An idea. Combine two things to solve a big problem: Solar Water Still and Greenhouse– greenhouse that runs on salt water.
A “solar water still” is often a tent that has salt water at the base and captures the evaporated water and drains it into a bucket. Solar stills are “the simplest device that are used to obtain freshwater using solar energy as the sole energy supply”.
What if that tent were also a greenhouse, and the fresh water was used to water the plants? The plants could be in a raised bed that is above the pool of salt water that was under the full floor. This inexpensive construction would be decidedly low tech– low energy inputs, and low maintenance, but we would be growing plants using saltwater.
Then the Desalinating Greenhouse would be a hothouse that grew plants in the freshwater humid warm air and watered with the evaporated water. There would no complicated reverse-osmosis desalinization system or electric energy to drive it– just use salt water to grow freshwater vegetables.
Combine a Solar Water Still:
with a Greenhouse:
Then we are using the sun to create the freshwater for the plants out of the saltwater. The salt water needs to be supplied and saltier water needs to be removed, but this is a simple pump if there is nearby salt water.
A Solar Still generates .06 gallons to .09 gallons (1/2 to 3/4 lbs) of water per day per square foot, and the peak water use in a greenhouse is 0.3 to 0.4 gallons of water per day. So we need maybe 2-3 times more salt water pool space than growing bed. This does not seem unusual in raised bed greenhouses.
This could be done anywhere there is salt water. Say coastal regions, on islands that are notoriously short of fresh water, and floated out in the open ocean (living the seasteading dream 🙂 ). You would need to pump the water to the greenhouse and return the more salty water, but this is low-tech.
Maybe we could grow fish in the salt water and get some aquaculture going. (This is not “aquaponics” since that uses the nitrogen from the fish to fertilize the plants, but since these are salt water fix, we can not pour that water on the plants. A freshwater pool with fish could be a fun add-on if things get mature.)
I bet this whole thing has been tried, as almost everything has, but maybe the coming crisis of fresh water will propel development. There is a paper about a similar system but seems more complicated than it needs to be:
Another proposal that is a bit less complicated:
But I think we can do better. Any ideas, anyone interested in trying?