There’s a lot of talk about firming up Australia’s plentiful and cheap renewable energy with storage. But are we putting our time and money in the right place?
Australia’s population mass lives at a latitude of regular weather fronts, where there’s a pattern of a few days of sunshine, then wind, sunshine then clouds, translating into days of good renewable output, and inevitably some with a lot less.
As the proportion of renewable energy in the grid increases, these gaps in energy generation are going to be increasingly problematic, with massive amounts of storage needed to fill them.
Some of this storage is already in existence or under construction, in pumped hydro projects like Snowy 2.0 and transmission-scale lithium-ion battery arrays like the Hornsdale Power Reserve in South Australia and the recently announced Riverina Energy Storage System (RESS).
See RenewEconomy’s Big Battery Storage Map of Australia
Hydro and lithium-ion storage technologies are being prioritised at present, and both have merit. But if we are to have a truly renewable-powered electricity sector we will need to diversify our storage options and invest in the development and commercialisation of other storage technologies.
Mature technologies: lithium-ion and pumped hydro
The most mature energy storage technologies in Australia are lithium-ion batteries and pumped hydro, both of which have their place in a secure future energy system relying on variable renewable generation. However, each technology has strengths and weaknesses that limit their use.
Lithium has excellent energy-to-weight performance: it’s the lightest known metal and the least-dense solid element with the greatest electro-chemical potential.
This makes lithium-ion batteries ideal for mobile applications – phones, transport, computing – where low size and weight are critical.
Other benefits of Lithium-ion batteries are their high round-trip efficiency (~90%), rapid response time, low lifetime GHG emission impact and falling costs – it is no surprise that Deutsche Bank predicts lithium-ion batteries to account for 97% of battery use in energy storage alone by 2025.
However, according to the University of Technology Sydney’s (UTS) ‘Sustainability Evaluation of Energy Storage Technologies’ report, lithium-ion batteries have the greatest environmental and social impact at the front-end of the supply chain. The rare-earth metals and minerals in the cells are difficult to obtain, high-impact and expensive.
This technology should be saved for applications that need high-density, lightweight storage – applications that are huge and growing.
Scaling lithium-ion batteries is expensive and the batteries have limited longevity (typically around 15 years if they cycle twice per day to meet morning and evening peaks) and short storage duration (four hours or less). (See table below.)
Pumped hydro energy storage (PHES) can provide inertia to stabilise energy systems against disturbances, and has the highest round-trip efficiency of any high-volume bulk-energy storage technology.
PHES also has the all-important black-start capability, and other key advantages including its long-duration potential at full power (up to 20 hours), and low operational costs over a long expected lifetime of 50-100 years.
However, PHES is a long-term asset and faces associated risks, especially in the fast-changing market that is the Australian energy sector, with these risks increased by the long construction time of PHES projects. PHES also has unique geographical requirements, with possible large environmental and social impacts, depending on the project.
At present the Australian government supports PHES as an energy storage system because of local expertise and the large number of potential sites. (ANU estimates there are approximately 22,000 including off-river PHES, which could facilitate 50-100% penetration of variable renewable energy.)
The findings from the ‘Storage Requirements for Reliable Electricity in Australia’ report by UTS and the Institute for Sustainable Futures round out the summary of these two storage technologies.
This report analysed the levelised cost of storage (LCOS) for bulk storage technologies, and found that PHES (and lithium-ion batteries) have a greater LCOS per MWh than alternative solutions.
Other energy-storage systems: liquid air storage and flow batteries
Emerging energy-storage technologies are being adopted overseas to diversify duration and delivery time and provide storage suitable for specific applications. These technologies seem well suited to Australia’s needs. For example, the United Kingdom has adopted a number of storage technologies, including liquid air energy storage and flow batteries.
Liquid air storage (or cryogenic energy storage) uses energy to cool air until it liquifies into its main constituents: nitrogen and oxygen. When the energy is needed, the air is returned to its gaseous form and drives a turbine, generating electricity.
The process is simple and does not differ greatly from PHES, with the main advantages being that it is not limited by geography and there is far less impact on the environment: there is no need to build large facilities and redirect water.
This storage technique can have reasonable round-trip efficiencies (60-70%) when the waste heat and cold of the liquefaction process is captured. Liquid air storage systems can be scaled relatively quickly and easily by adding more storage tanks, with the price of energy dropping (per MWh) as the size of the storage system increases – a key advantage over lithium-ion.
This technology is particularly suitable for use in Australia, which already has a natural-gas industry with existing materials, understanding and expertise. If the technology can be scaled up (and thus reduced in cost) liquid air storage could be prioritised for stationary applications where size and weight don’t matter.
Other key attributes of this storage technology are that it is capable of handling up to 12 hours of energy storage, and has an expected lifespan of 30-40 years.
Flow batteries are similar to conventional batteries in their electrochemical reactions; it is in their storage technique that they differ.
Flow batteries store energy in an electrolyte solution containing vanadium, which exists as ions with different charges. Flow batteries have several key advantages over lithium-ion batteries. They do not lose efficiency over time, enabling indefinite charge and discharge.
Their storage duration is typically ten hours, response time is milliseconds and they have a lifespan of approximately 25 years, after which the material components can be reused in other energy storage or metallurgical applications.
Diversity and purpose
Massive amounts of storage will be needed to modernise Australia’s grid: the affordability of wind and solar is irrelevant unless we have the ability to store this energy in an efficient, stable and suitable way that maintains grid security and reliability.
A mix of technologies is required to solve this problem while minimising the environmental and social impact, and flow batteries and liquid air storage have the potential to be a significant part the solution.
It’s good to acknowledge the nascent work being done by ARENA and others on these alternative technologies, but it seems inadequate.
We only have ten years before we will need these technologies at scale. It’s time to put our skates on and get these technologies down the cost curve.
 Lithium-Ion Battery Value Chain report pg 6
 Deutsche Bank Market Report, Lithium 101, May 2016.