Inspect, service and maintain small scale solar photovoltaic systems
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.
Assessment criteria
Topic Overview
The City & Guilds Level 3 Award in the Installation and Maintenance of Small Scale Solar Photovoltaic Systems is a vocational qualification designed for electricians and experienced electrical installers. It covers the complete process of designing, installing, commissioning, and maintaining solar PV systems up to 16A per string (typically domestic or small commercial). This award is part of the wider Construction & Building Services framework, aligning with the UK's drive towards net-zero carbon emissions and the growing demand for renewable energy technologies.
The course is structured around key areas: understanding solar radiation and PV cell operation, selecting appropriate components (panels, inverters, mounting structures), ensuring electrical safety in accordance with BS 7671 (IET Wiring Regulations), and performing system testing and fault finding. Students also learn about grid-tied systems, which are most common in the UK, including how to comply with Distribution Network Operator (DNO) requirements and the Microgeneration Certification Scheme (MCS) standards.
Mastering this topic is crucial for any electrician looking to expand into renewables. With the UK government's Smart Export Guarantee (SEG) and the increasing affordability of solar panels, the market for small-scale PV is booming. This qualification not only enhances employability but also equips you with the skills to contribute directly to the UK's renewable energy targets. You'll be able to confidently advise clients, design efficient systems, and ensure safe, compliant installations.
Key Concepts
Core ideas you must understand for this topic
- →Solar PV cell operation: Understand how photons create electron-hole pairs in semiconductor materials (typically silicon), generating DC electricity. Key parameters include irradiance (W/m²), temperature coefficient, and the IV curve.
- →System components: Know the function of each component: PV modules (monocrystalline vs polycrystalline), inverters (string, micro, or power optimisers), mounting systems (roof-integrated, on-roof, ground-mounted), and balance of system (cables, isolators, overcurrent protection).
- →Electrical design and safety: Apply Ohm's law and power calculations to size cables, select protective devices (fuses, MCBs, RCDs), and ensure compliance with BS 7671. Understand earthing arrangements, surge protection, and the requirement for DC isolators.
- →Grid connection and compliance: Learn the DNO application process, G98/G99 type testing for inverters, and MCS installation standards. Know the limits for single-phase (up to 3.68kW) and three-phase connections, and the need for generation meters.
- →Commissioning and testing: Perform insulation resistance testing, open-circuit voltage (Voc) and short-circuit current (Isc) measurements, polarity checks, and functional tests of inverters and protective devices. Document results in an installation certificate.
Learning Objectives
What you need to know and understand
- Undertake the routine service and maintenance of a solar photovoltaic system installation, Undertake fault diagnosis work on a solar photovoltaic system installations, Undertake fault rectification work on solar photovoltaic system installations
Assessment Criteria
Key criteria assessors look for in your portfolio
- 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.
Assessment Guidance
Guidance for achieving higher grades
- 💡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.
- 💡Always show your calculations step-by-step, especially for cable sizing and voltage drop. Examiners award marks for method, not just the final answer. Use the correct formula (e.g., mV/A/m from BS 7671 tables) and state assumptions like ambient temperature.
- 💡Know the difference between G98 and G99. G98 is for inverters up to 16A per phase (typically ≤3.68kW single-phase), while G99 is for larger systems. Be prepared to explain the DNO notification process and when an application is required.
- 💡In practical assessments, demonstrate safe isolation procedure (prove dead, lock off, test) before touching any live parts. Also, remember to measure both Voc and Isc at the array before connecting to the inverter – this confirms correct string configuration and no faults.
Common Mistakes
Common errors to avoid in your coursework
- 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.
- Misconception: Solar panels work best in hot weather. Correction: While panels need sunlight, high temperatures actually reduce efficiency. The standard test condition (STC) is 25°C; for every degree above, power output drops by about 0.4% for crystalline silicon. Cool, sunny days are ideal.
- Misconception: A bigger inverter always means more power. Correction: Inverters must be matched to the array size. Oversizing can lead to clipping (wasted energy) and may violate DNO limits. The inverter's maximum DC input voltage and current must not exceed the array's Voc and Isc under worst-case conditions.
- Misconception: You can install any solar panel with any inverter. Correction: Compatibility is critical. The inverter's MPPT voltage range must match the array's Vmp, and the total string Voc must not exceed the inverter's maximum input voltage. Also, ensure the inverter is G98/G99 certified for grid connection.
Frequently Asked Questions
Common questions students ask about this topic
Pass / Merit / Distinction Evidence Checklist
How your portfolio evidence is graded for CITY AND GUILDS OF LONDON INSTITUTE Inspect, service and maintain small scale solar photovoltaic systems
Every vocational unit is marked against named criteria rather than an exam percentage. Your tutor's brief lists the exact codes for this unit — here is what each band is asking you to do.
Demonstrate baseline knowledge, accurate terminology, and core practical application.
Provide detailed analysis, structured explanations, and clear workplace reasoning.
Deliver thorough evaluation, original problem solving, and fully justified recommendations.
Before You Start
Prior knowledge that will help with this topic
- •A recognised Level 3 electrical qualification (e.g., City & Guilds 2365 or 5357) or equivalent experience, as the course assumes knowledge of BS 7671, safe isolation, and basic electrical theory.
- •Understanding of AC and DC circuit theory, including Ohm's law, power calculations, and series/parallel circuits. Familiarity with three-phase systems is helpful but not essential for small-scale PV.
- •Basic knowledge of building construction and roof types (e.g., pitched, flat, slate, tile) to assess mounting suitability and structural load.
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Key Terminology
Essential terms to know
- Undertake the routine service and maintenance of a solar photovoltaic system installation, Undertake fault diagnosis work on a solar photovoltaic system installations, Undertake fault rectification work on solar photovoltaic system installations
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