Many more articles are available through the Energy Bulletin homepage

The Wind does NOT Blow “Only 1/3 of the TIme”

Craig Severance, EnergyEconomyOnline.com
… The misconception that “wind only blows one third of the time” comes from the fact that wind farms now typically operate with an average “Capacity Factor” of around 30%. A 30% Capacity Factor means that over the course of a year, a wind generator will produce total kWh’s equivalent to 30% of the number of kWh’s that would be produced if the windmill ran at its top rated output (Rated Capacity) for every single hour of the year.

The Rated Capacity of a windmill is similar to how fast your car could go if you ran it at top cruising speed. We all have speedometers that lead us to believe our cars are “made to go” somewhere over 100 mph. However, we don’t actually drive that fast. Sometimes we drive 45 mph, sometimes 75 mph — and we get where we need to go.

If every time you got in your car, you floored it and cruised only at top speed, your car would have a Capacity Factor of 100%. However, with the way you actually drive, it wouldn’t be uncommon if your average driving speed was somewhere around 30% of the “Capacity” that could have been delivered at top cruising speed. This does NOT mean you were only able to use your car 30% of the time.

The same is true for a wind generator. A 30% Capacity Factor does not mean the generator is dead stalled 70% of the time, and operating at full Rated Capacity 30% of the time. Rather, in the very windy locations where wind farms are built, the wind blows almost all the time. The wind turbines therefore operate almost all of the time, but over a range of speeds and power outputs.

Power Increases by CUBE of Wind Speed Increase. This physical law which is at the heart of wind turbine operations helps put a “30% Capacity Factor” into perspective very dramatically. The 30% is actually a very impressive figure.

Most wind turbines will begin producing power (“cut in”) at about 12 miles per hour, and reach their maximum Rated Power Output at about 25-29 mph.
(8 May 2009)
Author Craig Severance writes:
This Article debunks the popular phrase “the wind only blows 1/3 of the time” and other popular myths which attempt to argue that wind’s intermittency make it unsuitable as an energy source. It discusses the U.S. Dept.of Energy’s “20% Wind Energy by 2030” study (July 2008) and describes how that study concluded wind could be integrated into the electric grid up to a 20% penetration without the need for energy storage without affecting grid reliability or performance.

Yes, we can solve the energy crisis

David MacKay, The Times
We have an addiction to fossil fuels, and it’s not sustainable. The developed world gets 80% of its energy from fossil fuels – Britain gets 90%. This is unsustainable for three reasons.

First, easily accessible fossil fuels will run out, so we will eventually have to get our energy from elsewhere.

Second, burning fossil fuels is having a measurable, and very probably dangerous, effect on the climate…

…There is no shortage of advice on how to “make a difference”, but the public is confused, uncertain whether the schemes proposed are fixes or fig leaves. People are rightly suspicious when companies tell us that buying their “green” product means we have done our bit. They are equally uneasy about the national energy strategy. Are wind farms merely a gesture to prove our leaders’ environmental credentials? Is nuclear power essential?…

…Where numbers are used, their meaning is often obfuscated by enormousness. Numbers are chosen to impress, to score points in arguments, rather than to inform. In contrast, my aim is to present honest, factual numbers in such a way that the numbers are comprehensible, comparable and memorable…

Sustainable Energy – Without the Hot Air, by David MacKay, is published by UIT Cambridge, priced £19.99.