But the startup Electrified Thermal Solutions is pursuing a far cleaner approach: tapping piles of bricks. The Boston-based company has developed a thermal battery system that uses electricity to heat metal-oxide firebricks for hours at a time. “That is hot enough to do the job of fossil fuels in virtually any application,” said Daniel Stack, Electrified Thermal’s CEO and co-founder. The thermal energy is then discharged by running air through the brick stacks that can be piped as hot gas directly into factories. Electrified Thermal is poised to start delivering its first units to customers’ facilities at the end of this year or in early 2027, he added.