A Solar ‘Breakthrough’ Won’t Solve Cement’s Carbon Problem

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Anyone who says there’s nothing new under the sun hasn’t made a recent trip to Lancaster, California. There, on the outskirts of the Mojave desert, 400 giant mirrors, each the size of a large flatscreen TV, twitch in the sunlight. Their reflective faces are turned toward a nearby tower that looms over the lot like an industrial eye of Sauron. Each of these robotic heliotropes are at the beck and call of an algorithmic conductor, which directs them to focus their sunbeams toward a small target on the tower. Here temperatures soar above 1800 degrees Fahrenheit, or roughly a quarter of the surface temperature of the Sun.

It sounds like a doomsday machine cooked up by a comic book villain, but this is a device meant to help save the world, not end it. It’s called the Heliomax and its superpower is making cement.

The system was developed by Heliogen, a six-year-old startup that just came out of stealth mode this week and is partially bankrolled by Bill Gates’ investment firm. Its goal is to use concentrated solar energy to power industrial processes that require a lot of heat, such as steel and cement manufacturing. These industries are literally and figuratively the foundation of modern civilization, but their toll on the climate has made them prime targets in the push to limit carbon emissions. The cement industry is a particularly bad offender, releasing 2 billion tons of carbon into the atmosphere annually—more than twice as much as the airline industry. Indeed, nine tons of carbon is produced for every 10 tons of cement.

Heliogen’s technology has many possible uses, including as a way to produce hydrogen, but the company plans to work with cement production facilities first. According to Heliogen CEO Bill Gross, the company has already installed a small cement oven on the top of the tower and used it to replicate the most carbon-intensive step in the production of cement. It was a proof-of-concept, but it worked. Now that the company is out of stealth mode, Gross says he and his team have received dozens of inquiries from cement companies around the world and begun the hunt for an industrial partner to test the technology at a commercial scale. “Cement is the most versatile building material there is; if you look around it’s everywhere,” Gross says. “But it accounts for 8 percent of emissions. So we’re starting with cement first because these heavy industries have been untouched by renewables.”

It’s an innovative solution that’s being widely hailed as a breakthrough, but Heliogen isn’t the first to go this route. A European project known as Solpart aims to create a partially solar-powered cement plant in Spain by 2025. Last year, its researchers used an experimental solar reactor in France to replicate the same step Heliogen has now demonstrated.

That carbon-intensive step is called calcination, and it happens early on in production, says Gkiokchan Moumin, a doctoral student at the German Aerospace Center’s Institute for Solar Research and a member of Solpart. To make cement, crushed limestone is fed into a kiln and heated to roughly 1500 degrees Fahrenheit, at which point it breaks down into lime and carbon dioxide. Powering this step with renewable energy would go a long way toward reducing the cement industry’s carbon footprint—and Solpart proved it was possible.

The Odeillo solar furnace in southern France is the largest in the world and was the testing site for the Solpart experiments.

Photograph: Getty Images

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