Iron as an inexpensive storage medium for hydrogen

Original Article ↗ Hacker News Discussion ↗

Overall concept and claimed advantages

  • System reduces iron oxide with hydrogen in summer, then re‑oxidizes iron with steam in winter to regenerate hydrogen and heat.
  • Main selling points in the thread: cheap, abundant, non‑toxic materials; solid, inert long‑term storage; usable waste heat (e.g., district heating); potential for campus‑scale demonstration.

Efficiency, thermodynamics, and losses

  • Reported lab round‑trip efficiency is ~11%, with theoretical values up to ~79% if scaled and well‑insulated.
  • Multiple commenters highlight many loss stages: electrolysis (60–80% efficient), iron-oxide reduction, hydrogen release, and final conversion to electricity or motion.
  • Some back‑of‑the‑envelope chains suggest overall efficiency could fall well below 50%, especially when including compression, piping, and conversion.
  • Others argue efficiency matters less if input electricity is very cheap or surplus; heat co‑use (district heating, industrial processes) could improve system value.

Comparison with other storage technologies

  • Batteries: Seen as far more efficient; sodium‑ion and sodium‑sulfur mentioned as potentially very cheap for grid storage. Critics say an iron/hydrogen path starting at ~30–60% net efficiency is non‑competitive for anything but seasonal storage.
  • Seasonal storage: Some argue this competes with water reservoirs or synfuels, not daily‑cycling batteries.
  • Hydrogen storage: Compressed H₂ tanks have near‑perfect storage efficiency but require high pressure and face leakage and embrittlement; supporters of iron note its safety and density.
  • Related concepts: iron‑air batteries, direct reduced iron as fuel, peroxide, ammonia, metal hydrides, “baking soda” hydrogen storage, and synthetic hydrocarbons (methane, propane, kerosene) are all discussed as alternatives with their own trade‑offs.

Economics, “free” energy, and demand elasticity

  • Debate over whether “free” summer solar will really exist: some expect highly elastic demand (smart appliances, flexible industry) to absorb cheap power so prices rarely hit zero.
  • Others think overbuild will still create long cheap periods, where even lossy storage or energy‑intensive industries (e.g., smelting, compute) make sense.
  • Question raised whether simply adding more PV (especially where winter drop is modest) might be cheaper than complex hydrogen‑based seasonal storage.

Safety and practical issues

  • Fine iron powder can self‑heat and pose fire risks; direct reduced iron is regulated as a hazardous bulk cargo.
  • Hydrogen leakage, material embrittlement, and high‑pressure infrastructure are ongoing concerns.
  • Some see handling dense solids at very large scale as a logistical challenge; others note iron oxide can be stored cheaply “in a hole in the ground.”

Broader system debates

  • Disagreement over the role of hydrogen at all in the energy system; some view it as inherently inefficient, dangerous, and historically unsuccessful at scale.
  • One subthread argues nuclear could provide reliable baseload without such storage complexity; others counter with current nuclear cost, deployment time, and safety/approval barriers.
  • General consensus that no single storage technology will solve intermittency; a “hierarchy” of options (batteries, thermal, chemical, reservoirs, demand‑shifting) is likely needed, but the precise niche for iron-based hydrogen storage remains unclear.