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Choosing a small wind turbine for your station
Catch the wind
Wind generators are anything but unobtrusive. To catch the proper amount of wind, they are typically mounted around 50 feet above the ground or higher; and so this requires a tower. Several of the manufacturers recommend at least one acre of ground on which to place the tower. The turbine will need to be above trees and buildings for the most part so that its access to the wind is unencumbered. Unless you are in a rural (or semi-rural) area, that amount of space can be hard to come by. It goes without saying that you must obtain the proper permissions and construction documents from the local authorities prior to purchasing and installing a wind generator system.
Now let's look at the specific uses I mentioned previously. First, let's assume you are building a new transmitter site on a mountain top, far enough from power lines that it is not economical to actually install a feed from the power grid. One manufacturer's website (out of several) useful for this application is that of Bergey Windpower (www.bergey.com). According to Bergey, if your load draws a continuous power or 50W or less, then a 100 percent PV solution is called for. For continuous loads between 50W and 300W, a combination of PV and wind power makes sense.
Wind and solar power obviously complement each other well; when the sun isn't shining, the wind is often blowing. Likewise, when the wind is calm (like during the summer months) the amount of energy available via direct sunlight is often at its greatest.
In this example, the wind generator and the PV system have dc outputs used to charge battery banks that provide power to equipment via dc, or by way of inverters that make 120Vac out of 24 or 48Vdc. It's clear that the amount of energy stored in the batteries must be enough to carry the entire load of the system for some amount of time during which there is no other energy source for recharging. That amount of time will be determined during the engineering process. If the combination of the wind generator and PV are not enough to keep the system powered, a backup generator may need to be added.
It isn't necessary to have battery banks to use the wind generator and PV combination to supplement ac grid power though. Some of the wind generators have 220Vac outputs that can be connected directly to the power grid. A system can be constructed with an ac output from both the wind generator and an inverter powered by PV cells. These inverters sense the line voltage and phase of the grid, adjust themselves accordingly, and then connect themselves so that they provide energy to the load, either supplementing or completely replacing (depending upon the wind and solar resources available at the moment) the power absorbed from the public utility source.
And finally, the wind generator can be installed to operate on its own, providing ac power for the load, supplementing that drawn from the public utility, or depending upon the wind resource available at the moment, completely replacing that drawn from the public utility. That of course is the ideal, and the amount of time during which that actually occurs will depend upon the average wind resource available along with the average load seen by the wind generator.
Wind generator manufacturers
There are several wind generator manufacturers I want to cover in this article. The first is Bergey Wind (mentioned earlier). The largest wind generator mentioned for this article is the BWC Excel, its 10kW tower-mounted turbine. It comes in a battery charging version — with dc outputs of 24, 48, 120 or 240V. It also comes in the grid-connected version. It's interesting to note that the peak output is in excess of 10kW in the grid-connected version, while it is 7.5kW in the battery-charging version (30 MPH wind speed). Minimum tower height appears to be 60'. Bergey also offers its XL.1, which is capable of 1,000W, but in a battery-charge mode only.
Proven Engineering is a Scottish firm offering several small wind generators including the Proven 2.5 (2.5kW peak) and the Proven 6 (6kW peak).
African Wind Power is another manufacturer of small wind turbines. Its AWP3.7 will source up to 2kW of power in a grid-connect version.
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