Heliogen, which was funded by Gates, created a solar oven — one capable of reaching temperatures that are roughly a quarter of what you'd find on the surface of the sun, if you happened to go there on a holiday.

The breakthrough means that, for the first time, concentrated solar energy can be used to create the extreme heat required to make cement, steel, glass and other industrial processes. In other words, carbon-free sunlight can replace fossil fuels in a heavy carbon-emitting corner of the economy that has been untouched by the clean energy revolution.

Bill Gross, Heliogen's founder and CEO said: "We are rolling out technology that can beat the price of fossil fuels and also not make the CO2 emissions. And that's really the holy grail."

Heliogen, which is backed by billionaire Los Angeles Times owner Patrick Soon-Shiong, believes the patented technology can reduce greenhouse gas emissions from industry. Cement, for example, accounts for seven percent of global CO2 emissions, according to the International Energy Agency.

"Bill and the team have truly now harnessed the sun", said Soon-Shiong, who also sits on the Heliogen board. "The potential to humankind is enormous. ... The potential to business is unfathomable."

The tech means that cement makers can dispense with fossil fuels.

Unlike traditional solar power, which uses rooftop panels to capture the energy from the sun, Heliogen is improving on what's known as concentrated solar power. This technology, which uses mirrors to reflect the sun to a single point, is not new.

Concentrated solar has been used in the past to produce electricity and, in some limited fashion, to create heat for industry. It's even used in Oman to provide the power needed to drill for oil.

The problem is that in the past, concentrated solar couldn't get temperatures hot enough to make cement and steel.

"You've ended up with technologies that can't really deliver super-heated systems", said Olav Junttila, a partner at Greentech Capital Advisors, a clean energy investment bank that has advised concentrated solar companies in the past.

That means renewable energy has not yet disrupted industrial processes such as cement and steelmaking. And that's a problem because the world has an insatiable appetite for those materials. Cement, for instance, is used to make the concrete required to build homes, hospitals and schools. These industries are responsible for more than a fifth of global emissions, according to the EPA.