By Chris Alden

Solar power and seawater to produce energy, food and water in Sahara Desert

Mention the words “Sahara Forest” to anyone over the age of 20, and they’ll soon recall the old joke about the woodcutter who says that’s where he learnt his trade. “Surely you mean the Sahara Desert?” his questioner replies. “Ah,” says the woodcutter, “That’s what they call it now.”

These days the Sahara Forest Project is the ambitious name given to a British proposal which aims to produce clean energy, food and water in coastal desert regions such as North Africa or the Middle East – while helping to revegetate desert land.

The idea is to exploit synergies between two technologies: i) the “Seawater Greenhouse” designed by Charlie Paton (part of the Sahara Forest team), which evaporates and distils seawater, at the same time producing cool, humid environments for plants; and ii) concentrating solar power (CSP).

“Both work well in hot, sunny conditions,” said Michael Pawlyn, Director of Exploration Architecture, also part of the Sahara Forest team. “CSP needs a supply of demineralised fresh water to keep mirrors clean – and that’s what the Seawater Greenhouse produces.”

“And CSP produces a lot of waste heat – [which] we could use to heat seawater going into evaporators, [which] can create more fresh water.” He added that if a CSP plant were on the downwind side of the greenhouses, less dust would accumulate on the mirrors, making power generation more efficient.

Pawlyn declined to give potential figures on costs for the project, but said it could take eight months to a year to become operational, after which payback on the investment would take between six and twelve years. He said the team was in “fairly advanced” discussions with two clients over a demonstration plant.

As for the delivery mechanism for power, Pawlyn said a small-scale plant would probably be built close to a population centre – and speculated that a larger-scale scheme might be linked to a high-voltage DC supergrid, if one is built.

Reese Tisdale, a solar and renewables analyst at Emerging Energy Research, said the scheme was “innovative” but warned that in the current financial climate, investors were risk averse. Even more straightforward CSP projects, he said, could have trouble raising money from a bank in the near term.

Meanwhile in Israel, construction has begun on the “world’s first hybrid solar-gas turbine”, developed by Aora Solar in Kibbutz Samar. The 100kW plant (which also burns biofuels at night) will heat air to 1,000°C to drive its turbines. The company, which hopes to expand in the future, says its modular, “decentralised” business model means small-scale plants can be built in a matter of weeks.

Tisdale said the heated-air design is currently third in the CSP development curve behind the most established method, heating water for steam, and a further innovation, heating salts. In Seville in Spain, Torresol Energy has secured €171 million to build a 17MW CSP plant which will use molten salts, and is set to be operational in 2011.

Green Futures is published by Forum for the Future and is one of the leading magazines on environmental solutions and sustainable futures. Its aim is to demonstrate that a sustainable future is both practical and desirable – and can be profitable, too.

Photo credit: Green Futures.