Liquid Air Batteries – Seriously?

Electricity is a fickle energy source. By its nature, electrical power must be used instantaneously – supply and demand need to match precisely at every moment in time. An imbalance in the supply-demand relationship creates network stability problems that can result in nasty consequences for the network and end-users alike.

To reduce the impact of mismatched supply and demand, energy storage devices – batteries by any other name – are now being used quite commonly, particularly when generating power from intermittent renewable sources such as wind, solar, and tidal. However, designing and manufacturing batteries large and robust enough to deploy on electrical utility networks while keeping them affordable remain a tough challenge.

What’s required?

For a utility-scale battery to serve as useful storage, it must meet five fundamental requirements:

  1. Store sufficient energy to supply power over long durations, typically 12-24 hours

  2. Deliver enough power to manage peak utility power demands

  3. Be low enough in cost to make such storage financially viable

  4. Be adaptable to the location and easily scalable as demands for power increase

  5. Remain environmentally friendly to manufacture, operate, and eventually recycle.

Options to consider

Currently, lithium-ion (Li-ion) batteries are the go-to solution, but they don’t tick all the boxes. Yes, they can deliver a lot of power – the largest Li-ion battery installation globally is a Tesla facility in southern Australia at 100 megawatts (MW) – but they’re relatively expensive to manufacture. And from an environmental standpoint, there’s much to dislike about the damage inflicted by the extraction of lithium and battery manufacturing and disposal processes.

On the far end of the scale, there’s the hydro option – massive water reservoirs behind dams or from pumped water that store tremendous potential energy that easily convert to generated electricity for as long as required. However, these facilities are costly to construct, require the appropriate location, and are often devastating to existing ecosystems.

Flow batteries are another type of energy storage device that employ liquid electrolyte anode and cathode cells separated by a membrane. These batteries last for decades, and they can supply power for longer durations than Li-ion batteries. Still, they exhibit lower energy density, which limits the usable power they can offer an electrical grid.

Is this technology the answer?

And so, we arrive at liquid air battery technology. Characterized by high energy storage capacity and useful duration, liquid air batteries neatly bridge the shortcomings of the solutions we just discussed. See Figure 1.

Figure 1 – Liquid air batteries effectively bridge the wide gap between Li-ion and flow batteries and pumped hydro energy storage while offering additional advantages.

Importantly, the technologies required to construct utility-scale liquid air battery facilities are well-proven, available off-the-shelf, and boast decades of successful track records in use by similar industries. Components are modular and scalable from 5 MW up to hundreds of MW, and construction and start-up costs are relatively low. Better yet, they comprise standard and non-toxic components and generate no harmful emissions.

Additionally, it’s an easy matter to design such facilities to offer a useful life of 40 years or longer.

How a liquid air battery operates

Following is a summary of how a liquid air battery facility operates for utility-scale energy storage:

  1. Air is drawn through a scrubbing system to remove dust and other particulates, moisture, and CO2. The clean air is then cooled down to cryogenic temperatures to produce liquid air that is stored in well-insulated steel tanks at about 15 times atmospheric pressure, well within conventional liquid-gas storage parameters commonly used by industry.

  2. When the electrical grid demands power from the battery facility, the stored liquid air is pumped to a higher pressure using cryogenic pumps. Ambient air temperature ‘boils’ the liquid air to a gas, which then passes through a conventional turbine at high pressure to drive a generator that produces the required power.

  3. The process neatly extracts the heat generated by the compression stage of the refrigeration system when producing liquid air. It also captures and stores the cooling effect resulting from liquid air changing its state to gas in advance of the turbine, assisting the refrigeration step. Optimizing the process in these ways elevates overall system efficiencies to a very respectable 60% or so.

  4. Scaling such a battery facility to increase energy storage is a relatively inexpensive and straightforward process of adding more liquid air storage tanks. It does not require additional scrubbing systems, air liquefiers, nor turbine generators. As a result, doubling the capacity of a liquid air battery facility imposes a cost roughly half that of a wholly duplicated system.

Helping to alleviate another issue

Designers of liquid air battery facilities employ technologies with which oil and gas engineers are intimately familiar. This fortunate coincidence bodes well for technical and operational experts who migrate from the fossil fuel industry to enjoy gainful and challenging employment in this cleantech sector.

As far as I can tell, liquid air batteries fill the bill from every angle. Will they become the next best thing since sliced bread?

Figure 2 – Companies like Highview Energy in the UK and others are building liquid air battery facilities, and they’re demonstrating such facilities can readily scale to meet higher peak electrical demands.

A special thanks to Dave Borlace for supplying the illustrations and educating me on the subject matter. For more insights, check out his YouTube channel “Just Have a Think” and his YouTube video discussing liquid air batteries.

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