The problem is designing a solar water heater system to keep a 4500 gal tank of water at 140F during the day. The tank in question has the following properties: 5000gal Volume 4500gal water It loses about 1.8 degrees F/hr if not heated. I first need to figure out amount of energy needed to maintain temps. I did this using the following math: 4500gal of solution times 8.3 lbs/gal of water = 37350lbs of solution 37350 * 1.8 = 67,230 BTU/h of energy needed. Seems pretty straight forward so far??? (Math Errors?) How do I go about finding out how much collector area and efficiency of solar collectors and heat transfer?