Vegetables on a sand background

Seawater greenhouses: growing food in the world's driest regions

As conventional farming and climate change aggravates water and food shortages, a handful of entrepreneurs are growing food in the world's driest regions. But can they help?

Sun, sea and sand aren't just for beach holidays. These elements, if harnessed correctly, can and have been used to grow fruit and vegetables in the desert.

Once a lighting designer and maker of special effects, Charlie Paton came up with the idea around 20 years ago. Fascinated by light and plant growth, Paton turned the conventional greenhouse concept on its head and developed what is now widely known as the 'seawater greenhouse'.

Put simply, instead of trapping heat, the seawater greenhouse acts as a cool house for growing crops while producing fresh water for irrigation. Ideally sited on flat, arid land close to the sea, seawater is pumped to the greenhouse and piped over honeycomb cardboard pads that provide a large surface area for evaporative cooling.

The air cools, humidity increases and the now concentrated brine is discharged from the system. This can be used outside to cool evaporative hedges – honeycomb cardboard structures that cool passing air – reviving surrounding agriculture.

Paton reckons a seawater greenhouse can cool the air by up to 15°C and raise humidity up to 90 per cent, providing the necessary conditions to grow food in the most inhospitable of climates. And 20 years on, his concept is being applied around the world.

Micro-climate and economics

Now managing director of the business, Seawater Greenhouse Ltd, Paton first set up an experimental pilot greenhouse in Tenerife, and has since designed and built structures in Abu Dhabi, Oman and Australia. Each is tailored to its location, and as Paton says: "We put a lot of effort into thinking how to make it as economic as possible to exploit prevailing conditions."

Micro-climate data has proved crucial to optimise growing conditions. "We want to know where the prevailing wind comes from; its strength and variability over the year and the amount of sunlight," explains Paton. "We don't like averages; we may need hourly or three-hourly information over several years to establish the extremes."

While the fundamental technology is simple, the detail is not. For example, in his Abu Dhabi plant, Paton experimented with different types of sheeting and arrays of pipes to optimise shade for plant growth and also varied ventilation air flows to alter temperatures as required.

Research and mathematical modelling has revealed that temperatures inside a seawater greenhouse are influenced by complex three-dimensional patterns of air movement as well as long wave radiation from interior hot surfaces. As he puts it: "Simple network models do not adequately represent the observed behaviour."

Amid the complexities of greenhouse design, what is crystal clear is that Paton is committed to sustainable development. Right now, he is working on greenhouse schemes to produce tomatoes in the Horn of Africa countries such as Somaliland, Somalia, Djibouti, Eritrea and Yemen. Each nation is high on the list of food aid recipients, and Paton's solutions can help.

"Greenhouses in Europe tend to have very high capital, labour and land costs," he says. "But in less developed places such as these, land and labour tends to be much cheaper and the only energy that is needed is for pumping water."

Evolving designs

While Paton's seawater greenhouse started out with simplicity at its core, several organisations have since adapted the concept, and are planning ambitious integrated projects that include solar energy among other technologies.

In 2010, for example, a commercial seawater greenhouse system began operating in Port Augusta, south Australia. Originally based on Paton's philosophy of simplicity, the project was established as a joint venture between Paton's business and Isle of Man-based private agriculture investment business Saumweber Holdings. Paton has since relinquished involvement, with Saumweber driving the high tech operation, now known as Sundrop Farms, forward.

The facility uses solar power to desalinate water and to provide a carefully controlled environment and constant temperature where tomatoes, peppers and cucumbers are grown without soil. This hydroponic growth requires a computerised growing system so that each and every plant is provided with the right amount of nutrients and fertiliser.

Crucially, these perfect conditions produce unblemished and uniform crops, and Sundrop Farms is currently expanding the Port Augusta facility to 20 hectares, aiming to produce more than 15,000 tonnes of tomatoes a year for markets across Australia.

An equally ambitious scheme called the Sahara Forest Project is using the seawater greenhouse concept to not only produce food, freshwater and energy in arid areas but reverse the trend of desertification.

At a one-hectare pilot facility in Doha, Qatar, seawater greenhouses have been developed to grow vegetables as well as produce fresh water. As with Paton's original concept, desert air is blown into the greenhouse to meet a perforated cardboard wall cooled with saltwater.

"Seawater trickles down this cardboard wall, and part of the water evaporates as small freshwater droplets," says chief executive Joakim Hauge. "The air inside the greenhouse becomes cooler and more humid, which lowers the plants' demand for water. This also makes it possible for us to condensate droplets at night, for use as part of the irrigation."

