Hi,
I saw a report on Wired News (wired.com/news/technology/0, … ories_html) that seems to be a press release from Terra Moya Aqua. The headline is “New Turbine May Boost Wind Power.” In the article, it said:
Gee, I thought we were doing better than 40%, and I can’t believe any commercial wind turbine converts just 20% unless it’s broken. I wonder where they got these numbers.
I sure would need to see a certified power curve before I could believe their claims. Does such a power curve exist?
It depends on how you define your parameters. For example, a hypothetical 1.5MW turbine on an 84 meter tower at a site with an average windspeed of 5.8m/s and a sheer exponent of 1/7th with a rotor Cp of 0.5 will convert about 22.8% of the available kinetic energy in the wind into electricity. Do we call that 22.8%, 38.6% (Betz energy used as a base), or 50% (the rotor Cp)?
The 22.8% number is not because of poor rotor aerodynamic performance or poor drivetrain performance, it’s because a lot of energy is intentionally wasted while the turbine is running at rated power. This is the tradeoff you make when you design a turbine for high capacity factor (aka large rotor, small drivetrain).
If that machine’s drivetrain was expanded to 3MW, it would then convert 30.5% of the available energy to electricity but capacity factor would drop from 40.3% to 26.9%. That results in an additional cost for transimission and balance of station (not to mention the drivetrain itself) so you have to trade that off against all the extra energy produced.
Lee Jay