Open source hardware: open kit for redox flow batteries

In a world that is urgently looking for sustainable energy storage solutions, lithium-ion batteries dominate the market. They are compact, powerful and ecologically problematic. This is because the mining of lithium is harmful to the environment, it is almost impossible to repair the cells and after a few years, high-tech becomes hazardous waste. But there is an alternative: FLOW batteries. Not only could they be more sustainable in the future, they could also be built by almost any reasonably talented hobbyist.

Redox flow batteries (RFBs) are considered a promising solution for long-term energy storage. Their functional principle differs fundamentally from conventional batteries: Instead of storing energy in solid-state cells, RFBs use two liquid electrolytes that are stored in separate tanks and pumped through an electrochemical cell during operation. A redox process takes place in this cell in which electrical energy is stored or released. The separation of energy and power components allows the capacity to be scaled independently of each other by the tank size and the power by the cell surface area. In addition, due to their modularity, they are potentially maintainable, repairable and even transformable, meaning they can be adapted to changing circumstances.

However, although the technology would in principle be well suited to storing large amounts of energy over long periods of time – i.e., exactly what a power grid with a high proportion of wind and solar energy needs –, it has hardly been used in everyday life to date. There are many reasons for this: high material costs, complicated system technology and the size of the systems. Various prototypes have often failed in practice due to detailed technical problems. Nanotechnology specialist Dr. Daniel Fernandez and Kirk Smith, a doctor of electrochemical engineering, criticize that the companies behind these prototypes then take the experience gained with them into insolvency.

To change this, they have founded the Flow Battery Research Collective (FBRC), an open-source hardware project that aims to democratize access to RFBs. “Our goal is to open up the infrastructure for the operation of FLOW batteries,” say the founders. Their project aims to show that RFBs can also be researched and replicated using simple means – far away from large academic laboratories or industrial pilot plants.

Research gaps: What is still holding RFBs back today

Although the technology has been known since the 1960s, there are still some challenges. These arise above all when the systems are scaled up. The battery of pipes, tanks, and pumps must be very tight over a long period of time, the materials must be chemically resistant, and the liquids must not leak, as they are potentially toxic chemicals. Ultimately, these are plumbing problems, but they are technically very challenging, according to the founders of FBRC. There are also other challenges. For example, the electrolyte must not run backwards, as this would cause short circuits. Most patents in the field of RFBs would address this problem.

Another problem is the electrolytes. Chemists are working on their stability and availability. In practice, vanadium redox flow batteries (VRFBs) are the most widely used, but vanadium is expensive, and its price is volatile. Alternative materials such as organic molecules or iron-chromium systems promise cost reductions, but suffer from issues such as low solubility, instability, or side reactions such as hydrogen evolution. Non-aqueous systems offer higher cell voltages, but bring with them new risks such as flammability and high viscosity.

In addition, there is a lack of reliable data on long-term use. Many companies “start with great promises and go bankrupt before we know what caused them to fail”, criticizes the FBRC. Valuable knowledge is lost because proprietary research is not published. Yet open exchange would be essential to achieve progress – for example, through shared test results on material combinations or sources of error in the system architecture.

Why open-source hardware can help

A key obstacle to the further development of RFBs is that the technical infrastructure behind them is difficult to access. The FBRC wants to change this. Since 2023, Fernandez and Smith have been developing an open-source kit that contains all the components needed to build a simple FLOW battery. They attach particular importance to “readily available materials, even outside Western countries”. For example, they use photographic paper as a separator – a cost-effective solution with a long tradition, even if it is not maximally efficient.

This approach opens up new perspectives: “FLOW batteries provide power to the user because they can be maintained, repaired and transformed. They should therefore also exist as an open-source solution.” This means that not only well-funded companies or academic research units should have access to this technology, but also committed inventors, students, teachers and independent researchers.

In order for RFBs to develop their potential as a key technology for sustainable energy systems, more innovation cycles and an open exchange on conditions for success are needed. An open platform on which experiments, designs, and data are freely available could massively accelerate development.

The FBRC is intended to show that this is not a distant ideal, but concrete practice, according to those responsible. By the end of 2025, they plan to develop a larger system in the kilowatt range – always with the aim of making it easier for others to get started. “In principle, anyone can come along and turn it into a commercial product. We would like that.”

If redox flow batteries are to be available on the DIY market one day, we need more projects like this – open, documented, cooperative. Not just for research, but for a fairer, sustainable energy system of the future.

(vbr)