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Solar panels that heat the weather, can it be?  |  Science |  News |  Sun

Solar panels that heat the weather, can it be? | Science | News | Sun

CThis is a question that several researchers have posed in recent years, since its premise is indisputable: the part of solar energy that is reflected on the Earth’s surface is actually greater than that of solar panels. On average, the Earth reflects around 30% of the Sun’s light back into space (it is said to have an “albedo” of 0.30), although this varies from place to place: it is around 80% for the fresh snow, 40% in deserts, 25% in meadows and 12-15% in forests. In the case of solar panels, it is only 10% reflected, the rest is converted into electricity (about 15%) or dissipated into heat (75%). Please note that even the electricity part will inevitably end up as heat when used up.

So it’s obvious that solar panels can have a warming effect, at least on a local scale. But is this enough to negate its environmental benefits, that is, the fact of producing electricity without GHG (or almost)? There are two things to consider here: first, a potential “heat island” effect, which would be essentially local; and then a possible climate effect on a larger scale.

There seems to be little doubt that solar power plants can create heat islands, especially when installed in places with high albedo, such as deserts, which often happens, by the way, since deserts are perfect places to maximize energy. production of solar panels. Therefore, an American study published in 2016 in Scientific reports found a 3-4 ° C difference overnight between a solar power plant and a desert area a few hundred meters away. A Chinese study obtained results that went in the same direction Next year.

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Note that this does not always seem to be the case, as French works He suggested that in the city and with thermal panels (which convert heat, not light, into electricity, which is apparently more efficient), these reduce temperatures by 0.2 to 0.3 ° C on average. So, let’s keep in mind that the final effect seems to depend a lot on the context in which you install the solar panels: a black panel that replaces the black asphalt shingles, clearly is not the same as a black panel that covers a transparent surface.

But while “solar farms,” ​​as they are called south of the border, can promote heat islands, it is not entirely clear that they have the ultimate effect of warming the climate. First, simulations presented in 2013 during a conference of photovoltaic specialists concluded that if the temperature at 2.5 m from the ground in the middle of a large solar power plant was almost 2 ° C higher than that of the surroundings, the difference dissipated very quickly, to the point of ceasing to be measurable at an altitude of only 5 m, and that the temperature difference completely disappeared overnight. This suggests that the effect would be very localized and not global.

Other works have focused on the global effect of solar panels, not only from the albedo point of view, but also from the GHG that solar panels avoid us. Within Nature – Climate change in 2015, researchers from the University of Boulder, Colorado, concluded that “in general, … the global climate changes potentially induced by the use of solar panels are small compared to the climate changes expected from fossil fuels.” Therefore, it seems that even taking into account the greater proportion of solar radiation that remains on Earth, these panels are still “profitable” from a climatic point of view.

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However, there is still the possibility (at least theoretical) that this energy source may have a marked, and not necessarily positive, influence on the climate. If solar power projects ever reach truly pharaonic proportions, then the “regional” effects could be so strong that they would alter the climate on a planetary scale. For example, modeling work published in 2018 in Sciences indicated that if we cover 20% of the entire Sahara (!) with photovoltaic panels, it would increase the surface temperature by about 2 ° C in this desert, and in an area large enough to change the atmospheric circulation. One consequence of this would be increased rainfall over the Sahara and the Sahel (the semi-arid area south of the Sahara), which would favor vegetation. This would then add to the precipitation (because the plants “pull” a lot of water out of the ground and “sweat” it through their leaves), which would bring in even more vegetation, which would absorb even more energy from the ground. the earth, the sun, etc. These consequences are described as “beneficial” in the study, and it’s easy to understand why, but it shows that, at least under certain circumstances, truly giant solar power plants can alter the climate on a large scale.

TO another study on the same topic for his part, he concluded that a solar power plant covering 20% ​​of the Sahara would have literally planetary effects (drought in the Amazon, increased warming in the Arctic, etc.). It is for the moment a simple modeling, so we will have to see if others arrive at comparable results -and then, if these predictions are transposed to reality-, but let’s say yes, in principle it is possible that solar plants, if they are gigantic and built in a particular context, they have global effects on the climate. Not necessarily by heating it up, as Mr. Le May requested, but that can theoretically “upset” it.

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