The Seawater Greenhouse: Eco-friendly farming in the desert
Did you know that large-scale greenhouse agriculture often takes water out of the ground faster than it can be replenished? Not the Seawater Greenhouse: This simple technology allows farmers to irrigate huge crop fields without harming the environment at all but rather helping to restore it. Read More
In less than five years, 20% of Australia’s tomatoes will probably be grown in a completely sustainable, energy self-sufficient way. They will be irrigated by seawater and require no energy other than sunlight. By the same time – and with the same technology – Somali farmers may have created fertile oases on their arid land to grow their crops: The Seawater Greenhouse enables them to irrigate the desert without harming the environment.
Have you ever wondered how some coastal areas can be too arid for anything to grow? British scholar Charlie Paton did. As an 18-year-old, he hitchhiked through the Middle East and North Africa. In Morocco in particular he found it perplexing that one of the most arid parts of the world – the Sahara – could exist next to an infinite ocean – the Atlantic.
The question took hold of him and left him no peace. Charlie studied engineering, specialised in solar energy and started experimenting with methods of solar desalination in the mid 80’s. He built different solar-powered stills, discarded many of his initial ideas, and developed new ones. The result was the Seawater Greenhouse: a self-sufficient greenhouse that uses nothing but seawater and solar energy to grow crops in desert areas.
Desalinating seawater is nothing new. But it usually requires huge amounts of energy, which is difficult to provide by solar energy alone. In conventional mechanical desalination, for instance, water is pushed through a very fine filter membrane, which requires very high pressure and constant power. Furthermore, plants in desert areas need a lot of water due to high evaporation rates. Neither holds true for the Seawater Greenhouse, which takes four to eight times less water than conventional greenhouses and is so energy-efficient that solar energy is enough to power both desalination and irrigation of the crops. Farmers even have some purified drinking water left over along with some table salt and nutrients extracted for the plants.
Charlie is convinced that this technology can help mankind tackle some of the most pressing global challenges. He talked to us about his innovative technology, about international agricultural policy and about his struggles with EU bureaucracy.
Charlie, you’re from the UK, the country of eternal rain and cloudiness. How did you decide to develop an idea for desert areas in particular?
It was a combination of curiosity, some knowledge about sunlight and some experience of travelling around the Middle East and North Africa. I had developed a reasonably effective solar still that could produce six litres a day by collecting one square meter of sunlight. But then I did some calculations and realised to irrigate Morocco using this technology, you would have to cover half the country with solar stills – which isn’t such a good idea. So I dug further into alternative methods of desalination and irrigation and finally developed the Seawater Greenhouse in 1994.
Your greenhouse requires very little energy for irrigation, despite being designed especially for hot, arid areas. What’s its secret?
The underlying idea is that while plants grow faster the more sunlight they get, they grow less the more heat they get. Therefore, we try to make the climate inside the greenhouse cooler and more humid, so the plants will need less water. This is also an economic argument. Let me give you an example: If you want to grow a kilo of tomatoes, how much water do you think you would need?
Perhaps about 500 litres?
Yes, quite likely. If these 500 litres cost you 2 euros, then your tomatoes become rather expensive. But if you can reduce the amount of water to 20 litres, then the cost of the water becomes rather insignificant.
Cooling is usually pretty energy-intensive too, especially in hot areas. How do you reduce the amount of water needed without increasing energy use?
We achieve this by evaporating seawater to create water vapour. While it is expensive to turn seawater into fresh water, it costs very little to turn seawater into water vapour and cool air. The walls of the greenhouse are made from a porous cellulose open sponge like structure that is permeable to wind. A pump lifts the seawater from the ground up to two metres high and trickles it over the evaporator. As the wind from outside blows through the walls, the water evaporates and the air inside the greenhouse gets cooler and more humid. The salty water is then again pumped over the evaporator. The amount of energy you need to do that is tiny, and the Seawater Greenhouse can easily do it with the solar energy it collects from it’s integrated PV panels.
Does the water in the greenhouse have drinking water quality?
Yes. You can even install a tap and use it for drinking or cooking. And you can also extract nutrients from the seawater.
Seawater contains all the nutrients needed to sustain life – magnesium, potassium, phosphorus, chlorides, nitrates etc – in different concentrations. That’s why the sea sustains marine life. We use all of it, and we even make table salt from the leftover salt.
In your information booklets you state that the Seawater Greenhouse even irrigates the areas around it…
Yes, the walls of the greenhouse are permeable to wind, just like a Bedouin tent. When the air blows through the walls, the cool air goes into the greenhouse first, but then it goes out the back. This creates a kind of oasis at the back of the greenhouse that you can use for protected agriculture as well. We’re currently developing greenhouses for farmers in Somalia who will benefit particularly from this effect. Most family farms are about 1 hectare in size. The greenhouse will occupy about one fifth of the plot – 0.2 hectares – and will also generate cool and humid air in the area around it. It will allow them to grow orchards, vegetables or fodder for goats and sheep using traditional farming methods.
