Australia has plenty of sunshine but the more PV we build the harder it becomes to use all that solar energy. Storage is the answer, if your budget stretches that far. A cunning combination of solar and storage is concentrated solar thermal, where mirrors focus the sun’s rays to heat a solution to make steam to drive a turbine to – presto – make electricity.
An All-Energy 2020 panel chaired by Australian Energy Market Operator stream lead sector coupling Dr Cameron Potter looked at how the generation-with-storage solution is shaping up.
About 6.2GW of concentrated solar thermal is installed around the world, with 1.5GW under construction. Parabolic troughs are the most popular installed generation, near 5GW, but towers are gaining attention as an apparent lower LCOE advantage becomes more obvious. A notable failure is SolarReserve’s 110MW Crescent Dunes facility in the US, due to come back online after repairs next year.
‘Dramatic lack of knowledge’
Abengoa Energy business development director Asia-Pacific Alberto Alba Rodriguez said in regions where penetration of renewables exceeds 30% non-controllable growth in generation can have severe consequences. Hybrid “smart solar concepts” that incorporate concentrated solar power (CSP) with low-cost wind and solar generation, he says, will help policymakers get their heads around the technology, where “there is still a dramatic lack of knowledge about the benefits it can provide”.
John Cockerill business development manager Ildo Agnetti explained the technology, where sunlight concentrated by a field of heliostats heats molten salt from about 300°C to near 600°C. This stored heat can be dispatched to create steam to drive a turbine. “It works in a very similar way to a coal-fired power station, except the energy comes from the sun,” Agnetti said. Having a steam turbine in the process also allows an owner to provide services to the grid, such as FCAS.
Apart from complementing large-scale solar projects in the various renewable energy zones under development around Australia, Agnetti said hybrid plants incorporating CSP with solar and wind are a great match to replace diesel at remote mining sites where land is cheap and the solar resource is most intense. One study for a client showed such a facility could satisfy about 97% of load, he said, and any spillage could be used to make hydrogen. The company has delivered CSP projects in Chile, South Africa, Dubai and China.
Storage times can vary between facilities, and Agnetti cited John Cockerill results that varied between a 50MW plant in South Africa capable of five hours storage and a 110MW plant in Chile able to provide 17.5 hours of storage. These durations place CSP near pumped hydro, he said, and LCOE is about the same as offshore wind.
A match for coal retirements
ITP Thermal managing director Dr Keith Lovegrove explained the steam turbines used in CSP were similar to ones used in coal plants but because they are smaller they are quicker to respond. CSP systems can last at least 30 years, he said, and the narrow temperature differential between the cold tank, which at about 300°C is anything but cold, and the hot tank – around 600°C – makes the solution “cheap”.
As negative pricing becomes more of a bother in the market the electric heating elements in the tanks can provide valuable load, he suggested, even with a round trip efficiency of about 40%.
Around the world, China is tearing ahead of the pack with CSP. Since 2018 the Middle Kingdom has competed eight of 20 projects in a 1.35GW pilot program for CSP, a mixture of trough and tower facilities.
In Australia, a CSP plant has been operating at a tomato farm in South Australia since 2016 and local CSP technology company Vast Solar is operating a 1MW demonstration facility with plans for a 50MW integrated system in Mt Isa, Queensland. The Kogan Creek Solar Boost, a 44MW plant using technology from French company AREVA, was abandoned by CS Energy in 2016, only 75% complete.
Lovegrove said ITP has advised on a CSP proposal near the future NSW-South Australia interconnector, where it found 14 hours of storage would be the solution to maximise profit from pricing events.
Australian company RayGen has developed a concentrated solar technology where heliostats focus sunlight onto high-efficiency PV cells, very different from concentrated solar thermal.
If Australia wants to take CSP seriously, as Spain did, it could achieve 40% compound growth in deployment, “as long as the settings are there to keep that pipeline going,” Lovegrove said. “If we did that, CSP alone could easily match the capacity in coal retirements anticipated.”