Europe's deepest mine to become giant gravity battery
Europe’s deepest mine in Finland is being proposed as a “gravity battery,” using sand or other mass raised and lowered in its 1.4 km shafts to store and release electricity. Commenters weigh the concept against alternatives like pumped hydro and lithium batteries, questioning its poor energy density, unclear economics, and technically illiterate media claims (e.g., confusing MW with MWh), while noting that existing mine infrastructure and grid connections could lower costs. There is cautious interest in repurposing abandoned mines and offsetting decommissioning expenses, but many remain skeptical that solid-weight gravity storage can scale beyond small pilot projects or compete with more mature storage technologies.
Concept and appeal
- Many find gravity storage in an existing deep mine more sensible than purpose‑built towers: the shaft already exists, grid connections are often in place, and it could provide post‑mining economic activity.
- Some note gravity storage need not be vertical shafts; hillside rail/funicular systems and “gravity trucks” with regenerative braking are cited as analogous ideas.
Scale, physics, and engineering limits
- Multiple commenters do back‑of‑the‑envelope calculations: potential energy is low per unit mass and height, so huge volumes of sand/rock are needed for meaningful storage.
- Example figures discussed:
- 1 m³ of dry sand raised 1,400 m ≈ 6.1 kWh.
- 10 m³ of sand over 1,400 m yields only ~61 kWh, implying many parallel lines or very wide shafts for MW‑scale power.
- 1,000 kg of lead at 1,500 m ≈ 4 kWh, whereas 1,000 kg of lead‑acid batteries store ~25 kWh.
- Concerns include rope/cable strength, wear on moving parts, humidity and abrasion in shafts, and complex bucket/hand‑off mechanisms.
Economics vs alternatives
- Strong skepticism that solid‑weight gravity systems can compete with:
- Pumped hydro, which one commenter estimates to be roughly an order of magnitude cheaper per Wh than lithium batteries.
- Grid‑scale batteries (e.g., Megapacks) that already reach GWh and hundreds of MW.
- Some link analyses claiming all non‑hydro gravity schemes are far more expensive than batteries; others argue those critiques underplay the benefit of using existing mines.
- The pilot’s reported scale (≈2 MW power, probably only a few MWh) is viewed by several as trivial and possibly uneconomic; future designs of 20+ MWh are mentioned but not detailed.
Mines, grid ties, and water issues
- Mines are already large power consumers (multi‑MW hoists, ventilation, processing), so commenters argue grid interconnects are often adequate or close.
- Dewatering energy and long‑term flooding risks are raised; flooded mines historically drove the development of steam pumps.
- Using water instead of sand is debated: easier to pump but may destabilize rock and require costly waterproofing; sand may be cheaper to handle at very large capacities.
Framing, hype, and ambiguity
- Many criticize media and marketing for:
- Confusing power (MW) and energy (MWh), making claims like “2 MW of energy”.
- Quoting global “70 TWh potential” without clarifying it’s storage capacity, not generation or duration.
- Some see the project as an interesting testbed; others predict it will be quietly written off in a few years.