HOME WIND GENERATORS
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There are three basic types of renewable energy power systems: Off grid, Grid-tie, and Grid-tie with battery backup.
Stand-alone (or off-grid) systems operate independent of the electric utility grid. Since the turbines do not store energy and can generate electricity only when there is sufficient air movement, for continuous power flow the energy generated by the turbines have to be stored in the batteries.
If the system has no other power source, the battery bank would have to be significantly oversized. To reduce its size, off-grid wind systems are normally supplemented by a PV system or by an auxiliary genset that is fueled from a diesel or propane tank.
Grid-Tied systems are connected parallel to the utility grid. The energy they generate is fed directly into the household wiring which reduces the consumption of electricity from the utility. Whenever the power produced by the turbine is greater than the household needs, the inverter will send the surplus to the utility grid. However contrary to common misconception, a batteryless grid tie system will not provide any back up during power outages even when there is a sufficient wind: during power outage the inverter will automatically disconnect from the mains in order to prevent backfeeding into unenergized utility lines.
Grid-Tied systems with battery backup will reduce the utility bills similarly to grid tie systems. However, under normal conditions, a portion of the energy is used to keep the storage batteries charged. During a blackout, the inverter's built-in transfer switch will automatically disconnect the grid and will continue powering the entire home or selected loads from the energy accumulated in the battery bank.
The wiring routed from the turbine down the tower goes to the tower base junction box, from which you can run a cable to home entrance junction box, and then to the rectifier, optional battery bank and an inverter. Some turbines rectify the output at the tower top, and transmit it as DC. Commercially available residential wind generators normally come with a control box that combines the functions of a rectifier and a battery charger. It provides a DC output typically suitable for 12V or 24V batteries or inverters with low input voltage. If a model's description specifies a DC output, it means an inverter is not included and has to be purchased separately. Higher power systems (>1 kW) usually include an inverter. Such systems use higher level rectified DC voltage, up to 600VDC.
If you are going to build a homemade wind generator, consider the following. The turbines are generally designed to generate maximum output at wind speeds around 24-36 mph (10.5-16 m/s). In reality you rarely get this speed. At the lower speeds you obviously get less power. Generally, an average air speed greater than 9 mph (4 m/s) is required for small installations. The turbines have to be mounted on a toll tower to harvest more wind energy. It is generally recommended to place them at least 10 feet (3 meters) plus the blade length above the top of any obstruction such as a tree or a building within 300 feet (100 meters). That is why wind generators is used primarily in rural homes. You need to check your local zoning rules which may impose certain height restrictions on any structures. Many zoning ordinances have a height limit of 35 feet. The wind power systems for home use usually utilize guyed towers, which consist of lattice sections, a pipe, and supporting guy wires.
Turbine manufacturers data sheets should provide power curves and specify cut-in and cut-out speeds. Cut-in speed is the minimum wind speed needed to turn a wind turbine and produce electricity. Cut-out speed is the maximum wind speed that a turbine can handle. A turbine automatically stops spinning at winds speeds greater than the cut-out to prevent its damage. There are wind energy resource atlases that provide data on annual average wind speed for various geographical areas. A power curve however will not tell you how much power you will produce at a certain average wind speed. It all depends on how that average came about, i.e. if winds vary a lot, or if the wind blows at a relatively constant speed. For more information see Wind system's energy calculation.
Wind energy generators remain relatively expensive. A complete installed residential system may cost $4,500-$6,000 per kilowatt capacity before credits and rebates (generally, the higher capacity the lower cost per kW). For a small home the total cost is typically $15,000 to $30,000 before incentives. This is lower than an average cost of a solar electric system, which is $8,000/kW. Note that unlike electricity from traditional sources, the power flow from wind generators is erratic as winds rise and fall. However, in a remote location without easy access to utility lines, such system may help you stay off-grid and avoid the high costs of extending utility power lines to your place.
REFERENCES AND ADDITIONAL INFORMATION
Small Wind Generators for Homes -
a consumer's guide
Homebrew Wind Power - a hands-on guide to building a wind system in a home workshop
Homebrew Wind Power - a hands-on guide to building a wind system in a home workshop
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