The pilot plant is supported by photovoltaics and also coupled with concentrating solar power. Heat from the CSP mirrors is used to drive the evaporative desalination system for production of distilled water for the plants in the greenhouse and outside. The waste heat is used to warm the greenhouses in the winter and to regenerate the desiccant used for dehumidifying the air.

To reverse desertification, outdoor evaporative hedges create sheltered and humid conditions for plant cultivation. At the same time, photobioreactors and open-pond cultivation systems support algae agriculture, while outdoor hydroponic raceways are used to grow halophytes, plants tolerant of irrigation with salty water. These experimental facilities are used by project partners such as the US Department of Energy to investigate the use of microalgae for biofuel.

Saltwater infrastructure

The project's long-term aim is large-scale rollout of integrated technologies in low-lying desert areas around the world. As Hauge highlights: "The basic principle that we set out for the Sahara Forest Project is that we want to use what we have enough of – saltwater, carbon dioxide, desert and sunlight – to produce what we need more of; sustainably produced food, water and renewable energy."

"Our approach is based around saltwater infrastructure. We integrate the technologies so that the waste from one system serves as a resource for another system," he adds.

And the approach is working. The facility allows year-round production of some 19 different plants, vegetable and grain crops, with yields comparable to leading European greenhouse operations.

The greenhouses achieve up to 15°C cooling in summer with water usage half that of comparable greenhouses in the region. Meanwhile, the evaporative hedges have provided a 10°C mean temperature reduction in outdoor growing zones.

Indeed, the cooler air, shelter and increased humidity provided by these outdoor 'hedges' has enabled plants, from desert species to barley and melons, to establish in the surrounding desert.

"Establishing plant species very soon introduced a broader ecosystem," adds Hauge. "More birds and insects were attracted to the area. A year after operation we saw a more complex ecosystem of species than when we started. That is a long-term aim: to build up the organic content in the soil and build up the ecosystem."

Clearly the results from the Sahara Forest Project's Qatar pilot operation are impressive, and much needed in the arid nation. For example, right now, more than 90 per cent of Qatar's food is imported, but just eight hectares of greenhouse production could match the yearly import of cucumbers. Meanwhile, 40 hectares of production would meet the yearly demand for imported tomatoes and 60 hectares would match the quantities of cucumbers and tomatoes as well as peppers and aubergines currently imported.

But despite the success, some industry players have questioned the scheme's sustainability on a commercial scale. The £5m pilot facility was backed by Norway-based fertiliser giant Yara International and Qatar-based Qafco, the world's largest single-site producer of both ammonia and urea.

Still, according to Hauge: "This is a facility for a scientific programme – the costs are not relevant for commercial production. The next stage, a test and demonstration centre will be sufficient size for commercial operations, plus we will have innovation hubs for various technologies."

Indeed, work to build the first stage of a 20-hectare test and demonstration centre in Jordan will start later this year. Jordan is dependent on imported gas and oil and the country experiences very high levels of water stress, making food security a constant challenge.

Hauge says the Jordan facility will be built 15km inland from the Bay of Aqaba, 40m above sea level, and seawater from the Red Sea will be delivered by pipeline. The site will be large enough to allow a tenfold expansion using the same pipeline.

"The results coming out of Qatar exceed expectations and we feel confident that the Sahara Forest Project [will be] good for the environment, good for social development and have long-term viability," he says. "People see deserts as a symbol of hopelessness; we want to show they can be the starting point for new growth."

Low-cost solutions

So while in the beginning Paton set out to implement his straightforward idea for growing crops in hostile environments, some 20 years on the seawater greenhouse concept has been demonstrated in several pilot facilities and has evolved under different regimes.

Paton's Seawater Greenhouse Ltd business develops low-cost local solutions, while Sundrop Farms has taken the core idea and added high-tech equipment to ensure reliable production of unblemished crops.

The Sahara Forest Project has taken the idea one step further and added extra systems to expand operational potential. Crop production inside and outside the greenhouses takes place while new economic activities such as biomass and biofuel production are being established.

Development of schemes is still in its infancy and only time will tell which, if any, of these approaches will become established across the deserts of the world. What's Paton's take on his concept's development?

As he puts it: "The challenge is how to introduce greenhouse technology into a place where nobody has any money. I favour simple, low-cost economic solutions that deliver the goods. They can stand on their own." 

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