An open-source flow battery kit

Original Article ↗ Hacker News Discussion ↗

An open‑source DIY flow battery kit is prompting debate over whether such systems can move beyond classroom experiments toward practical home or grid‑scale energy storage. Commenters compare its low-voltage, low‑power prototype to cheap lithium‑ion packs, but note that flow batteries trade energy density for advantages like scalability, long life, low self‑discharge, and improved fire safety. The project’s creators position the kit as a research and teaching platform to explore new chemistries and designs that might one day yield affordable, non‑toxic storage for solar and microgrids.

Scope and Purpose of the Kit

  • Many view the kit primarily as an educational and R&D platform, not a practical battery yet.
  • Defenders argue this is a deliberate first step: validate chemistry and membranes at small scale, then build larger cell stacks and tanks.
  • The current design uses positive-displacement pumps, so it’s explicitly not optimized for real-world storage; later versions would change this.

Performance, Efficiency, and Scalability

  • Reported energy: ~18 Wh per liter of electrolyte; some compare this unfavorably to cheap 18650 Li-ion cells with far higher energy and power density.
  • Others note flow batteries are intended for “high energy, low power, low cost” grid/home storage, not mobile or high-power use.
  • Internal resistance and power output are key concerns: critics doubt usefulness if large total kWh can only deliver low watts; proponents respond that many building-scale uses need low C-rates.
  • Coulombic efficiency with a paper-based microporous separator is ~85–90% at certain current densities; pumping losses in well-designed flow systems are cited as ~1–2% of round-trip energy.
  • Power (kW) scales with cell area/stack count; energy (kWh) scales mainly with tank volume, letting them be sized independently.

Chemistry and Materials

  • Current chemistry is zinc–iodine: chosen for availability, oxygen tolerance, and low hydrogen evolution; iodine cost and regulatory attention are noted as potential issues.
  • Iron-based and other low-cost chemistries (quinones, common elements) are discussed as promising but challenging (e.g., hydrogen evolution, pH and deposition issues).
  • Membranes are a major cost/complexity driver: state-of-the-art ion-exchange films can be very expensive; cheap microporous separators are attractive but leakier.

Safety and Use Cases

  • Flow batteries are repeatedly praised for safety: a puncture leads to leaking saltwater-like solutions, not thermal runaway fires.
  • Comparisons to Li-ion highlight that some chemistries (NMC) are fire-prone, while others (LFP) are much safer.
  • Suggested applications include home backup, microgrids, farms, and long-duration or even seasonal storage, though some argue many competing storage technologies exist.

Commercialization, Openness, and Frustration

  • Commenters lament slow deployment of commercial flow batteries and investor reluctance to fund scaling.
  • The open-source nature of this project is seen as a way to “democratize” experimentation, lower R&D barriers, and potentially enable future breakthroughs.
  • Some remain skeptical that DIY flow batteries will ever beat industrial Li-ion or other storage options, but others emphasize that many successful technologies began as “toys” and student projects.