"Sand batteries"—large insulated silos of sand heated to hundreds of degrees—have emerged as a surprisingly low-tech answer to a high-tech problem: how to store surplus wind and solar energy as useful heat for hours, days, or even seasons. Rather than chasing round-trip electrical efficiency, these systems aim for very cheap €/kWh-thermal and integration with district heating and industrial processes. At Energy Solutions, we focus on the engineering boundary that matters: electricity-to-heat shifting at high temperature.
At its core, a sand battery is a large, insulated vessel filled with sand or similar granular material. Electric heaters raise the storage temperature when electricity is cheap. Heat is later discharged via air/HTF loops into district heating or industrial processes.
| Technology | Typical Temp. Range | Installed Cost (per kWh-th) | Use Case |
|---|---|---|---|
| Water tank | 40–95 °C | $2–$10 | Short-term building and district heating storage. |
| Molten salt | 250–565 °C | $20–$50 | CSP, some industrial heat. |
| Rock / sand bed | 200–800 °C | $10–$30 | District heating, industrial processes, seasonal concepts. |
A ~10 MWh-thermal sand battery connected to district heating should be read as a buffer (MWh-th = MW-th × hours), not as a seasonal supply. Delivered duration depends on network load.
Sand and rocks are cheap, widely available, and stable at high temperatures. Water is excellent for low-temperature storage; at atmospheric pressure it cannot exceed ~100 °C, while pressurised hot-water systems can run above 100 °C with added complexity. Molten salts work well but are more complex and often tied to CSP plants.
Dry sand is non-flammable. Key risks relate to hot surfaces and integration with heat exchangers and ducts; insulation and safety interlocks are essential.
Yes, particularly in networks already using electric boilers or large water tanks. Sand batteries can be added as another heat source, but temperature levels and control strategies must be engineered.