LARGE SCALE IMPLEMENTATION
The Sahara Forest Project proposes a facility located some distance from the coast in a desert region. The scheme is proposed at a significant scale such that very large quantities of seawater can be evaporated. The greenhouses are arranged as a long 'hedge' to provide a windbreak and shelter to the outdoor planting scheme, and to maximize the area of evaporation. If the location is at or below sea level, pumping costs are minimized or avoided altogether.
At intervals along the "hedge" of greenhouses CSP towers would be installed. Along the windward edge of the greenhouses an elevated CSP parabolic trough collector would provide added benefits to the Seawater Greenhouses by acting as wind catchers.
Orchards are planted in the vicinity of the greenhouses which provide water for their irrigation, and a micro climate of humid air. Further downwind, the planting of native species and drought tolerant energy crops such as Jatropha is envisaged as a source of bio-fuel and to enhance soil fertility.
In most desert regions, humidity falls with increasing distance from the coast. Lower humidity translates to cooler growing conditions, enhanced fresh water production and enhanced rates of evaporation. These conditions will in turn increase the rate of night time dew formation, particularly where low night time conditions are experienced. A 10,000 hectare area of Seawater Greenhouses will evaporate over a million tonnes of seawater per day. If the scheme were located upwind of higher terrain then the air carrying this 'lost' humidity would rise and cool, contributing to the occurrence of cloud and dew.
CSP systems need water for cleaning the mirrors and for the generation of steam to drive the turbines which the greenhouses can provide. The Greenhouse evaporators make very efficient dust traps, as do plants that are growing outside. In solar thermal power plants, only about 25% of the collected solar energy is converted into electricity. If combined with sea water another 50% of the collected energy, normally released as heat, can be used for desalination. This way up to 85% of the collected solar energy can be used, and with each TWh of power, 40 million m³ water can be desalinated in cogeneration. (http://www.desertec.org)
By combining these technologies, the processes both enhance each other, and there is a huge commercial potential to create a Restorative growth: Reforestation and creation of green jobs through profitable production of food, freshwater, biofuels and electricity.