First up, I like wind turbines. I think they offer a compelling value proposition. Sure, fossile fuel fired powerplants are a bit cheaper, but those fossil fuels come from somewhere and you can only burn them once. If you burn them somewhere where you don't make use of the superior energy density of fossil fuels, you're wasting them. Then you've got the strategic and economic advantages of not paying countries with questionable policies, and using that money to invest into high-tech domestic companies.

Naturally, everything has downsides. Things such as noise, the perceived ugliness, dead birds, high up front costs and other stuff. This has, in the recent years led to a lot of 'new and exciting' designs with questionable claims of removing all those downsides. These stories get gobbled up by the press and a lot of the public. It's quite an 'unknown' technology for most people and also quite counterintuitive, because how can a few small blades extract all the energy in that circle? I wont bother you with that, but it's easy to understand the basics. And with a bit of knowledge, it's quite easy to punch through most bogus claims.


Behold : the wind power formula:

Illustration for article titled This article has me annoyed.

Not hard right? Knowing this formula is enough to quickly determine if a wind turbine article is worth your time.

If a turbine with a small surface area claims to be very efficient 'even at moderate windspeeds', this means that regardless of the actual performance coefficient (C) in the formula, you wont get a whole lot of power. Because the A is small, and the velocity goes cubed. You're not interested in 'low to moderate windspeeds'. If there is no power in the wind, you can't take it out.


If you define efficiency as dollar per power unit, you want a large turbine in a place where there is a lot of wind. Aerodynamic efficiency is nice, but not the goal of a turbine. The goal of a turbine is power.

Now, on aerodynamic efficiency, there is a maximum efficiency factor possible, and that is a lot lower than 1. Taking energy out of the wind means slowing the wind down. If you take out all the energy the wind comes to a standstill just behind the turbine Which means there is no wind that goes through your turbine. Which means you don't get any power. So there is an optimum, computed back in the early 1900's, which is the Betz-Joukowski limit. This is the solution for the optimal power production (deriviation is easily found) that ends up at 0.593. This limit does not presume any wind turbine shape. It only presumes a 'surface of magic' in energy is extracted. So it applies to every wind turbine shape you could possibly dream up. Because the surface is magic.


Large modern turbines get up to 80% of the mentioned limit. So if any article claims a dramatically more aerodynamically efficient turbine than current designs, it means a 20% decrease in wind energy cost at the impossible most (neglecting the generator).

The article I've 'republished' here fails on every account.

PS, i've failed at Kinja since I published it to my personal blog while i wanted to save to oppo. I'm sorry for dragging you out of oppo


Share This Story

Get our newsletter