For optimum efficiency, there should be no shade on the panels of your SDHW system from 10:00 am to 3:00 pm on a summer day. A solar hot water panel is roughly 27 sq. ft. (4' by 7') or 2.5 sq.m. (1.25m by 1.8m), so you will need a non-shaded space on a south-facing roof that will accommodate the number of panels required for your hot water needs. A sloped roof can be used or a flat roof with panels mounted on racks is also possible. The amount of shading on the collectors four hours before or after solar noon is important to the performance of the solar panels. The position and height of trees and structures must be taken into account when locating the solar panels. Thought must be given to the effects of snow accumulation on or around the solar collectors. A flat plate panel only needs minimal sun to start the snow melting process from the panel.