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A valuable feature of photovoltaic systems is the ability to connect with the existing power grid which allows owners to sell excessive electricity back to the utility with a plan known as (5) Net Metering. At times when you are not using all of the electricity produced by your system, your meter will spin backwards selling the electricity back to the (6) utility power grid at retail rate.

the world’s fastest growing renewable energy source for more than a decade with an average annual growth rate of over 20%.

increasing generating capacity by 50%. With more than 25,170 MW of wind energy

ind energy in the United States could provide as much as 10,777 billion kWh annually

Wind turbines are responsible for the deaths of between 10,000 and 40,000 birds each year, according to the American Bird Conservancy.

the Altamont Pass site kills the largest number of birds - about 4,700 each year

The American Wind Energy Association contends wind turbines are far less lethal to birds than other man-made structures, such as windows (responsible for more than 100 million deaths each year in the U.S.) and power lines (between 130 million and 174 million), or than cats, which remain the number one bird killer.

Wind is simply air in motion. It is caused by the uneven heating of the Earth's surface by the sun. Because the Earth's surface is made of very different types of land and water, it absorbs the sun's heat at different rates. One example of this uneven heating can be found in the daily wind cycle.

The Daily Wind Cycle During the day, the air above the land heats up more quickly than the air over water. The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating wind. At night, the winds are reversed because the air cools more rapidly over land than over water. In the same way, the atmospheric winds that circle the earth are created because the land near the Earth's equator is heated more by the sun than the land near the North and South Poles. Wind Energy for Electricity Generation Today, wind energy is mainly used to generate electricity. Wind is a renewable energy source because the wind will blow as long as the sun shines

Like old fashioned windmills, today’s wind machines (also called wind turbines) use blades to collect the wind’s kinetic energy. The wind flows over the blades creating lift, like the effect on airplane wings, which causes them to turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity. With the new wind machines, there is still the problem of what to do when the wind isn't blowing. At those times, other types of power plants must be used to make electricity.

Tidal energy use harnesses the water flow created primarily by the moon orbiting the Earth. As water is pulled toward the gravity of the moon, currents are created that can turn generator turbines.

Tidal energy use involving dams creates many of the same environmental concerns as damming rivers. Tidal dams restrict fish migration and cause silt build up which affects tidal basin ecosystems in negative ways. Systems that take advantage of natural narrow channels with high tidal flow rates have less negative environmental impact than dammed systems. But they are not without environmental problems. Both systems use turbines that can cause fish kills. But these are being replaced by new, more fish friendly turbines. The art and science of environmentally friendly hydro engineering is well advanced and will certainly be applied to any tidal energy project.

Because of intermittency and variable flow problems of tidal energy, it is a very limited resource. The DOE Tidal Energy link, above, states that there are only about 40 really good sites on Earth with high enough flows to be considered economically practical

The Brazilian government still awaits a reduction in solar prices to create a specific auction by the end of 2013 or the beginning of 2014. However, the Ministry of Mines and Energy (MME) does not demonstrate any signs of this happening.

In 2013, however, revenue and capacity installed are expected to double: projects will be delivered, the resolution 482/2012 will have a major impact, and X% of the National Association of Electric Energy’s (ANEEL’s) research and development (R&D) will conclude. Capacity installed expectations in 2013 will near X megawatts (MW); in 2014, X MW; in 2015, X MW; and beyond, faster expansion is expected. Currently, capacity installed for the solar market is X MW, but it is expected to reach X MW by 2017. The total possible capacity installed for Brazil is close to X gigawatts (GW). This market revenue will have a X% compound annual growth rate (CAGR) during the forecast period (2012–2017) due to ANEEL´s R&D, international events, and the resolution 482/2012 cost reductions. Now, market revenue is close to $X million and can reach $X million by 2017.

Distributed generation could grow faster with financial support, better service from energy concessionaries, and cost reductions; nonetheless, it will grow considerably.

The Pelamis is an offshore wave energy converter that uses the motion of waves to generate electricity.

The machine operates in water depths greater than 50m and is typically installed 2-10km from the coast. The machine is rated at 750kW with a target capacity factor of 25-40 per cent, depending on the conditions at the chosen project site. On average one machine will provide sufficient power to meet the annual electricity demand of approximately 500 homes.

The Pelamis machine is made up of five tube sections linked by universal joints which allow flexing in two directions. The machine floats semi-submerged on the surface of the water and inherently faces into the direction of the waves. As waves pass down the length of the machine and the sections bend in the water, the movement is converted into electricity via hydraulic power take-off systems housed inside each joint of the machine tubes, and power is transmitted to shore using standard subsea cables and equipment.

The BLM manages 20.6 million acres of public lands with wind potential. The BLM has authorized 39 wind energy development projects, including connected-action projects that include electric transmission support authorizations, with a total approved capacity of 5,557 megawatts, enough to supply the power needs of over 1.5 million homes. 

For more than a decade, wind energy has been the fastest growing energy technology worldwide, achieving an annual growth rate of over 30%. In the United States, the current total installed capacity is over 60,000 megawatts of wind projects.