cost of solar water heating.. really depends upon if you are building your own. If you are buying expect to pay $700 - $1200 per panel. if you are planning to build first quality home built. Expect to pay $100 -$200 per very similar output. Question are you planning on home built heated water storage or are you buying $1000 tanks to hold the water? Reality.. if you do it DIY you can pretty well figure $1000 including pipe, insulation, panels, pump, and perhaps power hook up. So it really depends upon how you wish to do this project.. Pay back time? with out more information .. 18 months to 18 years.