A single wind turbine can generate from several kW to several MW of electricity. Turbines with capacity under 100 kW are sufficient for many small applications such as farms. homes, schools, or small industrial facilities. Larger capacity turbines are considered "utility scale" and are typically grouped together into wind farms that produce significant amounts of electricity for delivery to the grid. Such wind farms must provide sufficient space between turbines for efficiency. Otherwise, the disruption to wind flow around one turbine will impact adjacent turbines and reduce overall power generation.
Some industry sources quote that a wind farm typically requires between 2 to 40 acres per megawatt of capacity, depending on a variety of factors. Open, flat terrain requires the most land, but only a very small amount of that land is used for turbines and associated infrastructure, such as access roads. Figure 1 illustrates wind farm land uses - total wind farm area vs. direct impact area, which includes both permanent and temporary use. A majority of the total land use is available for other uses, such as farming or ranching.
A standard rule of thumb is that turbines should be spaced in a 5D x 10D grid, with D = diameter of rotor. As an example, a GE 1.6 MW turbine with an 82.5 m rotor would require a little over 50 acres per MW. A 2009 report from the NREL
studied land area uses for operating US wind farms and provided data showing that average area densities ranged from about 1 MW/sqkm to 8 MW/sqkm. Converted to acres per MW this range is about 30-250, wihich shows that the rule of thumb grid spacing falls within, but at the lower end of this range. It would also indicate that there hasn't been a strong incentive in the past to minimize spacing of turbines.
Figure 1 illustrates the change in visual appearance of a portion of the Altamont Pass Wind Farm after replacing older model turbines with fewer new, larger, modern turbines. Figure 2 shows one of the first wind farms near Tehachapi, CA from 1980 with a jumble of closely situated, relatively small turbines.
There is an opportunity to reduce the land required for a given capacity wind farm by utilizing vertical axis wind turbines (VAWTs) as opposed to HAWTS. Recent research suggests that VAWTs may be placed much more closely together so long as they are sited strategically to take advantage of downwind turbulance from neighboring turbines. See OWOE: What are Vertical Axis Wind Turbines?
for more information on VAWTs.