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Australia’s hydro energy storage systems are getting long in the tooth: maybe it’s time to look at liquid air. Michael Mazengarb

The missing link: why Australia needs energy storage

In visiting Australia regularly for the last two decades I have never quite understood why greater value is not placed on the nation’s latent solar and nuclear energy assets. Perhaps it is because Australia thinks there is a vital missing link: the ability to store energy.

With renewable sources such as wind, wave and solar, energy is often created in the wrong place at the wrong time, making it difficult to utilise. Australians aspire to use renewable resources but are thwarted by the practicalities of renewables’ use in future energy generation and supply systems.

In Australia, climate change legislation is driving decarbonisation. This will shift the energy provision and create new markets. The public mind however is on cost, accessibility and security of supply.

In the UK, the electricity generation mix and the opportunities are very different. In November the UK Chancellor announced that energy storage technology was critical to the future UK economy and will be worth £10B a year by 2050.

This value comes from understanding where the different energy storage technologies fit into the grid at generation, transmission and distribution. It’s not simply a matter of providing storage capacity. Governments have to determine how to configure a robust energy system to suit the changing energy mix and minimise the cost of transmission investment as the demand for electrical power grows.

Which way is the best way?

Different applications demand appropriate storage characteristics and a range of technologies are needed to suit the specific needs. Technologically speaking, energy can be stored in mechanical, electrical or chemical devices and in the form of heat. All are probably needed, but - apart from hydro-storage dams - Australia has few examples at a significant scale.

So what might energy storage mean for Australia?

It certainly should not mean simply filling the country with batteries for storing renewable energy.

There have been some extensive battery park trials for regional storage in China and in the US (Figures 1 and 2) and in other energy constrained countries (such as Chile), but this does not appear to be a widespread option suited for Australia.

Figure 1: Chinese energy storage.
Figure 2: US energy storage.

Conventional batteries of different types have their place, but society really needs an alternative. This is not only driven by realisation of the cost, resource wastefulness, environmental impact and scarcity associated with rare earths components, but also by a growing public misgiving about safety.

Battery-related safety incidents have been growing rapidly over the last few years, in vehicular and air transportation, computers, large scale battery parks and wind/solar on site storage locations.

A range of energy storage methods are currently available; most of these have been reviewed recently. Figure 3 shows a summary based upon the scale of power rating and the call down time, expressed here as a discharge time at rated power.

Figure 3: System power ratings.

Liquid air a great alternative

As Figure 3 shows, there are alternatives to batteries. For example, in the UK there is a growing interest in the notion of cryogenic liquids. These are reported to be a cheaper and better way to use solar energy to drive compressors to compress air to liquid air (as cryogenic fluids).

Liquid air is potentially an energy vector in itself; vapourising the liquid using low grade waste heat makes for a very efficient system that then drives a generator.

The round-trip efficiency of these systems rivals batteries. These have now been demonstrated at a small scale with 350kW/2.5MWh scale for on-grid electrical storage and further developments to scale out to beyond 10MW are underway. Some 100MW+ systems with GWhs of storage are deliverable using existing supply chains and components. Some comparisons of estimated costs for comparative storage systems have been mooted (see Table 1).

Table 1: Costs of storage systems.

Such systems offer a means for low cost off-grid generation. This can smooth power requirements and provide security of supply by creating a national reserve.

Liquid air can also be used directly as a fuel. The first “cars that run on air” are currently being evaluated and are attracting significant attention. Australia, like the UK, has existing infrastructure to support early adoption. The technology is from a mature supply chain and components with proven long life whose costs are known.

Liquid air storage is at low or atmospheric pressure, resulting in low cost, above ground, safe bulk tanks. There is no fuel combustion risk. There are no geological or geographical constraints to location of stores or distribution pathways.

The energy density of liquid air compares favourably to other low-carbon competitors. There is great synergy with other industrial processes, including use of waste heat and provision of cold. And liquid air can be used as an energy vector to transport this stored energy around by road (as is currently done) or ship (as with LNG).

A major review of this opportunity is underway and may have profound application for Australia if it turns out that liquid air can be used as a fuel. Meanwhile the UK Energy and Climate Change Minister John Hayes believes that liquid air may offer some radical solution with real economic stimulus to the economy.

Putting a value on energy storage is difficult. The value lies in different places for different applications. Take solar: the business model has a feedstock (sun) that is free, which means arguments based purely on technical process efficiency and cross-comparisons to other processes are not germane. Rather, it’s the benefit that needs to be quantified.

Australia too will need to grasp these emerging concepts as new opportunities emerge to better utilise renewable energy and mitigate escalating infrastructure costs associated with energy supply and security. I am increasingly confident that the decarbonisation drivers may open up significant new economic opportunities ahead.

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