Wind Power: Cool Breeze or Hot Sirocco?

Jamie Bull brought to my attention a paper saying that land based wind turbines are likely to create a small degree of earth surface warming.

Jamie was concerned that there might not be a net surface cooling, even once the effects of reduced greenhouse gas emissions were taken into account. He did some calculations, and showed that the net effect of wind power on surface temperatures was still strongly negative.

He need not have worried. An understanding of the mechanism of this surface heating, and the conservation of energy make it clear that the surface heating effect of wind is smaller than the surface heating effect of thermal electricity generation such as coal, gas, nuclear, and Concentrating Solar Power (CSP) on a per kWh basis.

Conservation of energy tells us that all the energy in wind is eventually dissipated by friction, creating heat. The effect of wind turbines is to take some of this energy that might have become heat in the atmosphere, and create electricity, which will eventually become heat on the earth’s surface, and some will become heat in the turbine itself.

The net heat added to the Earth by wind turbines is zero: heat that would have been created in the atmosphere is now created on the surface instead, and the net effect is zero.

Now consider thermal electricity generation. When a fossil fuel is burned, or when a nuclear power plant or CSP plant makes steam, heat is either created from a fuel or captured from the sun, reducing the amount that would reflect back into space. All this heat is dissipated at some point near the earth’s surface, creating more surface warming than wind power, and also creating net warming where wind power creates none.

The direct surface heating effect from wind is likely to be only a fraction of the direct surface heating effect of thermal electricity, even before the effects of greenhouse gasses are accounted for.

Solar PV and Solar CSP capture heat from the sun that might otherwise reflected into the atmosphere, so more precise calculations are probably needed to determine if their net effect is negative before the effects of greenhouse gasses, but wind is clearly cool by any thermometer.

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4 Comments

  1. Jamie Bull said

    I’ve often wondered about that direct heating effect from thermal plant, cars, etc. I just did a scratch pad wikipedia-sourced calc of it using the annual energy use from thermal technologies (80 – 90% of global energy use http://en.wikipedia.org/wiki/World_energy_resources_and_consumption) of 15TW. Given the earth’s surface area of 510,072,000km2 that’s a rate of 23.5 to 26.5 W/m2. Quite a lot.

    Then I found another wiki article which addresses the issue directly (http://en.wikipedia.org/wiki/Waste_heat#Anthropogenic_heat) and it quotes an anthropogenic waste heat flux of 0.028W/m2. Much smaller. Strangely it looks like it’s a factor of a thousand out. Can you see any error in the logic or arithmetic?

  2. Tom said

    23-26 W/m^2 is too high. Sunlight is about 120 W/m^2 12 hours a day, or 60 W/m^2 on average. The heating effect of anthropogenic waste heat flux is not a significant fraction of the solar flux, since we all observe that anthropogenic heat sources only have locally significant effects on temperature.

    So the wikipedia number is more likely to be accurate.

    Re-doing your calculation, I got the Wikipedia number. I’m guessing you assumed there were one thousand square meters per square kilometer, when in fact there are a million sq meters per square km.

  3. Jamie Bull said

    Also, bear in mind that although “The net heat added to the Earth by wind turbines is zero: heat that would have been created in the atmosphere is now created on the surface instead, and the net effect is zero”, it is surface warming that affects us, and surface warming over land at that.

    You’re absolutely right that the net effect is zero and that is what the paper found. There is a corresponding cooling in the upper atmosphere, much like the cooling in the stratosphere due to increased greenhouse effect.

  4. Jamie Bull said

    “assumed there were one thousand square meters per square kilometer, when in fact there are a million sq meters per square km”

    Of course. That’ll teach me to do calcs after midnight and too many glasses of wine!

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