Setting the Angle for the Heating Season

What tilt is best for winter heating?

A common starting rule: for all-year output, tilt about equal to latitude. For winter emphasis, add 10 to 20 degrees. Southern Alberta sits near 50 degrees north, so a winter-biased collector would tilt in the neighbourhood of 60 to 70 degrees from horizontal, and a vertical wall is not far off. A flatter angle, around 30 to 40 degrees, favours spring-to-fall output.

These are rules of thumb. The real optimum depends on the load, the storage and the climate, so a modelled estimate with local weather data should settle it. Compare with the PV advice in the best direction for solar panels guide, which targets annual kilowatt-hours rather than winter heat.

Why does the sun angle matter so much?

In December at 50 degrees north, the noon sun stands only about 16 to 17 degrees above the horizon. A steep surface faces it almost square-on, so more light lands per square metre. A flat surface sees the same light spread thinly and loses more of it to reflection. Snow-covered ground in front of the array also bounces light back up, a modest bonus for steep collectors.

What about azimuth and shading?

True south is the target, not magnetic south, which differs by several degrees in much of Canada. An error of 15 to 20 degrees in either direction costs a small share of output, so a slightly off-south roof is still usable. Shading is worse. In winter, low sun casts long shadows from neighbouring houses, trees and even the collector rows in front. A rooftop that is clear in June may be shaded for the whole of December. Do a site check at the time of year you want the heat. The peak sun hours guide explains how to read the available resource month by month.

A simple way to check shading is to stand where the collectors will be on a clear day around the winter solstice, or use a shade-analysis tool that logs the horizon at that spot. Note the time the sun clears the neighbour's roofline in the morning and when it disappears behind the tree in the afternoon. Even two lost hours at midday in December can remove a large part of the winter yield, since the sun is above the horizon for only about eight hours at that latitude.

What are the trade-offs of a steep tilt?

A steep angle lowers summer output, which is useful if you have a heating-only system and a stagnation problem in July. It sheds snow better, because snow slides off a steep slope sooner. It increases wind load, so mounts and racks need to be designed for it. And it needs more spacing between rows to avoid self-shading. The cost guide lists the mounting work that affects a quote.

How was this handled at Drake Landing?

The Okotoks project put its 800 flat-plate collectors on garage roofs along the back lanes, so the array was shaped by where the garages stood. Because the heat went into a borehole field that carried it from summer to winter, the design did not depend on catching the most January sun, and the seasonal swing was handled by storage rather than by angle alone. A household with no seasonal storage has to weigh the angle more carefully. The solar collection page and the solar space heating guide go further into the design.

For a household system the answer is therefore a compromise: choose a tilt that suits the months you need heat, check shading in December, and accept that a roof with a fixed pitch may limit the choice. A tilted rack on a flat roof gives freedom, at the price of extra wind-load design and cost. The installer's yield model should show monthly output for the proposed angle and one or two alternatives.

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