Merging Seawater Greenhouses and Concentrated Solar Power (CSP)
Since the 1980’s, rainfall has increased in several regions, while drying has been observed in the Sahel, the Mediterranean, southern Africa, Australia and parts of Asia.
In his report for the Fourth World Conference on the Future of Science “Food and Water for Life” held in Venice last September, Charlie Paton put it this way: The Sahara Forest Project aims to provide a new source of fresh water, food and renewable energy in hot, arid regions, as well as providing conditions that enable re-vegetating areas of desert. The Sahara is used here as a metaphor for any desert that formerly supported vegetation and could do so again, given sufficient water.
This ambitious proposal combines two established technologies – the Seawater Greenhouse and Concentrated Solar Power (CSP) – to achieve highly efficient synergies. Both processes work optimally in sunny, arid conditions. Demonstration plants are already running in Tenerife, Oman and the United Arab Emirates. The estimate that building 20 hectares of greenhouses combined with a 10MW CSP project would cost around $104 million, (€80m) (£65m).
A member of the Sahara Forest team, Paton is the inventor of the Seawater Greenhouse concept, with the engineering provided by Philip Davies. Seawater Greenhouses have been built and running successfully in some of the hottest regions on earth such as Abu Dhabi and Oman, where they create freshwater from seawater, while providing cooler and more humid growing conditions, enabling the cultivation of crops all year round. Both technologies work extremely well in hot, dry desert locations, the greenhouse produces more than five times the fresh water needed to water the plants inside so, in addition to producing water to clean the CSP mirrors, some of it can be released into the local environment.
Seawater Greenhouses use the sun, the sea and the atmosphere to produce fresh water and cool air. The process recreates the natural hydrological cycle within a controlled environment. The entire front wall of the building is a seawater evaporator. It consists of a honeycomb lattice and faces the prevailing wind. Fans assist and control air movement. Seawater trickles down over the lattice, cooling and humidifying the air passing through into the planting area. Sunlight is filtered through a specially constructed roof, The roof traps infrared heat, while allowing visible light through to promote photosynthesis. This creates optimum growing conditions – cool and humid with high light intensity. Cool air passes through the planting area and then combines with hot dry air from the roof cavity. The mixture passes through a second sea water evaporator creating hot saturated air which then flows through a condenser. The condenser is cooled by incoming seawater. The temperature difference causes fresh water to condense out of the air stream. The volume of fresh water is determined by air temperature, relative humidity, solar radiation and the airflow rate.
Concentrated Solar Power (CSP) is increasingly seen as one of the most promising forms of renewable energy, producing electricity from sunlight at a fraction of the cost of today’s photovoltaics. The process uses mirrors to concentrate sunlight to create heat which is used to drive conventional steam turbines to generate electricity. Less than 1% of the world’s deserts, if covered with concentrating solar power plants, could produce as much electricity as the world now uses.
The Sahara Forest Project, an ingenious proposal from a team of architects and engineers, that gives us a new source of fresh water, food and energy. Looks like there’s hope for our world after all!
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