Turning the tide with vanadium flow batteries

Online Editor

Matt Harper reveals how vanadium flow batteries unlock the potential of tidal power and green hydrogen

Generating clean energy from the rise and fall of the tide has captured the imagination of engineers for decades. The potential is huge, particularly in the UK, where it has been suggested that wave and tidal stream energy could meet up to 20% of the total electricity demand.

There has been real progress for the industry, with European tidal power recently surpassing a 60 gigawatt-hour cumulative electricity production milestone and over €45m invested in the technology in 2020.

And the best is yet to come. Many of the best project sites around the world are yet to be commercially developed, providing fertile ground for tremendous growth within the industry over the next decade.

One location that has pioneered the testing and demonstration of tidal energy technology is the European Marine Energy Centre (EMEC) in Orkney, Scotland.

Established in 2003, EMEC is the world’s leading facility for testing wave and tidal energy converters in real sea conditions. The centre offers independent, accredited grid-connected test berths for full-scale prototypes, as well as test sites for smaller scale technologies, supply chain companies, and equipment manufacturers.

However, not content with pioneering two transformative energy technologies, the Centre has since expanded activities into new sectors including green hydrogen and installed a hydrogen production plant on the island of Eday, which neighbours the tidal test site. This enables the integration of tidal power with green hydrogen production.

The commercialisation of green hydrogen is an essential step toward a 100% renewable future. Green hydrogen is created and consumed without carbon emissions and can replace fossil fuels in the power sector, as well as enabling the decarbonisation of heavy industry and transport sectors.

Vanadium flow batteries: A unique battery for a unique operation

Tidal generation is predictable yet variable, as turbines generate energy four times a day with the ebb and flow of the tide. This sinusoidal energy generation potential does not provide the continuous supply of power optimal for hydrogen production, so EMEC looked to battery energy storage to address the issue.

For a battery to effectively manage tidal generation it needs to charge and discharge up to four times a day, a duty cycle that would rapidly degrade the lithium-ion batteries that currently dominate the stationary energy storage market.

Solar-coupled energy storage projects typically require just one charge and discharge daily, so by comparison regulating tidal generation presents an extremely heavy duty cycle for a battery system.

EMEC has therefore partnered with Invinity Energy Systems, supported by the Scottish Government, to deploy a 1.8MWh vanadium flow battery (VFB) to ‘smooth’ tidal generation and create continuous, on-demand electricity to generate hydrogen.

Vanadium flow batteries are a form of heavy-duty, stationary energy storage that are ideal for high-utilisation, industrial settings. They provide hours of continuous power, one or more times per day, through decades of service. Most importantly for EMEC, they suffer no degradation of their performance based on the number of charge and discharge cycles they complete. This makes them the perfect candidate for balancing tidal energy’s cyclical generation patterns.

At EMEC, the flow battery system will store electricity generated by tidal turbines while the tides are flowing, and discharge power at slack tide when the turbines are less active to deliver consistent power to EMEC’s electrolyser. This will optimise hydrogen production at the site to enable tonnes of green hydrogen generation each year.

The projected operation of the battery is shown in the graph (right), which models the total number of cycles per month that the battery is expected to deliver at the EMEC site. It particularly highlights the heavy-duty nature of the application with over 100 deep charge/discharge cycles per month regularly required, a level of utilisation that would quickly accelerate a lithium-ion battery towards end-of-life degradation levels, not to mention likely contravening the manufacturer’s warranty conditions!

Are vanadium flow batteries the missing link in the energy transition?

The potential for flow batteries goes well beyond supporting tidal power with the generation of green hydrogen, as Invinity’s batteries can support any high utilisation application.

The firm recently announced that it will be delivering Australia’s first dispatchable ‘solar power plant’ to a project in South Australia. An 8MWh VFB will be combined with a 6MWp solar array, to unlock low-cost, low-emission energy for the Australian grid.

The vanadium flow battery will charge from electricity produced by solar panels when the sun is at its peak. This electricity can then be delivered when it is most needed, in the evening when grid loads are high from consumer demand, but solar generation is no longer available.

By using vanadium flow batteries to complete this ‘time shift’, solar power becomes dispatchable, as the site will produce approximately 10GWh of solar power each year that can be deployed to the grid when it is most valuable, at any time of day or night, competing directly with conventional coal and gas generation for the first time.

These projects demonstrate that vanadium flow battery energy storage is heading to maturity, and with the market for this technology expected to exceed US$4.25 billion by 2028, flow will play a leading role in the global transition to renewable energy.

Matt Harper is chief commercial officer at Invinity Energy Systems