Conventional turbines are perched 60 to 80-m off the ground where the wind is stronger. But what about the wind below those elevations? California-based Wind Harvest International says it has a solution in a straight-bladed, vertical-axis wind turbine that offers the first cost-effective solution to harvesting high energy, turbulent near-ground winds. “Using a methodical approach of designing, building, and verifying, we’ve constructed 11 different models,” says WHI CEO Kevin Wolf. “In that process, we discovered the coupled-vortex effect,” he adds.
“We had run one turbine by itself collecting data for a year and then placed others on either side of it, spacing them so blades were two to three feet apart,” says Wolf. “Surprisingly, the energy output from the center turbine increased. Adjacent turbines counter rotate, so the area between blades generates a convergence area with the wind speeding up there, letting the turbines capture more energy than if more widely separated.” Wolf’s turbine array are patented for the discovery.
He says they have discovered something with each model. For example, a mechanism on the lower portion can pitch to stall in high wind. And the external structure keeps damaging loads off the center bearings. As a result, WHI’s Linear Array Vortex Turbine Systems (LAVTS) can hit peak efficiencies near the theoretical limit for any type of wind turbine design and will be among the most cost effective of any design.
The largest market for LAVTS is expected to be wind farms with good near-ground wind resources, the “understory” or area beneath horizontal-axis wind turbines. This includes most wind farms in California and about one-fourth of others around the world.
There are other large markets for the company’s turbines, says Wolf. “One is the UK’s feed-in-tariff market, which is limited to turbines with less than 100kW in capacity. WHI’s models 636 and 1500 meet U.K. requirements and will be profitable at high-wind sites.
Another is a “standalone” market, one in which buyers install WHI’s Linear Array Vortex Turbine Systems in locations where there are no tall horizontal axis wind turbines.
“Our time line is to install in Sept-ember and then go through four to six months of durability tests in Scotland,” says Wolf. He estimates that about one-fourth of existing wind farms around the world have 14 mph or better winds at 30 ft above ground. The estimate comes from large geographic areas with features such as passes, ridgelines, mountains, coastal bluffs, and mesas. For example, all major passes in California qualify with a capability of collectively doubling the existing 3,000 MWs with LAVTS. Wolf says many other countries also have promising terrain.
The non-wind-farm market is also growing, says Wolf. For example, the U.K. instituted a feed in tariff in April 2010 that will let people, businesses, and municipalities purchase wind turbines up to 100 kW and receive an equivalent of $0.15 to $0.50/kWh produced. Installation is restricted to sites with less than 5 MW of capacity.
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