How Unbound Potential rethinks flow batteries
To play its part in the fight against climate change, Germany must become climate-neutral by 2045 and secure its energy supply exclusively from renewable sources. The pressure to act has also increased as a result of the Ukraine war, as gas has lost its appeal as a transitional technology and - and Germany's independence in terms of energy supply has become massively more important. In view of these new existential threats, the increasingly frequent natural disasters and extreme weather events, the share of renewable energies must rise sharply over the next two decades. At the same time, baseload nuclear and coal-fired power plants are to be completely taken off the grid by 2038 and replaced by wind and solar power.
In this context, long periods without significant solar and wind energy potential pose a particular challenge, so-called dark lulls. During these dark lulls, the output of wind and solar power is only a fraction of the usual average output, so that the energy demand cannot be met even with the help of load management and short-term storage. In Germany, several dark lulls with a length of more than 48 hours occur per year, but in individual cases they can also last for up to ten days. During these periods, long-term energy storage, i.e. energy storage with a storage duration of at least ten hours, plays an essential role in ensuring the stability of the power grid. In addition, long periods usually extend through the winter, during which energy generation will lag behind energy demand in the future.
Long-term energy storage is a central building block for energy autonomy and the achievement of climate targets, and at the same time a growing multi-billion market, which, however, can only be served inadequately with the currently market-ready technologies.
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The Challenge: Store energy and efficiently provide power for more than ten hours without using critical raw materials.
The Challenge will identify breakthrough technological approaches that enable long-term, efficient, and cost-effective energy storage. Key factors are raw material and system costs, self-discharge, storage efficiency, lifetime, energy density, and technical and economic scalability of the project idea.
Teams participating in this Challenge are fully challenged. SPRIND therefore provides intensive and individual support. This includes funding the teams with up to €1 million in Stage 1 of the Challenge and up to €3 million in the 2nd and final Stage. In order to help the teams develop their full potential, SPRIND provides them not only with financial support but also with a coach who accompanies, advises and networks the work of each team.
To enable the teams to concentrate fully on their innovations, we provide funding quickly and unbureaucratically. At the end of the first stage of the Challenge, after one year, the jury decides on the basis of interim evaluations which teams will continue to participate in the Challenge. As finalists, these teams are given the opportunity to drive their project forward for another year and a half and to comprehensively demonstrate their breakthrough.
Thinking one step further: Ideas with the potential for a breakthrough innovation must be brought to market to benefit us all - promising projects in this sense can therefore continue to be supported by SPRIND after the Challenge has ended.
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In November 2023, the expert jury selected the participants for the second and final stage of the 'Long-Duration Energy Storage' challenge. Four teams will each receive up to 3 million euros over the next 18 months for the further development of their long-term energy storage technology.
Reverion
“The new energy world is binary,” says Felix Fischer: "There is either a surplus of electricity or a shortage.” When the sun shines, electricity prices fall; when it doesn't, prices rise, and the rapid provision of stored energy becomes increasingly important.
HalioGen Power
Thin walls protect redox flow batteries from short circuits while allowing ion exchange between the electrolytes: Membranes have been used in batteries for decades. But this could change.
Ore Energy
Iron, air and water: Ore Energy is using these three elements to revolutionise the battery industry. The team's iron-air battery is designed to provide 100 hours of power and to step in when no renewable energy is available.
Unbound Potential
Radically simple design – that's the secret behind Unbound Potential's new flow battery. The company is working on a membrane-less battery to rival lithium-ion batteries.
Science Youtuber Jacob Beautemps introduces the Challenge teams at Breaking Lab
The Jury
Gitanjali DasGupta
Sebastian Scholz
Anna Grevé
Pasquale Salza
Pilar Gonzalez
Nick de la Forge
Do you have any questions about the Challenge? Write to us at challenge@sprind.org.
Radically simple design – that's the secret behind Unbound Potential's new flow battery. The company is working on a membrane-less battery to rival lithium-ion batteries.
Membraneless batteries save costs and are more efficient, but there are challenges. “The most trivial problem, that the liquids mix without a separating membrane, can be solved by using two immiscible liquids – comparable to oil and water,” explains David Taylor, CEO of Unbound Potential.
Membraneless batteries save costs and are more efficient, but there are challenges. “The most trivial problem, that the liquids mix without a separating membrane, can be solved by using two immiscible liquids – comparable to oil and water,” explains David Taylor, CEO of Unbound Potential.
“When you have a battery, which is a closed system, and you pump liquid into one side, you increase the pressure in the system. This increase in pressure automatically causes liquid to leak out the other side. But you have no control over exactly how much anolyte and how much catholyte is pushed out,” says Taylor, explaining the problem. “If the flow resistances at the outlet are not perfectly matched to the viscosity of the fluid, which can change rapidly with temperature, there may be slightly more catholyte coming out than going in – and the interface shifts accordingly, meaning the battery no longer works optimally.”
“The real challenge in scaling up membraneless systems is that you need active control loops to control the inflow and outflow rate of each fluid in each cell.”
