In my last instalment I explained that Australia is going to need at least seven time more energy storage if we are going to have a chance of achieving a reliable and stable 80% renewables target by 2030. I will be upfront here and state that I don’t believe that that this notional target can possibly be met – with medium to long term storage being the big elephant in the room. The reason for this is that pumped hydro is the most critical component needed for large-scale long-term storage. The environmental approvals alone can take years before construction can even start so it is naïve to think that the quantum of required storage can be brought on line before the early 2030s. The current experience with Snowy Hydro 2 provides an object lesson.
Storage Basics
The basic unit of power for energy generation or storage is watts. Typically, we refer to large scale energy systems having a capacity of mega (million) watts or giga (1000 million) watts. In my last blog I noted that Australia is going to need about 22 GW of storage by 2030 to balance the grid. HOWEVER, I did not clarify what this means in terms of duration of storage, and how generation and storage must be matched to ensure we have a 24/7 electricity supply. This critical issue was picked up in some of the comments I received.
So, firstly a primer on energy storage systems (ESS). ESSs are not primary electricity generators. That is, they do not generate electricity from a fuel such as coal or gas, or from a solar PV system. They must use electricity supplied by separate electricity generators or from an electric power grid to charge the storage system, which makes ESSs secondary generation sources. ESSs use more electricity for charging than they can provide when discharging and supplying electricity. This is contrary to what many people believe because the perception is that the commonly used rechargeable power sources are actually power generators. They are technically “power banks”.
The Power capacity of an ESS is the maximum instantaneous amount of electric power that can be generated on a continuous basis and is measured in units of watts – megawatts [MW], or gigawatts [GW])
The Energy capacity of an ESS is the total amount of energy that can be stored in or discharged from the storage system and is measured in units of watthours – megawatt hours [MWh], or gigawatt hours [GWh])
A battery (eg Li Ion) can be built with an instantaneous capacity of 100MW, BUT it is typically only capable of maintaining this for 2 hours. Thus, you will see this battery being described as 100MW/200MWh. This time rating is somewhat analogous to the capacity factor concept for power generation that I have discussed previously
To put this into practical context such a battery would last for a maximum of 2 hours at full discharge load to supply about 30,00 homes. This would tide the consumers over the 2h peak period in the evening but no more. At least 6 of these batteries would need to be fully charged and ready to go to supply the rest of the night, and the low solar dawn and dusk periods, assuming no other source of power (eg coal, gas, wind, hydro). This is a simplification but what it does show is that a LOT of storage is going to be needed to keep a renewable-based electricity system running 24/7, given that solar can only supply for 7 to 8 hours on a good day, and the intrinsic variability of wind.
How Much Storage?
In fact, the National Electricity Market (NEM) is forecast to need 36 GW/522 GWh of storage capacity by 2034-35 (Figure below) if the current policy trajectory is realised, and coal power is phased out according to these policy settings. (https://aemo.com.au/energy-systems/major-publications/integrated-system-plan-isp/2024-integrated-system-plan-isp).
To put this number into context, the first of the so-called big batteries installed (in South Australia) has a capacity of only 0.13GWh, and the current total system storage is about 20GWh.
Source: Figure 20, 2024 Integrated System Plan, AEMO (https://aemo.com.au/energy-systems/major-publications/integrated-system-plan-isp/2024-integrated-system-plan-isp)
I have constructed the figure below from the data provided in the ISP 2024 to more clearly show the magnitude of the task ahead over the next 5 years. The use of the word “significant” by the authors of this plan doesn’t even come close to describing the order of magnitude increase in storage capacity that is going to be needed.
Storage Duration
Different forms of storage are needed to firm both consumer-owned and utility-scale renewables at different times of the day and year. These vary according to the length of time that electricity can be discharged at maximum output before they are exhausted. https://www.energycouncil.com.au/analysis/battery-storage-australia-s-current-climate/
Li-batteries are only capable of providing short duration storage of 2 to 4 hours, compared to a typical stockpile of coal providing a one-to-two-month buffer at a coal fired power station. As mentioned in my last blog it is somewhat perverse that coal-fired power stations are effectively providing the night time storage in energy supply to keep the electricity system in this country running through the night!
The next in line proven and commercially available technologies to provide medium duration storage (4-10 hours) for electricity from renewables are flow batteries – with the Australian developed vanadium flow battery technology being an example. Compressed air storage and solar concentrator/molten salt are others. These storage types can typically last up to 10h. The medium duration storage can also be provided by pumped hydro.
https://www.ess-news.com/2024/11/06/australian-made-vanadium-flow-battery-project-could-offer-storage-cost-of-166-mwh/ https://www.nsw.gov.au/ministerial-releases/broken-hills-energy-future-secured-by-hi-tech-air-energy-storage-system https://arena.gov.au/blog/commercial-concentrated-solar-one-step-closer/
Even the largest utility-scale battery installations, cannot yet provide the deep or long-duration storage for many hours, or even multiple days that the grid of the future will need as renewables start to take up an increasing proportion of the generation mix.
Beyond 10 hours and up to the many days that may be needed in the event of a solar and/or wind drought, pumped hydro is the best and most proven option The key difference between a pumped hydro scheme and a traditional hydropower operation is that pumped hydro is not a net generator of electricity. It is both a load and a generator, at different times, as needed. https://www.csiro.au/en/work-with-us/services/consultancy-strategic-advice-services/csiro-futures/energy-and-resources/renewable-energy-storage-roadmap
In my next instalment I will be taking a deeper dive into batteries and pumped hydro, looking at their strengths and weaknesses and summarising where Australia currently sits in the deployment of these technologies.
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