Water Worries Could Slow the Green Hydrogen Boom

Making clean hydrogen fuel takes a lot of water — not just to run the machines, but also to keep them cool. A new study finds that many of the best places to build green hydrogen plants are in hot, dry regions where fresh water is already hard to find. Scientists say this mismatch between water supply and energy demand could be a big problem for the future of clean energy.

Green hydrogen is made by splitting water into hydrogen and oxygen using electricity from renewable sources like solar panels or wind turbines. This process, called electrolysis, requires machines that get very hot and must be cooled using large amounts of water. Most plants today use evaporative cooling, which works like a giant swamp cooler and uses even more water in hot, dry weather.

Researchers found that cooling water needs change a lot depending on where a plant is and what time of year it is. In cold regions, plants need about 19 liters of water per kilogram of hydrogen made. In hot, dry places like North Africa or the southwestern United States, that number can nearly double to 39 liters.

The seasons matter a great deal too. During the hottest months, cooling water needs can spike by as much as 25 percent above the yearly average. This means even places with normal climates could face water shortages during summer, when cooling demand is at its peak.

To measure the danger, scientists built a tool called the Water Risk Index. It combines how much cooling water a plant needs with how stressed the local water supply already is. The index runs from 0 to 100, with low scores labeled Go, middle scores labeled Caution, and high scores labeled Other Solutions.

About 40 percent of the world's land scored in the safe Go range. However, 43 percent of all planned green hydrogen projects are being built in Other Solutions zones, where water is dangerously scarce. Scientists say this is a serious problem that planners need to address right away.

Solar energy is closely linked to this water problem. The sunniest spots on Earth are also the driest, and 63 percent of the best solar energy zones fall in Other Solutions areas for water. Giant projects in Saudi Arabia, Namibia, and Australia will likely need to pull water from the ocean using desalination, which is expensive and complicated.

Wind energy is a brighter story. Wind is often strongest along coasts and in mountains, where there is more rain and cooler air. About 31 percent of top wind energy zones are in safe Go areas, giving wind-powered hydrogen projects far more flexibility than solar ones.

Scientists are urging hydrogen plant planners to always check the local water situation before building. They recommend using dry or hybrid cooling systems in water-scarce areas. Clean energy should not come at the cost of communities running out of fresh water.