Matt Ferrell from Undecided investigates the emerging residential market for thermal energy storage (TES) — batteries that store energy as heat rather than electricity — spotlighting sand and water-based systems now entering homes.
Key insights:
Sand is an ideal thermal medium due to its low specific heat, high density, non-toxicity, and non-flammability, with commercial systems achieving round-trip efficiencies above 90%.
Latvia’s Batsand buries a 40 cubic metre underground sand tank (similar to a septic system) capable of storing 10,680 kWh, while the Netherlands’ NEStore offers a compact water-based unit from €5,000–6,000 with a 95% efficiency rating.
TES excels at storing heat but drops to 50–70% efficiency when converting back to electricity, making it best suited as a complement to chemical batteries rather than a replacement.
The US Inflation Reduction Act offers a 30–40% tax credit on TES devices, potentially accelerating residential adoption as renewable energy makes electric heating increasingly cleaner than gas.