This is a small scale test system for the idea of using temperature differentials to operate a ebb and flow hydroponic system.
The theory behind it is the idea gas law PV=mRT. That is an increase in temperature in the gas trapped in the reservoir leads to an increase in volume of the gas.
Step 1: Materials
A 2 liter bottle
a 1 liter bottle
aquarium hose and fitting
Step 2: The coupler
The coupler is made by joining two bottle tops together face to face, if you heat the surface of each breifly with a lighter you can then super glue them together. Once the super glue dries drill a hole through the adjoining faces of the caps and glue in an aquarium tubing fitting, then add a length of tubing sufficient to reach the bottom of the 2 liter bottle.
Step 3: The reservoir
is made from the 2 liter bottle. Wrap the threads with tape and run a strip down one side, now spray the bottle with black paint to increase the amount of energy captured.
When dry remove the tape and fill half way with your nutrient mixture.
Step 4: The pot
is just a 1 liter water bottle with the bottom cut off and an overflow hole, to account for extraordinary rainfall, placed half way up the side.
Step 5: Assemble and test
The coupler is screwed onto the reservoir bottle and the 1 liter bottle screwed on top of the coupler. Take the bottle outside and place in the sun, watch as the water is pumped up into the bottle as the reservoir is heated by the sun.
Although the original theory was based on the differential between day and night temperatures, observations showed that clouds passing in front of the sun was sufficient to cause a rapid change in the water level, providing a continual refreshing of the nutrient to the plant.
Step 6: Set it and forget it
Fill the "pots" with perlite and plant. In one I planted gota kola, another onion seeds and the third a basil cutting, place somewhere sunny and forget it until instructables has a bottle contest ;-).