Finnish City Inaugurates 1 MW/100 MWh Sand Battery
Economics and ROI
- Several commenters note no public return-on-investment numbers; some infer that if ROI were clearly strong, it would be advertised.
- Others counter that this is effectively a pilot/R&D project, so strict short‑term ROI is less relevant, and externalities (reduced fuel use, pollution, know‑how, resilience) matter.
- Discussion on expected returns: investors often want ~10%/year; a 50‑year payback is poor financially, but may still be socially/environmentally worthwhile.
- Concern that as more storage is built, price spreads between low- and high‑price hours will narrow, potentially squeezing future operating margins.
Why Sand (Actually Crushed Soapstone) Instead of Water
- Core rationale: high-temperature storage. The system heats the material to ~500–600 °C, impossible with liquid water without extreme pressures.
- Water has ~3x the specific heat of sand/rock but can only be heated to ~100 °C (practically) versus hundreds of degrees for rock/concrete, so volumetric energy capacity favors solids at high temperature.
- Sand/soapstone are chemically very stable in this range and non-corrosive; water at high temperature/pressure brings serious safety, corrosion, and vessel-cost issues.
- Sand doesn’t convect, is a decent insulator itself, and “mostly stays where you put it,” simplifying containment and reducing catastrophic-release risk compared to superheated water.
Efficiency, Use Case, and Grid Integration
- Clarification: this is thermal storage, not primarily for electricity. The cited ~90% round-trip efficiency refers to heat-in/heat-out with good insulation.
- Converting stored heat back to electricity would be much less efficient (~40–45%), far worse than batteries. Versus heat pumps, overall electrical‑to‑usable‑heat efficiency may be closer to ~15%.
- Supporters argue that the main value is aligning cheap surplus renewable electricity with winter heat demand via district heating, not regenerating power.
- Some contrast with lithium plus heat pumps: far higher thermodynamic efficiency, but much higher material and capex costs; sand is simple, cheap, and often local.
Scale, Duration, and District Heating Context
- Rated 1 MW / 100 MWh: at full output that’s ~4 days of heat; with lower average draw it buffers up to a couple of weeks, seen as useful for weather-related swings, not seasonal storage.
- Rough back‑of‑envelope comparisons suggest tens to perhaps low thousands of well‑insulated homes, depending heavily on climate and building stock.
- The system relies on existing district heating networks; Finland already has extensive district heating and prior large-scale water-based heat stores, including underground cavern storage.
Engineering, Safety, and Implementation Details
- Heat is moved via hot air through loose granular material (more like crushed soapstone than beach sand), potentially using fluidization techniques for better heat exchange.
- Commenters note advantages of above-ground silos (cheaper construction, easier access) versus excavated underground stores, though underground water tanks also exist in the region.
- Longevity: the sand/stone itself should last essentially indefinitely; real lifecycle limits come from piping, pumps, heat exchangers, and controls, which must be maintained or periodically replaced.
Terminology, Units, and Politics
- Debate over calling it a “battery”: several argue any device storing energy for later use fits the term, regardless of whether it’s electrical, thermal, mechanical, etc.
- Power/energy are expressed in MW/MWh, consistent with SI usage in Europe; some side discussion on why kWh dominates over joules and why BTU is largely avoided outside the US.
- Some pushback on the article’s jab at a skeptical YouTube commenter as “MAGAlomaniac”; critics see it as unnecessary politicization that discourages legitimate questions about ROI.