Operations: Monitoring, Performance, and Safe System Management
The Operations domain tests how a commissioned PV system is run: monitored data quality, performance metrics, safe switching, outage response, and records. Expect scenario items that give production, irradiance, and temperature data and ask you to judge performance or choose a safe operating step. The exam expects familiarity with IEC 61724 monitoring concepts and NFPA 70E safe-work practices, not just NEC installation rules.
Core rules
- Compare energy to a weather-normalized baseline, not to last month's kWh. Use plane-of-array (POA) irradiance from a sensor in the array plane; global horizontal irradiance (GHI) will bias PR.
- Performance ratio: PR = actual AC energy / (POA irradiation × array STC rating / 1 kW/m²). Reference yield is POA irradiation in kWh/m² divided by 1 kW/m², giving hours.
- Specific yield = annual kWh / kWp; capacity factor = annual kWh / (kWp × 8760 h). Availability separates downtime from resource and performance losses.
- Flag data-quality issues first: stale timestamps, clipped inverter output, missing irradiance, sensor soiling, and time-zone drift can look like energy loss.
- Safe operations: establish an electrically safe work condition with lockout/tagout, verify absence of voltage, and treat PV source and output conductors as energized until proved otherwise. Rapid shutdown does not de-energize all conductors.
Worked example
A 100 kWp array produces 12,000 kWh in a 30-day month. POA irradiation is 150 kWh/m². Reference yield = 150 h. PR = 12,000 kWh / (100 kW × 150 h) = 0.80. Specific yield = 120 kWh/kWp. If the modeled PR was 0.82, the gap is about 2.4% of expected energy, so check soiling, clipping, sensor calibration, and downtime before condemning modules.
Traps
Using nameplate AC inverter rating instead of array STC; comparing PR across different climates without context; calling clipping lost generation without checking the inverter AC limit; ignoring a pyranometer that is dirty or not co-planar.