Seawater Greenhouses

Using greenhouses to create freshwater from seawater in arid countries.
21 June 2009

Interview with 

Charlie Paton, Seawater Greenhouse Ltd



Helen -   It doesn't matter how you grow your crops, whether they're organic and it doesn't matter on how you're going about, trying to deal with pests.  There's one thing that crops will always need and that is water.  Well we're now joined by Charlie Paton and he's the Managing Director of a company called Seawater Greenhouse and the name might be a bit of a give away but we're going to find out from him, all about what he's been up to. Hi, Charlie! Thanks for joining us.

Charlie -  Yes, hello.

Helen -  First of all, could you describe what this Seawater Greenhouses are and what's the problem you're hoping to solve with and why do we need them?

Charlie - Okay.  The greenhouse is - most people think of greenhouses as hot houses - well these are "cool houses" because we cool them with sea water.  So they're designed for hot Arab climates like North Africa and the Middle East and Australia, and we cool them by using sea water which we pour over a kind of construction which is a honeycomb cardboard material which is a cross between a honeycomb and if you like, a sponge.  So we have a very large surface area of wall that is wetted with sea water.  Now, when the air comes through that, it's cooled and the humidity goes up.  So, by cooling the air and raising the humidity, we create conditions that plants will grow in, when they wouldn't have otherwise.

Helen -  So, you want to grow plants in the middle of the desert where really, they just wouldn't grow normally because it's hot, too dry, there's not enough water.

Charlie -  Exactly.

Helen -  So you're cooling things down and you're creating water as well.

Charlie -   And we're creating water as well because at the back end of the greenhouse, we have another arrangement with a similar evaporator but this time, we put hot water, hot sea water over the back evaporator before the air goes out of the greenhouse.  And then it passes through a small heat exchanger which is cooled by the water that we cooled on the front wall.  So, it's rather like having a hot shower and seeing water condense on bathroom mirror.

Helen -  Right.  Now, do these things have to be built near the sea?  And then also, what do you do with the salt once you get rid of it, when you've produced this fresh water?  Presumably, you have a very strong brine left over at the end.  What do you do with that?

Charlie -  At the moment, we put the salt back into the sea water, but our intention is, in the future to separate out the various minerals and indeed, use it a lot of them for the plants themselves.

Helen -  So, you can use that as well to help grow the plants but the plants do need those salts but in different quantities and different amounts?

Charlie -  Well, exactly.  If you can, in simple terms, if you can take the salt that is a sodium chloride out of sea water, you've got a very good, babybio type mixture which has got all the trace elements and a lot of the nutrients that the plants need.  And in fact, seaweeds and fish meal are perhaps the best fertilizers you can get.

Helen -  Now, does this need any electricity because I believe, one of the big problems with using desalination plants, is they're really energy hungry.  You have to use a lot of energy to create that fresh water.  Are you using any electricity at all in you're greenhouses?

Charlie -  Yes, we are.  It's a very small amount of electricity and it's extremely efficient.  We use, typically, if I can put this in perspective, we need power for the pumps and the fans which regulate the airflow and typically, we use around two kilowatts of electricity to remove about a megawatt of heat.

Helen -  So that's good, is it?

Charlie -  It's very efficient.

Helen -  Excellent.  And in terms of the efficiency of what you're growing and say, how big a greenhouse would you need to feed a family or maybe a village, if you like?

Charlie -   Oh, there is no limit.  I mean, greenhouses are made in a modular sort of way and there's no limit to the scale.  I mean, at the moment in Europe, we get a lot fresh of our fresh produce from greenhouses and those in the South of Spain for example, there was  40,000 hectares of greenhouses, primarily producing out-of-season crops for us in Europe in the winter months.

Helen -  So, would this work in countries like Britain or are you really aiming at those very dry, arid countries?

Charlie -  No.  It's aimed at places like North Africa, the Middle East, Australia, India, and those sort of places.

Helen -  I believe you've got a project, is that right?  Called the Sahara Forest project.  What's that about?

Charlie -  That's right.  We've sort of taken it one step further and I'm not sure if you're familiar with concentrated solar power.  But it's a process that's getting more and more interesting and people getting more excited about. Where you very simply have an array of mirrors in a hot sunny place and the mirrors are focused onto something that heats up water and you turn that water to steam and you use that steam to drive a steam turbine.  And there are various different versions of them, but several have been built and there were quite a lot being planned.  And there's some fairly grand schemes for Europe to actually source its electricity from the Sahara through these systems.  Now, our thinking is that as with any thermal process that makes electricity, there's a lot of heat to be got rid of.  And that if we have that sea water greenhouses in the vicinity of these power plants, we can take that waste low grade heat and use it to evaporate and condense a lot more water.

Helen -   Thanks Charlie, that was Charlie Paton, he's the Managing Director of Seawater Greenhouse - they're developing an elegant system to both grow crops and supply freshwater to arid areas!


Your article on changing sea water for the plants in inspiring! Can it be done in the Sudan, or the Middle East where people need good water?

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