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Vertical Axis Wind Turbines

February 19, 2013
Paul Gipe

Market, cost, and technical analysis of vertical and horizontal axis wind turbines—A review


“For all wind turbines, other than those used for more decorative purposes, the cost of energy is important.”

I came across this decade-old document while searching for factual information on Vertical Axis Wind Turbines (VAWTs) on the web. Market, cost, and technical analysis of vertical and horizontal axis wind turbines Task #2: VAWT vs. HAWT technology was written by Global Energy Concepts, a US consulting company.

While the report doesn’t clearly focus on small wind turbines, the conclusion surprisingly addresses small VAWTs and HAWTs specifically.

Early in the report, the author makes a telling observation: “For all wind turbines, other than those used for more decorative purposes, the cost of energy (COE) is important.” This one sentence encapsulates what both I, Mick Sagrillo, and others are constantly saying about “new” or “revolutionary” VAWTs, they have to compete with existing wind turbines and they must prove their worth. Otherwise, they are just lawn ornaments or “dynamic sculptures.” Most often they are not even dynamic and are merely “static” sculptures, but not wind turbines.

One limitation of VAWTs in comparison to conventional wind turbines is that typically they produce less electricity relative to their size. That is, the annual specific yield of VAWTs is less than that of HAWTs.

In the following table the HAWT is a 1.5 MW design done for NREL. The VAWTs are represented by the DAF-Indal 6400, a large curved-blade Darrieus, and Sandia National Laboratories 34 meter diameter “test bed” for curved-blade Darrieus. The gist of the table is that at a decent wind site, the VAWTs will generate significantly less electricity relative to their swept area than a conventional HAWT.

VAWTs have also been plagued by very high rotor loadings and very high specific mass. That is the specific mass in kg/mis an order of magnitude greater than that for an equivalent size conventional turbine. In this chart from the report Pinson is an articulating, straight-blade VAWT; Turby is a curved-blade Darrieus; FloWind and [DAF]-Indal are large (for the day) curved-blade Darrieus turbines. SWWP represents the Air micro turbine; Bergey is a 7-meter diameter household-size wind turbine; Vestas’ V47 and the WindPACT 1.5 MW are large HAWTs.

 

Overall the report provides a good, factual comparison between VAWTs and HAWTs that any VAWT inventor should read before embarking on a costly and often unsuccessful development program.

The summary well captures the document and the state of the technology then and now.

“The following recommendations are made concerning the viability of developing small VAWTs or HAWTs.

  • The maximum aerodynamic efficiency of any VAWT will be lower than available HAWT designs. This difference is likely to be between 15 and 25%.
  • Due to the lower efficiency, the VAWT will capture less energy for the same swept area.
  • For a given swept area, the mass of the rotor and support structure of a VAWT will be greater than that of an equivalent HAWT. This mass difference is likely to translate into a cost difference.
  • The savings that a VAWT may enjoy due to lower drive train and maintenance costs are unlikely to balance the lower energy capture and higher initial rotor costs.
  • The same diseconomies of scale apply, in theory, to both HAWT and VAWT configurations.
  • Both HAWTs and VAWTs suffer from fatigue loads. The basic aerodynamic principles of the VAWT lead to fatigue loads at the harmonic frequencies, but the VAWT is not as sensitive as is the HAWT to the effects of turbulence. However, the VAWT is more likely to suffer resonant conditions especially if operated at variable speeds.”

Market, cost, and technical analysis of vertical and horizontal axis wind turbines Task #2: VAWT vs. HAWT technology by David Malcolm, Global Energy Concepts, Lawrence Berkeley National Laboratory, 23 pages, 2003


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