Orientation to path of sun

Two angles describe the orientation of the collector:

• The azimuth* angle α, also called “compass orientation”: The angle in a horizontal surface between the collector and the due south direction. Due south, towards the equator, is by definition an orientation of 0˚.
• The tilt angle β (“sky ward orientation”): The angle between the collector and the horizontal surface.†

Costs for supporting structures can be saved by mounting collectors flush with an existing, suitable surface or structure. Tools (brackets etc.) are usually available from the supplier of the collector, which will suit various common surface types like tiled or sheet metal roofs, brick or wood walls etc. The fittings should provide sufficient strength to endure extreme weather conditions like wind and snow loads. It is important that the mounting and structure comply with local standards and regulations.

If mounted in line with an existing structure (e.g., a wall surface) the orientation may be less than optimal, in many cases. The effects of these compromises are often less than expected. This is shown in Figure 2.7. A deviation from the maximum yield tilt and orientation can be compensated for by a larger collector area, if space and costs permit.

A rule of thumb for optimum exposure to solar radiation is that a collector should face the equator (orientation of 0 degrees, due south) with a tilt angle of 0.7 times the Latitude of the location (but at least 10 degrees, or the minimum working angle of the collector). This applies to heating domestic water systems.

The optimum collector tilt angle for the usage of solar energy during winter months is higher because the average sunlight incidence angle is lower. Choosing a larger tilt angle provides a yield that is geared towards winter heat demands. The optimum collector tilt angle for the winter months is higher than the latitude, for example 50 degrees for a site at 45 degrees latitude. Deviations up to 60 degrees from these optimum angles generally will lead to a loss of solar radiation of less than 15% compared to optimum angles. Note that the annual yield also depends on many other factors such as the heat demand characteristics or the storage capacity.

Choosing a smaller tilt angle gears the yield towards the summer. Usually a summer bias increases the potential overall annual yield of a collector, but only if this extra yield can be used. Solar thermal systems are thus often sized by matching the collector yield during the summer period with the hot water heating need (called economical collector sizing), any increase in collector area will increase the fraction covered in winter, but will also increase the stagnation periods and duration during summer. Refer to Section 3.4.2 for an explanation of stagnation.