Solar Shading Analysis
An assessment of shadows cast on a roof throughout the year from trees, chimneys, and neighboring structures — essential before system design to avoid installing panels where they will underperform.
Solar shading analysis quantifies how shadows affect potential panel locations throughout all hours and seasons. Even small shadows — a narrow chimney, a 6-inch dormer, a neighboring tree — can significantly impact production, especially with string inverters.
Professional analysis uses tools like Aurora Solar, Solargraf, or physical shade measurement devices (Solar Pathfinder, Solmetric SunyEye). These tools generate shade-hour maps showing the percentage of annual solar resource available at each potential panel location. Installers typically use 80% or higher as the minimum threshold for panel placement.
The Solar Access Value (SAV) of a location — the ratio of actual to theoretical solar production absent shading — determines financial viability. A roof with 60% SAV due to tree shading may not be worth installing on at current electricity rates. Tree trimming or removal is sometimes cost-effective: a $1,500 tree trimming that increases SAV from 70% to 90% on a $30,000 system increases production value by roughly $2,800/year over 25 years.
Real-World Example
Aurora Solar's shade analysis showed that the large maple on the southwest property line cast shade covering 40% of the back roof from October to February; the installer designed the 10-panel array to avoid those positions entirely, even though it reduced system size from 10 to 8 panels.