Getting hold of plastic bottles wouldn't be a problem, there's millions of them out there. I'm personally trying hard to cut back on plastics around me (my house if full of the stuff though, so hard to avoid).
My allergy specialist years ago told to remove it all from my sleeping area due to the fumes they put out. I still have problems if I have to sit in a conference room full of plastic chairs - especially if I'm surrounded by countless people wearing their chemical filled perfumes as well. Headaches, sore eyes and that horrible vagueness that comes over you when you have an allergic reaction.
I don't like the idea of all that plastic, sitting in full sun and degenerating, surrounding the plants I intend to eat.
For all that, the condensation idea is a clever and simple one and there must be other alternatives to plastic. The plastic is cheap/free and readily available. The alternatives would not be.
I started experimenting with this approach...then the Ex Trop Cyclone Oswald rains came.
It was very easy to set up & very cheap using local milk containers for the 'dome' and soft drink bottles for the aquifer.
I monitored the condensation and felt the soil underneath.
However, I suspect that in my conditions of sandy soil, the setup would work if I planted a seedling and as I did I surrounded the plant with four of these setups. If I didn't need to water the plant -- and it thrived -- then Voila!
But as a wet pot substitute I suspect that the distance between setups would have to be much less as the process is different. Terracotta wet pots rely on gravity and hydrostatic pressure to operate. Whereas these are simply soil wetters driven by evaporation and condensation.
The advantage being that the hotter the day, the more water is condensed.
So I've yet to decide on this as I haven't done the experiments to my satisfaction.
I'd be really happy if you keep letting us know how it goes Dave.
I know the circuit operates as it is easy to monitor the beads of condensation on the walls of the greenhouse.
While I'm using upturned milk comtainers that have a square base, what concerns me is that there is still plenty of water in the buried tank. To work efficiently I'd assume more water would need to evaporate....
But then, aside from my flat roof, my chamber is translucent.But surely the enclosed temperature is such that the evaporation/condensation circuit is soaking the underlying soil?
"Feeling' the soil for dampness isn't a useful guide -- but the volume in the tank must be ..and that is disappointedly high..
Maybe but the beauty of condensation is that it's meant to be slow. The best indicator is going to be what happens to your plants.
I have tweaked my methods and report on the experiment here: http://brisbanelocalfood.ning.com/profiles/blogs/solar-drip-irrigat...
And another report