posted 11 years ago
I've been reading up on these solar water heating units, and notice a common theme. Everyone likes to brag that "no pump is required". This is because the convection of the heated water draws it up, and cool water flows in below.
But what keeps the heated water from over pressuring and trying to flow backwards into cool stream? Is everyone relying on a positive pressure on the cool side due to city water or a well pump?
What I'm trying to figure out, is if I used a passive water heater in a closed loop (with some way to rapidly dump heat so it circulates readily), could I use that to power something like a water wheel for mechanical gain, or maybe a turbine to lift water in a separate system.
I'm considering an aquaponics system and thought at first I could just use it as a lift mechanism to get water from my sump to the peak and let gravity run it back down, and it would get heated along the way to keep tilapia happy. But these systems can get up 130°F! That would cook my fish and plants. Hence the need for parallel systems where the water heater just circulates water to drive a pump of some sort which then would lift water for the aquaponics.
Did I miss something obvious? Friction and inconsistent flow seem to be the biggest risks. But I'm also wondering if it's a net loss, like putting a wind turbine I front of a fan, or trying to use the refrigerator to cool your house. Also I'd have to figure out how to rapidly dump the heat from the water to circulate, but I figure that be as simple as some shaded riffles to stir it up.
So what am I missing?