Solar Panel Fault Finding UK: Diagnostic Methods and Testing (2026)

When a solar system underperforms or stops working, identifying the specific fault requires a systematic approach using the right diagnostic methods. Different types of faults require different detection techniques: some issues are visible to the naked eye, others show up only on thermal cameras, and some can only be found through electrical testing. Understanding which diagnostic method to use for which problem saves time and money by avoiding unnecessary testing and getting to the root cause efficiently.

The main diagnostic methods range from simple visual inspection and monitoring data analysis that homeowners can do themselves, through to specialist techniques like thermal imaging, electroluminescence testing, and IV curve tracing that require professional equipment. A UK study of over 3.3 million solar panels found that 36.5% had thermal defects detectable by infrared imaging, with around 900,000 showing hotspots. Many of these faults were not visible during standard visual inspection, highlighting the importance of using the right diagnostic tools.

This guide explains each fault finding method, what types of faults each can detect, when to use each approach, and how the methods work together to provide a complete diagnostic picture. We cover both what homeowners can check themselves and what requires professional equipment and expertise, including typical costs for professional diagnostic services in the UK.

Quick Overview

Types of Solar Panel Faults

Panel-Level Faults

Two of the most common panel-level problems deserve their own guides: see solar panel hotspots explained and solar panel microcracks for the detail on causes, impact and what to do about each.

Electrical and Connection Faults

Inverter and System Faults

Inverters usually tell you what’s wrong via their display and monitoring app – see our guide to solar inverter error codes for interpreting the most common messages across GivEnergy, Solis, Huawei, SolarEdge, Fronius and others.

Visual Inspection

What Visual Inspection Can Detect

What Visual Inspection Cannot Detect

How to Conduct Visual Inspection

Monitoring Data Analysis

What Monitoring Data Can Tell You

Monitoring data is the homeowner’s most powerful diagnostic tool – if something’s underperforming, the data usually shows it before the damage becomes visible. For context on expected output, see our guide on how efficient solar panels are.

Patterns That Indicate Faults

Comparing to Expected Output

Thermal Imaging

How Thermal Imaging Works

Thermal imaging cameras detect infrared radiation emitted as heat. When solar panels operate normally, they produce heat relatively uniformly across their surface. Faults disrupt this uniform heat distribution, creating detectable thermal anomalies. Defective areas that cannot conduct electricity efficiently convert energy to heat instead, making them appear hotter than surrounding cells. Thermal imaging is non-destructive and can be performed while the system is operating.

Thermal Anomaly Patterns

Temperature Thresholds

Thermal Imaging Methods

Electroluminescence (EL) Imaging

How EL Imaging Works

Electroluminescence imaging works by applying current to solar panels, causing them to emit light (the reverse of their normal operation). A specialised camera captures this emitted light, revealing the internal structure of cells. Defective areas that cannot conduct electricity appear dark because they cannot emit light. EL imaging can detect microcracks and cell damage that are invisible to both visual inspection and thermal imaging.

What EL Imaging Can Detect

EL vs Thermal Imaging Comparison

Electrical Testing

Insulation Resistance Testing

Insulation resistance testing measures the resistance between conductors and ground, detecting degradation in cable insulation that could cause ground faults. A megohmmeter applies a high DC voltage (typically 500V to 2500V for solar systems) and measures the resulting leakage current. Low insulation resistance indicates damaged insulation, moisture ingress, or contamination.

Interpreting Insulation Resistance Results

IV Curve Tracing

IV curve tracing measures the current-voltage characteristics of solar panels or strings, comparing actual performance to manufacturer specifications. The IV curve shape reveals information about panel health, shading, and connection quality. Deviations from the expected curve indicate specific fault types.

IV Curve Fault Signatures

Continuity Testing

Systematic Diagnostic Approach

Step 1: Gather Information

Step 2: Basic Checks

Step 3: Data Analysis

Step 4: Targeted Investigation

If the problem turns out to be a soiling issue – bird droppings, pollen, traffic film – often a simple clean is the fix. See our guide to solar panel cleaning for safe methods.

Step 5: Confirm and Document

Thorough documentation isn’t just good diagnostic practice – it’s essential evidence if the fault turns out to be a manufacturing defect or insurable event. See our guides on solar panel warranty claims and solar panel insurance claims for what to record.

Professional Diagnostic Services UK

Service Types and Costs

When to Use Each Service

Finding Qualified Professionals

DIY vs Professional Fault Finding

What Homeowners Can Do

What Requires Professional Help

Summary

Effective solar panel fault finding requires using the right diagnostic method for the suspected problem. Visual inspection and monitoring data analysis are good starting points that homeowners can do themselves, identifying obvious issues like soiling, physical damage, or clear underperformance patterns. However, many faults are invisible to the naked eye and require specialist diagnostic techniques to detect.

Thermal imaging is the most widely used professional diagnostic tool, capable of detecting hotspots, connection faults, and bypass diode issues while the system operates normally during daylight. A UK study found that over a third of solar panels had thermal defects detectable by this method. For faults that thermal imaging cannot see, such as microcracks and internal cell damage, electroluminescence imaging provides detailed visibility of the panel’s internal structure.

Electrical testing complements imaging methods by measuring the actual performance characteristics of the system. Insulation resistance testing is essential for diagnosing ground faults, while IV curve tracing compares electrical performance against manufacturer specifications. These tests require specialist equipment and expertise to perform safely and interpret correctly.

A systematic approach to fault finding starts with gathering information and performing basic checks, then uses data analysis to narrow down the problem area before deploying targeted diagnostic methods. This approach saves time and money by avoiding unnecessary testing and getting to the root cause efficiently. For complex or safety-critical issues, professional diagnostic services provide the expertise and equipment to identify faults accurately and provide documentation for warranty claims or insurance purposes.