By David Craik

Compact Linear Fresnel Reflector technology or CLFR has been aggressively promoted by energy giant Areva since its acquisition of Ausra Solar last year.

The technology is unique from other CSP processes such as parabolic troughs in that it uses modular flat reflectors to focus the sun’s heat onto stationary receivers consisting of a system of water filled tubes. The concentrated sunlight boils the water, which generates high-pressure steam without the need for costly heat exchangers or intermediate heat transfer fluids such as oil or salt.

After years of testing, Areva Solar sees the opportunity to use the technology in a standalone power plant powered by solar energy with a natural gas-fired backup boiler, as a solar steam power booster for fossil-fuelled power plants or in enhanced oil recovery.

This was most recently demonstrated at Areva’s ‘commercial flagship’  Kimberlina  Solar Power Station in Bakersfield, California where it has produced high pressure super-heated steam over the course of the last three years.

“The system substantially beat our commercial model by 13 per cent in terms of thermal performance at conditions roughly equivalent to what a parabolic trough could do. That is 370 degrees Celsius super-heated steam,” says Areva Solar’s vice president of engineering Bill Conlon. “We expect the system to run well above 400 degrees Celsius which is an advantage over oil which degrades rapidly at those temperatures. That’s a fundamental limitation of trough.”

The Kimberlina system is now set for use at the 750MW Kogan-Creek coal fired power station in Australia. Areva will bring an additional 44MW electric boost from the super-heated steam it produces when operations begin next summer.

“CLFR is the most land efficient solar technology,” says Conlon. “That helps utilities as units can be located close to their power stations and is therefore lower cost than a stand-alone PV plant.”

Next door to the Kogan plant is Solar Dawn, a 250MW solar thermal gas hybrid power plant, which will also use Areva’s CLFR technology using gas back-up from 2015.

Steady progress

Novatec Solar is another linear-Fresnel developer making progress with its technology. Its PE1 demonstration solar power station, using linear-Fresnel collectors, has an electrical output of 1.4MW. Its PE2 project, still in construction, is the world’s ‘first utility scale solar thermal power plant’ and will produce 30MW from linear-Fresnel.

A spokesperson says PE1’s performance has met ‘guarantees’ and proved its superiority over troughs by using less materials and more efficient land use.

Novatec Solar's new Supernova solar boiler will also produce higher temperatures than parabolic troughs at 450 degree Celsius.

Germany’s Solar Power Group says its linear-fresnel project to provide steam to the coal-fired Mejillones plant in Chile is still being worked on so no comparative cost figures with other technologies can be given.

But Mauricio Rojas. of the firm’s business development team, says: “Fresnel systems require less glass and steel for equivalent energy outputs compared to troughs. However some Fresnel components have to be sourced at high costs due to low volumes. The final promise of lower costs will be achieved when a certain critical mass of Fresnel projects is achieved and you get the cost benefits of mass production.”

For Rojas the future goal is to increase working temperatures and pressure. The incorporation of thermal storage, currently unavailable to direct steam generator systems, will also help drive the technology forward. Rojas expects that to come from 2015 onwards.

Beyond booster

So do all these projects mark a breakthrough into the mainstream?

Brett Prior, senior analyst at Greentech Media, suggests not. He says that CLFR is still a ‘marginalised technology’.

 “The number of CLFR projects worldwide is almost invisible,” he says. “The CLFR guys say they are cheaper than trough per kilowatt-per hour generation and at $0.137 compared to $0.155 they are. But investors are uncomfortable with technology using water not oil.”

He says Solar Dawn is CLFR’s big opportunity as it can “demonstrate that CLFR can roll-out on a larger scale at costs low enough to challenge PV”.

Arnold Leitner, founder of solar thermal technology firm SkyFuel, says that large-scale direct steam generation has not yet been proven. Only Novatec has a single megawatt unit with some operating experience, while Areva plans a big leap in bringing this technology to commercial plants from a few demonstration units.

“At the current state of the market, DSG-linear Frensel and effectively all CSP technologies need to re-establish that they can produce energy at a lower cost than PV”, he says. For example, a DSG-Linear Fresnel system needs to oversize its solar field with respect to the power block capacity to reach capacity factors commensurate with other CSP systems or single-axis tracking PV. This will add costs to the solar field.

“Therefore, competitiveness for DSG-linear Fresnel depends on the promise that the solar thermal energy collection can be done cheaply." On the other hand, Leitner highlights, if DSG can prove to be a cheap source of solar steam “it could be the right CSP technology in enhanced oil recovery applications as it may produce steam at the lowest cost of any CSP technology and be modular at the same time”.

To respond to this article, please write to the Editor:

Rikki Stancich: rstancich@csptoday.com

Image credit: Areva's CLFR technology

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