In terms of theoretical efficiency, they are every bit as efficient as a Carnot cycle (heat) engine such as one used for generating electricity on a power plant. While they may not have achieved the same efficiency as that engine yet, what was the efficiency of a state-of-the-art steam engine 30 years after the first ones were produced commercially?

Also, in practice, the electrical generation plants of today only get about 30% of the possible energy from the fuel, and even that is pushing it.

Finally, wind is an essentially infinite "fuel". We run out of oil and gas in about 40-50 years, just like we ran out of whale oil. I would rather work on these technologies now then when the lights are going out from lack of power.

Even driving up to them on a bright, sunny day like today, you get thrown off because you see a good size structure, and it just keeps getting bigger and bigger and bigger. It took me a good 10 minutes from first sight to reach them, and they were obscured by trees initially.