Shading Considerations for Solar Thermal Collectors

You are here

The ideal location for a solar thermal collector array is one in which the sun's radiation falls full and unobstructed on the collector surface between the hours of 9:00 a.m. and 3:00 p.m., with the collector facing the noon sun directly. However, the perfect location isn't always available, so here are some pointers to help you decide whether a site is acceptable or not.

Prioritize Roof Mounting

Different collector placement options to optimize solar energy collection

The roof is usually the best site for collectors. It's higher up, so there's less chance of obstructions to block sunlight. It is space that you're not likely using for anything else and, unlike a ground mounting, is safe from most aggressors (vandals, large animals and small children included). It requires less piping between the collectors and the rest of the system.

While all of these are significant advantages, roof mounts are not always ideal. Your home may have beautiful or rare trees that shade the south-facing roof and keep your yard and home cool in the hot summer months. Those trees may also be home to wildlife that you do not wish to disturb or may help form a visual or sound barrier between you and your neighbors for privacy. In these cases and many others, a ground-mounted array or a shed-mounted setup in a sunny spot can be a better option.

No South-Facing Roof

Many collectors will work even if they're not mounted on a south-facing roof... or even on a roof at all. You can set the collectors on a rack on an east- or west-facing roof space using saw-tooth mounts to keep them facing the sun. An awning or a porch roof can provide the space needed for a collector. They can even be ground-mounted.

The important thing is to ensure an open solar window , wherever you end up locating the collector array. As long as the sun heats it and your chosen system allows the siting, the only problem is the practicality of getting the collectors safely in place and facing the right way.

Partial Shade

Unlike PV arrays, collectors still work in partial shade – they're just less efficient than in full sunlight. If your collector site has less than 10% shade throughout the prime collection hours, it's still acceptable in most cases.

You may also be able to reduce shading. If the obstruction is something natural, such as a tree's branches (which can block 50%-75% of all the sunlight passing through its leaves), you can cut back the offending parts to clear a path for solar radiation. Just remember that trees grow and solar collectors don't, so you'll have to maintain a clear path through the years or suffer reduced efficiency.

Bottom Shading

Some roof-mounted collectors suffer from obstructions at the bottom end of the solar window. Throughout the hotter part of the year, when the sun is higher, such obstructions are not an issue; it's only in the colder months, when the sun is closer to the horizon, that they get in the way.

If the obstruction is minor, it may not be a problem as it only