The Seawater Greenhouse is a technology that enables the growth of crops in arid regions, using a greenhouse structure, seawater and solar energy. The technique involves pumping seawater (or allowing it to gravitate if below sea level) to an arid location and then subjecting it to two processes: first, it is used to humidify and cool the air, and second, it is evaporated by solar heating and distilled to produce fresh water. Finally, the remaining humidified air is expelled from the greenhouse and used to improve growing conditions for outdoor plants. The technology was introduced by British inventor Charlie Paton in the early 1990s and is being developed by his UK company Seawater Greenhouse Ltd. The more concentrated salt water may either be further evaporated for the production of salt and other elements, or discharged back to the sea. The Seawater Greenhouse can be seen as one response to the global Water crisis and Peak water.
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The technique is applicable to sites in arid regions near the sea. The distance and elevation from the sea must be evaluated considering the energy required to pump water to the site. There are numerous suitable locations on the coasts; others are below sea level, such as the Dead Sea and the Qattara Depression where hydro schemes have been proposed to exploit the hydraulic pressure to generate power, e.g. Red Sea - Dead Sea Canal.[1][2]
The Seawater Greenhouse project dates back to 1991 when the concept was first researched and developed by Charlie Paton's company Light Works Ltd, now Seawater Greenhouse Ltd. The first pilot project commenced in 1992 with the search for a test site which was eventually found on the Canary Island of Tenerife. A prototype Seawater Greenhouse was assembled in the UK and constructed on the site in Tenerife. The results from this pilot project validated the concept and demonstrated the potential for other arid regions.[3]
The original pilot design evolved into a lower cost solution using a lighter steel structure similar to a multi-span polytunnel. This structure is designed to be cost effective and suitable for local sourcing. This design was first tested and validated through a second Seawater Greenhouse that was constructed on Al-Aryam Island, Abu Dhabi, United Arab Emirates in 2000. The year 2004 saw the completion of a third pilot Seawater Greenhouse near Muscat, Oman in collaboration with Sultan Qaboos University, providing an opportunity to develop a sustainable horticultural sector on the Batinah coast. These projects have enabled the validation of a thermodynamic simulation model which given appropriate meteorological data, accurately predicts and quantifies how the Seawater Greenhouse will perform in other parts of the world.[4]
In 2010 Seawater Greenhouse built a new commercial installation in Australia. The enterprise is now independently operating as Sundrop Farms Pty Ltd .[5][6]
The Seawater Greenhouse uses 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 front wall of the building is a seawater evaporator. It consists of a honeycomb lattice and faces the prevailing wind. Fans 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. Seawater that has been heated in the roof passes through a second 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. These conditions can be modeled with appropriate meteorological data, enabling the design and process to be optimised for any suitable location.
The Seawater Greenhouse evaporates much more water than it condenses back into freshwater. This humid air is `lost´ due to high rates of ventilation to keep the crops cool and supplied with CO2. The higher humidity exhaust air provides some benefit to the cultivation of more hardy crops downwind of the greenhouse.
This phenomenon could enable the cultivation of biofuel crops in the area surrounding the Seawater Greenhouse.
If carbon-neutral PV panels were available, the Seawater Greenhouse could be carbon neutral in its operations. Unfortunately, current methods of PV production are not perfect. The electrical energy it requires to operate pumps and fans is best produced by solar PV as its demand for power is proportional to sunlight. .
The use of pesticides is reduced or eliminated as the seawater evaporators have a biocidal effect on the air that passes through them.
The Seawater Greenhouse produces biological residues. This biomass can be used to help create and enrich the surrounding soil, or alternatively digested to produced bio methane, albeit with less, but still significant quantities of soil nutrients.
The Sahara Forest Project[7][8] is a scheme that aims to provide fresh water, food and renewable energy in hot, arid regions as well as re-vegetating areas of uninhabited desert. This proposal combines the Seawater Greenhouse and concentrating solar power (CSP) working in synergy. CSP is a form of renewable energy that produces electricity from sunlight using thermal energy to drive conventional steam turbines. It is claimed that, together, these technologies will create a sustainable and profitable source of energy, food, vegetation and water. The team behind the Sahara Forest Project comprises experts from Seawater Greenhouse Ltd, Exploration Architecture, Max Fordham Consulting Engineers and the Bellona Foundation. The scale of the proposed scheme is such that very large quantities of seawater will be evaporated. By using locations below sea level, pumping costs are eliminated. Among planned activities are one pilot project in Jordan and one in Qatar [9][10][11][12]
Watch Seawater Greenhouse videos here
The technology has won a number of awards including: