The world’s most hostile deserts could be the best places on Earth to harvest solar energy – the most abundant and cleanest source of energy we have. Deserts are spacious, relatively flat, rich in silicon – the raw material for semiconductors from which solar cells are made – and never run out of sunlight. In fact, the 10 largest solar power plants in the world are all located in deserts or dry regions.

The researchers imagine that it would be possible to transform the world’s largest desert, the Sahara, into a giant solar farm, capable of meeting four times the current global energy demand. Plans were drawn up for projects in Tunisia and Morocco that would provide electricity to millions of homes in Europe.

While the black surfaces of solar panels absorb most of the sunlight that reaches them, only a fraction (about 15%) of this incoming energy is converted into electricity. The rest is returned to the environment as heat. Panels are usually much darker than the ground they cover, so a vast expanse of solar cells will absorb a lot of extra energy and emit it as heat, affecting the climate.

If these effects were only local, they might not matter in an arid, sparsely populated desert. But the scale of the facilities that would be needed to reduce global fossil fuel demand would be vast, covering thousands of square kilometers. The heat re-emitted from an area of ​​this size will be redistributed by the flow of air into the atmosphere, having regional and even global effects on the climate.

Clockwise from top left: Bhadla Solar Park, India; Desert Sublight Solar Farm, United States; Hainanzhou Solar Park, China and Ouarzazate Solar Park, Morocco. // Image courtesy of The Conversation

A greener Sahara

A 2018 study used a climate model to simulate the effects of low albedo on the land surface of deserts caused by the installation of massive solar farms. Albedo is a measure of how well surfaces reflect sunlight. Sand, for example, is much more reflective than a solar panel and therefore has a higher albedo.

The model found that when the size of the solar farm reaches 20 percent of the total area of ​​the Sahara, it triggers a feedback loop. The heat emitted by the darker solar panels (compared to the highly reflective desert soil) creates a large temperature difference between the land and the surrounding oceans which ultimately lowers the atmospheric pressure at the surface and causes the elevation and condensation of the sea. humid air in raindrops. With more monsoon rain, plants grow and the desert reflects less of the sun’s energy, as vegetation absorbs light better than sand and soil. With more plants present, more water evaporates, creating a more humid environment which causes vegetation to spread.

The model found that when the size of the solar farm reaches 20% of the total area of ​​the Sahara, it triggers a feedback loop.

This scenario may sound fanciful, but studies suggest that a similar feedback loop kept much of the Sahara green during the African wet period, which ended only 5,000 years ago.

So a giant solar farm could generate enough energy to meet global demand and simultaneously transform one of Earth’s most hostile environments into a habitable oasis. Sounds perfect, right?

Not enough. In a recent study, we used an advanced model of the Earth system to take a close look at how Saharan solar farms interact with climate. Our model takes into account the complex feedbacks between the interacting spheres of the global climate – the atmosphere, the ocean, and the land and its ecosystems. He showed that there could be unforeseen effects in remote parts of the land and the ocean which outweigh any regional advantages over the Sahara itself.

Drought in the Amazon, cyclones in Vietnam

Covering 20 percent of the Sahara with solar farms increases local temperatures in the desert by 1.5 degrees Celsius, according to our model. At 50 percent coverage, the temperature increase is 2.5 degrees Celsius. This warming eventually spreads around the world through the movements of the atmosphere and oceans, raising the global average temperature by 0.16 degrees Celsius for 20 percent coverage and 0.39 degrees Celsius for 50 percent coverage. percent. The global temperature change is not uniform, however – the polar regions would warm more than the tropics, increasing the loss of sea ice in the Arctic. This could further accelerate warming, as melting sea ice exposes dark water that absorbs much more solar energy.

This massive new heat source in the Sahara is reorganizing the global circulation of air and oceans, affecting precipitation patterns around the world. The narrow band of heavy rainfall in the tropics, which accounts for more than 30 percent of global rainfall and supports the tropical rainforests of the Amazon and Congo Basin, is moving north in our simulations. For the Amazon region, this causes droughts because less moisture comes in from the ocean. Roughly the same amount of additional precipitation that falls on the Sahara due to the surface darkening effects of solar panels is lost in the Amazon. The model also predicts more frequent tropical cyclones hitting the North American and East Asian coasts.

Global temperature, precipitation and surface wind changes in simulations with 20 percent solar panel coverage and 50 percent of the Sahara. Lu et al. (2021). // Image courtesy of The Conversation

Some important processes are still missing from our model, such as dust blown by great deserts. Saharan dust, carried by the wind, is a vital source of nutrients for the Amazon and the Atlantic Ocean. Thus, a greener Sahara could have an even greater overall effect than our simulations suggest.

We are only beginning to understand the potential consequences of establishing massive solar farms in the deserts of the world. Solutions like this can help society shift away from fossil fuels, but Earth system studies like ours underscore the importance of considering the many coupled responses of the atmosphere, oceans, and land surface when examining their benefits and risks.

This article is republished from The Conversation under a Creative Commons license.