There is no escaping the fact wind and solar farms have an effect on their local environment, wherever they are placed. It's not quite the 4.2 million deaths from air pollution, as in the case of fossil fuels, but they do influence the area around them. Some effects are detrimental, but some are surprisingly beneficial to their environment. A new study has shown that large-scale solar and wind farms could increase rainfall and vegetation, even in the Sahara desert.

The study, published in Science, focuses on the most famous arid region in the world (central Sahara receives on average less than 1 inch of rain a year).  It's not the first time that the effects of renewable energy megastructures on climate have been studied, but this is the first time the effect on vegetation has been considered. The team worked out that a huge solar and wind farm would increase rainfall by 1.12 millimeters per day. This would make the Sahara reach a precipitation level not too different from places like Greece or Argentina.

"Previous modeling studies have shown that large-scale wind and solar farms can produce significant climate change at continental scales," lead author Dr Yan Li from the University of Illinois said in a statement. "But the lack of vegetation feedbacks could make the modeled climate impacts very different from their actual behavior.

Instead, they found that wind farms caused a warming of near-surface air temperature, with larger differences in cooler temperatures, rather than warmer ones. The turbines mix ground air vertically leading to a greater nighttime warming by bringing warmer air from above. These changes would affect the microclimate, and if the installations were truly huge they could truly alter climate on a continental scale. 

"This was a doubling of precipitation over that seen in the control experiments," said Li. "This increase in precipitation, in turn, leads to an increase in vegetation cover, creating a positive feedback loop."

The wind and solar farm proposed is unlikely to actually be put into practice any time soon. At a humongous 9 million square kilometers (3.475 million square miles), it's almost the size of the whole Sahara, which is not practical, not least for political reasons. Plus, the dust from the Sahara has positive effects around the world, so if this enterprise were to go ahead, we would need to take those benefits into account.

There’s also a question of just not needing this, yet. A huge wind and solar farm stretching the whole desert would provide 3 terawatts and 79 terawatts of electrical power, respectively. Given that the world's current energy consumption is 18 terawatts, turning the desert into a huge power plant is a little premature.

While not a blueprint for the immediate future, the study shows that these power sources could have more beneficial effects, and installations in arid or semi-arid regions could help agriculture, economic development, and social wellbeing.