Inspect, service and maintain small scale solar photovoltaic systems — City and Guilds of London Institute Vocationally-Related Qualification Construction & Building Services Revision
This element focuses on the practical competencies required to safely inspect, service, and maintain small-scale solar photovoltaic (PV) installations. Lea
Topic Synopsis
This element focuses on the practical competencies required to safely inspect, service, and maintain small-scale solar photovoltaic (PV) installations. Learners must demonstrate the ability to conduct routine maintenance on PV arrays, inverters, and balance-of-system components while adhering to BS 7671 and MCS standards. The subtopic also covers systematic fault diagnosis using test instruments and manufacturer data, followed by effective fault rectification to restore system performance and ensure ongoing safety and compliance.
Key Concepts & Core Principles
- String sizing and voltage limits: The maximum system voltage must not exceed the inverter's maximum input voltage (typically 600 V or 1000 V for domestic systems). The string voltage must also stay above the inverter's minimum start-up voltage under all conditions, including high temperatures which reduce panel voltage.
- Maximum Power Point Tracking (MPPT): Inverters use MPPT algorithms to extract the maximum power from the PV array. You must understand how shading, orientation, and temperature affect the IV curve and how multiple MPPT inputs can optimise performance on roofs with different orientations.
- Earthing and bonding requirements: PV systems require careful earthing to protect against electric shock and lightning. This includes equipotential bonding of exposed metal parts, earth fault protection, and the use of appropriate RCDs (Type B or Type A depending on inverter type).
- DNO notification and G98/G99 compliance: For systems up to 16 A per phase, you must notify the DNO using the G98 (previously G83/2) process. Larger systems require G99 application. Understanding the difference and completing the correct paperwork is critical for legal compliance.
- Commissioning tests and documentation: After installation, you must perform insulation resistance tests, polarity checks, functional tests of the inverter, and verify the earth fault loop impedance. The commissioning report must include the system design, test results, and a customer handover pack.
Exam Tips & Revision Strategies
- Always follow a structured maintenance checklist aligned with MCS guidelines to ensure no critical step is missed during assessments.
- When diagnosing faults, start with the simplest checks (visual inspection, inverter display, isolator status) before progressing to advanced testing.
- Use manufacturer-specific data and specifications to compare actual vs. expected performance; deviations often pinpoint the fault location.
- In fault rectification scenarios, re-test the system to confirm the fault is cleared and record before-and-after readings to demonstrate effective remediation.
Common Misconceptions & Mistakes to Avoid
- Failing to isolate both DC and AC supplies before working on the system, leading to potential electric shock from live DC conductors even when AC is off.
- Misinterpreting inverter display codes or error logs without cross-referencing manufacturer manuals, resulting in incorrect diagnosis.
- Neglecting to check for environmental factors like shading, soiling, or vegetation growth that can reduce system output and mimic electrical faults.
- Assuming a faulty module is the cause of low string performance without testing individual components or bypass diodes, leading to unnecessary module replacement.
- Not recording baseline performance data before carrying out maintenance, making it impossible to quantify the effectiveness of the service or detect gradual degradation.
Examiner Marking Points
- Award credit for demonstrating safe isolation of both DC and AC supplies before commencing any inspection or maintenance work, including lock-off and proving dead.
- Award credit for correctly using test equipment such as multimeters, IV curve tracers, and insulation resistance testers to diagnose faults in PV modules, strings, and inverters.
- Award credit for providing clear evidence of systematic fault-finding procedures, including checking inverter error logs, string voltages, and module bypass diodes.
- Award credit for completing a comprehensive service report that records all test results, actions taken, and any recommendations for remedial work in line with MCS requirements.
- Award credit for identifying and rectifying common faults such as damaged cabling, loose connections, shading issues, inverter communication errors, and degraded modules, and then verifying system performance post-repair.