What business have they gotten into? Thermal storage of grid energy with a > 50% round trip efficiency. It heats sand with a compact resistive heater, stores the sand in insulated silos, and recovers the energy by a Brayton cycle system with a really interesting and compact fluidized bed heat exchanger. Storage capacity is sized for 100 hours of operation. Not just overnight, but four days.

https://www.babcock.com/home/about/corporate/news/babcock-wi...

Westinghouse is also doing thermal grid storage now. Pumped TES can have a round trip efficiency > 60%.

https://www.energy-storage.news/nuclear-power-company-westin...