Wind turbines have a small physical footprint, but wind farms themselves seem to take up large expanses of land. Large, empty spaces are the norm in most wind farms, hence why they often share space with farms and pastures. But how do engineers determine the amount of space between wind turbines? And how many turbines can comfortably fit on one acre of land?
Several factors determine the spacing necessary for wind turbines, with turbine size being the largest variable. Rotor diameter is the measure most often used to determine how many turbines can fit into a given area. Assuming an average rotor diameter between 90 and 120 meters, you can fit anywhere from 40 to 80 wind turbines on one acre of land.
Wind Turbine Spacing
Wind turbines need to be spaced appropriately to maximize efficiency. They need a steady flow of wind, which necessitates a lack of obstacles. This includes other wind turbines. The turbines extract energy from the wind and create an area of turbulence in the immediate area. Wind turbines that are spaced too closely will be less efficient, as they’ll create erratic wind patterns, and there will be less kinetic energy available overall. Therefore, wind turbine spacing is a crucial aspect of planning a wind farm.
It’s not all about efficiency either. Wind turbines placed too close to one another can have several other adverse effects. The turbulence will cause the turbines to oscillate, causing increased wear and tear on the internal machinery. Crowded wind farms also make more noise, which can bother nearby residents.
Wind turbines also need space for the associated infrastructure. They require a large concrete foundation to support their tall structure. There are also power stations and distribution lines that need to be built. Then there are the access roads that meander throughout the wind farm.
After researching the effects of spacing on wind farm efficiency, engineers have decided on an ideal ratio for wind turbine spacing. Turbines placed upstream or downstream of one another should be at least seven rotor diameters apart. This allows for ample space for turbulence to dissipate and wind speeds to recover. Wind turbines laid out side-by-side can be closer together and should be at least three rotor diameters apart. These suggestions are the bare minimum. The more space between turbines, the better.
If that sounds like a lot, that’s because it is. Wind turbine blades can get pretty long, so several rotor diameters is a pretty large distance. To give an example, the 2.2 MW Vestas V-120 is the largest in the Vestas 2 MW series of turbines, with a rotor diameter of 120 meters. That means that to optimize efficiency, the turbines must be 360 meters apart and 840 meters downwind. The V-90 is the smallest turbine in the 2 MW series with a rotor diameter of 90 meters. So these turbines must be 270 meters apart and 630 meters downwind to remain efficient.
So how many Vestas V-120 turbines can we fit on an acre of land? One acre is 4046.86 square meters. So if we set up a series of turbines adjacent to each other, they would each need 360 meters of space. That equates to 11 turbines. Now, if we go downwind, each row would have to be spaced at least 840 meters apart. We would have enough space for four rows of turbines. In all, we would be able to fit 44 turbines on one acre of land.
The V-90 has a smaller rotor diameter, and so we can fit more turbines per acre. If mounted side-by-side, we can fit 14 turbines across one acre. If installed downwind of one another, there would be space for 6 rows of turbines. That’s 84 wind turbines per acre.
Obviously, this is an ideal situation. In practice, actual distances between turbines vary. Large wind farms may be much more crowded, as landowners and wind companies may receive more in government subsidies for having more turbines. In these situations, the entire wind farm suffers from diminished efficiency. Also, the formulas behind spacing at wind farms are much more complicated than rotor diameter. Wind speed, terrain, and tower height must also be factored into wind farm configuration.
Wind turbines are notable for their small physical footprint. While wind farms do take up large amounts of land, that space is still open for other uses. It’s common to see wind farms share the land with farms, ranches, and pastures. Wind farms might also double as parks and recreation areas.
Besides the wind turbine itself, wind farms also need room for supporting infrastructure. A 2009 study by the NREL analyzed land-use patterns on 172 wind farms across the United States. They broke down land usage into two categories: the direct impact area and the total land area.
Direct Impact Area
The direct impact area of a wind farm consists of the spaces directly occupied by the wind turbine and infrastructure. This consists of the turbine and its surrounding foundation, access and arterial roads, power stations and distribution lines, offices, monitoring stations, and storage space. This might also include the area temporarily occupied during the construction of the turbine. The direct impact area of a wind farm tends to be pretty small, especially when compared to other types of power plants, like fossil fuel plants or nuclear power stations.
The NREL report determined that the average wind farm produces 0.4 MW per acre of land that is directly impacted. This takes into account areas that are permanently occupied as well as land that was temporarily impacted during construction.
Total Land Area
The total land area consists of the entirety of the space within the borders of the wind farm. This includes the direct impact area along with the undisturbed lands between the turbines. Due to the relatively large distances between turbines, the total land area tends to be pretty large, even if the direct impact area makes up a small portion of the total wind farm.
The areas that aren’t being directly occupied can be utilized for other purposes, even though they may fall into the boundaries of the wind farm. Farms, parks, and nature preserves are common uses. Major roads and highways may also cut through a wind farm.
The same NREL study also measured the total land area per MW. They found that the average power output per acre when the total land area was accounted for was 0.012 MW per acre.
Wind Farm Configurations
In addition to optimal spacing requirements, there are also configurations that optimize the efficiency of wind farms. Turbine spacing, local geography, and wind patterns must all be taken into account when creating the layout of a wind farm. Most wind farms fall into four general configuration patterns.
Single string patterns are when the turbines in a wind farm are arranged in a long line, all oriented in the same direction. This reduces interference as there are no turbines upwind or downwind of each other.
Multi string configurations consist of several strings of turbines. While the turbines within a string all face the same way, each string is oriented in a different direction.
Parallel string layouts are where there are several strings of turbines oriented parallel to each other. The strings are usually oriented in rows, though the rows aren’t always the same size.
Wind farms can also be arranged in clusters instead of strings. This is where the wind turbines are spread out over the wind farm with no discernable pattern.
Wind turbines need ample space to operate efficiently. They need to be far from obstacles to ensure a steady, undisturbed stream of air. As for just how many turbines can fit onto an acre, that depends on the size of the turbine. Larger turbines create larger wakes and more turbulence, and so need more space to maximize efficiency. While the turbines themselves have a small footprint, wind farms are spread out among several acres of land. They’re unique compared to other forms of power as the land can still serve other purposes, and usually shares space with farms, parks, and highways. Whereas being near a fossil fuel or nuclear power plant can be bad for your health, hanging out at a wind farm can be a pleasurable experience.
Frequently Asked Questions
Assuming an average rotor diameter of 90 to 120 meters, between 40 and 80 wind turbines can fit on one acre.
Wind turbines need at least three rotor diameters if placed side-by-side and seven rotor diameters if placed downstream from each other.
In terms of direct use, the average power output of a wind farm is about 0.4 MW per acre. When the total land area of the wind farm is accounted for, the average power output is about 0.012 MW per acre.
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