A team of ANU researchers led by Associate Professor Joseph Coventry has reached a ground-breaking temperature of 800 degrees Celsius in tests of a new thermal energy storage technology.
Developed in partnership with Graphite Energy, this new approach heats and pumps liquid sodium through metal tubes that snake their way through solid graphite. The graphite absorbs the heat, and the energy is stored for days, even weeks. Because renewable energy sources are weather-dependent, extending the duration of energy storage is an essential step in the transition away from fossil fuels.
“The real achievement here is the operation of a sodium lab in a test campaign at such high temperatures,” said Coventry. “This is the first sodium lab that's been set up in Australia, to my knowledge, and is I think, one of the highest temperature, if not the highest temperature, sodium labs in the world.”
Liquid sodium is one of the few fluids that remains liquid at such high temperatures. Using liquid sodium for heat transfer is a novel approach.
Why are high temperatures important?
Existing power generation technologies need to operate at high temperatures to be efficient and therefore need compatible storage systems. And there are a range of industries such as food and beverage, and pulp and paper, that directly use energy in the form of industrial process heat at high temperatures. In fact, industrial process heat makes up around 21 per cent of energy consumption in Australia. Currently the vast majority of this energy is provided by natural gas and coal. Storing thermal energy on-site is a low cost way for businesses to take advantage of electricity from wind and solar.
Graphite Energy COO Byron Ross says that being able to reach high temperatures is particularly important for them. “Our storage is a solid state storage, so the higher the temperatures that we can reach the more useful work we can do. As a general industry move, higher temperatures on the whole enable higher efficiency, particularly in thermal to electric conversion cycles. This testing at ANU is all part of the support activities that the industry needs to do to enable those pathways.”
Joe Coventry of ANU and Byron Ross of Graphite Energy discuss the results of the testing, which includes multiple charge-discharge cycles of Graphite Energy’s thermal storage unit at different temperature ranges and under different sodium flow rates.
Decarbonising the industry
Decarbonising energy production is essential for reducing carbon emissions. And, because renewable energy sources such as wind and solar rely on windspeed and daytime sun, it is essential to be able to store energy for later use.
The idea behind thermal energy storage is to take the electricity from the grid when it is cheap – when there is lots of wind or sun – and transfer that energy to a very low-cost form of storage so that it can be used when needed. Renewable energy plants can use it to store energy generated during periods of high production for sale during periods of high demand.
“Storing energy in the form of heat is a very efficient and low cost way of storing energy compared to batteries or other types of energy storage,” said Coventry. “We do need different kinds of storage technologies, but high temperature storage technologies allow you to store it at very low cost.”
The ANU sodium lab is the first of its kind in Australia. While it’s been in development for several years this is the first test campaign that the team has run with an industrial partner.
The collaboration between Graphite Energy and the ANU was supported by the Australian Solar Thermal Research Institute (ASTRI), which is funded by the Australian Renewable Energy Agency (ARENA) to facilitate domestic uptake of solar thermal technologies.
“ASTRI places a strong emphasis on collaboration between industry and academia to address the need for reliable, cost-effective, low emission technology solutions” said Director of ASTRI, Mr Dominic Zaal.
“Long-duration, renewable energy storage is essential for Australia’s transition away from fossil fuel energy sources. The collaboration between Graphite Energy and ANU demonstrates how renewable heat can be stored and then used for power or heat applications, when required, at any time of day or night,” said Zaal.
Graphite Energy had identified sodium as an important research pathway for high temperature thermal energy storage, particularly for next-generation solar thermal, and were looking for a research partner to test the technology.
“We have a very well-developed commercialisation program around the lower temperatures for food and beverage and fast moving consumer goods manufacturers,” said Ross. “They’re all on a journey to reduce their natural gas reliance, and decarbonise the production of their outputs. As we push into high temperatures, we need to look at different ways of getting that energy out to thermal storage.”
The partnership with the ANU team has allowed them to develop and fine-tune the performance simulation models that the company uses so that they can better understand their own technology and how it works.