Baring the secrets of Khi Solar One

Abengoa’s Khi Solar One power tower in South Africa represents a milestone in many aspects of CSP innovation.

The Khi Solar Tower in the arid Upington landscape, South Africa

By Jason Deign 

Any suspicions that South Africa would enter the CSP market with a run-of-the-mill solar thermal plant are quickly dispelled with Khi Solar One.

The 50MW power tower project, owned by Spanish developer Abengoa Solar in conjunction with the Industrial Development Corporation and the Khi Community Trust, is a unique structure rising from the barren land at Upington, Northern Cape.

What is even more unique than the 205-metre, futuristic tower is the number it innovations it contains.

Abengoa claims to have built on its experience of power towers including the PS10 and PS20 projects, operating since 2007 and 2009 respectively in Spain, to set new standards for CSP technology.

“Khi Solar One is Abengoa’s first solar tower outside of Spain and it includes many innovative features,” says an Abengoa insider. “We are building, controlling and operating a higher tower, with a higher number of heliostats, in a different country.

“The most challenging activity is the integration of all new components and having a final successful solution in different operating conditions. To overcome this challenge, however, Abengoa has been working on the design for this kind of CSP plant since 2008.

“As a result of this great engineering effort, we know the complete process in detail. The final design we are building in Khi Solar One is based on this previously developed engineering.”

Perhaps one of the most notable features of the plant, being built by Abengoa subsidiaries Abener and Teyma with €50 million of European Investment Bank funding, is that it bucks the current trend for using molten salt as a heat transfer fluid and storage medium.

Superheated steam

Instead, Khi Solar One, which will have a 576,800m2 solar field made up of more than 4,000 heliostats, uses a superheated steam cycle of the kind that Abengoa has been running since 2009 at a 3MW Solúcar Platform test plant near Seville, Spain.

With superheated steam, the South African plant should be able to reach a maximum operating temperature of 530ºC. “This temperature allows increased efficiency in the steam cycle,” says Abengoa.

“As an example, the Khi Solar One cycle reaches a 30% higher cycle efficiency than PS20.”

Accumulated saturated steam is also used to provide up to two hours’ worth of thermal storage at the plant. Despite relying on steam, however, Khi Solar One is frugal when it comes to water use, thanks to a unique dry cooling system installed by SPX Corporation.

The system is allegedly the world’s first large-scale natural draft condenser and uses towers to distribute air across fin blades in order to dissipate heat, instead of employing fans as is usually the case in air-cooled condensers.

“As this type of cooling tower operates without fans, the substantial amount of electric power otherwise required for large cooling tower systems is not needed,” claimed SPX in a press statement.

“Natural draft condensers also offer a higher efficiency and lower first and evaluated cost as compared to other dry natural draft technologies that utilise indirect cooling.”

Abengoa calculates the technology will allow Khi Solar One to use 80% less water than a wet-cooled CSP plant. And the list of innovations at the plant does not stop there.

Dry cooling

“In addition to the tower’s three advanced receivers, storage system and dry cooling, Abengoa is using a new advanced design of heliostat with higher reflective area,” says the company.

Dr Luis Crespo, president of the European Solar Thermal Electricity Association, ESTELA, believes Abengoa’s first power tower outside Spain is a shining testimony to the capabilities of Spanish CSP developers at a time when their home market is under siege.

“Having won the bid already meant they were well positioned,” he says.

Khi Solar One’s tower was completed last month, a milestone that was accompanied by a visit from South African government dignitaries.

Although he would not confirm the start date, Abengoa Solar South Africa’s general manager Dr Louis van Heerden told CSP Today that construction work was “going well.”

Khi Solar One is not Abengoa’s only project in South Africa, either. The company is also building KaXu Solar One, a 100MW parabolic trough plant, also in Northern Cape. As a more mature technology, parabolic trough offers less scope for innovation than a power tower.

But it is safe to say neither project will hurt Abengoa’s reputation for excellence in the CSP industry… nor South Africa’s ability to claim some of the best plants in the world.

To respond to this article, please write to Jason Deign

Or contact the editor, Jennifer Muirhead