Thomas Gebauer, Chief Executive Officer: Redox One
Companies and governments around the world are working diligently to establish renewable energy projects to meet the planet’s growing demand for sustainable energy. Vast solar fields and, huge on- and off-shore wind farms, harnessing the power of hydro-generation are being installed globally.
Renewable energy generation isn’t a one-size-fits-all solution. The problem is, where will the electricity come from when the sun doesn’t shine, or the wind doesn’t blow? This presents a massive problem which we believe is the perfect opportunity for energy storage solutions. Energy storage allows the storage of energy during generation so that it can be deployed when it is needed, especially when renewables aren’t generating energy. This increase penetration of renewable generation has given rise to the Long-Duration Energy Storage (LDES) market, with a number of different technologies to meet this gargantuan storage need. As with every technology, there are some solutions that are better suited to specific applications than others.
Know Your Battery
The most prevalent energy storage technology in the world today is the Lithium-ion battery – there’s one in your mobile phone, your laptop, your home solar PV storage or even your electric vehicle. Lithium-ion batteries offer a high energy density – meaning they can store a lot of charge for a relatively small volume, making them perfect for personal electronics and mobile applications. But this high-performance comes at a trade-off: cycle life. Li-Ion batteries suffer from capacity decay after cycling, and thus have a finite cycle life due to lithium ions plating on the negative anode. That explains why your cellphone’s battery life typically last roughly 2 years.
In your internal combustion-engine car, you have a lead-acid battery – the same as the familiar batteries that power small, non-rechargeable electronic devices like children’s toys or torches. Lead-acid batteries are wet-cell batteries which allow for high surge currents – like those required to start your engine – and have a relatively low energy density. The technology is well-understood and lead-acid batteries are relatively low-maintenance energy storage solutions.
Redox One Flow Batteries use an Iron-Chromium electrolyte solution instead of the two solid electrodes that would be present in a conventional integrated cell battery, to store energy by changing the charge state of each tank of electrolytes – this is referred to as a galvanic reaction, where electrons are transferred. To achieve this, the electrolytes are pumped through a stack of cells in one direction and charging or discharging is achieved by changing voltage polarity on the electrodes.
When charging, the battery stores energy by increasing the charge state of Iron ions in solution, while reducing Chromium ions in solution. Discharging is achieved by reversing polarity – increasing the state of Chromium ions while reducing the Iron ions.
There are many other kinds of batteries, using different reactions to store energy – but we want to illustrate why there are specific batteries for specific applications.
All Technology Has Limits
With the energy density and flexibility of Lithium-ion batteries comes a risk – including heat, smoke, the release of toxic gases and the potential for explosions. Lithium-ion batteries can catch fire from mechanical harm, such as crushing or penetration; electrical harm from a short circuit or if they overheat.
The optimal operating temperature for a Lithium-ion battery is between 20 and 40°C and battery management systems – which form a part of most of these batteries – stop it from operating when it reaches a threshold temperature of around 60°C.
If the temperature of the battery rises above this threshold, coatings within the battery start to decompose and, above 70°C, the electrolyte mixture will start to evaporate, increasing pressure in the cell, which can cause mechanical failure inside the battery. Heat increases the rate of reaction, which further increases the temperature of the battery temperature, and this rolling exothermic chemical reaction can trigger a thermal runaway across each cell.
This degradation can result in a leak, ignition and explosion. Many of the chemicals in the battery have a high flammability risk or are known to be harmful to living beings, internally or externally. One of the components, Hydrofluoric acid, is a corrosive compound which destroys the surface layers of the human body penetrating deep into the body causing cell necrosis, as well as a biological imbalance which can present as heart arrhythmias.
Events like this are not common but can occur – which is why the operation and disposal of Lithium-ion batteries needs to be managed extremely carefully. In large-scale installations, the effect of overheating or impact and the scale of the subsequent leak, reaction and fire are catastrophic at Megawatt and Gigawatt storage levels and pose a significant threat to human life and surrounding structures. Extensive fire suppression technology must also be deployed, and the batteries need to be spaced far apart to avoid setting off a chain reaction across the installation.
Lead-acid batteries are not perfect for LDES due to their weight, low specific energy and specific power, short cycle life and high maintenance requirements. There are also significant health hazards associated with lead and sulfuric acid during production and disposal. It’s vital that they are disposed of safely to avoid contamination or injury. Their capacity drops significantly at low temperatures – see trying to start your car on a cold morning.
Flow Batteries use ions dissolved in two fluids to store energy. These ions pump the fluids into a cell called a stack where the battery is charged or discharged. Flow Batteries use other minerals like Vanadium, Iron-Chromium, Zinc-Bromine to name a few in addition to many organic spices. The most common is Vanadium due to its four oxidation states, but geopolitical issues and its importance as a “critical mineral” cause unpredictable price fluctuations and supply chain instability. Currently, Vanadium is almost 10x more expensive than Iron-Chromium – Redox One has access to a multi-generational supply , thanks to our parent company Tharisa Minerals in South Africa’s North-West Province. Our Iron-Chromium Flow Batteries employ a microporous separator through which electrons are exchanged which is substantially cheaper than the fluorinated membranes deployed in most other Flow Batteries.
Large-scale Lithium-ion batteries can appear to come in at half the projected price of similar-capacity Iron-Chromium Flow Batteries – though that disregards the additional expense of the expanded footprint of a Lithium-ion installation due to spacing requirements, as well as the necessary fire suppression systems – but they suffer from significant capacity decay and have a shorter lifespan.
Iron-Chromium Flow Batteries Solve the LDES Problem
Redox One Flow Batteries use widely abundant Iron and Chromium, dissolved in a slightly acidic solution to create the electrolyte which allows for energy to be stored and discharged. This solution is not flammable and actually performs better at higher temperatures, making it ideal for deployment in hot climates and exposure to the non-corrosive electrolyte solution poses minimal health risks.
The electrolyte experiences virtually no capacity decay and is essentially an eternal asset. Should the time come for the battery to be recycled, the extracted electrolyte can easily and safely be restored to its original Chromium and Iron elements and used for other applications such a stainless steel, , supporting a just transition.
Finding the right storage solution involves, amongst other things, balancing cost, capacity, availability, site space and safety – and we believe that our renewable, non-toxic, non-flammable Redox One Iron-Chromium Flow Battery is the present and future of LDES.