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Vertical axis wind turbines trump others on land use

Caltech study finds that turbine placement and technology type can greatly affect power density, or power available per area, of wind farms.

In a test in Southern California, a farm vertical-axis turbines spaced close together generated more power per area than traditional turbines.
John Dabiri/Caltech

Typically, cost is the driving concern when choosing one renewable energy technology over another. But a pair of studies that consider land use give the edge to niche forms of solar and wind power generation.

Caltech researcher John Dabiri, a professor of aeronautics and bioengineering, this week presented results of a test that found that vertical-axis wind turbines have the potential to generate more power per square meter than the propeller-like, three-blade wind turbines. The key is that vertical-axis turbines can be placed close together without creating the type of wind disturbances that would sap performance of traditional turbines.

Dabiri conducted a test last summer with 24 vertical-axis turbines from Windspire energy, which are shaped like 10-meter tall columns, placed in 75-meter square space. He then calculated how much power per meter the small array of turbines can generate as a way to measure how much aerodynamic disturbances are caused by neighboring turbines.

The tests found that the power density of these vertical-axis wind turbines is about six to nine times that of modern wind farms with horizontal-axis turbines, which need significant spacing among them to prevent causing aerodynamic interference. Dabiri's conclusion is wind farm design and technology is as important the power rating of individual turbines.

"Whereas modern wind farms consisting of (horizontal axis wind turbines) produce two to three watts of power per square meter of land area, these field tests indicate that power densities an order of magnitude greater can potentially be achieved by arranging (vertical-axis wind turbines) in layouts that enable them to extract energy from adjacent wakes and from above the wind farm," he wrote in a paper published Journal of Renewable and Sustainable Energy. (Click for PDF.)

A concentrating solar photovoltaics collector. Amonix

The question of land use and power generation is a thorny one as siting energy projects is often problematic. Wind and solar farms, meanwhile, require more land compared to fossil fuel or nuclear plants for the equivalent amount of power generation.

A separate study issued this week by an industry group found that one type of solar power, concentrating photovoltaics (CPV), has a lower space and environmental footprint compared to other technologies. CPV systems use mirrors and lenses to concentrate light onto high-end solar cells to boost the output. The technology is suited for desert areas with good sunlight, but hasn't taken off broadly.

A University of California Berkeley study, commissioned by the industry group CPV Consortium, did a lifecycle assessment and found that CPV used less water, land, and materials than other solar technologies. "Concentrating solar minimizes overall land area use to a degree that almost nothing can beat, Daniel Kammen, director of Renewable and Appropriate Energy Laboratory at UC Berkeley, said in a statement.