Solar thermal: the search for cheaper storage solutions

A new Australian research program is looking to develop new materials that could reduce the volume of storage systems for solar thermal energy by a factor of 10, and deliver a significant reduction in costs.

Most of the storage systems being rolled out for solar thermal systems in Spain and elsewhere have used some form of molten salt, but a project being led by the University of South Australia is looking to exploit so-called “phase change” materials that can operate at higher temperatures, and either store more heat within the same volume, or require significantly less space.

The project – which also includes the Barbara Hardy Institute, and the University of Lleida in Spain, along with the Solar Oasis consortium which is developing a 44MW “big dish” solar power project in Whyalla, South Australia, and AORA Solar in Israel – is backed by grant funding from the Australian Solar Institute.

Project leader Professor Wasim Saman, from the department of sustainable energy engineering at the University of South Australia, said his team was likely to look at a number of different materials, including inorganic salts.

Professor Saman said his team is looking at a number of potential materials that can freeze and melt at 400°C to 800°C. In order to test these materials, a specialised test facility will be built which will be able to accommodate storage systems operating at temperatures up to 900°C.

He described the molten salt storage systems being used in Spain – where the salt is melted at high temperatures and stores in huge tanks – as similar to storing water in a giant thermos.

“So what we are looking to do, similar to what happens when you melt and freeze ice, is to store a lot of heat through the change of phase from solid to liquid and vice versa – and hopefully improve the economics of the storage system,” he told RenewEconomy.

“Hopefully we can reduce the size of those tanks by factor of five to 10. That would reduce costs, but we need the technology to enable a quick enough heat transfer between material and heat source.”

Saman says his team has been working with the Solar Oasis project for some time, and the university has a campus at Whyalla. The team intends to create a small-scale storage system to use with the big-dish technology. The partnership with AORA Solar in Israel will focus on smaller concentrating solar power systems. “In both cases, the differentiation is the potential to be dispatchable. That is something that solar thermal can do.”