An open-source flow battery kit

Original Article ↗ Hacker News Discussion ↗

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.