Solar String Performance Monitoring Checklist [FREE PDF]

Solar string performance monitoring is a systematic process of measuring open-circuit voltage, short-circuit current, and string-level power output to identify underperforming strings caused by soiling, shading, cell degradation, or wiring faults. NEC Article 690 and IEC 62446-1 establish mandatory requirements for commissioning and periodic performance verification of photovoltaic systems, including string-level electrical testing and documentation. Consistent monitoring reduces energy yield lo

Industry: Solar Energy
Frequency: Quarterly
Estimated Time: 60-90 minutes
Role: Solar Technician
Total Items: 42
Compliance: NEC Article 690 Solar Photovoltaic Systems (2023 Edition), IEC 62446-1:2016 Photovoltaic Systems – Requirements for Testing and Documentation, OSHA 29 CFR 1926.960 Power Transmission and Distribution, NFPA 70E-2021 Standard for Electrical Safety in the Workplace, ANSI/NETA MTS-2019 Maintenance Testing Specifications for Electrical Power Equipment

Pre-Inspection Safety & Electrical Isolation

Confirm all electrical safety measures, PPE, and arc flash assessments are completed before accessing live DC string circuits.

Has an arc flash hazard analysis been reviewed and the appropriate PPE level determined for this inverter/combiner?
Is all required PPE (arc-rated gloves rated CAT II+, safety glasses, arc flash face shield) donned prior to panel access?
Have the inverter AC disconnect and combiner box DC disconnects been opened and locked out before string circuit work?
Has absence of AC voltage been verified with a calibrated voltage tester at the inverter output terminals?
Are all personnel on-site aware that PV modules remain energized (DC voltage present) even with disconnects open during daylight hours?

Site & Environmental Conditions

Record ambient conditions that affect string performance measurements and enable normalization of results to standard test conditions (STC).

Has irradiance been measured and recorded using a calibrated reference cell or pyranometer?
What is the measured plane-of-array (POA) irradiance at the time of inspection?
What is the measured module back-sheet temperature at the time of testing?
Are sky conditions clear or lightly overcast (less than 20% cloud cover) suitable for meaningful string testing?
Has ambient air temperature been recorded at the time of inspection?

Module Visual & Physical Condition

Perform systematic visual inspection of all modules in the inspected strings for physical damage, soiling, discoloration, and structural defects.

Are all PV modules free from visible cracked glass, shattered cells, or physical impact damage?
Are module surfaces free from heavy soiling, bird droppings, or debris that would cause significant shading?
Are module frames, mounting rails, and inter-module gaps free from corrosion, deformation, or structural failure?
Are all module junction boxes closed, latched, and free from visible burn marks, melting, or discoloration?
Have any modules with visible cell discoloration (yellowing, browning, snail trails) been identified and documented?
Photograph and document any modules with visible defects or anomalies for the inspection record.

String Electrical Measurements (Voc & Isc)

Measure open-circuit voltage and short-circuit current for each string and compare against expected values calculated from module datasheets and current conditions.

Has the string open-circuit voltage (Voc) been measured and does it fall within ±5% of the temperature-corrected expected value?
Has the string short-circuit current (Isc) been measured and does it fall within ±10% of the irradiance-corrected expected value?
Are all string Voc measurements within 2% of each other for strings of identical module count and type?
Are all string Isc measurements within 5% of each other for strings of identical configuration?
Record the measured Voc for the lowest-performing string identified during this inspection.

DC Wiring, Connectors & Combiner Box

Inspect all DC string wiring, MC4 connectors, combiner fuses, and grounding connections for safety and code compliance.

Are all MC4 (or equivalent) PV connector pairs fully mated, latched, and free from water ingress or corrosion?
Is all DC string wiring routed in a way that avoids mechanical damage, UV exposure, and contact with sharp edges?
Are combiner box string fuses or circuit breakers of the correct OCP rating and are all positions populated?
Are all equipment grounding conductors (EGC) and module frame grounding connections intact and secure?
Is the combiner box interior free from moisture ingress, insect nests, or debris accumulation?
Is the DC arc fault circuit interrupter (AFCI) device present, correctly wired, and functional per last test record?

Inverter Input & Performance Data Review

Review inverter monitoring data to validate string-level energy production, MPPT performance, and fault history.

Does the inverter monitoring dashboard show all expected strings as active with no open-string alarms?
Is the inverter DC input power factor and MPPT efficiency within the manufacturer's rated specification?
Has the inverter's performance ratio (PR) been calculated and is it within the expected seasonal range for this site?
Are there any active fault codes, ground fault indications, or insulation resistance alarms present in the inverter?
What is the inverter's measured AC output power as a percentage of its rated capacity at current irradiance?

Thermographic (Infrared) Inspection

Conduct infrared scanning of modules and electrical components to identify hot spots, bypass diode failures, and connection anomalies.

Has thermographic scanning been performed on all strings under adequate irradiance (minimum 600 W/m²) conditions?
Were any module hot spots identified with a temperature differential exceeding 10°C above the average cell temperature?
Were any bypass diode failures detected (indicated by a single-cell or sub-string elevated temperature pattern)?
Were any elevated temperature anomalies detected at combiner box fuses, bus bars, or string connections?
Attach thermal images of identified hot spots or anomalous module patterns with GPS coordinates or array position noted.

Findings Summary & Corrective Actions

Document all identified deficiencies, assign severity ratings, specify corrective actions, and confirm the system is safely returned to service.

Have all identified deficiencies been logged in the CMMS with a severity rating and target completion date?
Has the inverter been safely restarted and confirmed to be producing power within 5% of pre-inspection baseline?
Have all lockout devices been removed in proper sequence and the system returned to full operational status?
Provide a summary of the top three findings from this inspection and recommended corrective actions.
Has this completed inspection report been shared with the site O&M Manager and filed in the site compliance documentation folder?

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Why Use This Solar String Performance Monitoring Checklist [FREE PDF]?

This solar string performance monitoring checklist [free pdf] helps solar energy teams maintain compliance and operational excellence. Designed for solar technician professionals, this checklist covers 42 critical inspection points across 8 sections. Recommended frequency: quarterly.

Ensures compliance with NEC Article 690 Solar Photovoltaic Systems (2023 Edition), IEC 62446-1:2016 Photovoltaic Systems – Requirements for Testing and Documentation, OSHA 29 CFR 1926.960 Power Transmission and Distribution, NFPA 70E-2021 Standard for Electrical Safety in the Workplace, ANSI/NETA MTS-2019 Maintenance Testing Specifications for Electrical Power Equipment. Regulatory-aligned for audit readiness and inspection documentation.

Frequently Asked Questions

What does the Solar String Performance Monitoring Checklist [FREE PDF] cover?

This checklist covers 42 inspection items across 8 sections: Pre-Inspection Safety & Electrical Isolation, Site & Environmental Conditions, Module Visual & Physical Condition, String Electrical Measurements (Voc & Isc), DC Wiring, Connectors & Combiner Box, Inverter Input & Performance Data Review, Thermographic (Infrared) Inspection, Findings Summary & Corrective Actions. It is designed for solar energy operations and compliance.

How often should this checklist be completed?

This checklist should be completed quarterly. Each completion takes approximately 60-90 minutes.

Who should use this Solar String Performance Monitoring Checklist [FREE PDF]?

This checklist is designed for Solar Technician professionals in the solar energy industry. It can be used for self-assessments, team audits, and regulatory compliance documentation.

Can I download this checklist as a PDF?

Yes, this checklist is available as a free PDF download. You can also use it digitally in the POPProbe mobile app for real-time data capture, photo documentation, and automatic reporting.