Site Assessment, Design, and Layout
Domain 3 tests whether you can evaluate a site, predict production, and lay out an array that is code-compliant, structurally sound, and serviceable.
Solar geometry
- True south (not magnetic) is optimal in the northern hemisphere; correct for magnetic declination using a compass or solar tool.
- Fixed tilt near latitude maximizes annual yield; steeper tilt favors winter, shallower tilt favors summer. Roughly 10–15° minimum helps snow and soiling shed.
- The usable solar window is about 9 a.m. to 3 p.m.; shade outside it matters less.
Shade and production analysis
Use a Solar Pathfinder, Solmetric SunEye, or a smartphone shade tool at several array points, and analyze in winter when the sun is low. Production estimate: kWh/day = array kW × PSH × derate (0.70–0.85 for wiring, inverter, soiling, temperature, and mismatch losses).
Layout rules
- Row spacing must prevent inter-row shading at the winter solstice: shadow length = object height ÷ tan(solar altitude).
- Structural: verify rafter size, spacing, and span before adding load; a residential array typically adds 2–4 lb/ft².
- Fire code: maintain required 3 ft access pathways and ridge/edge setbacks per the IFC and local amendments.
- NEC: disconnect location per 690.13 and working clearances per 110.26.
Worked example
An 8 kW array at a site with 5.0 kWh/m²/day and a 0.80 derate produces 8 × 5.0 × 0.80 = 32 kWh/day, roughly 11,700 kWh/year. A 0.5 m tall tilted row casting shadow at a 25° winter solstice solar altitude gives 0.5 ÷ tan 25° = 1.07 m; specify about 1.1 m minimum row gap before adding a safety factor.
Traps
- Designing to magnetic south and losing production.
- Measuring roof pitch with the phone held away from the roof plane.
- Ignoring future tree growth or planned construction shade.
- Dropping fire setbacks to fit extra modules.