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Solar and wind power stations will bring rain to the Sahara. If you build it all up

Large solar and wind power stations affect the local climate: both types of renewable sources increase the amount of precipitation and density of vegetation cover on a sufficient scale and potentially change the appearance of the Sahara, where it is theoretically possible to build such large stations. A study on this is published in the journal Science.

Yan Li from the University of Illinois and his colleagues modeled the hypothetical construction of huge wind and solar energy complexes in the Sahara on a total area of ​​9 million square kilometers – the Sahara area is estimated at 9.2 million square kilometers, an additional 3 million square kilometers kilometers to Sahel, the savannah to the south of the desert. The power of the hypothetical power stations in their model will be 3 and 79 terawatts respectively (with a total world energy consumption of 18 terawatts, as of 2017).

The authors note that usually in the modeling of the influence of such facilities on the climate, positive feedbacks are not evaluated that enhance the initial effect, primarily through the vegetation cover. Their climate model, in turn, showed that the construction of such power plants will significantly increase the local temperature, the amount of precipitation and the density of the vegetation cover. Wind power plants deliver warmer air down, mixing it, slowing the wind speed and increasing the surface temperature by about two degrees Kelvin; this increases evaporation from the surface, increases the amount of precipitation by about half, by 0.25 millimeters per day, and stimulates plant growth. 

The solar panels reduce the albedo, or the reflectivity of the surface on which they are installed, and also increase the temperature (by 1-1.2 degrees) and the amount of precipitation (one and a half times, or 0.13 millimeters per day). Vegetation in both cases creates a positive feedback, also reducing the albedo – the leaves are darker than the sand – and further increasing the amount of precipitation. Together solar and wind power stations will give an average increase in the amount of precipitation by 150 percent to 0.59 millimeters per day, and especially pronounced – up to 500 millimeters per year – it will be in the Sahel.

“We found that large-scale solar and wind power stations can increase the amount of precipitation and stimulate the growth of vegetation in these regions. The increase in precipitation is a consequence of the complex interaction of the earth and the atmosphere in the presence of wind generators and solar panels that create more uneven and dark surfaces, “said study co-author Eugenia Kalnay, quoting the press service of the university. The authors conclude that the impact on the climate for renewable energy objects of this scale will have more positive effects on the climate of the planet as a whole, and in the Sahara and the Sahel their construction can favorably affect the local climate. The spatial resolution of their model is small and allows simulating only very large objects: to refine the effect of smaller stations on the local climate, experiments with models with higher resolution are needed. 

In the appendix to the work, the authors do not give estimates of the realistic construction of stations of this size in the Sahara and their possible cost, but note that projects similar to the infrastructure needed to transport electricity to consumers in Europe and northern Africa exist already today, and the benefits of building such a the source of cheap electricity, primarily for the Sahel, will not only be economic – for example, it will help reduce the cost of desalination and improve access to drinking water for the inhabitants of the region.

The massive commissioning of renewable energy capacities – though not on such a scale – is necessary for mankind to reduce greenhouse gas emissions and to protect itself from the most dangerous consequences of global climate change. A group of European scientists earlier showed that if humanity will increase the share of renewable energy sources in the energy balance by two percent per year, it should begin to be done before 2035 – then with a 67 percent probability, warming by the end of this century will be stopped at two degrees. If you act more decisively and add 5 percent of renewable energy per year, deadline can be postponed for 10 years. Now the share of renewable energy sources in the world is only 3.6 percent.

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