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Saltwater-cooled greenhouse grows crops in the Sahara
How do you grow vegetables in arid areas? Reverse the trend of desertification, the Sahara Forest Project proposes.
The project combines existing technologies — such as the evaporation of saltwater to create fresh water along with solar thermal energy tech — to utilize what we have (saltwater, CO2) to produce what we need (food, fresh water and energy).
This week, the project, which is supported by fertilizer companies, reached a milestone. Its Qatar pilot plant produced 75 kilograms of crops (like cucumbers) per square meter annually while consuming only sunlight and seawater, Science reports. That’s comparable to commercial farms in Europe.
At the center of the project is a saltwater-cooled greenhouse, Science explains:
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 surprising side effect is how the cool, moist air that was leaking out encouraged plants to grow spontaneously outside. By reducing exterior air temperatures with “evaporator hedges” (pictured), the plant was able to grow crops like barley and salad rocket (arugula), along with useful desert plants around the seawater greenhouse.
Another key element of the facility is the 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.
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“The big question is economic feasibility,” says Richard Tutwiler at the American University in Cairo. “How much did it cost to produce 75 kg of cucumbers per square meter?”
The project has also experimented with culturing heat-tolerant algae, growing salt-tolerant grasses for fodder or biofuel, and evaporating the concentrated saline the plant emits to produce salt, Science reports.
The Qatar plant is 1 hectare with 600 square meters of growing area inside. Next up: a 20-hectare test facility near Aqaba, Jordan.
Images: Sahara Forest Project