Could Falling Particles of Solar Energy Help Us Reach Net Zero?

Our sun-baked continent offers endless supplies of net-zero energy. However, majority of the electricity grid (67%) is still powered by fossil fuels. This is because of the challenges associated with catching and storing solar energy in a sustainable way.

This is a trajectory Australia can no longer afford, as climate change continues to impact the world’s natural environment.

As such, decarbonisation and solarbased renewable energy technology is becoming more urgent.

Australia’s national science agency, CSIRO, is at the forefront of bridging the gaps between research and practice.

At CSIRO’s concentrated solar thermal research facility in Newcastle, practitioners have investigated the potential of ‘falling ceramic particles’ to capture and store solar energy as heat.

Dr Jin-Soo Kim, who leads the solar technologies team, said the group recently achieved a critical milestone temperature of 803 degrees Celsius for the first time at the falling particle receiver employing a new and novel concept.

"This is significant because it creates the opportunity for greater renewable energy storage when combined with our patented heat exchanger," Jin-Soo said.

This technology is crucial for delivering low-cost renewable energy at scale, which helps to decarbonise much of Australia’s heavy industry.

"Over eight years of development and thousands of hours were invested to reach this outcome."

At the heart of this process is Concentrated Solar Thermal (CST), which uses mirrors to concentrate sunlight and convert it to heat.

This practice can be stored or used to generate electricity to power Australian homes and businesses. The concept of CST is not entirely new. In fact, the idea dates back to the 1800s when European inventors tinkered with sunlight concentration.

More recently, a range of concentrated solar thermal power technologies have evolved, including a parabolic dish circled by mirrors, and tower systems filled with molten salt.

CSIRO researchers believe tiny ceramic particles, as fine as sand, could be the next frontier in this body of work.

These ceramic particles can endure high temperatures, and store record amounts of heat for up to 15 hours.

Dominic Zaal is Director of the Australian Solar Thermal Research Institute (ASTRI), who said these particles could provide power during periods of low solar input, like winter.

"The technology is a smart, costeffective way to store a large amount of high temperature heat for 10–15 hours," he said.

The energy is released when the particles cool down, which offers a suite of applications as Australia transitions towards a net-zero future.

How Are Falling Ceramic Particles Boosting Concentrated Solar Thermal?

Traditional CST practices, which rely on heat transfer liquids like molten salt or oil at a high temperature, can typically handle up to 600 and 400 degrees Celsius respectively.

However, ceramic particles developed by the CSIRO research team can endure temperatures over 1,000 degrees Celsius.

These particles absorb and store the sun's heat, which simplifies the existing system and reduces costs.

Falling ceramic particles rely on gravity to generate heat. When they are dropped from a hopper at the top of the tower, they are heated as they pass through focused solar energy.

In a short fall, their temperature can shoot to 800 degrees Celsius, and even higher with more advanced setups.

Once the particles are heated, they are stored accordingly and then used to produce steam for power generated when needed.

The research team overcame challenges—like when the particles fell too fast—to develop a 'catch and release' method.

This involves the particles landing in a trough, and slowing them before they were allowed to fall into the next trough.

What Are the Benefits of This?

Australia's growing use of solar and wind energy has fast-tracked the closure of many old coal-fired power stations.

These stations do not match the affordability of daytime solar power, which is known as photovoltaic (PV) solar energy.

“CST doesn't compete with PV solar energy,” Mr Zaal said.

“PV gives you power when the sun is shining, whereas CST takes energy from the sun, stores it and then allows the user to use that energy when the sun isn't shining, such as overnight or on cloudy days.”

As such, researchers rely on CST with ceramic particles to offer a dependable and green power source.

CSIRO’s pilot system used 400 mirrors, but researchers believe a full-scale model could use over 10,000 larger mirrors, which can generate power similar to a 100MW coal plant.

Wes Stein is CSIRO’s Chief Scientist for Solar Technologies and ASTRI’s Chief Technologist, who said the challenge is how to convert energy safely and efficiently into heat and store it for later use.

“The power generation from CST technology resembles a coal-fired power plant without the 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 the heat to superheat the steam, we capture energy from the sun and store it for 10 to 15 hours,” he said.

There are 6,460MW of projects currently in operation across 18 different countries, with another 3,859MW of projects under construction.

Where to Next?

Researchers are confident in developing the commercial viability for this project.

Mr Zaal said with significant infrastructure support, falling particle CST could potentially account for up to 40% of Australia's electricity generation and process heat requirements in remote areas by 2050.

“This would make a significant contribution to Australia's emissions reduction targets and help us to achieve a more sustainable energy future.”

This is an essential step in Australia’s net-zero emissions reduction strategy, which has been legislated by the Federal Government.

Mr Zaal said the falling ceramic particle technology will expand the role that 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 use and emissions. There is now strong industry interest in how to abate thermal emissions.”