What pulls winter output down
Three factors combine in the colder months:
- Shorter days. Fewer daylight hours mean fewer hours of generation, regardless of panel quality.
- Low sun angle. A sun that stays near the horizon delivers light at a shallower angle to a roof-pitched panel, reducing the energy captured per hour.
- Snow cover. A panel covered by snow produces little until the snow clears.
One factor works the other way: photovoltaic cells are slightly more efficient in cold air than in summer heat. This does not offset the loss of daylight, but it means a clear, cold, sunny winter day can still produce usefully.
Where tilt helps
A steeper tilt addresses two winter problems at once. It points the panels more directly at the low winter sun, and it encourages snow to slide off sooner so the glass returns to producing. This is why winter-weighted designs often lean steeper than a strict latitude match, a theme introduced in the orientation guide.
Annual figures hide the seasonal swing. A system sized only on a yearly total may still see long stretches of low winter production, which matters for households that use the most energy in winter.
A qualitative monthly picture
Without quoting site-specific numbers, the general shape of a Canadian rooftop year is consistent: a strong middle, a weak start and end. The table describes the direction of each season rather than precise yields.
| Period | Daylight | Typical output direction |
|---|---|---|
| Mid-winter | Shortest | Lowest; snow cover possible |
| Spring | Lengthening | Rising quickly |
| Summer | Longest | Highest |
| Autumn | Shortening | Declining |
Setting expectations
For a Canadian household, the practical message is to expect meaningful summer production and a notable winter reduction, and to treat any single annual number as an average across that swing. Designing with the winter months in mind, through orientation, tilt, and clearance for shedding snow, keeps the cold-season floor as high as the site allows.
Public modelling tools and regional solar data are available through bodies such as Natural Resources Canada, which can illustrate how seasonal variation looks for a given location.