Zhengyao Lu, Lund University and Benjamin Smith, Western Sydney University
The world’s forbidden deserts could be the best places on earth to harvest solar energy – the most abundant and cleanest source of energy we have. The deserts are spacious, relatively flat, rich in silicon – the raw material for the semiconductors from which solar cells are made – and without sunlight. In fact, the ten largest solar systems in the world are all located in deserts or arid regions.
Researchers envision that it might be possible to turn the world’s largest desert, the Sahara, into a huge solar park that can meet four times the world’s current energy needs. Plans have been drawn up for projects in Tunisia and Morocco that will supply electricity to millions of households in Europe.
While the black surfaces of solar panels absorb most of the sunlight that reaches them, only a fraction (about 15%) of this incident energy is converted into electricity. The rest is returned to the environment as heat. The panels are usually much darker than the ground they cover, so a large area of solar cells absorbs a lot of extra energy and gives off as heat, which affects the climate.
If these effects were only local, they could not play a role in a sparsely populated and barren desert. However, the scale of the facilities that would be required to contain the world’s fossil fuel needs would be huge, spanning thousands of square kilometers. The heat given off by an area of this size is redistributed in the atmosphere by the air flow and has regional and even global effects on the climate.
Clockwise from top left: Bhadla Solar Park, India; Desert Sublight solar park, USA; Hainanzhou solar park, China and Ouarzazate solar park, Morocco. Google Earth, author stated
A greener Sahara
A 2018 study used a climate model to simulate the lower albedo effects on the land surface of deserts caused by the installation of massive solar farms. The albedo is a measure of how well surfaces reflect sunlight. Sand, for example, reflects much more than a solar panel and therefore has a higher albedo.
The model showed that a solar park size that reached 20% of the total area of the Sahara triggers a feedback loop. The heat given off by the darker solar panels (compared to the highly reflective desert floor) creates a steep temperature differential between the land and the surrounding oceans, which ultimately lowers surface air pressure and causes moist air to rise and condense into raindrops. With more monsoon rains, plants grow and the desert reflects less solar energy because the vegetation absorbs light better than sand and earth. When there are more plants, more water is evaporated, creating a more humid environment for vegetation to spread out.
Read more: Should we turn the Sahara into a giant solar park?
This scenario may seem fanciful, but studies suggest that a similar feedback loop preserved much of the Saharan green during the African wet season that ended only 5,000 years ago.
So a huge solar farm could generate ample power to meet global needs while turning one of the most hostile environments on earth into a habitable oasis. Sounds perfect right?
Not quite. In a recent study, we used an advanced Earth system model to study exactly how solar parks in the Sahara interact with the climate. Our model takes into account the complex feedback loops between the interacting spheres of the world’s climate – the atmosphere, the ocean and the land and its ecosystems. It emerged that there could be unintended impacts in remote parts of the country and ocean, offsetting regional advantages over the Sahara itself.
Drought in the Amazon, cyclones in Vietnam
The coverage of 20% of the Sahara with solar parks increases the local temperatures in the desert according to our model by 1.5 ° C. With a coverage of 50% the temperature increase is 2.5 ° C. This warming is ultimately caused by the atmosphere and the Ocean movement spread all over the world, increasing the average temperature of the world by 0.16 ° C at 20% coverage and 0.39 ° C at 50% coverage. However, the global temperature shift is not uniform – the polar regions would warm more than the tropics, which would increase sea ice loss in the Arctic. This could further accelerate warming as the melting sea ice exposes dark water, which absorbs much more solar energy.
This massive new source of heat in the Sahara is reorganizing global air and ocean circulation and affecting rainfall patterns around the world. The narrow band of heavy rainfall in the tropics, which accounts for more than 30% of global precipitation and supports the rainforests of the Amazon and the Congo Basin, shifts northwards in our simulations. For the Amazon region, this leads to droughts as less moisture comes from the ocean. About the same amount of additional precipitation that falls over the Sahara due to the surface darkening effects of solar panels is lost from the Amazon. The model also predicts more frequent tropical cyclones on the North American and East Asian coasts.
Global temperature, precipitation and surface wind changes in simulations with 20% and 50% solar collector coverage of the Sahara. Lu et al. (2021), author provided
Some important processes are still missing from our model, e.g. B. Dust from great deserts. Saharan dust carried by the wind is an important source of nutrients for the Amazon and the Atlantic. A greener Sahara could therefore have an even bigger global effect than our simulations suggested.
We are only just beginning to understand the potential consequences of building massive solar parks in the world’s deserts. Solutions like these may facilitate society’s transition from fossil fuels, but Earth system studies like ours underscore the importance of considering the many coupled reactions of the atmosphere, oceans, and land surface when examining their benefits and risks.
Zhengyao Lu, Physical Geography Researcher, Lund University; and Benjamin Smith, Research Director, Hawkesbury Institute for the Environment, Western Sydney University
This article is republished by The Conversation under a Creative Commons license. Read the original article.
HT / Michael D.