Rondo’s “brick toaster” heat storage system is 98% efficient, and stores cheap renewable energy for industrial use at 20% the cost of an electrochemical battery. Rondo Energy

These stoves are full of plain ol’ bricks, made out of plain ol’ clay, sometimes with a bit of sand in there, but certainly nothing special in terms of materials. Nothing toxic, nothing that decays over time. These bricks will still be storing heat just as well in 40 or 50 years’ time, when chemical batteries have gone through several generations of complex recycling.

Source: “Brick toaster” aims to cut global CO2 emissions by 15% in 15 years