Australia’s transition to renewables is gaining momentum, but something is looming problem with storage. We will need a lot more long-term storage to get through the night once coal and fossil gas leave the system.

We also need to find new and better ways to generate heat for industrial processes. Renewable energy sources can provide much of that heat during the day, but energy storage will be needed to meet industry’s nighttime heat needs.

Solar thermal technology has the potential to provide both long-term storage and industrial heat, but is largely overlooked in the Australian context. That’s going to change.

The CSIRO Renewable Energy Storage Roadmap identifies that a mix of technologies will be needed, across all sectors, to meet Australia’s energy storage needs, particularly at night. Solar thermal energy will be an important part of the mix.

You won’t make it with batteries alone. They are good for short term storage ranging from a few minutes to an hour or two. But you would need an awful lot of them, at a huge cost, to cover 8-12 hours. Solar thermal becomes cost-effective for long-term storage at scale, and brings other benefits as well.

Introduction of thermal energy storage

The Australian Energy Market Operator (AEMO) identified storage from four to twelve hours as “the most pressing utility-scale need in the next decade”. That is what is needed “to manage stronger diurnal variations in solar and wind production and to meet consumer demand, including during more extreme days, when coal capacity is declining.”

Most people are familiar with the (chemical) storage of lithium ion batteries and pumped hydro (mechanical) storage. However, thermal energy storage is not well understood or recognized. This is partly due to perceived costs and technical challenges. However, as concentrated solar thermal plants are being built all over the world – 30 are being developed in China alone – the knowledge base is growing.

Over 80% of Australia’s total energy consumption is a thermal process:

• burning coal and gas for electricity
• combustion of fuels for transportation
• combustion of fuels for industrial process heat.

A large part of these existing fossil fuel-based thermal processes can be accommodated with sustainable thermal energy storage.

The CSIRO Energy Center in Newcastle contains the only operational high temperature solar thermal research facility of its kind in Australia. This is the largest solar panel with a high concentration in the southern hemisphere. CSIRO, author provided

The CSIRO roadmap showed that thermal energy storage was a relatively low-cost solution with multiple applications, including utility-scale power generation, renewable fuel production, and industrial process heat.

For utility-scale power generation, the least expensive eight-hour storage technology by 2050 is thermal energy storage using concentrated solar thermal energy. The cost in 2050 was just over A$100/MWh, compared to a lithium-ion battery at A$140/MWh and pumped hydro at around A$155/MWh.

For 24-hour storage technologies in 2050, thermal energy storage was again the lowest cost at A$99/MWh, compared to pumped hydro at A$145/MWh or grid-charged electric (using photovoltaics and wind) thermal energy storage at A$ 150 /MWh.

Short-term storage is likely to remain the domain of lithium-ion batteries for at least two hours, and perhaps as long as four hours.

This is how it works

Concentrated solar thermal energy uses mirrors to convert sunlight into heat energy. This heat energy is usually stored.

The stored thermal energy can then be used at any time of the day or night as required to produce steam for electricity production or heat/steam for industrial processes.

The system typically provides six to 24 hours of operation. This means that concentrated solar thermal energy can provide continuous, on-demand power and/or process heat 24/7. It can also simultaneously generate power and store heat at the same time.

The stored thermal energy is usually used at night. Concentrated solar thermal systems deployed in China, Spain, the United States, South America, Africa and the Middle East generally have more than ten hours of storage capacity, enabling renewable energy and heat to be generated overnight.

Concentrated solar thermal power is also a synchronous technology because it uses a traditional spinning turbine (identical to those used in coal-fired power stations). This creates much-needed system strength and frequency services to the grid. When coal plants close, concentrated solar thermal power is essentially a technology that can continue to provide essential system services.

While more than 100 concentrated solar thermal installations, generating 7GWh of electricity, have been deployed around the world, the technology has not yet been widely deployed in Australia. That will soon change with the construction of Extensive solar energy of a 30 MW concentrated solar thermal facility in Port Augusta, supported in part by the federal government. The project will have ten hours of thermal energy storage to generate power for delivery to the grid, mainly at night. The project will also provide renewable heat and power to produce more than 7,000 tons of green (renewable) methanol annually. (Methanol is an essential chemical building block for hundreds of consumer and industrial products such as paints, carpets, fabrics, building materials and liquid fuels).

In Vast Solar’s modular design, deployed at the Jemalong Pilot Plant in central western New South Wales, there are five separate arrays, each concentrating solar radiation on its own 27-metre high thermal receiving tower. Fixed solar power, author provided

Heed the warning

We need to start building renewable energy storage systems now so that we have safe and reliable power when the sun isn’t shining and the wind isn’t blowing. We also need to replace fossil fuels used to create industrial process heat.

Sectors such as mining, industry, transportation, agriculture and households all need safe, reliable and affordable renewable energy. For many sectors, this need occurs at night and storage is required for that.

Editor’s Note: Dominic Zaal contributed to the CSIRO Renewable Energy Storage Roadmap as one of a number of internal and external technical advisors.