- Solar energy and wind power are replacing fossil fuels as sources of green energy.
- But an efficient method of storing that energy, for use when needed, remains a serious problem.
- Many believe the answer lies in large scale chemical flow batteries.
- In June (2020) the UK Government loosened the planning rules on large scale energy storage units making the outlook for battery technology industry brighter.
Following up on his interview with ‘Vanadium Queen’, Maria Skylass-Kazacos published in our September issue, Dermot Martin looks at why the UK Government has given the green light for easier route to energy storage technology.
The Vanadium redox flow battery (VRFB)
One battery design in particular stands out – the Vanadium redox flow battery (VRFB). Redox flow batteries have been touted as one answer to storing renewable energy, so it is surprising that progress with their development has been glacial.
Contrast to Lithium batteries
This is in contrast to Lithium batteries which are now ubiquitous in the myriad of small electronic devices we use, but only when it comes to large scale or utility energy storage applications, Lithium-ion based batteries do not seem to cut the mustard.
Took four decades
It took four decades for Lithium-ion battery technology to reach its zenith, but they lack crucial ability to offer large scale storage potential.
Lithium-ion batteries need supporting trace elements, Cobalt and Nickel and this has created headaches around geo-politics and economics as well as raising questions about protection of the environment.
When it comes to recycling, the traces of Cobalt, Nickel and organic electrolytes are problematic.
About 60 per cent of that Cobalt comes from one country, the DR of Congo, where the use of child labour in mining is rife and corruption in the Cobalt supply chain is well documented. Lithium batteries have also proved to be a fire hazard in certain conditions.
The need to find a cheap efficient means of large scale storing of energy generated by wind power and solar power has been a long-standing challenge.
A vote for Vanadium?
The electrochemistry of the transition element Vanadium and the evolving design of Vanadium re-dox flow batteries offers a path to large scale energy storage units.
The bulk of the engineering problems around VRFB batteries has been resolved and the first major (800MWh) storage plant is under construction in Dalian, China.
It is likely to be followed by many others and the global market for VRFBs is set to reach £3bn by 2028 according energy analysts.
Two chemicals that change valence state
Most batteries rely on two chemicals that change valence state (or charge or redox state) in response to electron flow which converts chemical energy to electrical energy and vice versa.
In the Vanadium flow batteries, one electrolyte is used but in varying oxidation states in the form of salt solutions.
A crucial component is the membrane which separates them.
The solar panels or wind turbine usually provides electrons and pumps push spent electrolyte back through the electrodes, where the electrolyte is recharged and returned to the holding tank. Membrane research associated with Vanadium batteries has opened a whole new programme of study among electrochemists and engineers.
Batteries to store more power
Scaling up these batteries to store more power requires more tanks or larger tanks full of electrolyte.
The big advantage is in applications where higher or various ratios of capacity to power, that’s the number of kilowatt-hours per kilowatt, are needed – usual ratios are between 5:1 to 10:1.
There is no limit theoretically to the energy capacity that can be stored and often the investment costs can actually decrease with an increase in the energy to power ratio, because the energy storage medium usually has comparatively low cost.
Other advantages of the VRFB design
There are other advantages of the VRFB design.
They have a lengthy lifecycle; outstanding stability; it is easy to regenerate or recycle the electrolyte and low flammability means they are safe from fire risk.
Vanadium redox flow batteries advocates say they offer the best option in terms of design not least because the Vanadium is more abundant than Lithium.
Though it is fair to say that the cost of Vanadium extraction does ebb and flow.
The beauty of Vanadium
The beauty of Vanadium is its flexible chemistry. As a transition element, it is stable in several ionic species in solution, V(2+,3+,4+,5+), each having different numbers of electrons around its nucleus. Fewer electrons gives a higher positive charge.
The VRFB stores energy by gaining electrons forming V(2+,3+), and releases energy by losing electrons to form V(4+,5+).
The standard V flow battery design consists of two tanks of liquid, which simply stand inanimate until required. When pumped into a chemical reactor, the two solutions flow adjacent to each other past a membrane, and generate charge by moving electrons back and forth.
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Source: Lab News
