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Silent wind power revolution

Turbines in low-wind areas

Capacity factor is an indicator of how many hours a year a power generator runs. Today, guest author Bernard Chabot talks about how surprisingly high capacity factors are for wind turbines in areas with little wind.

At the end of April, I pointed out that the capacity factors of Germany's two current offshore wind farms is quite high – and what a commotion that article caused! (I would, however, ask those of you with my e-mail address to post comments in the box below instead of writing directly to me so we can have a discussion together.)

One person from the solar sector told me that capacity factors are a stupid indicator for wind power. For instance, he said, turbines being put up in areas with little wind have large swept areas but small generators. They are therefore, he concluded, turning too little of the kinetic wind energy into actual electricity.

But in fact, the same holds true for roofs that faced East and West – we would get more energy from sunlight if these panels were optimally oriented towards the south (or tracking the sun, for that matter). In reality, however, solar proponents in Germany have been pointing out for years that East/West-facing roof arrays help spread solar power production more evenly across the day, which facilitates grid integration.

The same roughly holds true for wind turbines in low-wind areas.  They do not focus on the production at certain times to produce slightly more power over the year as a whole, but a more even level of power production across the year to improve reliability. Essentially, the comparison should be not between power from low-wind turbines and larger generators that run for fewer hours, but between wind power without storage (in the former case) and wind power plus storage (in the latter).

So what is the capacity factor of low-wind turbines? Check out Bernard Chabot's analysis in this PDF. (Craig Morris)

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4 Comments on "Turbines in low-wind areas "

  1. Fernando Vivas - 23.05.2013, 22:19 Uhr (Report comment)

    I agree with you, James. The key point is Cost of Energy, no matter what source of energy we are talking about. Regarding energy, the grid itself can behave as an enormous battery, as long as we have enough interconnection capacity. Electrical losses are really low. For example, in Spain, annual energy losses in EHV grid are around 1.5%, and total losses are under 8%. So on-site storage might not be so important. Today increasing the interconnection capacity between electrical areas, such as France and Spain, and implementing intra-hour schedulling is the less expensive and more efficient way of "storing" energy. Milligan and Kirby, from NREL, have released a series of brilliant articles that explains all this better than me. For example: http://www.nrel.gov/docs/fy11osti/51860.pdf

  2. Pat Kelley - 16.05.2013, 16:21 Uhr (Report comment)

    One technical solution to make a turbine efficient at varying wind speeds is to use multi-winding generators that increase load by engaging more windings (and resistance) in response to wind speed. That avoids the problem of attempting to focus on a single optimum generator size. Increased load also helps keep rotor speed down and delays the need to feather as wind speed increases. This improvement would extend the production capability of a given turbine over a wider range of wind speeds.

  3. Eduardo Martinez - 08.05.2013, 15:27 Uhr (Report comment)

    This is my first post and let me say straight away that I know very little compared to the majority of 'experts' who post here. My point is that all the talk about peak power generation and capacity factors seems to be a deliberate ploy to confuse ordinary people. Why doesn't the industry just quote the mean annual energy production expected per day in kWh/day
    A 40W light bulb left on all day uses approx 1 kWh. I would get an idea of exact how much is being generated (on average of course) from the verious renewable sources and I could relate it to what I use.

  4. James Wimberley - 06.05.2013, 14:01 Uhr (Report comment)

    Wind opponents don't understand that the capacity factor of a turbine is a technical choice not a God-given natural constraint. Suppose you start with a large rotor and a small generator. This will have a high capacity factor, but you are throwing away the extra energy available when wind speed is high. So it often pays to increase the generator size, capturing more total energy but lowering the capacity factor. The optimisation depends not only on wind conditions but on market prices. At presnt the market seems to be rewarding high availability over peak output, and we are seeing more of these turbines with a high ratio of swept area to generator size.

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