How to work out Solar Collector Tilt Angles

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Solar365 Solar Thermal

Almost all residential solar installations mount the collector on the roof or a ground frame. Once you've done your research and figured out where the best location for your solar collectors is, you'll need to work out the optimum tilt angle – the angle the collector array surface makes with the horizon.

Their facing is easy: as close to magnetic south as possible. In an ideal world, collectors would start the day facing east and slowly swivel to follow the sun as it tracks across the sky, ending the day facing the sunset in the west. Anyone who has planned a PV panel installation knows that this can, in fact, be done with tracking arrays. Unfortunately, solar collectors can't track the sun for two reasons:

  • Solar collectors use solar fluid carried in rigid pipes rather than electrons in flexible wires. There are no flexible pipes available today that can handle the extremely high temperatures solar thermal applications need.
  • Solar collectors are comparatively very heavy, so any energy they generate would be all but negated by the cost of the power used to turn them throughout the day.

Since you're going to mount the collector array in a single, fixed position, you need to choose the optimum tilt for the whole year. The noon sun is a lot higher in summer than in winter and its path varies daily, so you'll have to compromise between the two seasonal optimum angles.

  • If you're using your solar hot water system all year round, the best angle is equal to your site's latitude.
  • If you only use your solar hot water system in summer, subtract ten degrees from that angle.
  • If you live in an area that gets a lot of snow and use the system year-round, remember to angle the collectors at more than forty degrees (so the snow slides off).

If you're installing a solar space heating system, the best angle optimizes the winter sun: set the array at your latitude plus fifteen degrees. This goes for combination systems as well. Although you will get less output per collector in summer because of the winter angle, your installation will be larger to cope with the winter requirements so you'll have plenty of hot water.