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Solar Sahara

Plans to tap the suns energy in the Sahara are gaining pace, with a new project about to get underway in Spain. Ed Owen reports.

Wouldn’t it be wonderful to do something useful with all that desert sun in northern Africa? The constant heat, which makes the Sahara rather inhospitable, is of course a potential energy source.

Last year a consortium of German companies hit on the idea that generating power in North Africa may turn into a moneyspinner. Led by reinsurance firm Munich Re, but including a dozen more companies including RWE, Eon, and Abengoa, the Desertec group believes clean energy can be piped from north Africa to Europe.

The problem is that the project comes with a hefty price tag − some £350bn ( €400bn)− and large-scale projects have never been attempted. The Desertec plans aim to supply a “large proportion” of the local energy needs, and then some 15% of the European Union’s total needs.

The sun would be harnessed using concentrated solar power (CSP), which has a simple concept − the sun’s rays are reflected and concentrated using curved mirrors to focus the sun’s rays, and the heat generated is used to produce power.

“18,500 piles and 1500t of tubular steel was used and installed in eight weeks”

Duncan McGregor, Screwfast technical director

One of the Desertec members, Abengoa, is already installing commercial CSP plants in Spain. Spain is an ideal testing ground for CSP, with similar amounts of sun to that in North Africa and some 3GW of solar power already installed.

The latest will be two 50MW plants near Ecija. British firm Screwfast has been hired to install much of the plant.

“This project uses the trough design,” explains Screwfast technical director Duncan McGregor, whose company installed the foundations, superstructure and some of the panels.

Troughs use parabolic mirrors to reflect the sun onto a strip suspended in front of it. The strip contains oil that is heated to 4000c and used to boil water via a heat exchanger and turn a conventional turbine.

The works also demand a lot of conventional engineering. “Around 18,500 piles and 1500t of tubular steel was used and installed in eight weeks,” says McGregor.
Screwfast built special rigs to drive the piles into the soil.

“Our experience in transmission, desalination and solar projects in North Africa will make a significant contribution.”

Santiago Seage, Abebgoa chairman

“The soils are firm and fairly deep. But strong. Pile lengths were just 3.5-4m, so not really deep, but very firm,” he said. Screwfast is in talks to expand its solar business and is in talks with Abengoa to build more plants, and is drawing up designs for possible work at the Abu Dhabi eco city Masdar.

CSP is surprisingly versatile, and larger ‘Tower’ designs focus the light from many panels onto a tower and can produce even greater heat, up to 1,000 degrees, melting salt which is used to boil water and turn a turbine.

Other applications such as ‘cracking’, or breaking water into its constituent parts of oxygen and hydrogen. CSP can also be used to desalinate water, vital in the dry Sahara.

Using melted salt rather than heating water directly to generate electricity means heat can be retained and used at night, after the sun has set.

German academic Gregor Czisch believes CSP to be too expensive to be a credible way to generate power in North Africa − he favours using conventional wind turbines in North African hills (NCE 10 September 2009).

Project approval

Nevertheless, the concept is gaining currency, with advocates of the renewable supergrid beginning to back the desert CSP concept. Eleven pilot CSP projects have also been approved around the Middle East and North Africa, with £5.2bn set aside to build sites.

Desertec’s plans are ambitious − it estimates 100GW of power requires 2,500km² of the desert surface covered with solar power plants, and a further 3,500km² for the high-voltage direct-current transmission lines.

Despite this, Abengoa is confident the plans will become reality. It is already building North Africa’s first private integrated solar combined cycle plant in Algeria.

“Tomorrow Abengoa’s experience in transmission, desalination and solar projects in North Africa will make a significant contribution to the success of the Desertec objectives,” says Abengoa chairman Santiago Seage.

Readers' comments (1)

  • Great stuff (apart from one or two editing issues - check your operating temperatures for the two solar plants).

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