Flow batteries offer a durable and cost-effective alternative to lithium-ion batteries for large scale energy storage, and could be used to bring more renewable sources of power in emerging economies if challenges around cost and manufacturing can be solved.

Edinburgh-based battery innovator StorTera has been working with researchers from the University of Strathclyde to improve the efficiency of an innovative graphite polysulfide single liquid flow battery that could offer reliable, low-cost, low carbon power to homes and businesses in sub-Saharan Africa. The technology has the potential of supporting critical infrastructure such as telecommunications towers, facilitating the increased deployment of renewable power sources in the region, and supporting the displacement of expensive and polluting fossil fuel-based back up generation.

The collaboration, managed by Faraday Institution, is funded with UK aid from the UK government via the Transforming Energy Access (TEA) Platform. The TEA Platform supports early-stage testing and scale up of innovative technologies and business models that will accelerate access to affordable, clean energy-based services to poor households and enterprises, especially in Africa.

By the numbers
50% reduction in catholyte cost
50-70% reduction in production cost
>20% reduction in upfront costs of the system
20% increase in durability
20-50% cost savings achieved by liquid flow batteries relative to Li-ion and lead acid chemistries when used in micro grids
>99% round trip efficiency of the prototype on charging/discharging
£5mfunding for StorTera from the UK government’s Net Zero Innovation Portfolio

Liquid flow batteries store energy in the electrolyte instead of at the electrodes. The energy stored by the cell can be increased by adding a larger liquid tank, without a corresponding increase in power. This is a key difference between the technology and other commonly used types of battery, such as lithium-ion, where power input and energy storage grow in tandem. What’s more, some flow battery technologies operate well in widely varying temperatures, making them suitable for use in harsh climates.

This combination of low power, high capacity and long service life means liquid flow batteries are potentially well suited to powering low-carbon energy grids in emerging economies. But use of the technology is not without problems, as manufacturing is complex, and the materials currently used are expensive.

StorTera flow battery installed at Perth and Kinross Council.StorTera believes it has developed a solution to the manufacturing issue, with a Spiral Flow Battery that can be manufactured using a roll-to-roll process, leading to increased efficiency, cost savings and a higher production rate. It turned to the team at the University of Strathclyde to refine the system design and improve the electrolyte and electrode materials chemistry (including to make the liquid component of the battery suitable for Sub-Saharan climates) while reducing costs.

The Electrochemical Engineering group at Strathclyde, led by Dr Edward Brightman, worked closely with StorTera to synthesise and characterise novel electrolyte formulations using lower cost, more sustainable solvents. They also investigated the influence of the graphite current collector and separator types on the cell performance. Researchers demonstrated a reduced catholyte cost of 50% and reduced production costs of 50-70%, leading to an overall reduction of >20% in upfront costs of the system (to £70/kWh), and a 20% increase in durability, albeit at small scales.

StorTera then built a prototype system incorporating Strathclyde’s system improvements, which was tested by PDNC (formerly known as the Power Networks Distribution Centre) in Scotland. The system demonstrated >99% round trip efficiency on charging/discharging in a 15W/20Wh configuration. Fortuitously, testing during the UK-wide heatwave in July 2022 enabled the tests to be completed at temperatures comparable to those the flow battery would experience in Sub-Saharan Africa.

In parallel, a team from Strathclyde’s Energy for Development group carried out a techno-economic modelling study, surveying stakeholders in Malawi and Zimbabwe about how the technology will be used and their requirements. This found that the liquid flow batteries can achieve cost savings of 20% – 50% over Li-ion and lead acid chemistries when used in micro grids. A scientific paper is being prepared to report the results of the study.

Design of the StorTera SLIQ 25 kW / 200 kWh module.

The prototype device developed is small, and the challenge for StorTera is now to demonstrate that the technology works at much larger scales – the aim is to build a 200kW/1.6MWh demonstrator by 2024. The company has subsequently secured £5m of funding from the UK Government’s Net Zero Innovation Portfolio (NZIP), which will support the development of a long-lasting megawatt scale battery that can operate for up to eight hours. The funding will enable the number of company employees to double to 28. The prototype cell performance also requires further improvements to achieve the desired cycle life and power density, which is the focus of ongoing work by StorTera.

For the University of Strathclyde team, working with StorTera has provided a pathway to take part in follow-on projects, as well as to potentially publish the outcomes of their research. As a result of the project the university and StorTera have committed to jointly fund a PhD studentship, starting in the autumn of 2023, to build on the team’s work with a more in-depth study of the durability of flow batteries.

Pasidu PallawellaPasidu Pallawela, StorTera’s Chief Technology Officer, says: “Using this kind of battery in developing countries, especially sub-Saharan Africa, is very feasible, and could be a cost-effective solution to integrate more renewable energy into the grid. These kinds of technologies will be required all around the world as we move towards Net Zero.

“Working with the Faraday Institution and Strathclyde University has been extremely useful for us. It has given us access to a network of academics who have done a lot of work in this area. Being able to call on their expertise has been invaluable as we look to bring this innovative product to market.”

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Case study published May 2023.