Wind Turbine power output is increased ten-fold by careful spacing, and direction of rotation, when compared to existing best practices.
Summary: A new study from CalTech shows that wind-turbine spacing, location, and direction of rotation can increase average power output per acre (hectare) by ten-fold, compared to existing best practices. Professor John O. Dabiri of California Institute of Technology (CalTech) published a paper describing the impact on power production of spacing, location, and direction of rotation on vertical-axis wind turbines.
For images and video, see http://dabiri.caltech.edu/research/wind-energy.html
A preprint of the paper is available at http://dabiri.caltech.edu/publications/Da_JRSE11.pdf (675 kB)
VAWT (vertical axis wind turbines) that are spaced approximately 4 diameters apart, with adjacent VAWTs rotating in opposite directions, yield a ten-fold increase in power output per unit of land area, from 2 – 3 Watts per square meter of land, to 21 - 47 Watts per square meter when compared to modern horizontal-axis wind turbines.
This has great implications for new wind-farm projects, especially the economics and environmental impacts. It does not, however, address the Achilles heel of wind power, the intermittency of power production and the need to time-shift power production by some economic means of grid-scale storage and discharge.
From Dr. Dabiri’s paper:
Modern wind farms comprised of horizontal-axis wind turbines (HAWTs) require significant land resources to separate each wind turbine from the adjacent turbine wakes. This aerodynamic constraint limits the amount of power that can be extracted from a given wind farm footprint. The resulting inefficiency of HAWT farms is currently compensated by using taller wind turbines to access greater wind resources at high altitudes, but this solution comes at the expense of higher engineering costs and greater visual, acoustic, radar and environmental impacts. We investigated the use of counter-rotating vertical-axis wind turbines (VAWTs) in order to achieve higher power output per unit land area than existing wind farms consisting of HAWTs. Full-scale field tests of 10-m tall VAWTs in various counter-rotating configurations were conducted under natural wind conditions during summer 2010. Whereas modern wind farms consisting of HAWTs produce 2 to 3 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 VAWTs in layouts that enable them to extract energy from adjacent wakes and from above the wind farm. Moreover, this improved performance does not require higher individual wind turbine efficiency, only closer wind turbine spacing and a sufficient vertical flux of turbulence kinetic energy from the atmospheric surface layer. The results suggest an alternative approach to wind farming that has the potential to concurrently reduce the cost, size, and environmental impacts of wind farms.