In 2008 reports of a new style of wind turbine for producing electricity began showing up on “techie” web sites. The turbine was touted as a small powerful shrouded turbine which would produce energy in low winds and because of the shrouded design much less likely to be dangerous to birds and bats. On a website in 2008 Phillip Ridings claimed that his turbine design, patent-pending, was so efficient that it produced more energy than simple physical principles would allow. His turbine is called the dragonfly-turbine.
When asked about the violation of the physical law known as Betz limit, Mr Ridings replied “I did read “Betz Law” and it does not affect it because of Dragonfly’s unique design. If you want to apply Betz Law then its about to be broken.. just like the sound barrier!“
In 2010 Mr Ridings was interviewed on another website and claimed that his as yet unbuilt turbine would produce 2.4 to 4 times as much energy as a conventional turbine (or was 60% more efficient depending on which part of the interview one was reading.)
Although as of this writing there is still no real turbine, Mr Ridings claimed to have orders for turbines and was establishing a network of dealerships. None have been built, much less tested, other than via computer modeling.
Dragonfly Industries International was founded in Texas with Phillip Ridings as the managing member of the limited liability corporation in September 2014. The company is seeking or has purchased a 311 acre parcel of land in Northwest Arkansas to develop a wind farm. They claim to have a 1 megawatt (MW) shrouded turbine design ready to be built. The plan is to deploy 80 of these turbines on only a small portion, 80 acres, of the site, hence an 80 megawatt wind farm.
This is physically impossible. On a land use basis alone the farm is highly unlikely. Wind farms require a lot of space because turbines create wind shadows and turbulence. The National Renewable Energy Laboratory, a division of the Energy Department, reviewed the data for wind sites around the country, mainly in the midwest where winds are strong and found that the average area needed per megawatt of energy captured was 85 acres. That’s 85 acres per MW. Dragonfly claims to need only 1/85th as much land to produce the same amount of power, 1 acre per MW.
The proposed 20 foot diameter turbine is claimed to be able to produce 1 MW of power from a 17 mph wind. It is unlikely that there is a consistent 17 mph wind in Northwest Arkansas, but regardless, a turbine of this size cannot produce that much power. The maximum amount of power in wind can be calculated if you know the swept area of the turbine and the wind speed. For the claimed turbine the maximum power available is slightly less than 8 kW. But due to Betz limit it is about 5 kW and for a turbine of this size considering mechanical inefficiencies about 3 kW is realistic estimate. Not 1000 kW.
A simple analogy is instructive. Take an orange and squeeze the juice out. You could get about 2 to 3 ounces. If however you were as good at squeezing as this turbine is at producing power, you could get 2 to 3 gallons! If it sounds too good to be true…