Seawater Greenhouses Produce Tomatoes in the Desert

by Renee Cho | February 18, 2011

According to the World Health Organization, about 20 percent of the world’s people live in regions that don’t have enough water for their needs. With the global population increasing by 80 million each year, a third of the planet will likely face water shortages by 2025. This looming water crisis is inextricably linked to food production because agriculture accounts for 70 percent of all fresh water used, and obtaining irrigation water in arid regions has serious environmental impacts. Drilling wells can deplete groundwater, and desalination is energy-intensive and leaves behind concentrated brine.

The Seawater Greenhouse, however, provides what may be an economical and sustainable way of producing fresh water and crops in hot, dry regions near the ocean. Marco Goldschmied, president of the Royal Institute of British Architects, said in 2000,“The Seawater Greenhouse is a truly original idea which has the potential to impact on the lives of millions of people living in water-starved areas around the world.”

A seawater greenhouse produces crops year-round in hot dry areas using only seawater and sunlight. Tomatoes, cucumbers, peppers, lettuce, strawberries, herbs—anything that can be grown in traditional greenhouses—can be grown in seawater greenhouses. The award-winning technology, invented by Seawater Greenhouse Ltd. founder Charlie Paton, was inspired by the natural water cycle where seawater heated by the sun evaporates, cools to form clouds, and returns to earth as precipitation.

The humidification and de-humidification that result from differences in temperature between surfaces heated by the sun and cold water from the sea are the keys to the seawater greenhouse system.

Seawater is pumped into pipes in the greenhouse and is trickled down over the first evaporator, a large spongy honeycomb-like surface. As air is drawn through the honeycomb and into the greenhouse by fans, it is cooled by the seawater and becomes more humid. The cool humid air creates favorable growing conditions for the greenhouse crops. At the back of the greenhouse, the cool air is drawn through a second evaporator containing seawater that has been heated by the sun in the ceiling pipes. The air then becomes hot and humid to the saturation point. When the hot humid air meets an array of vertical pipes containing cold seawater, fresh water condenses (just like hot steamy air in your shower condenses on the cooler mirror and tile surfaces). The fresh pure water is then piped to a storage container and used to irrigate the crops.

The sustainable system is clean, efficient, and elegant in its design. The greenhouse control system, pumps and fans are powered by electricity produced completely by solar power. The honeycomb evaporator filters out pollen and pests that are killed by the saline water so the greenhouse doesn’t need much pesticide. Nutrients harvested from the brine are pumped back into the irrigation system to fertilize the crops, and the rest of the salt is made into gourmet salt crystals that Seawater Greenhouse Ltd. sells.

Because the greenhouse produces its own fresh water, and uses no fossil fuels or pesticides, its operating costs are 10 to 25 percent less than those of a traditional greenhouse. Its fixed costs are 10 to 15 percent less because it doesn’t need to purchase cooling, heating, or desalination equipment, and because it is usually built on cheap land where little can grow.

Seawater greenhouse technology works best in arid regions by the sea, and near consumer markets so crops can be easily transported. Areas of Europe such as Crete, France, Greece, Italy, Portugal and Spain; California and Mexico in North America; large parts of China, India, Pakistan and Turkey in Asia; and much of Australia, the Middle East and northern Africa, are good candidates for seawater greenhouse projects.

The seawater greenhouse concept was first developed in 1991 by Light Works Ltd. in the UK. A successful pilot project on Tenerife in the Canary Islands in 1992 led to research projects on Al-Aryam Island in Abu Dhabi and Muscat, Oman. In 2005 Seawater Greenhouse began collaborating with the architects Nicholas Grimshaw & Partners on the harbor redevelopment of Las Palmas de Gran Canaria, exploring the use of its technology to cool a more urban environment. They are designing the 1.9-mile promenade, botanic garden, and Water Theatre using some of the same principles to produce fresh water and cooling.

In 2009, private investors backed the first commercial Seawater Greenhouse in Port Augusta, South Australia. The 2,000-square-meter structure, which draws seawater from the Spencer Gulf, is capable of producing 100,000 kilos of tomatoes each year. The excess fresh water it produces will be used to grow citrus plants outdoors. The Port Augusta greenhouse, which cost $2 million, produced its first crop of tomatoes in December.

This January, water-scarce Jordan and Norway joined forces on the Sahara Forest Project, a 200,000-square-meter demonstration center near Aqaba on the Red Sea that will produce fresh water, food, energy, and sustainable biomass. The project is being developed by London-based Seawater Greenhouse, Max Fordham Consulting Engineers, and Exploration Architecture, and the Bellona Foundation, a Norwegian environmental NGO.

The Sahara Forest Project will use water from the Red Sea in seawater greenhouses to produce fresh water for the crops and grow algae in open ponds for fuel and food. The project will also grow halophytes, plants tolerant of salty conditions, that have potential to be an energy crop. Because each 10,000 square meters of seawater greenhouse evaporates 50 tons of water daily, the greenhouse will help restore vegetation on the surrounding arid land through ventilating the “lost” humidity to create a cooler and more humid micro-climate downwind of the greenhouse. The “lost” humidity will also increase the chance for precipitation in the area. The algae, crops and other plants will sequester carbon dioxide from the air. Extra fresh water produced by the seawater greenhouse will be heated by a concentrated solar power plant (CSP), generating steam that will turn a turbine to produce electricity. The CSP’s excess heat will be used to desalinate seawater for drinking water. A single Sahara Forest Project facility with 50 MW of concentrated solar power and 50 hectares of seawater greenhouses would produce 34,000 tons of produce, employ over 800 people, export 155 GWh of electricity and sequester more than 1,500 tons of CO 2 each year. If the demonstration project is successful, Aqaba will provide 200 hectares for a larger scale facility.

Construction on the demonstration center will start in 2012, with the commercial scale development scheduled to begin in 2015. The creators are planning a large-scale commercial facility comprised of a 10-million-square-meter area of seawater greenhouses, CSP towers, orchards, native species such as Jatropha for biofuel, and a desalination facility.

“The Sahara Forest Project is a fiercely ambitious effort…but ambitious is exactly what we must be,” said Bellona’s president, Frederic Hauge. “A critical prerequisite for solving both the climate crisis and the world’s food problem is to enable developing countries to produce their own food, their own water, and their own clean energy…”

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