The quest for carbon-free energy storage needs facts and hard data that are hard to find

Untold riches await whoever can provide long term energy storage without a high GHG tariff, says Ed Ansett, founder and chairman of i3 Solutions Group, as he examines the complexities of the emerging energy storage technology scene.

Nothing is cost-free and few things in energy storage are carbon-free. The discussion around calculating the whole of the life carbon cost of different energy storage technologies that will aid the energy sector transition to net zero is only just beginning.

Advocates for different technologies will paint the greenest picture possible for their favoured solution categories such as gravity storage, compressed air, liquid air, new (and old) battery tech or fuel cells. As we await agreed international standards, finding hard data on the carbon profile of existing energy storage solutions for traditional approaches and emerging technologies is not straightforward.

Large scale projects, such as pumped hydro and mechanical gravity, clearly have huge upfront carbon costs – in the millions of tonnes – but proponents would claim that the long term and low carbon nature of the operation make them a good whole of life low carbon solution.

However, there is little available data on the embodied carbon cost of digging a giant reservoir and dam building. The Three Gorges dam in China is a “straight-crested concrete gravity structure… 2,335 metres (7,660 feet) long with a maximum height of 185 metres (607 feet). It incorporates 28 million cubic metres (37 million cubic yards) of concrete and 463,000 metric tonnes of steel into its design.”

For mechanical gravity storage where large masses such as hundreds of ‘bricks’ (even those made from recycled materials) weighing 50 tonnes or more, or concrete pistons that weigh 100s of tonnes, the embodied carbon cost of manufacture cannot be dismissed. Downstream through the grid and within power-intensive user environments such as data centres, energy storage is top of mind.

For example, in Nevada Google is building a $1bn 690MW solar farm along with a 390MW Lithium-ion battery farm to power its nearby data centre. Down the road in Reno, Nevada, liquid metal battery technology maker Ambri is supplying 250MWh to a developing data centre that will run on solar and geothermal power.

At the grid BESS level, where to date projects mostly use Li-ion battery technology there are notable projects of scale in Australia and the US ranging from 70MW to 100MW in capacity. But already there are questions about the carbon cost and long-term sustainability of Li-ion.

All battery and other storage technologies require life cycle assessment (LCA). Here, there will be carbon emissions differences due to variables in raw material extraction and processing, manufacturing processes, charging and discharging emissions and disposal and recycling.

A 2019 paper from IVL Swedish Environmental Research Institute – The Life Cycle Energy Consumption and Greenhouse Gas Emissions from Lithium-Ion Batteries – reviewed available life cycle assessments on lithium-ion batteries for light-duty electric vehicles, using the results to draw conclusions on how the production stage impacts greenhouse gas emissions (not including the use phase of lithium-ion).

The study found greenhouse gas emissions of 150-200kg CO2-eq/kWh battery that ‘looks to correspond to the greenhouse gas burden of current battery production.’ The paper asked: “How large are the greenhouse gas emissions related to different production steps including mining, processing and assembly/ manufacturing?” Here it speaks of a lack of transparent data between the different lines.

In answer to another question: “Do emissions scale with the battery weight and kWh in a linear or non-linear fashion?” It says: “Very little data are available on this subject, but what data there are points to a near-linear scale-up of greenhouse gas emissions when the battery size increases.”

In terms of disposal and recycling, Lithium-ion also poses numerous challenges. Whether in materials, manufacture or operation, all battery technologies have carbon or GHG cost. For example, liquid metal batteries must operate at greater than 240°C in order to maintain molten-state electrodes and the high conductivity of electrolytes.

Other battery technology cheerleaders, such as Washington State University for Sodium-ion, say work is ongoing to improve the chemistry’s charge retention over 1000s of cycles. It claims its Sodium-ion (Na-ion) battery “is able to store as much energy as commonplace Lithium-ion (Li-ion) batteries, but with a much-reduced environmental cost.”

The UK’s Faraday Institution, an independent institute for electrochemical energy storage research, launched NEXt-GENeration NA-ion batteries (NEXGENNA) to research the post-Lithium-ion future of battery energy storage. It too points to the environmental benefits citing the accessibility and abundance of sodium which makes it easier and less costly to source. It says Sodium-based batteries are a good option, particularly for static storage, where cost is a more important factor than weight or performance.

As with all new energy storage technologies whether battery at scale or Liquid Air or Compressed Air at scale, it is the integration with renewable energy sources that is usually cited as driving huge carbon reduction benefits. However, reliable and verifiable embodied and emission carbon data for liquid air and compressed air energy storage solutions are equally difficult to source.

For some, the holy grail for a carbon-free energy storage future is hydrogen – the simplest and most abundant element in the universe. However, here on Earth, it is difficult to break the bond between Hydrogen and Oxygen in water. It requires the use of spare power capacity from solar and wind to make it practical. And once that challenge is solved, there still remain questions to address regarding storage, transportation and energy conversion. Carbon-free of course!

There are many smart people, big institutions and large companies working to solve the carbon-free energy storage problem. Watching the data will be key to success, however, they remain in short supply. Finding a viable and practical solution is an urgent undertaking and for whoever succeeds, the rewards will be huge.

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