Flow batteries work by having two different electrolyte liquids flow continuously into the battery, where they are either charged or discharged depending on the charging process, and then flow out of the battery. “You have an inflow rate and an outflow rate for two fluids. That means you have four control variables per cell,” explains Taylor. Among other things, a membrane ensures that the ratio between the two electrolyte liquids remains the same. However, if the membrane is missing, exactly the same amount of electrolyte liquid must flow in and out of the battery so that the invisible separation layer between the liquids in the battery does not shift.
Flow batteries work by having two different electrolyte liquids flow continuously into the battery, where they are either charged or discharged depending on the charging process, and then flow out of the battery. “You have an inflow rate and an outflow rate for two fluids. That means you have four control variables per cell,” explains Taylor. Among other things, a membrane ensures that the ratio between the two electrolyte liquids remains the same. However, if the membrane is missing, exactly the same amount of electrolyte liquid must flow in and out of the battery so that the invisible separation layer between the liquids in the battery does not shift.
According to Taylor, effective and active control of the inflow and outflow rates of the electrolyte fluids is not feasible on a large scale. That's why Unbound Potential is daring to do something revolutionary: “We don't measure, control or regulate anything. We have a completely different design concept that takes advantage of the fluidic boundary conditions to ensure that the same amount of fluid always flows in and out automatically,” says Taylor proudly.
This passive concept will be a game changer for membraneless flow batteries: “The idea behind Unbound Potential is to build the simplest stationary storage system possible, because we believe that simplicity and robustness are key criteria for the scalability of the technology,” says Taylor.
This passive concept will be a game changer for membraneless flow batteries: “The idea behind Unbound Potential is to build the simplest stationary storage system possible, because we believe that simplicity and robustness are key criteria for the scalability of the technology,” says Taylor.
Unbound Potential not only offers lower costs, but also better performance. “If the battery is charged and discharged very often per day, we have a performance advantage over lithium-ion batteries,” says Taylor. This is due to the good cycle stability of the flow battery, which has a lifespan of 20 years. Unbound Potential is primarily looking to store electricity from wind and solar power systems for four to ten hours, but the system can theoretically be extended to 20 hours.
The battery system will be housed in large containers. “A battery system will consist of about 40 containers, which equates to a capacity of ten megawatt hours,” says Taylor, admitting: "Energy density is not our strong point, but we can stack our containers to save space. You can't do that with lithium containers, which have to be several metres apart because of the risk of fire." In contrast, nothing can burn in the Unbound Potential containers, so all the containers can be placed close together. As a result, the space required for the entire system is no larger than a lithium battery system.
The battery system will be housed in large containers. “A battery system will consist of about 40 containers, which equates to a capacity of ten megawatt hours,” says Taylor, admitting: "Energy density is not our strong point, but we can stack our containers to save space. You can't do that with lithium containers, which have to be several metres apart because of the risk of fire." In contrast, nothing can burn in the Unbound Potential containers, so all the containers can be placed close together. As a result, the space required for the entire system is no larger than a lithium battery system.
Taylor enjoys developing creative technical solutions and, as a former researcher at ETH Zurich, he also enjoys building a team. “When I was thinking about my future as a researcher, I asked myself whether it made sense to spend the next 20 years tinkering with some research project, given all the problems we have – and the energy transition in particular. I felt that the concepts we were developing could actually be implemented and used, and at the same time I had a strong desire to build something tangible,” recalls Taylor, adding: “Starting a company was the ideal way to do what I'm good at and what I enjoy with maximum impact, with a clear goal and a clear impact that you can feel every day.”
Because Unbound Potential's flow battery has a fundamentally different design to previous flow batteries, the company also manages to have 90 per cent fewer sealing surfaces. “There are no channels, no membranes, nothing to clamp or seal,” explains the 37-year-old. “This massively reduces the CapEx, the upfront investment.”
Unbound Potential's main competitor is lithium-ion batteries, which are manufactured cheaply in China. However, in addition to the cost of the lithium-ion cells, there is the cost of the battery management system that controls the equal charging of the cells. There is also a temperature management system to cool the cells and dissipate heat, and copper cables to connect the cells. “All of this periphery has to be scaled for lithium-ion batteries,” explains Taylor. “Our aim is not to be cheaper than the cell itself, but cheaper than the whole package. Our system is so simple that we can undercut this unavoidable cost point for lithium-ion batteries and become the market leader for stationary storage solutions.”
Unbound Potential's main competitor is lithium-ion batteries, which are manufactured cheaply in China. However, in addition to the cost of the lithium-ion cells, there is the cost of the battery management system that controls the equal charging of the cells. There is also a temperature management system to cool the cells and dissipate heat, and copper cables to connect the cells. “All of this periphery has to be scaled for lithium-ion batteries,” explains Taylor. “Our aim is not to be cheaper than the cell itself, but cheaper than the whole package. Our system is so simple that we can undercut this unavoidable cost point for lithium-ion batteries and become the market leader for stationary storage solutions.”
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