Towards the end of 2022 I drafted this, consider it a work in progress - it was before I had joined forces with Daniel to form the Flow Battery Research Collective
Motivation for an open-source flow battery
This project aims to develop an open-source flow battery design suitable for mid-scale manufacturing by a well-equipped hackerspace or conventional machine shop. The design will incorporate principles from the appropriate technology movement and derisk suitable flow battery technologies from literature while communicating the science in lay terms. Inspiration is taken from the Piggott small wind turbine design and applied to stationary electrochemical energy storage.
The energy transition is underway and demand for sustainable, affordable, long-lasting energy storage capacity has never been higher. Despite large individual and community-level interest in flow batteries as a prospective technology that could address this demand, they have largely failed to live up to their hype. Furthermore, unlike lithium-ion, lead-acid, solar, and small wind technologies, flow batteries remain outside the capabilities of enterprising individuals to design and build their own energy infrastructure in an affordable fashion. This project plans to change that and democratize flow battery technology, moving specialized knowledge of their design and manufacture into the public domain.
Why are flow batteries worth developing?
Lead-acid and lithium-ion batteries are manufactured at the highest industrial scale. The main use case envisioned for this project is distributed stationary energy storage on the 10 kWh scale (roughly) for off-grid use, load shifting, and arbitrage. Lead-acid and lithium-ion are already fit for this purpose, so why bother with flow batteries? Briefly, lead-acid batteries are affordable, and sustainable by some metrics, but can require maintenance, and degrade within years of regular deep cycling requiring tedious replacement procedures. Lithium-ion is capable of more cycles at deeper depths-of-discharge than lead-acid with zero maintenance, but at greater initial expense and eventual capacity decline/replacement—and has concerns regarding supply chain sustainability. Also, lithium-ion has flammability risks whereas lead-acid does not.
Flow batteries, in this application of distributed, small-scale stationary energy storage, could offer a cheaper initial capital expenditure (vs. lithium-ion certainly), order of magnitude longer cycle/service life, and sustainable supply chain. This project is motivated by the promise of a cheap, long-lasting, sustainable, appropriate technology solution to distributed small-scale stationary energy storage.
Why you can’t buy a flow battery today
Flow batteries have existed for decades longer than the modern lithium-ion battery, yet a regular consumer or small enterprise cannot easily obtain a quote for one, much less go on to purchase one. Flow batteries have been highly publicized in recent years, and like hydrogen, fuel cells, fusion power, etc, many promoters of these technologies have overpromised and underdelivered. Flow batteries have not yet reached their promise of ultra-long-life, affordable energy storage.
Furthermore, the technology development deadlines allowed and the financial returns demanded by venture capital-backed startups in energy storage have largely led to the abandonment of the residential market, shifting focus to larger-scale commercial and industrial applications. This is partly due to the higher proportion of soft costs inherent to residential installations vs. commercial or industrial clients. Additionally, to install such a chemical battery in a residential setting would be subject to the strictest consumer health and safety regulations, pushing early-stage stationary storage companies away from the residential market and into telecoms and remote power applications as their “beachhead market.” Finally, the market “need” for grid-scale electrochemical energy storage is still developing, and some commercial attempts at flow batteries were simply ahead of their time and ran out of financing runway (see 90s and early 00s-era iron-chromium commercial attempts).
This failure to deliver as initially promised, however, is often not for technological failure—market timing and business strategy are key to proper execution, and firms attempting to commercialize emerging technology must cope with many non-technical destabilizing factors while simultaneously scaling up technological maturity. The market for portable electronics provided ample resources for industry to develop lithium-ion cells—both capital for R&D, and the relatively small energy capacity of portable electronics allowing for many more “widgets” to be produced. The instrinsic small size of batteries in portable electronics allowed the lithium-ion battery industry’s learning rate to benefit from an “economy of volume,” as discussed by [1]. Flow batteries, in contrast, have suffered the same fate as nuclear energy, in the sense that their respective industries have not been able to learn and improve over such a high number of iterations; the technologies have been low-volume, highly custom, and slow to build.
This figure from [2] shows how flow batteries are currently still design-intensive and customized - closer to a Type 3 technology than Type 1. This project will attempt to push towards a standardized open-source design for at least some of the component technologies.
Little academic research explores flow batteries above the benchtop scale. Promising technological developments often get sucked into universities’ Technology Transfer Offices for opportunities to license, spinout, and otherwise commercialize the work, even if the technology is extremely early-stage. Many flow battery startups then, in market-competitive, non-collaborative silos, simultaneously reinvent the wheels of process scaleup, stack design, shunt current control, etc. If they fail, the knowledge they gained often vanishes along with the company.
The goal of this present effort is to pick a suitable flow battery chemistry and develop it to the highest possible level in the most transparent fashion. An ideal outcome would be delivering an appropriate stationary energy storage solution into the lay, public domain—the Piggott small wind turbine design is an aspirational example, though may prove a difficult goal.
Which chemistry to pick? Applying some initial constraints
Rigorous justification (work-in-progress)
There are many flow battery chemistries to choose from. The concept of appropriate technology is used here to help downselect from the many chemistries and component options available. Some upfront design heuristics/principles result:
- safety is paramount: water-based, nonflammable electrolyte
- avoiding the requirement of a ion-exchange membrane
- no precious metals (ideally no need for catalysts at all)
- prioritizing elements in plentiful supply as defined by the European Chemical Society
- prioritizing passive over active design features
- designing for long cycle life
- designing for recyclability at end-of-life (compatability with the circular economy)
- minimize the use of heavy equipment for installation
- design for manufacturing by a regular machine shop
[3] provide a thorough review of flow battery chemistries and presents the available chemistries to choose from.
Incomplete list of explanations
Nonaqueous approaches are excluded under heuristic 1. Vanadium, the most common commercial chemistry, is not viable under heuristic 4. “Air-breathing” chemistries—such as zinc-air or iron-air, which utilize one or more oxygen electrodes—are also not possible without technically risky and sometimes precious-metal catalyst structures, so they are exluded based on heuristic 3. The iron-chromium chemistry is also excluded based on limited availability of chromium based on heuristic 4. Bromine and pure hydrogen are a safety concern.
References
*This concludes my draft motivation/manifesto for an open-source flow battery. It’s currently a side project of mine.
Citation
@online{pollard_smith2024,
author = {Pollard Smith, Kirk},
title = {Motivation for an Open-Source Flow Battery},
date = {2024-02-26},
url = {https://dualpower.supply/posts/motivation-OSHW-RFB/},
doi = {10.59350/fknwy-k7a54},
langid = {en}
}