Taken together, the generation and distribution of electric power in the United States is an astonishingly complex undertaking. Utilities may generate their own power or buy it from other utilities; that power travels over a grid of transformers and high- and low-voltage lines to your house. Ownership of utilities varies from nonprofits to cooperatives to for-profits. Federal regulators ultimately oversee the grid. Amazingly, when you flip a switch, electricity is there.
The conversion of the rotational mechanical power generated by the rotor blades (known as the prime mover) into useful electrical power for use in domestic power and lighting applications or to charge batteries can be accomplished by any one of the following major types of rotational electrical machines commonly used in a wind power generating systems:

Wind energy research dates back several decades to the 1970s when NASA developed an analytical model to predict wind turbine power generation during high winds.[136] Today, both Sandia National Laboratories and National Renewable Energy Laboratory have programs dedicated to wind research. Sandia’s laboratory focuses on the advancement of materials, aerodynamics, and sensors.[137] The NREL wind projects are centered on improving wind plant power production, reducing their capital costs, and making wind energy more cost effective overall.[138] The Field Laboratory for Optimized Wind Energy (FLOWE) at Caltech was established to research renewable approaches to wind energy farming technology practices that have the potential to reduce the cost, size, and environmental impact of wind energy production.[139] The president of Sky WindPower Corporation thinks that wind turbines will be able to produce electricity at a cent/kWh at an average which in comparison to coal-generated electricity is a fractional of the cost.[140]
Floatovoltaics are an emerging form of PV systems that float on the surface of irrigation canals, water reservoirs, quarry lakes, and tailing ponds. Several systems exist in France, India, Japan, Korea, the United Kingdom and the United States.[149][150][151][152] These systems reduce the need of valuable land area, save drinking water that would otherwise be lost through evaporation, and show a higher efficiency of solar energy conversion, as the panels are kept at a cooler temperature than they would be on land.[153] Although not floating, other dual-use facilities with solar power include fisheries.[154]
On most horizontal wind turbine farms, a spacing of about 6–10 times the rotor diameter is often upheld. However, for large wind farms distances of about 15 rotor diameters should be more economical, taking into account typical wind turbine and land costs. This conclusion has been reached by research[62] conducted by Charles Meneveau of the Johns Hopkins University,[63] and Johan Meyers of Leuven University in Belgium, based on computer simulations[64] that take into account the detailed interactions among wind turbines (wakes) as well as with the entire turbulent atmospheric boundary layer.
The first three are active solar systems, which use mechanical or electrical devices that convert the sun's heat or light to another form of usable energy. Passive solar buildings are designed and oriented to collect, store, and distribute the heat energy from sunlight to maintain the comfort of the occupants without the use of moving parts or electronics.

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]
The typical cost factors for solar power include the costs of the modules, the frame to hold them, wiring, inverters, labour cost, any land that might be required, the grid connection, maintenance and the solar insolation that location will receive. Adjusting for inflation, it cost $96 per watt for a solar module in the mid-1970s. Process improvements and a very large boost in production have brought that figure down to 68 cents per watt in February 2016, according to data from Bloomberg New Energy Finance.[69] Palo Alto California signed a wholesale purchase agreement in 2016 that secured solar power for 3.7 cents per kilowatt-hour. And in sunny Dubai large-scale solar generated electricity sold in 2016 for just 2.99 cents per kilowatt-hour – "competitive with any form of fossil-based electricity — and cheaper than most."[70]
Most current solar power plants are made from an array of similar units where each unit is continuously adjusted, e.g., with some step motors, so that the light converter stays in focus of the sun light. The cost of focusing light on converters such as high-power solar panels, Stirling engine, etc. can be dramatically decreased with a simple and efficient rope mechanics.[55] In this technique many units are connected with a network of ropes so that pulling two or three ropes is sufficient to keep all light converters simultaneously in focus as the direction of the sun changes.
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.
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".[194] 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.[195][196]
Wind-to-rotor efficiency (including rotor blade friction and drag) are among the factors impacting the final price of wind power.[16] Further inefficiencies, such as gearbox losses, generator and converter losses, reduce the power delivered by a wind turbine. To protect components from undue wear, extracted power is held constant above the rated operating speed as theoretical power increases at the cube of wind speed, further reducing theoretical efficiency. In 2001, commercial utility-connected turbines deliver 75% to 80% of the Betz limit of power extractable from the wind, at rated operating speed.[17][18][needs update]
“If the U.S. continues this kind of thing, I’m afraid the credibility of the number one leader country of the world may be in serious question,” Mr. Ban said. “We must have a global vision. It’s not the American economy. If the world economy is shaken by climate consequences do you think the American economy will be able to survive? We all sink together.”
Permanent magnets for wind turbine generators contain rare earth metals such as Nd, Pr, Tb, and Dy. Systems that use magnetic direct drive turbines require higher amounts of rare metals. Therefore, an increase in wind production would increase the demand for these resources. It is estimated that the additional demand for Nd in 2035 may be 4,000 to 18,000 tons and Dy could see an increase of 200 to 1200 tons. These values represent a quarter to half of current production levels. However, since technologies are developing rapidly, driven by supply and price of materials these estimated levels are extremely uncertain.[55]
Going forward, there is hope for the small wind future! Certification programs are under way in various places to provide real turbine performance data. In North America this is being spearheaded by the Small Wind Certification Council, which requires third-party certification of turbine performance in a standardized fashion. Manufacturers will no longer be able to fudge power curves, or specify ‘rated power’ at hurricane-force wind speeds. This will allow you, the consumer, to compare turbines on a much more even footing.

