"Don't worry, microinverters fix shading" is the most common half-truth in solar sales. Microinverters help, but they don't make a shaded roof produce like an unshaded one. Here's how to evaluate honestly.
How shading actually affects production
A single shaded panel in a string-inverter system can drag the entire string's output down by 50–80%. Microinverters and DC optimizers fix this — each panel operates independently, so shade on one panel only reduces that panel's output.
What microinverters can't fix: the shaded panel itself. If a panel is 50% shaded for 4 hours a day, it produces 50% less for those 4 hours, period. The optimizer just prevents that loss from cascading.
The 20% rule
If your shading analysis shows you'll lose more than 20% of theoretical production due to shade, you should:
- Get a quote with microinverters or DC optimizers (mandatory at this shade level).
- Ask the installer for a shade-corrected production estimate (PVWatts with shade input).
- Re-run the payback math with the lower production number.
If the corrected payback comes in under 12 years, solar still works. Over 15, it usually doesn't.
How to estimate shade without an installer visit
- Google Project Sunroof (free): gives a rough sun-hours-per-year for your specific roof.
- SunPath app (free): visualizes the sun's path across your roof at different times of year.
- Helioscope or SunEye (used by installers): proper shade analysis with measured percentages — request the report from any installer giving you a quote.
Tree removal: when it pays back
If a single tree is responsible for 15%+ of your shade loss, removing it can shift solar from "marginal" to "great." A $1,500 tree removal that recovers 1,000 kWh/year (worth $200) pays back in under 8 years — faster than most solar investments.
Run your shade-corrected numbers in the calculator with a manually-set system size that's 80% of normal to simulate the production loss.