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Firebrick thermal energy storage could reach 170 GW in the U.S. by 2050
(pv-magazine-usa.com)
This is a most excellent place for technology news and articles.
How else would you heat up a huge pile of bricks? This is for industrial applications or grid scale heating systems. They basically all use hot air.
They use hot air warmed by gas burners.
Since we're using electricity here, and this was mentioned in the study linked elsewhere, they used ceramic heaters.