4 hours a day seems light…[/quote]
This is a good estimate. The amount of light per square meter falling on the collector is proportional to the cos of the angle between a line to the sun and a line perpendicular to the surface of the solar collector. Therefore to do a ‘flat-line’ estimate, they use a effective value of about 4 hours. It does depend upon your latitude, the angle at which the collectors are mounted at vs sun-arc and whether the collectors are ‘trackers’.
