Via ecogeek.org, 13-07-2011
Wind energy production has so far been dominated by the horizontal axis wind turbine (HAWT). They can be scaled up to reach high in the air where the wind blows faster and produce a lot of energy per turbine (a 10 MW turbine is not far away), but researchers at Caltech say that vertical axis wind turbines (VAWTs) may actually be the better choice.
A recent study of turbine placement and output found that because VAWTs can be placed closer together, they’re capable of generating ten times as much energy per square meter than HAWTs.
In a series of field tests that placed six VAWTs in different configurations, it was found that a spacing of four turbine diameters apart (about five meters) got rid of any aerodynamic interference between the turbines. HAWTs require 20 turbine diameters of spacing in order to eliminate aerodynamic interference, equaling more than a mile between each turbine. The six VAWTs were able to produce 21 to 47 watts of power per square meter, while a comparable HAWT farm only produces about two to three watts per square meter.
The study also found that having each VAWT spin in the opposite direction of its neighbor allowed them to spin faster because the opposing spins reduced the drag on each turbine, which upped their efficiency even more.
To add to the list of benefits, VAWTs are also cheaper, smaller and less intrusive, allowing them to be installed in lots of places where large HAWTs just wouldn’t do.