Another Upside of Renewable Energy

This story, from the Los Angeles Times, predates the IPCC report by over a month, but I just heard about it today when it was excerpted in the Star Tribune's Sunday science and tech section. It's titled "Wind and solar farms can make their own weather, including extra rain over the Sahara."

The upshot is that researchers modeled three scenarios of renewable energy installations in the Sahara and the adjacent Sahel region: one all-wind, one all-solar, and one a mix of the two. Then they modeled the effects on the local climate.

The solar panel scenario covered 20 percent of the land. The wind turbines were 300' tall (no mention is made in the story of how much area they covered). The mixed scenario would produce about 82 terawatts of electrical power (for scale, that compares with 17 terrawatts currently used worldwide).

For the wind-only scenario, the researchers' first finding sounds like bad news:

...the giant turbines would cause warmer air from above to mix with cooler air below, bringing more heat close to the surface. Air temperatures near the ground would increase by nearly 4 degrees Fahrenheit.

But that heat has positive effects:

the turbines [also] would interrupt the smoothness of the desert surface. Winds blowing through the area would move more slowly.

That, combined with the added heat, would change the atmospheric conditions over the Sahara and bring more moisture to the area. Average rainfall would increase by up to 0.25 of a millimeter per day — about double what it would have been otherwise, according to the study.

The additional water would fuel plant growth, and those extra plants would reduce the amount of sunlight that’s reflected off the desert surface.

From there, it’s a positive feedback loop, the researchers explained: The reduced reflectivity (or surface albedo) enhances precipitation, which fuels plant growth, which reduces albedo, and so on.

The solar panels don't increase the temperature as much as the turbines, but also have a positive effect because their dark surfaces inherently reduce the desert's albedo and lead to a similar feedback loop of increased rain, more plants, and so on.

The scale of these imagined installations is obviously gigantic, but that's what it will take to replace our fossil-fuel-based energy system. It's good to see that it's possible the installations themselves can have positive effects in the places where they might be located.