Solar energy doesn’t hit the earth with the same intensity worldwide; the closer to the tropics, the higher the strength. Apart from a few sun guided systems (mostly for PV’s), all solar water heaters are supported by a fixed structure which will require some compromise since the sun changes position every minute of the day and during the year. The best compromise, for the Northern hemisphere above the tropics is as follows:

1. Solar collectors must be out of any shade; the northern you live, the longer the shade so the further away from an obstacle the solar collector must be mounted

2. Solar collectors must face South; if this is not possible you can install them with a +/- 15° from South difference, on the horizontal base, without losing more than 5% in efficiency.

3. Solar collectors must be raised of an amount of degrees calculated as: 90 minus the altitude of sun on the first day of either spring or autumn. In this way the sun will hit the collectors at a 90° angle giving optimum sun exposure. An enough close estimate is to raise the collectors of an amount of degrees calculated as: the latitude at which you install them plus 10. To give you an example, if you live in Milan, around latitude 45° N, your panel should be raised of 55° from a horizontal position.

In the following map you can read (the darker the color the higher the solar energy hitting a square meter of horizontal land) the amount of energy hitting the earth.

Map reproduced with permission; source European Commission Directorate General Joint Research Centre: http://re.jrc.ec.europa.eu/pvgis and http://re.jrc.ec.europa.eu/pvgis/cmaps/eur.htm