6 ms·
There are several things which aren't covered well in the article. I have spent quite a lot of time looking at the feasibility of the Seawater Greenhouse in mul
by bjelkeman-again 10y ago
There are several things which aren't covered well in the article. I have spent quite a lot of time looking at the feasibility of the Seawater Greenhouse in multiple locations, including a visit to this Australian location a few years ago. [1] I haven't been involved since the pilot installation in Port Augusta, so they may have changed a few things described below.
The Seawater Greenhouse design is not a conventional greenhouse. It cools rather than heats a crop, it is an open design, rather than a conventional "closed" design.
The system, as designed by Charlie Paton, uses evaporative cooling in the greenhouse. Essentially they have a cardboard wall, sort of like a thick honey comb with holes through it, over which they pour seawater. The air is pulled through the wall by large relatively slow fans. When the air moves through the "honey comb" wall, the air changes direction (30 degree angle channels). Particles and insects in the air essentially get stuck in the seawater. Seawater is particularly bad for insects and other small pests as the salt clogs up the exoskeleton and the breathing channels when the water evaporates.
Even though the greenhouse was standing in an area of vegetation with a significant insect population outside, we hardly saw any insects on the inside. But you could often find quite a few insects in the seawater tanks used to hold the water for the evaporators. The stable climate created in the greenhouse and the seawater "barrier" created by the evaporators means the pest insect pressure is lie and you can easily control it with natural enemies (bio control). (There where poisonous spiders in the canopy of the crop but they don't affect the crop, but act as biocontrol. Just don't let them bite you.)
Plants grow much better in a cooler and high humidity environment. The plants don't have to put so much effort into transpiration to keep an acceptable temperature for photosynthesis. The evaporators with seawater handles both of those things.
The temperature during my visit peaked on Christmas Day at 43 C, but inside the greenhouse it was a much more acceptable 35 C. (We had our Xmas dinner just behind the evaporators, the most pleasant place in Port Augusta at that point.) The energy used for this cooling primarily comes out of the water and the surrounding air. Some energy is used for pumping water. Without the evaporative cooling the temperature in the greenhouse would have been at a level which would have killed the plants. During my visit the plants and crop grew so fast that we had to help harvesting to keep up.
The evaporators are also covered by sea salt, which is hydroscopic (absorbs water) which means that when the temperature drops at the end of the day you don't get water (dew) collecting on the plants. This is important as dew on the plants and produce allows botrytis (mold) to grow and potentially destroy the produce. This also avoids having to burn sulphur in the greenhouse to kill the mold.
[1] pictures from my wife during the visit https://www.flickr.com/photos/ankertje/7044271777/in/album-72157625710401409/ https://www.flickr.com/photos/ankertje/7044271777/in/album-7...
- Cogito 10y agoGreat comment, thank you (and thank your wife for the photos, fantastic to see some of the workings!) Do you know how often the cardboard needs to be replaced?
- bjelkeman-again 10y agoIt seems that it lasts a long time, at least several years. But, no, I don't really know.
- strictfp 10y agoThank you very much for telling this story. I love HN for being filled with intelligent and interrested people from around the world. It feels very cool to be part of this community every time I read an insider story like yours!
- nitrogen 10y agoVery cool. P.S. The Wikipedia page for seawater greenhouses really needs some better photos. I've contributed to Wikipedia in the past but now lack the time/motivation, but if you or anyone has the motivation and permission, you could make the world a better place by adding some of these photos to Wikipedia.
- russdill 10y agoWhat happens to the concentrated sea water at the end of the cycle? Does it get pumped back to the ocean? Deposited into the ground?
- pm90 10y ago100% natural, environment friendly, organic non-GMO locally produced Australian salt!
- utternerd 10y agoHow would one even make genetically modified salt? The most you could do is to add additional genetically modified compounds to the salt, but salt in and of itself cannot be genetically modified.