Can family farms in Somalia actually run a greenhouse by themselves and even do the maintenance?
Oh yes, it’s less complicated than running – say – a tractor. Of course you have to look after things and if a pump breaks you need to fix it, but that’s like any kind of farming. The greenhouses in Somalia will start operating next year and we’ll train local people how to build them and how to grow crops in them.
What is the best size for a greenhouse? You spoke of family farms, but you’ve also already produced much bigger compounds.
You can make it any size you like. In Australia, we’ve built a greenhouse for a company of 0.2 hectares in size, but they made it 100 times bigger – it now covers 20 hectares, engages 300 employees, and will be growing 15,000 tons of tomatoes annually by the end of this year. But in Somalia, for instance, employing people raises a number of problems for farmers because of tribal or family traditions. So it seemed better to enable them to grow stuff themselves. In fact, this is also the way most greenhouse horticulture around the world works: About 80% of all food is produced on farms of four hectares or less.
How has your experience in these very diverse countries differed?
The climate varies from place to place and we spend a lot of time studying the conditions. But the social and economic factors also differ a lot. On the Canary Islands, for example, agriculture is almost not economically viable anymore, as you can get cheaper bananas and tomatoes from Morocco or Latin America. People would rather invest in tourism than in agriculture. It is completely different in Australia: Importing food as well as transporting food across this huge country is expensive. So local self-sufficiency is highly desirable. But as the cost of labour is high, the main challenge here is to reduce labour. It is the opposite in Somalia. About 85% of the population are rural farmers or pastoralists, but they are not very efficient owing to a lack of fresh water and still need to import 40% of their food. Because of all these considerations, it is much easier for us to work with local organizations when developing a new project. When we start a new project, it’s usually because a local organisation has contacted us beforehand.
There’s no end of environmental problems and they’re almost all related to water.
You once said that the Seawater Greenhouse could reverse the damage done by conventional greenhouses i.e. in Spain. Why?
The greenhouses in Spain – and in many other parts of the world – take water out of the ground five times faster than it comes in. As a consequence, the water table drops, many plants no longer have their roots in water and the water itself becomes more saline. Loss of vegetation causes desertification, which again causes less rainfall. I think there’s a potential for a complete game change with the Seawater Greenhouse.
Why do you think we need this game change?
The world has come to a number of tipping points: shortage of water, nutrients and fuel, deforestation and desertification coupled with population growth. There’s no end of environmental problems and they’re almost all related to water. Take a look at some of the world’s top problems: The civil war in Syria was preceded by three years of drought. Farmers had to move into the cities, which caused civil unrest. The Arab spring was preceded by drought in Russia and the US in 2008, which drove up the price of wheat and bread in North Africa by about 30%, and people took to the streets in protest. Many migrants who cross the Mediterranean today are economic refugees from Eritrea, Ethiopia, Sudan, Somalia or Yemen, where you can’t make a living growing crops. When a country can’t feed itself, it tends to fail. Somalia is perhaps the world’s most notorious failed state, with Yemen and Eritrea not far behind.
When a country can’t feed itself, it tends to fail.
Based on the great need for sustainable solutions – shouldn’t the popularity of the Seawater Greenhouse be much greater?
It is more complicated than that. Food and water are very political issues, and the world of agriculture is not a level playing field. The construction of our first greenhouse in Tenerife for example was followed by a 10-year legal battle with the European Commission. We had been awarded a shared cost grant by the Commission to build a pilot in 1993, but the Agricultural Directorate, which should have administered the project, apparently didn’t want us to succeed – they basically didn’t pay us. They were probably afraid that we would enable farmers in Morocco and Somalia to compete with farmers in Spain and the Netherlands. That was back in the 90s when the EU tried to protect its markets by even paying farmers not to grow crops. The Common Agricultural Policy has improved since then, but even today there are lots of subsidies that distort international trade. So despite all sorts of complicated free trade laws and regulations, in Nigeria, for instance, tomatoes from Spain are often cheaper than locally grown ones.
How many people work at Seawater Greenhouse?
We’re only four in the core team, but we work closely with consultants and academics. So all together, there are about 15 people working on the greenhouses.
Are you making any money?
So far, we’re surviving. But I think it will scale up. Within less than 5 years, we will be growing 20% of all of Australia’s tomatoes, which is quite a big shift. If you could apply that same technology to Africa, where two third of the continent is classified as desert, the potential is much greater.