The Australian Science Agency reports a breakthrough in concentrated solar thermal energy storage

“This is important because it creates an opportunity for greater renewable energy storage when combined with our proprietary heat exchanger,” Kim said. “This technology is key to delivering low-cost renewable energy at scale to decarbonise Australia’s heavy industry.”

At the heart of the new process is concentrated solar heat (CST). The concept involves using mirrors to concentrate sunlight, turning it into heat, which can then be stored or used to generate electricity.

CST is not exactly new. The basic idea dates back to the 1800s, when European inventors were concerned with concentrating sunlight. Several different concentrated solar thermal technologies have been developed in recent decades. They range from a parabolic dish surrounded by mirrors to tower systems filled with molten salt.

Today, the game changers are ceramic particles as fine as sand. Able to withstand incredibly high temperatures, they are ideal for storing significant amounts of heat.

These heated particles act like a battery, storing energy as heat for up to 15 hours. As the particles cool, they release this energy. They could provide power when needed, even at night and during periods of low solar and wind output.

Traditional CSTs are limited by the heat transfer fluids they use. Common fluids such as molten salt or high temperature oil can only withstand up to 600°C and 400°C respectively.

However, the ceramic particles the team worked with can withstand temperatures in excess of 1,000°C. These particles not only absorb the sun’s heat, but also store it, simplifying the system and reducing costs.

The “falling” part of this method uses gravity to heat these small, dark ceramic particles. Each particle is less than half a millimeter in size. Particles are released from a hopper at the top of the tower and heated as they pass through focused solar energy. In a shortage, their temperature can jump from 500°C to 800°C, and with more advanced settings, possibly over 1000°C.

Unlike traditional methods that rely on steel pipes, the particles fall freely. This approach avoids the thermal limitations of steel. Once heated, they are stored in a silo. When needed, they are used to generate steam for power generation or other industrial tasks.

Catch and release

Although successful, developing the process was not without its challenges. When particles fall too fast, they spread. This lets sunlight through and reduces efficiency. The answer was the catch and release method. After falling a short distance, the particles land in a trough, which slows them down before they are allowed to fall into the next trough.

“CST does not compete with solar PV,” said Dominique Saal. “PV gives you energy when the sun is shining, while CST takes energy from the sun, stores it, and then allows the user to use that energy when the sun is not shining, such as at night or on cloudy days.”

It’s a match made in heaven. CST with ceramic particles can offer a reliable and environmentally friendly energy source. And this is urgently needed, with 62 per cent of Australia’s coal-fired power stations now expected to close before 2033.

The CSIRO pilot system in Newcastle has 400 mirrors. But full-scale can use over 10,000 larger mirrors. They can generate power similar to a 100 MW coal plant.

“The challenge is not so much harvesting energy from the sun; it’s how to safely and efficiently convert that energy into heat and store it for later use,” said researcher Wes Stein. “Generating electricity from CST technology is like a coal-fired power plant without coal. It uses the same turbine. Typical coal-fired power plants use a steam turbine that operates at 540 degrees. Instead of using coal to create heat to superheat the steam, we capture energy from the sun and store it for 10 to 15 hours.

A global review reports 6,460 megawatts of CST projects currently operating in 18 different countries, with another 3,859 MW of projects under construction.

CST can help power industrial decarbonisation

Australia’s net-zero transition must include pathways for industrial decarbonisation, scientists say.

Saal said CSIRO’s new falling ceramic particle technology will expand the role CST can play in this mix.

“Process heat is the thermal energy used in industrial processes. And it accounts for over 20% of Australia’s total energy consumption and emissions. There is now a strong interest in industry on how to reduce thermal emissions,” he said.

ASTRI has a CST case in progress with pet food manufacturer Mars. Mars has a pet food processing plant based in Albury-Wodonga that uses more than 140 terajoules of gas per year.

The company is evaluating the potential installation of a CST system to provide renewable steam for its pet food manufacturing processes. It has the potential to displace up to 50% of their gas consumption.

“We need policies to encourage industry firsts to establish local supply chains and expertise, thereby accelerating the energy transition,” said Saal. “We want Australian industry to optimize its access to our abundant, low-cost solar resources. This will boost productivity and improve their competitive position in global and domestic markets. CSIRO CST Falling Particle Technology can provide renewable heat at the same high temperature that coal and gas provide, and for several hours.

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