ShelleyAnn,

I'll take a stab at this one, at least for your first question. When connected in parallel, the total flow rate will be much higher because there will be far less resistance in the solar panel piping compared to being connected in series. Think of it this way -- your pump is spinning at a certain fixed rate (RPM) so trying to force water through a longer but narrower pipe (i.e. solar panels in series) is much harder so will result in higher pressure and lower flow rates compared to forcing the water through a shorter but much wider pipe (i.e. solar panels in parallel) which will result in lower pressure and higher flow rates. When I refer to flow rates, I mean through the entire system into your pool, not "per panel".

Now it is true that the flow rate per panel when connected in parallel may be less than the flow rate when they are connected in series, but when in series the water heats up as it goes from panel to panel and this higher temperature water radiates its heat back into the air via a hot panel (the last panels in series, especially). When connected in parallel, the panels stay cool and absorb heat from the sun most efficiently. The much larger total flow rate more than makes up for the smaller temperature increase on output into your pool -- this is what Carl means when he says it is the BTUs that matter, namely the total heat that is transferred to your pool.

Imagine it this way. If you heated one cup of water to 100F higher temperature and added it to your pool, it would have the same effect if you took 100 cups of water to 1F higher temperature and added it to your pool (ignoring the small change in total water volume). It's the same amount of added heat in either case. The reason it is better to add more water volume at smaller temperature increase is that this is more efficient. You can imagine that having a cup of water at 100F higher temperature than your pool water won't stay that way very long sitting in a cup -- it will lose heat rapidly since it is so much hotter than the surrounding air. In the same way, water flowing through solar panels that is much hotter won't stay that way if the air around the panel is cooler (which is typically the case -- the air is cooler, but the sun's energy makes the panel slightly warmer and transfers this heat to the water flowing in the panel).

Richard