We already use batteries to power our phones, laptops and electric cars – and as Australia’s energy generation mix continues to evolve, we’re turning to them to help power our electricity grid, too.
Australia has been blessed with abundant wind and sunshine, but they are not always available so renewable energy has to be efficiently stored. That’s where batteries come into the picture.
How do batteries store energy?
A fundamental problem with electricity is that it cannot be captured and stored. Batteries are a way of getting around this problem – they store chemicals that can be converted into electrical energy, a process known as electrochemistry.
The power unit inside a battery is called an electrochemical cell. Each cell consists of three main components – two electrodes, called the anode and the cathode, and a chemical solution called an electrolyte that puts the anode and the cathode in contact with one another and allows for the flow of electrical charge between them. A battery can contain one or several of these cells.
If a battery is disposable, this process only works in one direction – electrons flow from the anode to the cathode, transforming chemical energy to electrical energy. Eventually, as the chemical potential of both electrodes wears down, so will the disposable battery.
In rechargeable batteries, however, this process can be reversed. As electrical energy from an outside source – like a charger that you plug into your wall – is applied to the chemical system and moves electrons from the cathode to the anode, it restores the battery’s charge.
This process greatly enhances the battery’s lifespan, but it can’t last forever. Every charge cycle degrades the electrodes further, until eventually, even a rechargeable battery will stop working.
There are many different types of rechargeable batteries, made from different materials that affect how the battery works. For many years, nickel cadmium batteries were common in portable consumer devices, but they suffered from a memory effect that diminished their capacity if they weren’t fully depleted before they were recharged. The toxicity of cadmium was another major drawback, leading to nickel cadmium batteries being largely replaced by nickel metal hydride batteries.
Today, lithium ion batteries are most commonly used for storing electricity. Lithium is the lightest metal, and has the highest electrode potential, which means batteries using lithium generally offer superior energy-to-weight performance. They also tend to be less susceptible to the aforementioned memory effect. Better yet, Australia is the world’s largest exporter of lithium, so the popularity of lithium ion batteries presents clear economic opportunities.
Originally used primarily for mobile applications like smart phones, tablets and laptops, lithium ion batteries made their way into electric cars in 2008, with the production of the first Tesla Roadster. Since then, they’ve become ubiquitous, used in virtually all electric car makes and models and countless other devices.
As Dr Alan Finkel AO recently noted in his Quarterly Essay piece, Getting to Zero, lithium ion batteries are being manufactured in ever-increasing numbers at ever-diminishing prices, with the average price of a battery pack for automotive use falling from US$1183 per kilowatt hour (kWh) in 2010 to US$156 per kWh in 2019. This makes lithium ion batteries an increasingly viable solution for a real problem facing the National Electricity Market (NEM).
How can batteries support a stable electricity supply?
There’s an increasingly large proportion of wind and solar generation in the NEM, and their output varies depending on the weather and the time of day. This leads us to the question that comes up whenever the topic turns to renewable energy: How will a system that’s increasingly reliant on wind and solar energy cope when the wind isn’t blowing and the sun isn’t shining?
The fluctuating nature of renewable energy presents a problem known as intermittency. To maintain the reliability of the National Electricity Market (NEM), variable renewable energy sources like wind and solar must be firmed up with dispatchable sources that can be ramped up quickly to cover shortfalls.
According to both the Energy Security Board’s (ESB’s) Post 2025 Market Design Directions Paper and the Australian Energy Market Operator’s (AEMO’s) 2020 Integrated System Plan, the projected influx of new renewable energy in the NEM over the next two decades will need to be supported by 6 to 19 gigawatts (GW) of new dispatchable sources to fill the intermittency gap.
The AEMO’s Integrated System Plan calls for large, grid-scale batteries to be part of this solution. The virtue of using batteries in conjunction with variable renewable energy generation is that batteries can store energy at times of low demand, and dispatch it at times of high demand. Batteries can also ramp up faster than fast-start gas generators (which are themselves faster than coal-fired power stations), providing the grid with much-needed flexibility.
The world’s first grid-scale lithium ion battery was commissioned in California in 2012. Batteries are measured in megawatts (MW) and megawatt hours (MWh) – the Californian battery provided 1.25 MWh of energy storage, capable of discharge at 5 MW, which meant it could run at full power for just 15 minutes.
Today, grid-scale lithium ion batteries are much larger and increasingly common. The largest in Australia – for now – is the Hornsdale Power Reserve in South Australia, famously commissioned after a state-wide blackout in 2017, which provides 194 MWh of energy storage, capable of discharge at 150 MW, which means it can dispatch electricity at full power for roughly an hour and a half.
Stanwell recently announced plans to develop a 150 MW, 300 MWh battery alongside the 1400MW Tarong Power Station in the South Burnett. The announcement followed Stanwell’s battery storage feasibility study, which found that locating a large-scale energy storage system here would capitalise on existing land and connection infrastructure, support investment in renewables within the region, and help maintain system security and reliability.
Stanwell acting CEO Adam Aspinall said a final investment decision won’t be made until the completion of front-end engineering design work in the second half of 2021. If the battery goes ahead, it’s expected to commence operation in 2023 and be capable of dispatching electricity at full power for two hours.
“Energy storage will be critical,” Mr Aspinall said, “as it helps facilitate the integration of renewable energy into the energy system by storing electricity generated by wind and solar and supplying it to the market when required.”
The Queensland Government has also announced plans to install five grid-scale batteries, with a combined capacity of 40 MWh, in regions throughout the state as part of a community battery trial.
Batteries alone won’t fill the intermittency gap – but alongside other energy storage technologies, like large-scale pumped hydro, they can help to support the increased use of variable renewable energy sources and ensure the continued stability of Queensland and Australia’s electricity supply.