CO2 batteries that store grid energy take off globally

Original Article ↗ Hacker News Discussion ↗

Round-trip efficiency & cost claims

  • Commenters find 75% round-trip efficiency from company/theory, comparing favorably to utility lithium systems (82%) and pumped hydro (~79%).
  • Some initially assume it must be much worse (25%), but others point out stored compression heat is recovered, not wasted, explaining the higher figure.
  • Many stress that for curtailed solar/wind, efficiency is secondary; capex per kWh stored and lifetime dominate economics.
  • The “30% cheaper than Li-ion” claim is viewed skeptically, especially given fast lithium cost declines and emerging sodium-ion prices.

Comparison with lithium / sodium batteries and materials

  • Debate over lithium scarcity: several argue lithium (and especially LFP chemistries) are abundant and recyclable; nickel and cobalt are more limiting, though LFP and sodium chemistries avoid them.
  • Sodium-ion is cited as potentially much cheaper and safer, with wide temperature tolerance; others argue it will take many years to truly undercut LFP at scale.
  • Lithium/LFP advantages: modularity, very low maintenance, long cycle life (thousands of cycles, decades at daily cycling), and strong recycling value.
  • CO2 systems may win on fixed-plant longevity and cheap “energy capacity” (vessels + bags) but lose on complexity, moving parts, and maintenance.

Use cases, duration, and system role

  • Many see this as complementary, best for multi‑hour to multi‑day shifting near large steady loads (e.g., data centers), not seasonal storage.
  • Others argue we already have good solutions for 4–8 hours (batteries) and the real gap is months‑scale storage (hydrogen, thermal, fuels).
  • There’s detailed discussion of separating “power capacity” (compressors/turbines) from “energy capacity” (tank/bag volume): this architecture scales cheaply in energy but not in power, favoring long-duration storage.

Safety and environmental concerns

  • Major thread on dome rupture: 2,000 tons of CO₂, heavier-than-air, could pool and suffocate nearby people; Lake Nyos is referenced.
  • The company’s claimed 70 m safety radius is widely doubted; topography, wind, and failure mode (small leak vs big tear) matter.
  • Suggestions include gas detectors, oxygen masks, partitioned domes, and possibly underground or dispersed structures.
  • Clarified that this is storage, not carbon sequestration; the CO₂ is “one-time” working fluid, not a net sink.

Why CO₂ instead of air or other gases

  • Key advantages mentioned:
    • Liquefies at relatively mild pressures/temperatures, enabling dense, cheap storage.
    • Supercritical/phase-change behavior well-suited to this thermodynamic cycle.
    • Lower pressures and simpler tanks than compressed air; safer than combustible gases.
  • Air or nitrogen would require much colder conditions or far higher pressures to get similar behavior.

Scale, maintenance, and practicality

  • Likely unsuitable for home/“washing machine” scale: turbines and heat systems are more efficient at large scale; small units would spin very fast and have high parasitic losses.
  • Concerns about long-term operations: gas containment, mechanical wear, thermal storage losses over time, and real-world efficiency across thousands of cycles.
  • Some see strong synergy with district heating/cooling or data centers, where “waste” heat and cold from the cycle can offset cooling loads.

Critique of coverage and open questions

  • Multiple commenters criticize the article for weak or missing numbers (capex, lifetime O&M, real field efficiency), confusing power vs energy units, and a “salesy” tone.
  • Unclear points flagged: actual all‑in $/kWh vs Li-ion and sodium; degradation of performance with longer storage duration; realistic safety modeling of large CO₂ releases; and lifecycle CO₂ impact given “purpose-made” gas.