© 2011 National Institute of Building SciencesLow temperature models perform at high efficiency levels when temperature differences stay within 5 to 30 degrees.
Medium temperature models show high solar collector efficiency rates when temperature differences stay within 15 to 200 degrees, and high temperature collectors cover temperature differences over and above the low and medium models.
Low and medium temperature units typically use a flat plate collector. High temperature units use evacuated-tube flat plates or parabolic dish reflectors.
Another factor affecting solar collector efficiency depends on whether the surface of the flat plate collector is glazed or unglazed. Glazing affects how easily the sun's rays are transferred into the solar compartment. Glazing also affects how easily the heat inside the compartment can escape. The amount of glazing used in the construction of a unit can significantly reduce or increase solar collector efficiency rates depending on the type of collector system used. Unglazed collectors are generally only used in solar pool heating. Selective coating further reduces heat loss for medium temperature flat plate collectors.
Evacuated Tube Collectors Minimize Heat Loss
The tube and reflector models used with high temperature units (evacuated tube collector) absorb solar heat and also create an insulative effect inside the solar unit through a vacuum. Ultimately, the types of materials used to manufacture a solar collector impact its efficiency levels under different climate conditions.
Collector Siting is of Key Importance
As solar collector units can be mounted on the roof or on the ground, the direction a unit faces can have a significant impact on the system's solar collector efficiency levels. Ideally, the unit should face south with little to no overhang or obstructions to block the sun's path. Since factors affecting solar collector efficiency have a lot to do with the climate conditions in a particular area, some areas will see better solar collector efficiency levels than others.