Most of the large-scale solar parks in the world are located in deserts. These landscapes provide ample vacant land and year-round sunlight for solar power production. Researchers have envisioned transforming the Sahara—the vastest desert region on earth—into a massive solar park that might have the potential of producing four times the world’s present energy demand.

But, there’s a major problem—dust. Gradual dust accumulation on solar panels can reduce their efficiency by almost 30 percent within one month of operation. For some context, solar power losses of only three to four percent on a global scale could mean an economic loss of at least 3.3 to 5.5 billion dollars. As climate change intensifies dust storms, there may be a rapid loss of solar panels’ efficiency unless they are cleaned several times a month.

Pressurized water jets and sprays are the most common method of cleaning solar panels. To avoid the risk of staining and damaging the glass of solar panels, only pure and demineralized water can be used. The need to transport clean water to dry or remote desert regions with scarce water supplies accounts for 10 percent of solar parks’ operations and maintenance costs.

While the global capacity of solar parks is currently above 500 gigawatts, researchers estimate that up to 10 billion gallons of drinking water are used every year just for cleaning solar panels. To put things in perspective, that amount of water can fulfill the annual requirements of approximately 2 million people living in developing countries.

“I was amazed at the sheer amount of pure water that is required for cleaning solar panels,” says Kripa Varanasi, a professor of mechanical engineering at MIT (no relation to the author). “The water footprint of the solar industry is only going to grow in the future. We need to figure out how to make solar farms more sustainable.”