Backyard Aquaponics
A place to discuss aquaponics

Do it like a stirling engine. Have you ever opened a empty bottle after its been in the sun? It blows hot air out. So all you have to do is heat some air the cool it to get air pressure which could move a piston. I was thinking about how to do this and recalling many times when I would shake a catchup squirt bottle that had been in the sun and watch the stream of warm ketchup blast out all over the place I decided that using a spray of hot or cool water would do it. The small drops would give up heat easily and the hot water would cool easy. So I tested the idea in a 55 gallon drum because to get a usable amount of pressure (volume) with a small change in temp requires a lot more space (like the ring boom engines). So anyway, I set a spray nozzle in the top of the barrel with epoxy. I then sprayed a short burst of solar heated water (160° F) into the top of the drum. Upon opening the bung I got a very large blast of air pressure. It worked!.. I then injected cool well water (63 °F) water and upon opening the bung I got a good suction. The power dropped off a bit on the next cycle as the air inside got to a temp other that ambient. However, I believe that there is real usable energy (form the sun) here. I have never had a chance to take this idea further into some kind of automatic system, but after reading this thread I think I need to try it. To pump water all I would just need 2 check valves and some pipe from a barrel to the sump, some timing circuit to inject hot and cold water and the pressure of the well water to push the water in; perhaps a small car washer motor pump.. I also think that the plastic drum was not strong enough as it would suck up on the cool cycle.. A hydronic water release float could be used to get rid of excess water build up in the drum or it could just flow down into the system.

DDM, have you seen the wheel generator thing that was made of propane bottles on a kind of water wheel? Sounds similar. That one worked on the change from liquid to gas or vice versa when the bottles are dipped in water.

Yes,I have seen that one and thought about making one, but I have to many other things to do.

Maybe something to keep an eye on:

http://thermofluidics.com/

There are lots of little ideas that can move given a small heat differential but actually getting any of them to do work for you is another story.

i loved the discovery channel show on perpetual motion where this french guy was sure he'd done it with this 100 foot high thing which used a set of switches that juggled weights about.
This physicist came out to have a look, and pointed out all he'd done was make a wind mill. the thing was just turning in the direction of the wind.
take shattered out of the dictionary and put this french guys face in it.

The solar pump idea above works great. Just have to remember that there is only so much energy in a square meter and there are efficiency losses. To pump say 1000 gallons an hour you would need to know how much energy it takes to move that volume of water to the height you are moving it then calculate the energy required to heat the water and thus then the air to the required temp to achieve the pressure to push the water.