Energy sources that provide power without producing CO2 are critical to addressing the challenge of global warming. The book Sustainable Energy – without the hot air prompted me to ask climate researcher Ken Caldeira what the prospects are for generating power from wind in the upper atmosphere.

Bill Gates: I just finished David MacKay’s Sustainable Energy – without the hot air.

He talks about every renewable form of energy I know of except for high wind.

He does a really good job of looking at the potential size of contributions from different things like geothermal and others.

I wonder if he didn’t include high wind because it is viewed as so difficult and unlikely to work or if the contribution potential is so small.

I remember you mentioned some start-ups in the high wind area.

I wonder if there has been any progress in their work.

I guess it is the physics of getting the kites to stay up even in storms and low wind combined with the problem of bringing the power down that is hard.

Ken Caldeira: I have spoken with several people in several companies and they all seem to think different things are the main impediment.

My understanding is that one of the big impediments is tether mass, and there are big tradeoffs with mass of the conductor and insulation versus how high up you can go. It might be that we would require something nearly magical to make such systems really work economically.

(Everything else you mention is also a concern.)

I would say that this is one area in which the size of the investment compared to the size of potential return is tiny, especially when compared with investments such as fusion power.

We recently did a study on steadiness and availability of high altitude winds. The conclusion is that there is a huge amount of power available but that it still is too unsteady to provide base load power without continental (or global?) scale distribution systems, back-up power, or unbelievable amounts of storage.

The other thing we should recall is that if we were to meet future power demand by this source exclusively, we must intercept more than 1% of natural flows. I think when we get above a 1% change in a natural system, we need to be concerned about large scale unintended consequences. Remember, global warming is basically a 1% problem – 1% warming of our 288 K planetary temperature. (That is one reason why solar is so attractive – with solar we are talking about capturing 0.01 % of the energy that hits the ground.)