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EWE Gasspeicher recharges flow batteries with massive new project

EWE Gasspeicher, a German gas storage company, is planning to build a giant flow battery big enough to power the whole of Berlin for an hour. The energy industry narrative has up till now focused on the potential of lithium-ion storage and distributed energy through smart grids. This announcement should make those in the sector reconsider the potential of flow battery technology.

EWE Gasspeicher plans to build a 700 MWh flow battery in Berlin. The battery will make use of the company’s gas storage assets – which currently uses caverns for gas storage and is looking to install the flow battery into the caverns by 2023. This planned level of storage capacity far overshadows the current largest lithium-ion battery storage project recently announced by South Australia in conjunction with Tesla – at 129 MWh of storage capacity.

The plan raises the question of whether consumers really need to be forced by the energy companies to change their usage habits and accept more distributed energy at the edge of the network under the guise of the ‘smart grid’ – such as smart meters, home storage, or demand response schemes. Largescale storage allows a utility to manage intermittent energy from renewable generation, by storing the generated electricity for use when there is sufficient demand on the network.

If flow batteries can deliver such high capacities of storage, then it could be unnecessary for utilities to push consumers towards smart grid adoption, at the edge of the network. Instead, adding a mixture of flow battery capacity and renewable generation assets to the center of the network could allow the utility to embrace cheap renewable energy without the customer noticing.

However, the solution to integrating clean energy generation, as now targeted by policy makers, will involve a combination of smart grid, distributed energy resources and storage at both the center and edge of the grid at varying scales. Also, the fact this project is aiming to be completed by 2023 indicates the current position of flow battery technology and the many years it still has till maturity – whereas lithium ion is good to go now.

A flow battery works by using a system of tanks containing chemical components dissolved in liquids, and a battery chamber with a membrane. One tanks contains a catholyte solution that accepts charge. A second tank contains an analyte solution that can attract electrons and can release charge.

The redox flow battery produces power by pumping liquid from the external tanks into a battery stack area, where the liquids are mixed. Inside the stack, ions pass through a selective membrane, charging the stack’s negative side. The energy capacity of a flow battery is a function of the electrolyte volume and the power a function of the surface area of the electrodes.

The maximum storage capacity is limited only by the size of the storage containers for the electrolyte liquids, according to EWE Gasspeicher’s website. Developers of flow redox battery technology contend that due to their long life-cycles and high potential storage densities, flow batteries are better suited to grid-scale storage than using lithium-ion battery cells. There are no solid-to-solid phase transitions occurring in flow batteries, enabling the long-life cycle – these are the transitions that cause lithium-ion batteries to lose capacity.

EWE is attempting a new type of flow battery in this project, that has been developed at the University of Jena. The process uses electrolytes based on recyclable polymers dissolved in salt water (brine). This approach, in theory, is more environmentally friendly than some other redox flow chemistries, such as those that rely on vanadium dissolved in sulfuric acid.

The project will initially test the technology at a smaller scale of 40 KWh. The company says this first attempt will be running by the end of 2017. A second prototype would then follow at the scale of 2.5 MWh.

The issue with large-scale deployments of lithium-ion battery cells is that they are degrading in capacity each time a charge cycle is completed. Following the assessment method set out in the paper ‘Modeling of Lithium-Ion Battery Degradation for Cell Life Assessment,’ after 20 years or 7,300 cycles (assuming one charge cycle per day) the batteries could have potentially degraded to 50-75% of their original capacity.

Lithium-ion batteries currently have a cost advantage for scale deployments, due to their wide usage in consumer electronics and now vehicles. This has had the effect of considerably reducing the cost of their deployment. Some estimates put the average price of a lithium-ion battery pack as falling as much as 80% between 2010–2016.

Comparatively, this has left the cost of redox flow batteries relatively high when compared to lithium-ion. However, the value of a flow battery asset, due to its considerably longer life cycle, means that the technology should be viewed differently – more akin to hydroelectricity.

We draw the comparison because since the Hoover Dam’s construction in 1936, it has acted as a continuous source of energy storage, till the present day – in which time, other forms of electricity generation have gone from development to decommission – nuclear being a case in point. The flow battery storage should have a much longer continuous lifetime than a battery-based equivalent.

If utilities are going to invest storage capacities at the significant scales that would enable a greater mix of renewable generation, as they are currently being pushed to do by policy makers, then we would think they would opt for the technologies with the longest potential shelf-life – to keep maintenance costs low.

The German energy market is currently characterized by a national effort to move towards a greater mix of renewable energy – so it is not surprising that projects of this nature are being deployed in the country.

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