Thanks, that is sort of what I thought. I got a catalog from InTheSwim and they have a system for inground pools that is about $450 that has 4 panels that are 2' by 10' - that is where I came up with the 80 sqft.

How much heat does you 600sqft system put out - what sort of temperature rise per hour or day do you see. If I did this it would be on the ground or on a slanted platform as my south facing roof is fairly full with a 10kw solar electric system which produces about 1200 kwh of electricy a month.