The locations with highest annual solar irradiance lie in the arid tropics and subtropics. Deserts lying in low latitudes usually have few clouds, and can receive sunshine for more than ten hours a day.[86][87] These hot deserts form the Global Sun Belt circling the world. This belt consists of extensive swathes of land in Northern Africa, Southern Africa, Southwest Asia, Middle East, and Australia, as well as the much smaller deserts of North and South America.[88] Africa's eastern Sahara Desert, also known as the Libyan Desert, has been observed to be the sunniest place on Earth according to NASA.[89][90]
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.[112] In the United States, 5,600 MW of solar thermal power projects have been announced.[113] Several power plants have been constructed in the Mojave Desert, Southwestern United States. The Ivanpah Solar Power Facility being the most recent. 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.[114]
Thorium is a fissionable material used in thorium-based nuclear power. The thorium fuel cycle claims several potential advantages over a uranium fuel cycle, including greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation[121][122][123] and reduced plutonium and actinide production.[123] Therefore, it is sometimes referred as sustainable.[124]
Other renewable energy technologies are still under development, and include cellulosic ethanol, hot-dry-rock geothermal power, and marine energy.[156] 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.[156]
Ross, something of a libertarian at heart, entered politics because he was ticked off that the municipal code prohibited him from paving the driveway to his historic home entirely in period-appropriate brick. (The code required some concrete.) He joined the city council in 2008 and was elected to his first term as mayor in 2014. He often likens the city to “Mayberry R.F.D.,” and it does have a town square with a courthouse, a coffee shop where you’re bound to run into people you know and a swimming hole. But it also has Southwestern University, and in 2010 university officials, following a student initiative, told the city council they wanted their electricity to come from renewable sources. The city had already set a goal of getting 30 percent of its power that way, but now, Ross and his colleagues saw their opportunity.

The New Zealand Parliamentary Commissioner for the Environment found that the solar PV would have little impact on the country's greenhouse gas emissions. The country already generates 80 percent of its electricity from renewable resources (primarily hydroelectricity and geothermal) and national electricity usage peaks on winter evenings whereas solar generation peaks on summer afternoons, meaning a large uptake of solar PV would end up displacing other renewable generators before fossil-fueled power plants.[127]
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).[58]
“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]

The reliability of small wind turbines is (still) problematic. Even the good ones break much more frequently than we would like, and none will run for 20 years without the need to replace at least some part(s). Despite their apparent simplicity, a small wind turbine is nowhere near as reliable as the average car (and even cars will not run for 20 years without stuff breaking). If you are going to install a small wind turbine you should expect that it will break. The only questions are when and how often.

This discussion is mainly about factory-made grid-tie wind turbines. The off-grid crowd has an entirely different set of decisions and goals. The main ones are that for off-grid use economic viability in comparison with the electrical grid is not an issue, and a wind turbine can make up for the loss of sunlight (and PV electricity) in the winter months. For the DIY group there are several good turbine designs available; Hugh Piggott and the two Dans have written books that outline this step-by-step. Building your own turbine can be a great hobby, and some of the topics touched below apply (such as proper site selection), but this discussion is not about those. The decisions involved in making your own turbine, and the cost basis, have little overlap with a the process of having an installer put a factory-made turbine in your backyard.
Even with plans to grow as much as 80 percent over the next five years, the city expects to have plenty of energy from these renewable sources. (To be sure, about 2 percent of the time, the Georgetown utility draws electricity derived from fossil fuels. Ross says the city more than compensates at other times by selling excess renewable energy back to the grid—at a profit.)
Climate change and global warming concerns, coupled with high oil prices, peak oil, and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization.[10] New government spending, regulation and policies helped the industry weather the global financial crisis better than many other sectors.[24] According to a 2011 projection by the International Energy Agency, solar power generators may produce most of the world's electricity within 50 years, reducing the emissions of greenhouse gases that harm the environment.[25]
Thorium is a fissionable material used in thorium-based nuclear power. The thorium fuel cycle claims several potential advantages over a uranium fuel cycle, including greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation[121][122][123] and reduced plutonium and actinide production.[123] Therefore, it is sometimes referred as sustainable.[124]
This solar resource map provides a summary of the estimated solar energy available for power generation and other energy applications. It represents the average daily/yearly sum of electricity production from a 1 kW-peak grid-connected solar PV power plant covering the period from 1994/1999/2007 (depending on the geographical region) to 2015. Source: Global Solar Atlas]