Restorative greenhouse solution converting saltwater into fresh water through evaporation
Farming in arid regions has so far been troublesome due to lack of fresh water. With a new design of greenhouses which incorporates desalination of saltwater through evaporation, a sustainable solution for growing crops in hot and dry climates is provided.
Historically, the increasing demand for fresh water has mainly been caused by population growth, industrial development and the expansion of irrigated agriculture. Agriculture consumes more water than any other sector - approximately 70% of the accessible fresh water worldwide - and wastes some 60 % of that through inefficiencies. Moreover, large parts of the world are arid with the sea as their closest or only nearby water source which implies difficulties of cultivating crops in these regions.
To meet these challenges, scientists and practitioners within various research fields such as water cycle management, land use & agriculture around the world are working to find new methods for recovering fresh water and growing crops in places that so far have been complex or impossible to farm. One such innovative solution is the Seawater Greenhouse.
The solution does not rely on fresh water, thus contributing to a more sustainable water cycle. The process is illustrated in the picture below: warm air enters the greenhouse where it is cooled and humidified by seawater dripping over an evaporator. This creates a favourable climate with cool and humid conditions which enables the crops to grow with small amounts of water. The result is higher yield and higher quality crops since the plants are not stressed by excessive transpiration. The air flows past the growing area to pass through a second evaporator over which sun-warm seawater is flowing in pipes above the growing area. Heat and humidity are taken up by the air before it meets a series of vertical pipes with cool seawater that acts as a condenser. When the hot and humid air meets the cool surfaces, fresh water condenses and can be collected and used for irrigating the crops through water-distribution systems.
The novel system reaches a level 9 on the TRL scale and brings both economic and environmental benefits to its users as there is no need for expensive desalination systems or greenhouse climate control equipment run by fossil fuels.
Why did it work?
Research related to the Seawater Greenhouses started in 1991, and this desalinating concept was first developed by Light Works Ltd in the United Kingdom. Since then, several pilot research projects around the world have contributed to the development of the technology; on the Canary Islands, in the United Arab Emirates, in Oman and in Australia.
The Seawater Greenhouse team is currently working on two developments: a solution for growing fresh produce in the Caribbean, primarily to help islands become self-sufficient in fresh produce (nearly all of which is currently imported), and also a low cost and simple design for the Horn of Africa region which can scale rapidly in a modular way.