In net metering the price of the electricity produced is the same as the price supplied to the consumer, and the consumer is billed on the difference between production and consumption. Net metering can usually be done with no changes to standard electricity meters, which accurately measure power in both directions and automatically report the difference, and because it allows homeowners and businesses to generate electricity at a different time from consumption, effectively using the grid as a giant storage battery. With net metering, deficits are billed each month while surpluses are rolled over to the following month. Best practices call for perpetual roll over of kWh credits.[97] Excess credits upon termination of service are either lost, or paid for at a rate ranging from wholesale to retail rate or above, as can be excess annual credits. In New Jersey, annual excess credits are paid at the wholesale rate, as are left over credits when a customer terminates service.[98]
Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources.
In the United States, one of the main problems with purchasing green energy through the electrical grid is the current centralized infrastructure that supplies the consumer’s electricity. This infrastructure has led to increasingly frequent brown outs and black outs, high CO2 emissions, higher energy costs, and power quality issues.[89] An additional $450 billion will be invested to expand this fledgling system over the next 20 years to meet increasing demand.[90] In addition, this centralized system is now being further overtaxed with the incorporation of renewable energies such as wind, solar, and geothermal energies. Renewable resources, due to the amount of space they require, are often located in remote areas where there is a lower energy demand. The current infrastructure would make transporting this energy to high demand areas, such as urban centers, highly inefficient and in some cases impossible. In addition, despite the amount of renewable energy produced or the economic viability of such technologies only about 20 percent will be able to be incorporated into the grid. To have a more sustainable energy profile, the United States must move towards implementing changes to the electrical grid that will accommodate a mixed-fuel economy.[91]

Construction of the Salt Tanks which provide efficient thermal energy storage[103] so that output can be provided after the sun goes down, and output can be scheduled to meet demand requirements.[104] The 280 MW Solana Generating Station is designed to provide six hours of energy storage. This allows the plant to generate about 38 percent of its rated capacity over the course of a year.[105]

While renewables have been very successful in their ever-growing contribution to electrical power there are no countries dominated by fossil fuels who have a plan to stop and get that power from renwables. Only Scotland and Ontario have stopped burning coal, largely due to good natural gas supplies. In the area of transportation, fossil fuels are even more entrenched and solutions harder to find.[198] It's unclear if there are failures with policy or renewable energy, but twenty years after the Kyoto Protocol fossil fuels are still our primary energy source and consumption continues to grow.[199]
In 2010, the United States led the world in geothermal electricity production with 3,086 MW of installed capacity from 77 power plants;[132] the largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California.[133] The Philippines follows the US as the second highest producer of geothermal power in the world, with 1,904 MW of capacity online; geothermal power makes up approximately 18% of the country's electricity generation.[132]

The Solar updraft tower is a renewable-energy power plant for generating electricity from low temperature solar heat. Sunshine heats the air beneath a very wide greenhouse-like roofed collector structure surrounding the central base of a very tall chimney tower. The resulting convection causes a hot air updraft in the tower by the chimney effect. This airflow drives wind turbines placed in the chimney updraft or around the chimney base to produce electricity. Plans for scaled-up versions of demonstration models will allow significant power generation, and may allow development of other applications, such as water extraction or distillation, and agriculture or horticulture. A more advanced version of a similarly themed technology is the Vortex engine which aims to replace large physical chimneys with a vortex of air created by a shorter, less-expensive structure.
My system has been installed for about a year now. When I first contracted with Envismart, the sales rep was very available and eager to help with my questions but after the installation, he was very hard to make contact with, seldom returned my calls, and when he did seemed to tell me what he thought I wanted hear and very seldom followed through. The system had a shaky start, it died after one day and after two new inverters and several optimizers over several months of on again, off again operation it seems to be running smoothly, at least for the last few months. Customer support was not very good, to be kind, but the service personnel that came out were prompt and there when they said they would be and very open about what the problems were and quickly fixed them. I was told my recurring system problems were a little unusual and I have to take their word on that but they gave me their personnel cell numbers and told me to call them when I couldn't get Customer Support to call - and when I called them, they came through and got me serviced a lot more quickly. They are the main reason I rated the company a 3.I have to say, the last month or so, it seems like the company is starting to work on changing its image. I have been called on several occasions by the "Quality Assurance" group at their initiation and asked if everything was OK with my system and I usually had an issue about something (admittedly, sometimes very minor). They always followed through with answers and corrected my concerns which was a big change from my previous experiences. I want to encourage them to continue improving their Customer Support after the sale in this manner as that is the real reputation for their company. I am still reserving my opinion but I am very much encouraged by their recent efforts - Keep it up!... read more
Manufacturers often claim that their vertical axis turbine is superior to a horizontal one, because it always faces the wind. So does any horizontal axis turbine, thanks to their tail or yaw mechanism. If the airflow is such that wind directions change drastically from one second to the next it means you have lots of turbulence, and that means it is a poor place to put any wind turbine, HAWT or VAWT.
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.
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]
Solar energy is a flexible energy technology: it can be built as distributed generation (located at or near the point of use) or as a central-station, utility-scale solar power plant (similar to traditional power plants). Both of these methods can also store the energy they produce for distribution after the sun sets, using cutting edge solar + storage technologies.
“University of Texas Study Highlights Wind’s Low Cost” • Wind, solar and natural gas have the lowest levelized cost of electricity in the majority of counties across the United States, according to a new report from The University of Texas at Austin’s Energy Institute, part of a series of white papers on the Full Cost of Electricity. [Into the Wind]

The trouble with rated power is that it does not tell you anything about energy production. Your utility company charges you for the energy you consume, not power. Likewise, for a small wind  turbine you should be interested in the energy it will produce, for your particular site, with your particular annual average wind speed. Rated power of the turbine does not do that. To find out about energy production take a look at the tables presented earlier.
Above this rated speed, the wind loads on the rotor blades will be approaching the maximum strength of the electrical machine, and the generator will be producing its maximum or rated power output as the rated wind speed window will have been reached. If the wind speed continues to increase, the wind turbine generator would stop at its cut-out point to prevent mechanical and electrical damage, resulting in zero electrical generation. The application of a brake to stop the generator for damaging itself can be either a mechanical governor or electrical speed sensor.
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: