3 June 2014

Supercritical solar - new frontier for power generation

CSIRO has used solar energy to generate hot and pressurised ‘supercritical’ steam, at the highest temperatures ever achieved in the world outside of fossil fuel sources.

Supercritical solar steam - the new frontier for power generation

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[Music plays and text appears: Supercritical solar steam: the new frontier for power generation]

[Image changes to show an array of mirrors reflecting sunlight onto a solar tower and then moves to show moving solar panels]

[Image changes to show Mike Collins, Research Projects Officer, CSIRO Energy Technology]

Mike Collins: Solar thermal energy works by concentrating sunlight using mirrors. The light is then shone up on top of the tower where there’s a solar receiver and in that receiver there’s a panel of tubes which steam is flowing inside. That steam is heated to high temperatures and then it flows back down the tower to a turbine at the bottom of the tower, a steam turbine. The steam flowing through that turbine spins the generator to generate electricity.

[Image changes to show Robbie McNaughton, Research Projects Officer, CSIRO Energy Technology]

Robbie McNaughton: The temperatures that we’ve obtained are over 550 degrees and at pressures above 24 mega Pascals. This is called supercritical steam generation and it’s a state where steam actually transforms without boiling.

[Camera moves back to the solar panels and solar boiler]

The steam conditions that we’ve achieved are comparable to what is running at the moment in fossil fuel power stations. So we’re able to actually either displace the steam that goes into these, reducing the fossil fuel reliance, or in some cases maybe even replace fossil fuel completely.

[Image has changed back to Robbie]

It’s really exciting to work on these types of projects. Doing a world first is always exciting but in this case what we’ve actually been able to do is potentially make a step change in the way solar thermal power is generated.

[Music plays and CSIRO logo appears with text: Big ideas start here www.csiro.au]

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Supercritical steam is a breakthrough for solar energy and means that one day the sun could be used to drive the most advanced power stations in the world, currently only driven by coal or gas.

CSIRO's Energy Director, Dr Alex Wonhas said this milestone is a game-changer for the renewable energy industry.

"It's like breaking the sound barrier; this step change proves solar has the potential to compete with the peak performance capabilities of fossil fuel sources," Dr Wonhas said.

"Instead of relying on burning fossil fuels to produce supercritical steam, this breakthrough demonstrates that the power plants of the future could instead be using the free, zero emission energy of the sun to achieve the same result."

Supercritical solar steam is water pressurised at enormous force and heated using solar radiation. Around 90 per cent of Australia's electricity is generated using fossil fuel, but only a small number of power stations are based on the more advanced supercritical steam.

The world record, set in May this year, was at a pressure of 23.5 megapascals (a measure of force per unit area), and temperatures up to 570 degrees Celsius. It is the combination of pressure and temperature demonstrated at scale that makes this such a breakthrough for solar power.

Commercial solar thermal power plants around the world use subcritical steam, operating at similar temperatures but at lower pressure. If these plants were able to move to supercritical steam, it would increase the efficiency and help to lower the cost of solar electricity.

The $5.68 million research program is supported by the Australian Renewable Energy Agency (ARENA) and is part of a broader collaboration with Abengoa Solar, the largest supplier of solar thermal electricity in the world. CSIRO and Abengoa Solar, with support from ARENA, are developing advanced solar storage to provide solar electricity at any time, day or night.

The breakthrough was made at the CSIRO Energy Centre, Newcastle, home to Australia’s low emission and renewable energy research. The Centre includes two solar thermal test plants featuring more than 600 mirrors (heliostats) directed at two towers housing solar receivers and turbines.

Although there is still work to be done before this technology is ready for commercialisation, ARENA CEO Ivor Frischknecht acknowledged the significant achievement saying it demonstrates the importance of research and development.

"This breakthrough brings solar thermal energy a step closer to cost competitiveness with fossil fuel generated power,"  Mr Frischknecht said.

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