Shading and solar: what it costs you
How trees, chimneys and neighbouring buildings affect solar in Canada, why winter sun angles matter, how shade hits strings, and when to skip a roof face.
5 min read · Updated 2026-10-30
Shade is often the biggest single factor in how much a solar system produces. A roof that looks sunny at noon in July can be in shadow for much of a December afternoon. Understanding where your shade comes from, and when, tells you whether a roof face is worth using and what equipment makes sense.
Where shade comes from
- Trees. The most common cause. Deciduous trees shade less in winter when leaves are down, but bare branches still cast shadows. Evergreens shade all year, and trees keep growing.
- Chimneys, vents and dormers. Small objects cast long shadows when the sun is low. A chimney can shade several panels in the morning or afternoon.
- Neighbouring buildings. A taller house next door, or a new addition, can shade the lower part of your roof for hours in winter.
- Your own roof. On complex roofs, one section can shade another.
Why winter sun angles matter in Canada
The sun sits much lower in the sky in winter, especially as you go north. At solar noon, the sun's height above the horizon is roughly:
| City | Winter solstice | Summer solstice |
|---|---|---|
| Toronto | About 23° | About 70° |
| Calgary | About 15° | About 62° |
| Edmonton | About 13° | About 60° |
These are worked out from each city's latitude. A low sun means long shadows. An object 3 metres tall can cast a shadow more than 7 metres long at noon in a Toronto December, and much longer in the morning and afternoon.
The good news is that winter matters less to your annual total than it seems. In our Toronto sample system, the three darkest months (November, December and January) produce about 7% of the year's energy, while May through August produce more than half. Shade that only appears in winter costs less than shade that blocks summer afternoons. See solar in Canadian winters.
How shade affects a string of panels
On a basic string inverter system, panels are wired in series, like a garden hose running through each one. Shade on one panel restricts the flow for the whole string. Panels have bypass diodes that limit the damage, but a shaded panel can still pull down the output of others on the same string.
With power optimizers or microinverters, each panel works more independently. A shaded panel produces less, but the rest keep producing at full strength. See microinverters vs string inverters.
How installers measure shade
A good installer measures shade instead of guessing. Common methods include:
- Satellite and 3D modelling tools that trace nearby trees and buildings
- Site visits with a shade analysis device or app that records the horizon
- Drone surveys
Ask what tool was used and for the shade figure by roof face, often given as a percentage of available sunlight. A quote with no shade analysis on a treed lot is a warning sign.
Natural Resources Canada publishes free maps of solar potential for more than 3,500 municipalities. They show what an unshaded system can make in your area, which gives you a benchmark.
Ways to reduce shade losses
- Trim or remove trees. Often the most effective step. Check municipal tree bylaws first, since many cities protect trees above a certain size, and a neighbour's tree needs their agreement.
- Use panel-level electronics. Optimizers or microinverters recover much of the loss from partial shade.
- Design around the shade. Leave the shaded corner empty, or put shaded panels on their own string.
- Choose a different roof face or a ground mount in a sunnier part of the yard. See ground-mount and flat-roof solar.
When to skip a roof face
Some roof faces are not worth covering. Consider leaving a face off if:
- It is shaded for much of the day from spring to fall, not just in winter
- It faces north, or close to north
- Covering it would add cost but only a small share of annual production
Each panel should earn its place. A smaller system on the best faces often pays back faster than a larger one that includes poor ones. Our system size tool helps you test this.
When shade means solar does not pay
If most of your roof is heavily shaded by trees you can't or don't want to remove, rooftop solar may not make financial sense. That is a fair conclusion. Alternatives include a ground mount in a sunnier spot, community solar where it exists, or buying green power. See solar for townhouses, semis and condos for those options.
Next step
Check your roof to see your roof faces and an estimate of production, then read is my roof suitable for the other factors.
Common questions
- How much does shade reduce solar output?
- It depends on when and how much of the array is shaded and on the inverter type. A little winter-only shade may cost a few percent, while shade on summer afternoons can cut output much more.
- Do microinverters help with shade?
- Yes. With microinverters or optimizers, a shaded panel produces less but does not drag down the others, so partial shade costs less.
- Should I cut down trees for solar panels?
- Trimming is often enough. Check your municipality's tree bylaw first, and remember that trees also provide summer cooling and other benefits.
- Is solar worth it on a shaded roof?
- Sometimes not. If most of the roof is shaded for much of the year, a smaller system on the sunniest face, a ground mount or another option may be better.
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