Wind turbines whose axes point upwards co-operate, boosting the output of those near them, a new study has found. The research makes a case for building wind farms this way, rather than using conventional designs, but history is against the idea.
Many designs have been tried in the effort to turn the wind's energy into electricity. One, however, has dominated. Known as the horizontal Axis Wind Turbine (HAWT) it's the one we are familiar with; a tall pole supporting a large turbine and long blades sweeping like the hands of a wall clock. HAWTs make 5 percent of the world's electricity and that is rising fast as ever-larger turbines capture higher altitude wins, many now out to sea where the winds are stronger.
No other wind-capturing device makes a thousandth of HAWT's contribution to clean energy production, but alternatives keep getting proposed. Not long ago one attracted publicity partly for its claimed (although deeply questionable) greater suitability for urban use, but mostly because it looks like a sex toy.
Laugh as we might, Professor Iakovos Tzanakis of Oxford Brookes University thinks some alternatives should be taken seriously. A windfarm of vertical axis wind turbines (VAWTs) can collect more energy over the same area than a field of HAWTs, Tzanakis claims in a paper published in the International Journal of Renewable Energy, with the potential to make wind energy cheaper and more compact.
Central to Tzanakis' claim is the way wind turbines affect each other when placed together. Tzanakis and co-authors modeled wind flow over turbines placed in 25 configurations. We know HAWTs tend to cut each other's lunch, with upwind turbines creating turbulence that reduces the output of those behind it. Despite innovative proposals such as making the blades of half the farm spin in the opposite direction, the solution is usually to place turbines far apart from each other, increasing construction and maintenance costs.
VAWTs, on the other hand, actually assist each other when placed in a grid formation, Tzanakis claims, with the waste wind from one set of blades imparting extra spin to the next.
“This study evidences that the future of wind farms should be vertical. Vertical axis wind farm turbines can be designed to be much closer together, increasing their efficiency and ultimately lowering the prices of electricity,” Tzanakis said in a statement.
The stakes are high. Wind power is already cheaper than fossil fuels over much of the planet, but once you add in storage to cover quiet periods, that advantage often disappears. Anything that reduces prices even modestly could shift the balance of this battle for Earth's future.
A 15 percent increase in power for downwind turbines is nothing to be sneezed at, particularly against a 40 percent decrease HAWTs can suffer. However, that still requires each individual VAWT to harvest wind efficiently, which has proven surprisingly challenging.
For decades VAWT cheerleaders have trumpeted their fewer moving parts, claimed greater ease of manufacturing and better adaptability to changing wind conditions. In practice, however, there has been a long list of VAWT failures, sometimes honorable, most embarrassing. Some VAWTs broke down in testing, others sent their makers broke after producing a fraction of the promised power and others proved a danger to life and limb. Still, if anyone gets them to work solo, they'll probably be even better together.