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If you've thought about dirty energy in the world, you've probably thought of some awkward scenarios. Solar panels in the space emit energy or cover Nevada in solar panels – that sort of thing. Well, a new study by Yan Li, Eugenia Kalnay and Safa Motesharrei at the University of Maryland is actually asking for something similar. What would happen in the Sahara if it contained enough wind and solar farms to meet the energy needs of the world many times?
Why the Sahara, you ask? Aside from the obvious things – lots of open ground and a pretty powerful solar resource – the climate in the area has been very sensitive to the nudges. The Sahel region between the Sahara Desert and the wetter lands to the south, in particular, can easily become wetter or drier with small atmospheric changes. And as other studies have shown that wind and solar farms can have an influence on the local weather, it is interesting to ask what effect they have had in North Africa.
Supersize me
Without constraints on their scenario, the researchers opted for the "oversized" version. In a climate model, they simulated the effect of adding three terawatts of wind energy – a little more than the current total electricity consumption of the world. Then they added 79 terawatts of solar farms. Global energy consumption of all types (including fuels) is about 18 terawatts today. It is therefore a scenario where everyone could want a growing world in the Sahara and where African drinking water would probably be desalinated. In all, it is about nine million square kilometers of wind and solar equipment – almost the area of the United States.
Although the wind farms produced a small portion of the total energy, they had the greatest impact on the climate in the model. The average temperature in the area increased by about 2 ° C, mainly because nighttime temperatures could not cool as much. Rainfall, meanwhile, roughly double. A model simulation with only solar farms showed a warming of about 1 ° C (this time mainly due to higher afternoon temperatures) and a 50% increase in precipitation.
With the wind and solar farms in the model, the effects of the rain combined for a 150% increase, while the temperature rose to about 2.7 ° C. While the neighboring Sahel benefits from With a similar surge of rainfall, it actually becomes slightly cooler than hot.
The weather processes at stake are slightly different for wind and solar farms. Wind farms on this scale make the surface of the Earth rougher, slow down the wind a little and change the mix of surface air with the air just above. Slower winds experience less of the Coriolis effect that curves winds in a straight line due to the Earth's rotation. The end result in this region is that the air masses are collected and mounted a little more strongly, bringing more moisture that condenses into rain clouds when the air that cools becomes cools.
Solar panels, on the other hand, reflect less sunlight than the sand of the desert. This causes a warming of the air at the surface, giving a boost that eliminates the humidity of the air.
Space for greenery
The real key is how vegetation responds to climate change in this climate model. More rain obviously means more plants in this landscape limited by rain. The vegetation effectively absorbs soil moisture and releases it as water vapor into the atmosphere. And plants, like solar panels, also reflect less sunlight. It turns out that only about half of the simulated temperature effects and 20% increase in precipitation are directly due to wind and solar farms. The rest is an additive effect provided by the expansion of small happy plants. In fact, the reason the Sahel is getting slightly cooler is that the release of water vapor from the plants cools the surface, just as sweating cools your skin on a hot day.
Although the change in rainfall is certainly not enough for the Sahara desert to be luxuriant, the researchers say that the difference in the Sahel "is important enough to have major ecological, environmental and societal impacts". So if we had to produce enough renewable energy in the Sahara to feed the world, not only would we eliminate the global climate impact of our energy system, but it would seem that arid life in the Sahara and Sahel would experience a driving rain .
Of course, there are a million logistical reasons why this scenario is not particularly practical or likely. The researchers also point out that the more efficient the solar panels become, the lower their influence on the local temperature. And for small wind and solar farms, their specific locations and amenities could also alter the impact of weather conditions.
The researchers played a little bit with the simulation of massive wind and solar farms deployed in other deserts, but nothing else showed results like the Sahara. The combination of size, location and color of the pale earth surface (which means more reflective) makes this area particularly sensitive to wind turbines and solar farms that change their time. So, if you want to dream big, the Sahara is an interesting place to do it.
Science, 2018. DOI: 10.1126 / science.aar5629 (About DOIs).
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