Quote Originally Posted by Teapot View Post
Maybe Carl, that's what I was waiting for clarification over. It's normally a pressure required to lift the water not necessarily a flow rate but in this case that 48 GPM maybe where the pump flow supplies sufficient pressure to reach the panels.
It takes time to transfer the solar energy into the water so to fast and the water won't absorb enough heat so the excess flow is just a waste of energy, there will be a point where to slow and the panel stays to hot so not supplying enough heat to the pool. Finding the sweet spot is the desirable point.
I'm sorry Teapot, but this is completely wrong and in contradiction to the laws of physics. It's a common mistake and INTUITIVELY it seems right, but, in fact, is not.

Remember: Transference of heat in or out is the same. By your logic you will cool your car's engine down FASTER by slowing down the water pump, the coolant flow, and by not going as fast through the air. Clearly, this is not true--you want to move the coolant through the system as fast as possible without cavitation or leakage in order to cool the engine down. And, the radiator fan goes ON when you slow down to keep air moving as fast as possible over the radiator fins and coils.
(Of course, if you don't want the engine to cool so much this isn't true--which is why there's a thermostat for those conditions).

What you are transferring is heat energy, not temperature. BTUs/Kcals, not degrees. In fact, the MOST efficient panels will NOT be getting much hotter than the pool water because they are transferring such a high percentage of heat to the water.

I have 30 solar panels, all 2'x4'. Originally, as built, they were all in a serial, one after another. My pool would heat up, but slowly and I had to keep the total water flow super-low so as not to cause leaks. Several years back, I re-plumbed the system so now there are two circuits of 15 panels each. I was able to increase the water flow, and I found my pool heats up about 40% faster than it did before. Greater flow=greater heat energy transfer.

Don't confuse heat energy with temperature. Would you rather have a flow of 10 gpm with water that's 5 degrees (F) warmer, or 1gpm of water that's 25 degrees warmer? Which has more BTUs?