Seawater Greenhouses To Bring Life To The Desert

This planned project proposes to use solar power to evaporate salt water, generating cool air and pure water; thereby, allowing food to be grown in the desert using desalinated seawater. It is being heralded as either the project most likely to set the world on it's ear or the biggest piece of "pie in the sky" ever. Or could this be the change that will send us irretrievably into total climate chaos? Decide what you think.

The Sahara Forest Project will use seawater and solar power to grow food in greenhouses in the desert. Or at least, that is the claim!!

Photograph: Exploration Architecture

Charlie Paton (creator of the seawater greenhouse), Michael Pawlyn (an architect of Exploration Architecture; previously of Grimshaw; and, lead architect on the iconic Eden Project) and Bill Watts (an engineer from Max Fordham & Partners which focuses on energy-efficient systems for the built environment) combine to form the trio of visionaries who launched the Sahara Forest Project. The Sahara Forest Project plans to combine two innovative technologies, concentrated solar power (CSP) and seawater greenhouses, to produce renewable energy, water and food in an area of the desert known to be one of the hottest places on earth.

Probably the most exciting aspect of the Sahara Forest Project is the fact that two totally different technologies are being used in the same place, to support each other and to optimize the operating capacity of each – thereby, producing energy, water; and, by proxy, vegetation.

The Sahara Forest project would turn deserts into lush patches of vegetation; according to its designers, and; without the need to dig wells for fresh water, which has depleted aquifers in many parts of the world.

Currently, there are aquifers under the Sahara desert with potable, running water in them. At the current rate of water use, these aquifers have a life expectancy of another 120 years. After these aquifers have dried up, the desert will reclaim all life including the oases – those life-saving places in the desert where water and fresh vegetation can be found.

Charlie Paton said his technology was a proven way to transform arid environments. "Plants need light for growth; but, they don't like heat beyond a certain point," said Paton. “Above a particular temperature, the amount of water lost through the holes in its leaves, called stomata, gets so large that a plant will shut down photosynthesis and cannot grow. The greenhouses work by using the solar farm to power seawater evaporators; and, then pump the damp, cool air through the greenhouse.

This reduces the temperature by about 15C compared to that outside. At the other end of the greenhouse from the evaporators, the water vapor is condensed. Some of this fresh water is used to water the crops, while the rest can be used for the essential task of cleaning the solar mirrors.

So we've got conditions in the greenhouse of high humidity and lower temperature," said Paton. "The crops sitting in this slightly steamy, humid condition can grow fantastically well."

Depending on the conditions that are maintained in the greenhouses nearly any crop can be grown. It has already been demonstrated in prototypes of the greenhouses that lettuce, peppers, cucumber and tomatoes do exceptionally well.

Seaweed (or kelp) is extraordinarily rich in nutrients and can be used as fertilizer for the plants as well as nutrients extracted from the seawater.

Michael Pawlyn said the seawater greenhouse and CSP provided substantial synergies for each other. "Both technologies work extremely well in hot, dry desert locations – CSP produces a lot of waste heat and we'd be able to use that to evaporate more seawater from the greenhouse," he said. "And CSP needs a supply of clean, dematerialized water in order for the [electricity-generating] turbines to function and to keep the mirrors at peak output. It just so happens the seawater greenhouses produce large quantities of this."

He went on to add that these greenhouses produce more than five times the fresh water needed to water the plants inside. This creates the opportunity to not only clean the CSP mirrors; but, to release some fresh water into the local environment to create a local microclimate just outside the greenhouse for hardier plants such as jatropha. Jatropha is an energy crop that can be used as a biofuel. Paton has already demonstrated the ability to sustain these microclimates in his existing prototypes.

Next blog: Why this project is different from similar projects that have failed in other countries?