May 2, 2006
by Paul Gipe
You can’t get something for nothing. North Americans who think a micro or mini wind turbine will meet all their household consumption are in for a rude surprise. A wind turbine with a rotor 1-2 meters in diameter (3-7 ft) will not provide a significant portion of their domestic electricity consumption unless they are extremely conservation minded.
North Americans uses a lot of electricity per household, more than almost anyone else on the planet.
Thus it takes much more of the wind stream–for a given wind speed–to meet the energy needs of a North American home than it does, say, for a German home.
The typical North American home requires a minimum of 13 m² of rotor swept area of a large-scale wind turbine at a site with a 6.4 m/s wind at hub height (900 kWh/m²/y). Using a small wind turbine to meet this consumption will require nearly twice the swept area of a large wind turbine. The reasons for this are complex and beyond the scope of this short note. For an explanation, see any book on wind power.
Translation: To meet the loads of a typical North American home a small wind turbine would need to sweep 26 m² of the wind stream. This is equivalent to a wind turbine with a rotor diameter of almost 6 meters (about 20 ft).
On average, Californians consume much less per household than the typical North American. They will require less of the wind stream to meet the household consumption, about 7 m² from a large wind turbine. Again, a small wind turbine will need twice the area to do the same job or 14 m2. This requires a small wind turbine with a rotor diameter of 4.2 m (about 14 ft).
At a site with a 5 m/s average wind speed at hub height, it would require a small wind turbine with nearly 40 m² of the wind stream to meet the needs of the typical North American home without electric heat. This a wind turbine the size of the Bergey Excel with a 7 m diameter (21 ft) rotor.
The typical European household uses almost one-fourth of the typical North American consumption. A German family, for example, will need only 4 m2 of the wind stream to meet their needs from a large wind turbine or about 8 m² from a small wind turbine. This is equivalent to a small wind turbine with a rotor diameter of 3.2 m (10 ft).
North Americans living off-the-grid may reduce their consumption to the levels typical of Europeans. Some may use even less electricity. Thus, they may be able to meet all their electricity needs with a hybrid wind and solar system. However, they are the exceptions.
If you’re a North American, be very wary of any wind turbine promoter who says that their small wind turbine with a rotor only 1-2 meters in diameter will meet all your electricity needs. They either don’t know what they are talking about, or they are preying on an unsophisticated market and you don’t want to do business with them.