the 1970s but the continuing appeal of these renewables is due, at least in part, to environmental benefits. Many of the technologies reflect significant advancements in materials.
A photovoltaic system converts light into electrical direct current (DC) by taking advantage of the photoelectric effect.[51] Solar PV has turned into a multi-billion, fast-growing industry, continues to improve its cost-effectiveness, and has the most potential of any renewable technologies together with CSP.[52][53] Concentrated solar power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Commercial concentrated solar power plants were first developed in the 1980s. CSP-Stirling has by far the highest efficiency among all solar energy technologies.
Most horizontal axis turbines have their rotors upwind of its supporting tower. Downwind machines have been built, because they don't need an additional mechanism for keeping them in line with the wind. In high winds, the blades can also be allowed to bend which reduces their swept area and thus their wind resistance. Despite these advantages, upwind designs are preferred, because the change in loading from the wind as each blade passes behind the supporting tower can cause damage to the turbine.
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If you regularly find your lawn furniture blown over, or have to collect it from the neighbour’s yard, your house needs to be repainted every year or two because it constantly gets sand-blasted, and where the trees have funny shapes (and not because your power company has been doing the pruning), that is when you know you live in a windy place where a wind turbine is likely to make economic sense.

The life-cycle greenhouse-gas emissions of solar power are in the range of 22 to 46 gram (g) per kilowatt-hour (kWh) depending on if solar thermal or solar PV is being analyzed, respectively. With this potentially being decreased to 15 g/kWh in the future.[121] For comparison (of weighted averages), a combined cycle gas-fired power plant emits some 400–599 g/kWh,[122] an oil-fired power plant 893 g/kWh,[122] a coal-fired power plant 915–994 g/kWh[123] or with carbon capture and storage some 200 g/kWh, and a geothermal high-temp. power plant 91–122 g/kWh.[122] The life cycle emission intensity of hydro, wind and nuclear power are lower than solar's as of 2011 as published by the IPCC, and discussed in the article Life-cycle greenhouse-gas emissions of energy sources. Similar to all energy sources were their total life cycle emissions primarily lay in the construction and transportation phase, the switch to low carbon power in the manufacturing and transportation of solar devices would further reduce carbon emissions. BP Solar owns two factories built by Solarex (one in Maryland, the other in Virginia) in which all of the energy used to manufacture solar panels is produced by solar panels. A 1-kilowatt system eliminates the burning of approximately 170 pounds of coal, 300 pounds of carbon dioxide from being released into the atmosphere, and saves up to 105 gallons of water consumption monthly.[124]

When a turbine is mounted on a rooftop the building generally redirects wind over the roof and this can double the wind speed at the turbine. If the height of a rooftop mounted turbine tower is approximately 50% of the building height it is near the optimum for maximum wind energy and minimum wind turbulence. While wind speeds within the built environment are generally much lower than at exposed rural sites,[29][30] noise may be a concern and an existing structure may not adequately resist the additional stress.
Sunforce Wind Generators are primarily used to recharge all types of 12-Volt batteries, including lead-acid automotive batteries, deep-cycle (traction type) batteries, gel-cell batteries, and heavy-duty (stationary type) batteries. When using this wind generator to run appliances on a regular basis, the use of deep-cycle marine batteries is recommended. This type of battery is designed to withstand the frequent charge and discharge cycles associated with wind power use. Attempting to run the wind generator on an open circuit without a battery may cause damage to the generator or connected equipment.
Compact Linear Fresnel Reflectors are CSP-plants which use many thin mirror strips instead of parabolic mirrors to concentrate sunlight onto two tubes with working fluid. This has the advantage that flat mirrors can be used which are much cheaper than parabolic mirrors, and that more reflectors can be placed in the same amount of space, allowing more of the available sunlight to be used. Concentrating linear fresnel reflectors can be used in either large or more compact plants.[16][17]
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