Giant 'sand battery' holds a week's heat for a whole town

Overview of the sand battery concept

• Thread discusses large sand-based thermal storage used with district heating, storing excess/cheap electricity as high‑temperature heat (up to ~600°C) for later use.
• It’s framed as “old tech in a new configuration”: resistive heating, insulation, and inert granular material in a big silo.
• Several commenters see it as particularly well-suited for town- or grid-scale heat storage, less so for individual homes where better insulation and smaller hot‑water tanks may be more practical.

Why sand instead of water or other media

• Water has much higher specific heat capacity and is cheaper and easier to pump.
• However:
  • Water is limited to ~100°C in unpressurized systems; sand can go to 500–1200°C, enabling higher energy density per volume via temperature range.
  • High‑temperature water needs pressure vessels and serious safety engineering; superheated water can explode and corrodes/rots plumbing.
  • Sand (or crushed rock/soapstone) is inert, non-pressurized, doesn’t freeze or boil in normal operation, and has low maintenance.
• Commenters note sand’s lower thermal conductivity: it loses heat more slowly to the environment but requires careful pipe layout to charge/discharge.

Comparisons to other storage approaches

• Ice/water “cold batteries” (e.g., IceBear) and chilled-water tanks: good for shifting A/C load but mostly an energy cost optimization; may face maintenance issues and competition from batteries and PV.
• Molten salt in CSP, graphite/bricks, aluminum-based blocks, Feolite, and building thermal mass (masonry, phase change materials) are discussed as related or alternative thermal storage.
• Water tanks and underground/soil heat storage (seasonal) are already used in some communities and experimental homes.

Economics, grid, and use cases

• Sand storage is seen as cheap per kWh of heat, especially when filled with industrial byproducts (e.g., crushed soapstone) that might otherwise incur disposal costs.
• Best fit is storing surplus/negative-priced or otherwise wasted renewable/industrial heat, not maximizing round‑trip electric efficiency.
• Some argue that PV+batteries or PV+heat pumps can outcompete solar-thermal in many residential cases; others highlight lifecycle and ecological advantages of direct thermal systems.

Concerns, open questions, and broader context

• Questions raised about heat losses, turbine integration (for electricity), cyclone separators and grit in turbines, and sand sourcing in some regions.
• Discussion touches on European prevalence of district heating, older housing stock, higher energy costs, and policy as reasons such systems advance faster there than in much of the US.