The trick is the use of computer vision (aka a form of AI) to align a large array of mirrors as they reflect sunlight on a solitary target. That allows for the kind of accuracy that hasn't been possible until now.
There's still a lot of work to go before the technology enters real-world use. Heliogen achieved the record heat levels the first day of its plant's operation, company founder Bill Gross told CNN. While impressive, it won't immediately translate to a practical solution.
Nonetheless, the implications are huge. As Gates noted in the announcement, industrial processes are responsible for over 20 percent of emissions. If the technology can cut even a portion those emissions, that could help keep global warming in check. Heliogen has greater ambitions, too. It ultimately hopes to reach temperatures of 2,732F, which would be hot enough to create hydrogen and synthetic gas. At that point, you'd have clean energy being used to produce more clean energy -- there would be relatively little need to generate emissions in the first place.