Agriculture uses 70% of the world’s available freshwater every year. With 20% of the world’s population living without access to adequate water giving 70% to agriculture is not very sustainable. Good thing there are really smart people out there, and some of them came up with a system of using the ocean’s abundant source of water to irrigate crops, an idea that transformed into seawater greenhouses.
The idea of seawater greenhouses was brought to the world in 1991 by a company called Light Works. The idea is somewhat simple at its most basic level; it mimics the natural hydrologic cycle. So how does it work? First, seawater is pumped into the greenhouse and it is then allowed to trickle down an evaporator, which in most cases is a cardboard honeycomb medium. Air is then drawn through this medium into the greenhouse, and because of the cold seawater the air becomes cool and humid which is the perfect condition for growing.
This cool air is then drawn to the opposite side of the greenhouse where it is pulled through a second evaporator. This evaporator contains seawater that has been warmed by solar energy. The air is warmed by the evaporator and becomes humid and saturated. From here the now warm air is pulled over pipes that are filled with cold seawater and this causes the air to condense (think of a cold drink on a hot day) and produce freshwater which is then stored and used to water the plants. That’s it! A simple but ingenious way to produce freshwater from the ocean.
One byproduct of this whole process that I thought was pretty cool was that some of the humid air escapes the greenhouse because they need to be kept well ventilated. This causes the air around the greenhouse to become more humid, and so after a couple of years there is the potential for other crops to be able to grow around the greenhouse. Here is an example from a seawater greenhouse in Tenerife; the left picture is from when they first started the greenhouse, and the right is 2 years later:
So I know what you’re asking yourself now; what happens to the brine and salt that is produced as a byproduct of desalinization? This waste is one of the biggest complaints against desalinization because it usually goes back into the salty water, making it more saline. When I was reading about seawater greenhouses I asked myself the same question,but don’t worry, they use it all. The brine can be processed and used as a fertilizer that goes back into the system. As for the salt, well…they turn it into household salt.
The electricity to run the pumps, fans, etc. is provided by solar energy to keep things sustainable. Also, there is no need for pesticides because the first cardboard type medium that the air is pushed through captures everything, and the salinity of the water in the medium kills the pests. This technology also allows food to be grown in arid places that no one ever thought could be productive. All you need is seawater nearby and you’re ready to grow (well, you also need the facility but you know what I mean).
Operating costs for seawater greenhouses are 10-25% less than a traditional greenhouse. This is attributed to all the water that is needed being produced at the greenhouse, not having to buy pesticides, and because all of the energy is produced from solar. The fixed costs are 10-15% lower because they don’t have to buy cooling and heating equipment, and because the land that the seawater greenhouses are built on usually are low cost due since they’re typically on land that is unusable to grow crops otherwise.
There are several of these seawater greenhouses already up and running throughout the world. This is a really cool, short video of one in Australia that was built by Sundrop Farms (this is the new name for Light Works, the company that invented the system), and shows how the whole system works.
There is also an ambitious idea being developed called the Sahara Forest project that aims to integrate renewable energy and seawater greenhouses to develop food in the desert on a large scale. Here’s an article on the Sahara Forest project if you’d like to read some more: Sahara Forest project
I think seawater greenhouses are the way of the future. Instead of pumping the groundwater at a rate that far exceeds how fast it can be replenished, which is what happens now, you take un-usable salt water and get the same results. Think of what you could do if agriculture use of freshwater went from 70% to 50%, or 30%; so many people could be helped. Plus these systems are run on sustainable energy so no pollution is coming out of them. I really don’t see any downside to these greenhouses, and hopefully they will continue to become more popular and help curb our unsustainable use of our limited freshwater.
Thanks for reading, and please leave a comment and let me know what you think of this technology. Also, if you liked this article you might want to check out another article I wrote: Water Saving Technologies: Film Farming