Solar panels that warm the climate, could they be? | science | news | the sun

cThis is a question that many researchers have asked themselves in recent years, because its hypothesis is indisputable: the portion of the Sun’s energy that is reflected off the Earth’s surface is actually larger than solar panels. On average, Earth reflects about 30% of sunlight back to space (it is said to have a “albedo” of 0.30), although this varies from place to place – about 80% for fresh snow, 40% in deserts, 25% in promoter and 12-15% in forests. In the case of solar panels, it is Only 10% is reflectedThe rest is either converted to electricity (about 15%) or is dissipated to heat (75%). Note that even a share of electricity will inevitably end up as heat when it is spent.

So it is clear that solar panels can have a heating effect, at least on a local level. But is this enough to deny its environmental benefits, i.e. the fact that electricity can be produced without (or nearly) greenhouse gases? There are two things to consider here: first, the potential “heat island” effect, which would be mainly local; Then a potential climate impact on a larger scale.

There seems to be little doubt that solar plants can create heat islands, especially when installed in places with high albedo, such as deserts – which they often do, by the way, because deserts are ideal places to increase solar panel production. So an American study دراسة Published in 2016 in Scientific Reports I found a difference of 3-4 degrees Celsius overnight between a solar power plant and a desert area a few hundred meters away. Chinese study obtained The results went in the same direction the following year.

Note that this doesn’t always seem to be the case since then French works He suggested that in the city and with thermal panels (which convert heat, not light, into electricity, which seems more efficient), these factors lowered temperatures by 0.2 to 0.3 degrees Celsius 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 replaces the black asphalt panels, obviously not the same as the black panel covering a clear surface.

But while “solar farms,” ​​as they are called south of the border, can promote heat islands, it’s not at all clear if they have the ultimate effect of warming the climate. First, Simulations were introduced in 2013 During a conference of photovoltaic specialists they concluded that if the temperature of 2.5 meters from the ground in the middle of a large solar power plant was about 2 degrees Celsius higher than the surrounding areas, the difference dissipated so quickly, that it no longer exists. Measurable at only 5 metres, the difference in temperature completely disappeared during the night. This indicates that the effect will be very local rather than global.

Other work has focused on the overall effect of solar panels, not only from the point of view of albedo, but also from the point of view of the greenhouse gases that solar panels avoid. at Nature – Climate Change in 2015, researchers at the University of Boulder, Colorado, concluded that “the global climate changes (…) likely caused by the use of solar panels are small compared to the climate changes expected from fossil fuels.” So it seems that even taking into account the greater share of solar radiation remaining on Earth, these panels remain “profitable” from a climate point of view.

However, there is still a possibility (at least theoretical) that this energy source will have a significant, and not necessarily positive, impact on the climate. If solar projects reach truly pharaonic proportions, the “regional” effects could be so powerful that they disrupt the climate on a planetary scale. For example, Modeling published in 2018 in Science He pointed out that if we covered 20% of the entire desert (!) with PV panels, the surface temperature would increase by about 2 ° C in this desert, and over an area large enough to change the atmospheric circulation. The result of this will be increased precipitation over the Sahara and the Sahel (semi-arid region south of the Sahara), which favors vegetation. This would add to the precipitation (because plants “take” a lot of water from the ground and “sweat” through their leaves), which would bring in more plants, which would absorb more energy from the earth, the sun and so on. These results are described as “helpful” in the study, and it’s easy to understand why, but they show that under certain circumstances at least, giant solar power plants can truly disrupt climate on a large scale.

a Another study on the same topic For its part, he concluded that a solar plant covering 20% ​​of the desert would have effects on the planet (drought in the Amazon, increased warming in the Arctic, etc.). At the moment it’s simple modeling, so we’ll have to see if others come up with similar results – and then, if those predictions are actually conveyed – but let’s say that yes, it is tentatively possible that solar plants if they are massive and built in a context Certain, it has global impacts on climate. Not necessarily by heating, as Mr. Le Mai asked, but could theoretically “disturb” her.