Here is a contrarian idea that keeps gaining ground: the cheapest way to store energy from the grid may not be a battery at all. It may be a pile of hot bricks. A 2025 Rondo Energy patent describes the industrial version of that idea, and the economics behind it are surprisingly compelling.
The mechanism could not be simpler in concept. When electricity is cheap and abundant — a sunny, windy afternoon with prices near zero — use it to heat a large mass of inexpensive, heat-tolerant material (Rondo famously uses brick) to very high temperatures. The heat sits there, well insulated, for hours or days. When you need energy back, draw the heat out: directly as industrial process heat, or to boil water into steam that drives a turbine for power. You have stored electricity as heat and spent it as heat or power.
Rondo's grant US12480719B2, "Thermal energy storage system for simple and combined cycle power generation," ties the stored heat to turbine-based generation — the steam-and-turbine half of the system. The reason this is interesting is what it competes with. A lithium battery is brilliant at storing and returning electricity. But a huge fraction of the world's energy demand is not electricity — it is industrial heat, for making steel, cement, chemicals, food. Delivering that heat from a battery means converting electricity to heat anyway, at a loss.
Thermal storage skips the middleman. If the end use is heat, store heat. Brick is one of the cheapest materials imaginable, it tolerates extreme temperatures, and it does not degrade with cycling the way battery chemistry does. For the specific job of soaking up cheap renewable power and delivering high-temperature heat to industry, hot bricks can undercut batteries dramatically on cost per unit of energy stored.
The honest boundaries: thermal storage returns heat efficiently but converting it back to electricity incurs the usual turbine losses, so it is not a direct rival to batteries for grid power services — it is a rival for the enormous, often-ignored market of industrial heat. A 2025 patent is a claim on a system, not a record of deployed plants. But it captures one of the most clarifying insights in the transition: match the storage to the end use, and for heat, the humble brick may beat the battery.