Australia is looking for new ways to put sunshine aside for later

Every morning, the sun tilts over the horizon and lights up the red dirt and saltbush around the South Australian town of Port Augusta. Soon, if an ambitious construction project here goes according to plan, the sun’s rays will be falling onto nearly 20,000 strategically placed mirrors in the area as well.

“Remember playing with a magnifying glass as a kid?” says Craig Wood, chief executive of the project’s developer, Vast Solar. “This will be like a giant industrial version of that.”

Harnessing energy from Australia’s scorching sun is nothing new: we have the highest per-capita uptake of photovoltaic solar panels in the world. But while rooftop panels convert sunlight directly into electricity, another technology, known as “concentrated solar thermal”, instead uses thousands of mirrors to focus solar rays on receiver points. It then converts the energy into heat that can be stored and used later to make steam, spin turbines and supply electricity, long after the sun goes down, for eight hours or even more.

As the transition from coal to cleaner energy continues at pace, the plan here at Port Augusta is one example of the creative ways that companies are trying to solve a burning problem: how to store large amounts of renewable energy that can be used in the evenings, overnight or prolonged periods of low wind and sunlight.

Artist render of Vast’s proposed concentrated solar project in Port Augusta.

While coal still makes up more than 50 per cent of east-coast electricity supplies, officials think it could be gone from the grid entirely by as early as 2040, making Australia’s transition to renewables one of the fastest in the world. The shift is good news for the climate – coal is a huge source of the greenhouse gas emissions that are driving global warming. But an energy system soon to be dominated by more wind and solar brings added challenges, and boosting our capacity to store renewable energy when it’s abundant will be essential to keeping the lights on.

For the most part, electric utilities and governments have been seeking to address this by building out a growing fleet of big batteries – mainly lithium-ion – which soak up surplus renewable energy and inject critical power discharges with near-zero start-up time. The other technology they are turning to is pumped hydroelectric dams, which use motors to pump water uphill to a higher reservoir, then release it downhill to spin turbines connected to generators whenever the grid needs topping up.

But both technologies have their limits. Today’s batteries exhaust their stored energy in two to four hours of maximum output, minimising their ability to plug longer solar or wind shortfalls. Pumped hydro, meanwhile, needs significant height differentials over short distances, making it difficult to secure the right locations such as mountain ranges, and then carry out construction on time and on budget. When it was announced in 2017, the Snowy 2.0 pumped hydro project, the biggest in the country, had an expected completion date of 2021 and a price tag of $2 billion. It has since blown out to $12 billion and a deadline of 2029.

With batteries set to continue dominating the shorter storage market, and pumped hydro able to run for days, “what you need is stuff in the middle,” says Wood.

“When you are talking to the big retailers, industry and government, long-duration storage is the next frontier, and they are looking for something that can reliably provide 12–20 hours every night.”

Vast Solar’s $360 million concentrated solar project in Port Augusta, with the backing of the Australian Renewable Energy Agency (ARENA), aims to bring to Australia a technology widely used in other parts of the world with strong solar resources, such as Spain, Morocco, Israel and Chile.

“Remember playing with a magnifying glass as a kid? This will be like a giant industrial version of that.”

Vast Solar’s Craig Wood

Rather than a central tower, typical of other concentrated solar plants, the Port Augusta project is planning multiple receiving towers that will be surrounded by different fields of mirrors known as heliostats. It will also use sodium as the heat-transfer fluid. Vast is aiming to make a final decision on the investment in coming months.

If the plant proceeds to construction, the intention is to run it daily, firing it up to dispatch electricity in time for the evening peak demand period when people typically begin arriving home and turning on air-conditioners while the sunlight begins to recede.

“If you assume the peak is going to start at 4.30pm when everyone gets home, turns their air-conditioners on and the sun starts to get low on the horizon, then you probably start to create steam at about 4pm, warm the turbine up and sync it at 4.30pm, then basically run it hard from 4.30 until 10pm to midnight,” says Wood. “You might also ease off turbine output overnight to allow you to service the morning peak.”

Just over the South Australia-NSW border, Canadian company Hydrostor is working on bringing to life another innovative energy storage solution: compressed air.

Artists rendering of Silver City Energy Project at Broken Hill, being developed by Hydrostor.

On the site of a disused zinc, copper and gold mine in Broken Hill, Hydrostor is planning the Silver City Energy Project as part of a push to replace the dirty diesel generators that supply back-up power to the town.

To charge the system, the 200-megawatt plant will draw power from the grid when it’s cheap at times of surplus wind and sunlight, then run it through an air compressor, explains Hydrostor’s Sara Taylor. This removes the heat and moisture out of the air, stores it to be used later, then puts the air down into an underground flooded cavern, 600 metres beneath the surface.

“When you push the air down into the cavern, it pushes the water from the cavern up to a surface reservoir and the compressed air is held under pressure in the cavern by that surface reservoir,” she says.

“So, when the sun isn’t shining and the wind is not blowing, you reverse the process – push the water into the cavern, that pushes the cold air to the surface, which is reheated with the heat you stored earlier, which then drives the turbine to create electricity.”

Taylor says the technology has some similarity to pumped hydro, but can be more “flexibly located”. “We aren’t looking for the perfect hill,” she says.

“We run longer than a battery,” she adds, “and we have a much longer lifespan.”

Hydrostor was drawn to Broken Hill after NSW identified long-duration storage as eight hours or more under its Electricity Infrastructure Investment Act, and followed it up with a revenue-underwriting program to support new developments.

But what really “tipped it over the edge”, Taylor says, was a deal it reached with transmission operator Transgrid for the supply of back-up power to the historic mining town.

“They had a reliability problem they needed to solve because the diesel generators that were providing back-up power in Broken Hill were coming to the end of their lives,” she says. “We thought this was the perfect opportunity to showcase the technology and all of its benefits by helping to create a mini-grid that connects all the existing renewable infrastructure there with projects like ours to keep the lights on and the mines operational when the transmission line to the town goes down.”

The company is aiming to begin construction of the eight-hour storage project later this year.

While Hydrostor’s global focus is on compressed air, the company has been advocating more broadly for market reforms in Australia that properly value the role of all long-duration storage technologies. The capacity to soak up excess renewable energy and use it smooth out supply and demand imbalances will ultimately reduce the need for baseload power and drive the grid to a greener future, says Taylor.

“The longer the duration, the better you can smooth over the times that you have low wind, like a wind drought, or successive days without solar,” she says.

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