Water is likely to be a big problem as the world tries to meet future demand for food. By 2050, we could need 60% more calories than we produce today. And yet, many parts of the world are already running short of freshwater necessary to grow crops (70% of all freshwater goes to agriculture).
That’s what makes the Sahara Forest Project interesting. Its saltwater greenhouse uses half as much freshwater as conventional greenhouses, and it could allow water-poor countries to grow food more sustainably while reducing the need for food imports. It could even help re-vegetate deserts in some countries.
The greenhouse has a cardboard screen at one end with hundreds of small holes in it. Saltwater trickles down from above and evaporates as it meets hot air coming in from outside. The air indoors becomes humid and up to 15 degrees Celsius cooler than normal, while the moisture condensates on the plants, helping them to grow.
At the same time, the greenhouse also has a series of pipes full of cold ocean water. When warm air hits the pipes, droplets form on the surface, which are captured and used for irrigation.
The most innovative aspect is the way the greenhouse is integrated with a concentrated solar system outside. The sun heats water so it becomes steam and turns a turbine to generate electricity. That powers the plant’s pumps as well as a desalination unit that produces more freshwater. In turn, the waste brine from the greenhouse helps cool the solar system, improving efficiency by up to 10% compared to a typical plant.
“It’s about turning waste streams from various technologies into resource streams for other technologies,” says SFP’s CEO Joakim Hauge.
The idea was born in northern Europe but is most likely to be applied in hot, desert regions. Last year, SFP ran a successful pilot at a site in Qatar, in the Gulf. It’s now at the early stages of building a full-scale facility in Jordan, with funding partly coming from the Norwegian government (SFP is based in Norway).
“Many of these arid areas have substantial water and food security issues,” Hauge adds. “Jordan is the fourth poorest country in the world when it comes to freshwater resources. So, it really makes a lot of sense to utilize other ways to achieve agricultural activity.”
The pilot showed that just eight hectares of greenhouses could produce all the cucumbers, tomatoes, peppers and eggplant Qatar consumes in a year. Currently, the country imports 90% of its produce from abroad.
The greenhouse also cooled the outside air, allowing SFP to grow 19 varieties of plants nearby, including arugula, barley, and several desert species. Hauge says the greenhouses could help reverse desertification, while trapping CO2 as the plants grow.
The big unknown is cost. Hauge admits the cucumbers grown in the pilot were substantially more expensive than what you might get at Whole Foods. But it’s probably an unfair comparison. The pilot was designed to test technology, not to optimize finances. The Food and Agricultural Organization took a look at the pilot and said “given yield levels in the pilot, the greenhouse can be profitable.”
In fact, greenhouses in super-dry regions are not as uncommon as you might expect. Not that that’s a good thing. For example, the Almeria region, in southern Spain, has 20,000 hectares of greenhouses that consume five times more water than what falls as rain. If these operations were ever forced to pay a higher price for the water they use, it may make the more expensive saltwater technology more attractive.
“We’re not in this to build pilot plants,” says Hauge. “Our ambition is to build large-scale operations and we have started dialogue in a number of countries. We believe we can do well for investors while providing social and environmental benefits at the same time.”