Topic: Salt water desert greenhouse. 75kg vegetables/sq meter/year

[Nemesis]

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A project to “green” desert areas with an innovative mix of technologies—producing food, biofuel, clean water, energy, and salt—reached a milestone this week in the Gulf state of Qatar. A pilot plant built by the Sahara Forest Project (SFP) produced 75 kilograms of vegetables per square meter in three crops annually, comparable to commercial farms in Europe, while consuming only sunlight and seawater.  The heart of the SFP concept is a specially designed greenhouse. At one end, salt water is trickled over a gridlike curtain so that the prevailing wind blows the resulting cool, moist air over the plants inside. This cooling effect allowed the Qatar facility to grow three crops per year, even in the scorching summer. At the other end of the greenhouse is a network of pipes with cold seawater running through them. Some of the moisture in the air condenses on the pipes and is collected, providing a source of fresh water.

One of the surprising side effects of such a seawater greenhouse, seen during early experiments, is that cool moist air leaking out of it encourages other plants to grow spontaneously outside. The Qatar plant took advantage of that effect to grow crops around the greenhouse, including barley and salad rocket (arugula), as well as useful desert plants. The pilot plant accentuated this exterior cooling with more “evaporative hedges” that reduced air temperatures by up to 10°C. “It was surprising how little encouragement the external crops needed,” says SFP chief Joakim Hauge.

The third key element of the SFP facility is a concentrated solar power plant. This uses mirrors in the shape of a parabolic trough to heat a fluid flowing through a pipe at its focus. The heated fluid then boils water, and the steam drives a turbine to generate power. Hence, the plant has electricity to run its control systems and pumps and can use any excess to desalinate water for irrigating the plants.

SFP researchers estimate that a facility with 60 hectares of growing area under greenhouses could provide all the cucumbers, tomatoes, peppers, and egglants now imported into Qatar.