The answer is – it doesn’t really matter – if you are using a Fafco Revolution 500 series Domestic Solar Water Heating System. These featherweight panels are just 8 pounds each empty, and 22 pounds filled. The additional dead load imposed on your roof is totally inconsequential. A traditional 40 square foot glass/copper solar collector system weighs over 180 pounds when filled! The pictured collector system is a 96 square foot Fafco Revolution system with four 2’x12′ solar panels, a photovoltaic panel for circulation, and an expansion tank. This low profile system is mounted on the roof and UV rated cross-linked polyethylene tubing (similar toRead More →