We now know that the electrical generator provides a means of energy conversion between the mechanical torque generated by the rotor blades, called the prime mover, and some electrical load. The mechanical connection of the wind turbine generator to the rotor blades is made through a main shaft which can be either a simple direct drive, or by using a gearbox to increase or decrease the generator speed relative to the rotational speed of the blades.

Additions of small amount (0.5 weight %) of nanoreinforcement (carbon nanotubes or nanoclay in the polymer matrix of composites, fiber sizing or interlaminar layers can allow to increase the fatigue resistance, shear or compressive strength as well as fracture toughness of the composites by 30–80%. Research has also shown that the incorporation of small amount of carbon nanotubes/CNT can increase the lifetime up to 1500%.

Manufacturers often claim that their vertical axis turbine is better at extracting power from low speed winds. Unfortunately the laws of physics get in the way here: There is very little power in low speed winds. The blade of a vertical or horizontal type turbine is equally good at extracting that power, though with the vertical type the blades move at an angle to the wind where they do not extract energy for part of every rotation, adding drag and making a vertical type turbine just a little less efficient than a similar sized horizontal one. There is no advantage when it comes to low winds.


By participating in a green energy program a consumer may be having an effect on the energy sources used and ultimately might be helping to promote and expand the use of green energy. They are also making a statement to policy makers that they are willing to pay a price premium to support renewable energy. Green energy consumers either obligate the utility companies to increase the amount of green energy that they purchase from the pool (so decreasing the amount of non-green energy they purchase), or directly fund the green energy through a green power provider. If insufficient green energy sources are available, the utility must develop new ones or contract with a third party energy supplier to provide green energy, causing more to be built. However, there is no way the consumer can check whether or not the electricity bought is "green" or otherwise.
Which is to say that Ross and his co-workers had options. And the city was free to take advantage of them because of a rather unusual arrangement: Georgetown itself owns the utility company that serves the city. So officials there, unlike those in most cities, were free to negotiate with suppliers. When they learned that rates for wind power could be guaranteed for 20 years and solar for 25 years, but natural gas for only seven years, the choice, Ross says, was a “no-brainer.”
†Offer is available to Texas residential customers who enroll using the Promotion Code “NIGHTSFREE”. Plan bills a monthly Base Charge, an Energy Charge, and passes through Utility Transmission and Distribution delivery charges. Energy Charges for usage consumed between 9pm and 7am each day is credited back on your bill. The utility charges, including delivery charges for night time hours, are passed through at cost and aggregated on your bill. See Electricity Facts Label for details.
In 2014 global wind power capacity expanded 16% to 369,553 MW.[83] Yearly wind energy production is also growing rapidly and has reached around 4% of worldwide electricity usage,[84] 11.4% in the EU,[85] and it is widely used in Asia, and the United States. In 2015, worldwide installed photovoltaics capacity increased to 227 gigawatts (GW), sufficient to supply 1 percent of global electricity demands.[86] Solar thermal energy stations operate in the United States and Spain, and as of 2016, the largest of these is the 392 MW Ivanpah Solar Electric Generating System in California.[87][88] The world's largest geothermal power installation is The Geysers in California, with a rated capacity of 750 MW. Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18% of the country's automotive fuel. Ethanol fuel is also widely available in the United States.
In 2004, the German government introduced the first large-scale feed-in tariff system, under the German Renewable Energy Act, which resulted in explosive growth of PV installations in Germany. At the outset the FIT was over 3x the retail price or 8x the industrial price. The principle behind the German system is a 20-year flat rate contract. The value of new contracts is programmed to decrease each year, in order to encourage the industry to pass on lower costs to the end users. The programme has been more successful than expected with over 1GW installed in 2006, and political pressure is mounting to decrease the tariff to lessen the future burden on consumers.

By 2040, renewable energy is projected to equal coal and natural gas electricity generation. Several jurisdictions, including Denmark, Germany, the state of South Australia and some US states have achieved high integration of variable renewables. For example, in 2015 wind power met 42% of electricity demand in Denmark, 23.2% in Portugal and 15.5% in Uruguay. Interconnectors enable countries to balance electricity systems by allowing the import and export of renewable energy. Innovative hybrid systems have emerged between countries and regions.[27]


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.
Anaerobic digestion, geothermal power, wind power, small-scale hydropower, solar energy, biomass power, tidal power, wave power, and some forms of nuclear power (ones which are able to "burn" nuclear waste through a process known as nuclear transmutation, such as an Integral Fast Reactor, and therefore belong in the "Green Energy" category). Some definitions may also include power derived from the incineration of waste.
The energy payback time (EPBT) of a power generating system is the time required to generate as much energy as is consumed during production and lifetime operation of the system. Due to improving production technologies the payback time has been decreasing constantly since the introduction of PV systems in the energy market.[128] In 2000 the energy payback time of PV systems was estimated as 8 to 11 years[129] and in 2006 this was estimated to be 1.5 to 3.5 years for crystalline silicon PV systems[121] and 1–1.5 years for thin film technologies (S. Europe).[121] These figures fell to 0.75–3.5 years in 2013, with an average of about 2 years for crystalline silicon PV and CIS systems.[130]
Also, the output voltage and power demand depends entirely upon the appliances you have and how you wish to use them. In addition, the location of the wind turbine generator, would the wind resource keep it constantly rotating for long periods of time or would the generator speed and therefore its output vary up and down with variations in the available wind.
Many residential PV systems are connected to the grid wherever available, especially in developed countries with large markets.[10] In these grid-connected PV systems, use of energy storage is optional. In certain applications such as satellites, lighthouses, or in developing countries, batteries or additional power generators are often added as back-ups. Such stand-alone power systems permit operations at night and at other times of limited sunlight.
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