Ask what limits solar in the Pacific Northwest and most people say the rain. It is not the rain. Our summers are long and bright and the annual numbers hold up fine. The thing that actually kills production here is standing thirty feet from the house and growing.
How much shade is too much for solar?
There is no single threshold, and anyone who gives you one is guessing. What matters is when the shade falls and on what. Shade across the middle of the day in June costs far more than shade at eight in the morning in November, and on a system with module-level electronics one shaded panel no longer drags its whole string down.
As a working rule: if the good roof plane is clear between roughly 9am and 3pm through the year, you are in decent shape. If a tree crosses that window in winter, the array needs rethinking rather than shrinking.
Why winter shade matters more than summer shade
Because of the angle. In December the sun tracks low across the southern sky, so a fir that clears the roof easily in July can lie right across it at midday in winter. That is precisely when your production is already at its weakest and your consumption is at its highest.
This is the single most common thing a desktop quote gets wrong. Satellite imagery is usually a summer photograph. A model built on it will not show you the December problem, which is why we model the specific roof across a full year rather than eyeballing an aerial view.
Whose tree is it?
An awkward question and a decisive one. If the tree causing the shade is on your property and removal or crown reduction is lawful and sensible, you have options. If it belongs to your neighbour, you are designing around something you do not control, and you should design around it rather than hoping.
Local tree ordinances vary across this region, and some cities regulate removal of larger specimens. We will tell you which trees affect production and by how much; what happens to the tree is your decision and your neighbour’s, not ours.
Trees grow. Does that get accounted for?
It should, and it usually is not. A Douglas fir can put on serious height across the twenty-five year life of an array. A design that just clears a treeline today may not in fifteen years.
Where that is a real risk we say so, and it sometimes changes the recommendation, a ground mount in a cleared area, a different roof plane, or a smaller array on the section that will stay clear. Getting this wrong is not a warranty issue; it is simply less power every year, quietly.
What are the options when the best roof is shaded?
- A different plane or building. West-facing production is lower but often viable, and a detached garage or shop sometimes sits in better light than the house
- Selective tree work where the tree is yours, often one limb rather than one tree
- A ground mount, where the lot has an open corner
- Waiting for a reroof, if the covering is near its end anyway
- Not installing, a real answer we give regularly, and one worth hearing before you spend money
If you want the technical measure behind all of this, it is Total Solar Resource Fraction, the share of the ideal solar resource your specific roof actually receives. We explain it in our TSRF guide.
Frequently Asked Questions
How much shade is too much for solar panels?
There is no universal number. What matters is when the shade falls: midday shade through the year is costly, early morning or late evening shade much less so. As a rule, a roof plane clear from roughly 9am to 3pm year-round works well.
Do I need to cut down trees to install solar?
Often not. Frequently it is a single limb rather than a whole tree, and sometimes a different roof plane or a detached garage solves it. Where the tree belongs to a neighbour, we design around it rather than counting on its removal.
Why does winter shade matter more?
Because the December sun tracks low across the southern sky, so a tree that clears the roof in July can shade it at midday in winter, exactly when production is lowest and consumption highest. Summer satellite imagery hides this entirely.
Will my panels still work in partial shade?
Yes, with reduced output. Module-level electronics mean one shaded panel no longer drags down its whole string, which helps considerably on Pacific Northwest roofs, but shade still costs production, and no equipment removes that.
Do you account for trees growing over time?
We should and we do where it is a real risk. A fir can add serious height over an array’s 25-year life, so a design that just clears a treeline today may not in fifteen years. Sometimes that changes the recommendation entirely.
Wondering whether your roof gets enough sun?
Call 360-313-7190 for a proper shade assessment, including the answer “not worth it” if that is what the model shows. Sunbridge Solar serves Camas, Washougal, Vancouver, Portland and the Columbia River Gorge.
