Where on Earth could you fit three million wind turbines?

What about the Sahara Desert?

A computer model in a recent large-scale climate modelling experiment simulated a Sahara with an astounding three million wind turbines and solar panels covering one-fifth of its nine million square kilometres of land.

"We put in an amount of solar generation capacity that would power all of the Earth's energy use four times over," Daniel Kirk-Davidoff told Quirks & Quarks' host Bob McDonald, quantifying it as some 79 terawatts of electrical generation from solar power.

A large scale wind farm in the Sahara could look a little like this one in Australia, just add 3 million turbines. (AFP/Getty Images)

Kirk-Davidoff, from the Department of Atmospheric and Oceanic Sciences at the University of Maryland, and his colleagues wanted to understand if massive wind and solar installations in the desert would have any side effects — good or bad.

It turns out that a vast, hot, barren expanse where few live and not much grows has huge potential: enough blazing sunlight and persistent wind to power the entire planet — and then some — and turn parts of the desert green along the way.

"When we put in about as much wind power as we thought you could reasonably put in the Sahara, we found that that would give you about three terawatts of wind generation," according to Kirk-Davidoff, who is also the lead research scientist in the renewable division of Underwriter's Lab in Albany, N.Y.

He said that at present, global electricity demand is only about 2.5 terawatts, and the world's total energy demand for last year was 18 terawatts.

Increase in rainfall, more natural vegetation

The study also found that a solar and wind farm could alter the climate and increase rainfall by 0.25 millimetres per day on average, which is about a 50 per cent increase. That is significant for an area that receives very little precipitation at all.

A large solar farm in Arizona. In the researchers' computer model, solar panels cover one-fifth of the Sahara desert. (Daniel Kirk-Davidoff)

Solar panels would do this by darkening and warming the surface of the Sahara, which would create a thermal updraft, Kirk-Davidoff said.

"If you warm up the surface, that would lead to condensation. Upward motion leads to clouds and condensation and that might lead to a little extra rain."

Wind turbines would also increase precipitation, but in a different way. The turbines mix warmer air from above and take as much momentum out of the atmosphere as possible. This makes it easier for wind to move from high pressure to low pressure areas.

"In this case, it happened to bring more moisture into that area, making it easier to form clouds and have precipitation."

According to the models, even that small amount of precipitation resulted in more natural vegetation in areas where there is already some plant growth, such as the Sahel region of the Sahara. And this created a positive feedback loop, according to Kirk-Davidoff.

"The extra vegetation itself absorbed a little more solar radiation and caused an additional feedback that continued to moisten the region a bit more."

The computer model suggests that a Sahara with maximum wind and solar energy would also see an average precipitation increase of about .25 millimetres per day (Daniel Kirk-Davidoff)

In the simulation, the Sahara becomes wetter and greener, and provides a wealth of power for the entire planet. The question is, how realistic is all of this?

Kirk-Davidoff admits the models were a little over the top, but adds that wind and solar are the future.

"We can't afford to be burning a lot more fossil fuels because it leads to global warming and that's bad for us. But more recently, wind and solar power have become extremely cheap and a place like the Sahara, with its huge resources, is very likely to be developed one way or another for wind and solar electrical generation."



