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-   -   Can Enough Windwills Cause Climate Change? (http://www.physicsforums.com/showthread.php?t=234667)

Drewman626 May12-08 06:37 AM

Can Enough Windwills Cause Climate Change?
 
I posed this question to my brother and father-in-law yesterday and they disagreed with the premise of the question, let alone the result. They debated the physics involved.

Weather is generally a result of the sun's uneven heating of the atmosphere and the resulting convection currents, ie. wind, follows generally constant patterns across the face of the earth.

A windmill, by the laws of conservation of energy, does not "create" electricity. It converts kinetic energy from moving air to motion of the windmill blades, which in turn is converted into electrical energy. Maybe a little more to it than that, but that's the gist of it.

So a windmill removes energy from the atmosphere. Obviously the wind exiting the windmill can't have as much energy as the wind entering the windmill (energy was "used" to move the blades) no matter how efficient and/or aerodynamic the blades are.

With each windmill then, the weather pattern is slightly affected. With enough windmills, would wind be reduced enough to affect weather? Could windmills be causing climate change?

My point of posting this on here is to pose the concept, but to debate the physics since that is what I was challenged on. Is my understanding of the conservation of energy principals above correct?

My in-laws said that the wind isn't affected because the blades are so aerodynamic and that wind behind a windmill actually moves faster. Thoughts?

russ_watters May12-08 08:20 AM

Your instinct is correct, but the number of windmills necessary to have a serious effect on global wind patterns would be absurdly high.

Cvan May12-08 08:35 AM

We'll just have to unevenly heat the earth more by causing localized pockets of greenhouse gas and ozone tears over major cities, thus resulting in more wind.

Problem solved. And it's not too difficult for society to implement. See? We've already started!

Lojzek May12-08 01:52 PM

I don't think windmills would significantly change the weather, even if all human energy supply would be generated by them. The energy that humans use is still very small when compared to the solar energy (that warms the Earth). Also the produced energy would finaly be returned to the air (for example in form of heat, which would cause air movement).

In addition changing wind speeds would only have a temporary direct effect on the weather: something that could be (aproximately) compared to the direct effect of heat which is today generaly produced from fossil fuels. The real danger for climate is not direct addition or removal of energy, but the produced substances (greenhouse gasses) that change the long-term energy exchange between the Sun and the Earth.

Loren Booda May12-08 10:39 PM

Consider all of the trees (approximately the height of a windmill) that have been cut down in human history and the little change that seems to have made with surface air currents and climate.

kenewbie May13-08 04:29 AM

Quote:

Quote by Drewman626 (Post 1726977)
My in-laws said that the wind isn't affected because the blades are so aerodynamic and that wind behind a windmill actually moves faster.

That would be quite an accomplishment! Time to call Newton.

k

Lojzek May13-08 05:03 PM

Quote:

Quote by kenewbie (Post 1728178)
That would be quite an accomplishment! Time to call Newton.

k

Don't bother to call Newton! We should place those wind accelerating windmills into a circular tunnel and register a patent for perpetuum mobile...

vanesch May14-08 01:56 AM

This is why one should associate a power plant to each wind mill farm: in summer, when it is hot and not windy enough, one could then make the power plant turn the windmills, and generate a gentle breeze... :bugeye:

That said, in this report http://www.stanford.edu/group/efmh/w...bal_winds.html
it is stated that the available wind energy worldwide is about 72 TW, while current global electricity use is around 1.6 TW. Although this means that there is "largely enough wind energy available" to power the entire world, I don't know what it would climatologically mean if you tap several percent of the wind energy from the atmosphere.


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