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With our planet's population booming, and global warming causing droughts and flooding, food is fast becoming a scarce resource. In a bid to help combat the global food crisis engineers are creating novel solutions to increase crop yields in more arid regions of the world.
One such solution comes from a firm called Seawater Greenhouse, who, as their name suggests, has developed a greenhouse that can use seawater to grow crops in countries that have limited or no access to freshwater.
Charlie Paton, managing director of Seawater Greenhouse and inventor of the technology behind the greenhouses says there are two main drivers behind the technology. The first is that many of the worlds’ hottest and most arid regions are coastal. The second is that while the increased sunlight of arid regions leads to more plant growth, the increased heat means more water evaporation from plant leaves, stems and flowers, which causes stomatal closure, wilting and eventually plant death
Saltwater solution
So, how does his Seawater greenhouses aim to boost crop productivity in countries with arid conditions solution work? The greenhouses are a stand-alone system, designed to pump seawater, or brackish water, using solar energy and convert it into freshwater for irrigation using desalination.
The remaining seawater is brought into contact with the air inside the low-cost net structures of the greenhouses, creating a cool and humid breeze to reduce plant transpiration. Salt extracted from the seawater can be utilised in cooking and preserving food.
The Horn of Africa project
Seawater Greenhouse has previously run pilots of its technology in sun-rich countries including Tenerife, Abu Dhabi, Oman and Australia. Now, in partnership with Aston University, it is to build installations in specially selected sites across the Horn of Africa, a region where temperatures regularly breach 40°C, water is scarce and food insecurity is very high.
The project aims to overcome the region’s inhospitable conditions to help farmers drastically increase their crop yields, providing them with a consistent, sustainable income. In Somalia, one of the chosen sites, only 1.5% of the country’s land is cultivated. The average annual crop yields per hectare are just 0.5 tons – compared to 700 tons per hectare in commercial greenhouses.
Decisions to be made
The Aston University team, led by Dr Philip Davies and Dr Sotos Generalis, are advising on climate control, desalination and airflow dynamics to optimise the performance of the structure and the layout of the greenhouses.
The desalination technology used in the greenhouses will be chosen based on a site-by-site basis and type of feed water available: seawater or brackish well water. Davies says that in the case of seawater, a reverse osmosis system usually recovers about 40-50% the freshwater from the incoming feed, and rejects the rest as brine.
The cooling system of the greenhouse is then able to further concentrate the brine, which is used to create salt in solar evaporation ponds. For a greenhouse covering 1000 m2, roughly 50-100 kg of salt could be produced daily.
For a brackish water source, Aston University has developed it's own more efficient system based on a batch rather than continuous flow concept.
Davies says: “The batch system works on a cyclic principle with a variation of supply pressure during the cycle. This is achieved using a positive displacement, which is the type of pump most suited to operation with photovoltaic panels.”
For the Horn of Africa project the greenhouse designs will be “substantially different” to previous versions. Rather than using photovoltaic fans to achieve cooling of 5-10°C, it will take advantage of wind ventilation, also minimising the use of expensive cladding and structure. Paton adds that the designs will also be more rugged than previous models.
In order to appeal to aid agencies and investors in Somalia the project hopes to create greenhouses with costs of around £50/m2, as opposed to typical commercial glasshouse costs of around £150/m2.
The chance of success
First installations in Africa are due to start in September and Davies is aware of the difficulties that may come in trying to convince less wealthy nations to adopt this technology. He also says it will be difficult to maintain equipment.
However, Davies is confident of success. “There is currently a lot of economic growth occurring in the Horn of Africa and - if the project can capitalise on this - I feel it stands a great chance of success. This would then provide a very good precedent as regards introduction in other developing countries.”