The master print of the Sahara Forest Project

The master print of the Sahara Forest Project

Imagine being able to grow crops, produce large amounts of renewable energy and reverse desertification all at the same time. Now imagine doing this in the hottest and most arid parts of the planet and at a manageable cost.

Sound implausible? Not according to Charlie Paton, Michael Pawlyn and Bill Watts, the three British designers behind the Sahara Forest Project. The scheme combines two existing and proven technologies - concentrated solar power and seawater greenhouses - in a simple yet innovative way.

Waste as an opportunity
The first technology,  concentrated solar power (CSP), is one of the most cost-effective and promising forms of renewable energy available. It uses mirrors to concentrate sunlight, create heat and power turbines that in turn produce electricity.

The second technology, the Seawater Greenhouse, was conceived by Paton and versions of it have been successfully built in Tenerife, Oman and the UAE. His invention, which mimics the natural water cycle, uses seawater to cool and humidify the air that ventilates a greenhouse and sunlight to distil fresh water from seawater. The water vapour is condensed at the other end of the greenhouse and used to water the crops.

Finding the perfect site
The team looked carefully at the Seawater Greenhouse and realised that it was only condensing about a tenth of the water it evaporated, the rest of it was blowing out the back as humid air. "The ideal site is one that has higher terrain downwind so that this mass of humid air that blows out can be forced to rise and form mist or cloud," Michael Pawlyn (one third of the design trio and one of the lead architects behind the iconic Eden Project in Cornwall) told Sideways News. "Then we can try to capture some of that [using fog-nets] and re-vegetate areas that are downwind, as well as in and adjacent to the greenhouses."

Building from waste
Another aspect of the "waste as an opportunity" concept is to do with the by-products of evaporating large quantities of seawater. "You can run the seawater greenhouses so that you deliberately allow calcium carbonate to build up on the evaporators," Pawlyn told Side ways News. Eventually the evaporators - which are made out of waxed, recycled cardboard - become so encrusted that you are left with "artificial limestone blocks" that you can potentially build with.

Heat from solar power
Lastly, vast quantities of waste heat produced by concentrated solar power. "We could make use of all that to heat the sea water," says Pawlyn, "so that we can evaporate more of it and boost the amount of water production to five or even ten times the amount needed for the plants to grow."

This is significant because not only is water increasingly becoming a source of conflict Pawlyn pointed out, but "once you’ve got water it makes all sorts of things possible". In this case the surplus water could be used to clean the solar mirrors of the CSP system (so it can run efficiently) and to grow jatropha, a drought-tolerant crop that produces a sustainable bio-fuel.

A virtuous circle
The Sahara Forest project is a radical idea because it goes beyond sustainable design to achieve restorative design; it aims to repair damaged eco-systems. "In many ways," says Pawlyn, "it reverses the model of conventional intensive agriculture from being an extractive process to a restorative one."

The scheme is not only about creating zero-carbon energy, zero-carbon food and abundant freshwater in some of the most water-stressed parts of the planet, it is also about taking large amounts of carbon out of the atmosphere and sequestering it in reactivated soils, in plant growth and potentially even in building products. A virtuous circle if ever there was one.

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