Rondo [USA] heat battery
https://rondo.com/how-it-works
Nothing is 100% efficiency, but if it can get to the high 90%, that’s awesome.
This is something that you could build for your farm or house to keep the barn or house warm instead of the grid.
From the website:
RHB100
Storage: 100 MWh
Discharge: 7 MWt
Charge: Up to 20MWac
Heat Delivered: Continuously 24/7
Emissions: Zero
Not exactly sized for farm or house ...
From the description, maybe possible to heat tons of bricks for a large farm?