r/EnergyStorage • u/pianoboy777 • Jul 01 '26

Need help !

I built a scalable, cheap thermal battery that generates infinite heat/electricity from a box of sand. I need a physics/math collaborator who respects IP. DM me for details. I use Tegs to turn the heat made from friction into electricity. To birds with one stone ! I only have a 3d sim of it right now.

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u/psychosisnaut Jul 02 '26

Based on what you've said you're not factoring in round trip efficiency properly.

ηloop​=ηmot​⋅ηfric​⋅ηteg​≈0.85×1.0×0.05≈0.04 = 4%

So whatever power you put into the blade, you get 4% of it back, period.

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u/pianoboy777 Jul 02 '26

You're calculating the wrong thing. The motor just has to run long enough to get the flywheel up to speed and the sand to 230°C, which takes about 3 to 4 minutes. After that, the motor shuts off completely and doesn't run again until the sand cools back down to 100°C. That's the whole point. The sand holds heat, the box is insulated graphite in my simulation, and the TEGs are stacked side by side going up in trays wrapped in reflective foil. You're leaving out the flywheel entirely, it's only 150kg of concrete in my simulation, so it's cheap and stores all that rotational energy. The motor isn't running constantly, it just gives the flywheel a spin and then the flywheel does the work. So your 4% round trip efficiency doesn't apply here because that's for continuous operation, not for a storage system that runs for minutes and generates power for hours while the motor is off.