The trick is to use computer vision (also known as AI) to align a wide variety of mirrors as they reflect sunlight on a lone target. This allows for the kind of accuracy that was not possible until now.
Much work remains to be done before technology enters the real world. Heliogen reached record levels of heat on its factory's first day of operation, said Bill Gross, the company's founder. CNN. Although impressive, it does not immediately translate into a practical solution.
However, the implications are huge. As Gates noted in the announcement, industrial processes account for over 20% of emissions. If technology can reduce even a portion of these emissions, it can help keep global warming under control. Heliogen also has bigger ambitions. Ultimately, it expects to reach temperatures of 2,732F, which would be hot enough to create hydrogen and synthetic gas. At this point, you would use clean energy to produce more clean energy – there would be relatively little need to generate emissions in the first place.