Domain 2: Site Assessment
Domain 2 is site assessment: collecting the physical, structural, and electrical facts that decide whether - and how - a PV system can be built. The exam tests which measurements matter, how shading and roof condition change production or cost, and where the electrical service limits interconnection.
Solar resource and shading
- Orientation and tilt: due south is optimal in the northern hemisphere; east/west arrays lose yield but can gain value under TOU rates with strong afternoon prices.
- Shading tools: a sun-path chart plus horizon scan (Solar Pathfinder, SunEye, or fisheye photo software) gives a shade factor by month. Model it; do not guess.
- Account for future shade from maturing trees and new construction.
Structural and roof condition
- Dead load for flush-mounted arrays runs roughly 2–4 lb/ft²; ballasted and elevated racks are heavier and may need structural review.
- Roof age and remaining life: replacing a roof under an array later is expensive, so note it in the proposal.
- Covering type, rafter spacing, attachment method, snow and wind loads per ASCE 7, and required fire setbacks.
Electrical and interconnection
- Service size, busbar rating, main breaker, space for a backfed breaker, meter location, and utility transformer capacity.
- NEC 705.12 busbar rules govern how much PV may be interconnected; a service upgrade is a major cost.
- Interconnection path options: load-side breaker, line-side tap, or supply-side connection; check whether the project passes the utility's fast-track screen.
Worked example
A 200 A panel with a 200 A busbar and 200 A main breaker. The 120% rule permits total supply (main plus PV) of 240 A, leaving 40 A for the PV breaker. Continuous inverter output must be 32 A or less after the 125% factor, so at 240 V the largest inverter is about 7.7 kW. A larger array needs a service upgrade, a line-side tap, or another code allowance.
Traps
Ignoring winter shading when the sun is low; recording tilt without an azimuth reference; missing a busbar derating; forgetting fire setbacks and HOA approvals.