Through collaboration, smaller buyers can benefit from economies of scale, while larger buyers can continue to see cost benefits while achieving their renewable energy goals. Aggregation allows companies to procure in a mutually beneficial way with relatively little give and take. For that reason, RMI believes this marks “the beginning of a trend,” Haley said.  

In cases of self consumption of the solar energy, the payback time is calculated based on how much electricity is not purchased from the grid. For example, in Germany, with electricity prices of 0.25 €/kWh and insolation of 900 kWh/kW, one kWp will save €225 per year, and with an installation cost of 1700 €/KWp the system cost will be returned in less than seven years.[91] However, in many cases, the patterns of generation and consumption do not coincide, and some or all of the energy is fed back into the grid. The electricity is sold, and at other times when energy is taken from the grid, electricity is bought. The relative costs and prices obtained affect the economics. In many markets, the price paid for sold PV electricity is significantly lower than the price of bought electricity, which incentivizes self consumption.[92] Moreover, separate self consumption incentives have been used in e.g. Germany and Italy.[92] Grid interaction regulation has also included limitations of grid feed-in in some regions in Germany with high amounts of installed PV capacity.[92][93] By increasing self consumption, the grid feed-in can be limited without curtailment, which wastes electricity.[94]
Photovoltaics (PV) uses solar cells assembled into solar panels to convert sunlight into electricity. It's a fast-growing technology doubling its worldwide installed capacity every couple of years. PV systems range from small, residential and commercial rooftop or building integrated installations, to large utility-scale photovoltaic power station. The predominant PV technology is crystalline silicon, while thin-film solar cell technology accounts for about 10 percent of global photovoltaic deployment. In recent years, PV technology has improved its electricity generating efficiency, reduced the installation cost per watt as well as its energy payback time, and has reached grid parity in at least 30 different markets by 2014.[115] Financial institutions are predicting a second solar "gold rush" in the near future.[116][117][118]
All these electrical machines are electromechanical devices that work on Faraday’s law of electromagnetic induction. That is they operate through the interaction of a magnetic flux and an electric current, or flow of charge. As this process is reversible, the same machine can be used as a conventional electrical motor for converting the electrical power into mechanical power, or as a generator converting the mechanical power back into the electrical power.
Sustainable energy is energy that is consumed at insignificant rates compared to its supply and with manageable collateral effects, especially environmental effects. Another common definition of sustainable energy is an energy system that serves the needs of the present without compromising the ability of future generations to meet their energy needs.[1] Not all renewable energy is sustainable. While renewable energy is defined as energy sources that are naturally replenished on a human timescale, sustainable (often referred to as 'clean') energy must not compromise the system in which it is adopted to the point of being unable to provide for future need. The organizing principle for sustainability is sustainable development, which includes the four interconnected domains: ecology, economics, politics and culture.[2] Sustainability science is the study of sustainable development and environmental science.[3]
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.

Solar energy, radiant light and heat from the sun, is harnessed using a range of ever-evolving technologies such as solar heating, photovoltaics, concentrated solar power (CSP), concentrator photovoltaics (CPV), solar architecture and artificial photosynthesis.[49][50] Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar 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. Active solar technologies encompass solar thermal energy, using solar collectors for heating, and solar power, converting sunlight into electricity either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP).
Geothermal energy - Just under the earth's crust are massive amounts of thermal energy, which originates from both the original formation of the planet and the radioactive decay of minerals. Geothermal energy in the form of hot springs has been used by humans for millennia for bathing, and now it's being used to generate electricity. In North America alone, there's enough energy stored underground to produce 10 times as much electricity as coal currently does.

A typical house usually requires a home wind turbine with a 5 kW generating capacity to meet all its energy requirements. A turbine that offers this much power would have to be around 13 to 18 feet in diameter and positioned in an area where strong winds often pass through. There are also plenty of smaller, cheaper turbines, but these variants produce less power and are less reliable than their more expensive counterparts.
Many industrialized nations have installed significant solar power capacity into their grids to supplement or provide an alternative to conventional energy sources while an increasing number of less developed nations have turned to solar to reduce dependence on expensive imported fuels (see solar power by country). Long distance transmission allows remote renewable energy resources to displace fossil fuel consumption. Solar power plants use one of two technologies:
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