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Climate change and energy

How heat from the sun could help clean up steel and cement

Serial entrepreneur Bill Gross has launched a new solar thermal venture, designed to cut climate emissions from industrial heat.
November 19, 2019
The Heliogen solar thermal site in Lancaster, California.
The Heliogen solar thermal site in Lancaster, California.Courtesy of Heliogen

Over the years, assorted startups and research groups have trumpeted the promise of solar thermal plants, which use a large array of mirrors to concentrate sunlight and produce electricity from the resulting heat. But the field has struggled to produce cheap power and gain a market foothold, even as the price of solar panels has plummeted.

Serial entrepreneur Bill Gross, however, remains a true believer in the technology. On Tuesday Gross, the chairman of the Idealab incubator and CEO of earlier solar thermal company eSolar, announced a venture that skips the electricity part and puts the heat to use directly in industrial processes.

Heliogen plans to achieve higher temperatures than previous commercial plants—enough heat to produce things like cement, steel, and hydrogen. The hope is that this solar heat could replace the fossil fuels usually required to drive the necessary reactions, reducing the greenhouse-gas emissions produced in the process.

If it works as hoped, it could provide a critical piece in the decarbonization puzzle. An October report from Columbia University’s Center for Global Energy Policy found that burning fossil fuels to produce heat for industrial processes produces about 10% of global carbon dioxide emissions, more than all the cars in the world. 

There would, however, be limitations on where and how this technology could be applied. Concentrated-solar plants generally only work in very sunny areas, and you can’t ship heat over long distances. So industrial companies that want to take advantage of this process may have to build new plants near these solar thermal facilities, or vice versa.

“The middle of the desert is not typically an industrial hub,” says Julio Friedmann, a senior research scholar at the Center for Global Energy Policy and lead author of the report. 

Heliogen, based in Pasadena, California, still needs to demonstrate that the technology will work the way it claims, and at competitive costs. The company employs about 25 people but declines to disclose how much money it has raised.

A standard solar thermal plant achieves temperatures of a little below 600 ˚C to heat a medium like molten salt. That, in turn, is used to convert water into steam, which cranks the turbine that produces electricity.

Heliogen’s trick is to use high-resolution cameras and computer vision software to make small adjustments to each of its mirrors, aligning every solar beam onto a single, tiny point. 

The company has already built a small thermal solar plant in Lancaster, California, which has reached temperatures above 1,000 ˚C. Gross says it’s the first time such temperatures have been reached in a commercial facility, and the press release proclaims it a “singular scientific achievement.” But observers in the field note that other commercial and research groups have achieved similar temperatures, at least in limited experiments, and that in any case, the trickier part is developing systems that can withstand, retain, and transfer the heat.

Heliogen says it could use various mediums, including ceramic particles, to ship heat to the places where industrial processes are conducted. Certain single-step processes, however, like lime manufacturing, could be heated directly onsite by the solar mirrors. 

But the startup will also need to reach (and retain) temperatures above 1,000 ˚C to carry out some of the applications it mentions. Steel blast furnaces operate at around 1,100 ˚C, while cement kilns work at around 1,400 ˚C, the Center for Global Energy Policy notes. And splitting water to yield hydrogen would require temperatures around 1,500 ˚C, Heliogen says.

Gross says the technology “completely enables reaching that,” and that the company will work toward that goal next year. But a technological road map isn’t a demonstration.

Hydrogen, which is usually derived from natural gas, is used in a variety of industrial processes, including the production of ammonia for fertilizers. A clean form could reduce emissions in those sectors, work directly as a fuel, or be combined with carbon dioxide to produce more energy-dense fuels.

Given the geographic limitations, thermal solar isn’t likely to displace existing industrial operations anytime soon, Friedmann says. But it could provide a low-emissions alternative for additional growth in these sectors, particularly in areas with strong climate policies, he says.

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