A C-46 contractor is designing a commercial PV system for a building with a large, unobstructed flat roof. The client wants to maximize the number of modules installed while adhering to fire code setbacks and minimizing row-to-row shading. The optimal tilt angle for the modules is 10 degrees. What is the MOST critical factor to consider when determining the spacing between module rows?
- AThe module height and tilt angle to prevent inter-row shading at solar noon on the winter solstice.
- BThe color of the roof membrane to optimize albedo.
- CThe availability of structural attachment points on the roof.
- DThe wind uplift ratings of the chosen racking system.
Show answer & explanationAnswer & explanation
Correct answer: A. The module height and tilt angle to prevent inter-row shading at solar noon on the winter solstice.
For maximizing module count while minimizing row-to-row shading on a flat roof, the most critical factor is calculating the necessary spacing to prevent inter-row shading. This calculation considers the module's height (when tilted), the tilt angle, and the lowest sun angle (winter solstice solar noon provides the longest shadows). This ensures that one row does not shade the row behind it during periods of significant solar production.
Why the other options are wrong
- B. Roof membrane color (albedo) affects module temperature and efficiency slightly, but not directly the physical spacing needed to prevent shading.
- C. Availability of structural attachment points is relevant for mechanical attachment systems, but the question implies a flat roof where ballasted systems are common, and for any system, shading prevention is paramount for production maximization.
- D. Wind uplift ratings are critical for structural integrity but do not directly determine the spacing required to prevent row-to-row shading.
PV Row Spacing (Flat Roof)
PV row spacing on flat roofs is the distance between parallel rows of tilted PV modules, primarily calculated to prevent inter-row shading, especially at the lowest sun angles (winter solstice), and to comply with fire code setbacks.
- Critical for maximizing energy production and module density.
- Determined by module height, tilt angle, and site latitude.
- Shadow length is longest at winter solstice solar noon.
- Fire code setbacks (e.g., 3-foot pathways) also dictate spacing.
Memory trick: Shade-free Spacing Secures Solar Success, Especially in Snowy Seasons.