Solar Panel Hotspots: Thermal Imaging Diagnosis Guide

Thermal imaging (IR thermography) is one of the most powerful diagnostic tools for solar arrays. It reveals defects that are completely invisible during visual inspection — faulty cells, bypass diode failures, and internal connection issues all show up as temperature anomalies. This guide explains how to interpret thermal scans and what different hotspot patterns indicate.

How Thermal Imaging Works on Solar Arrays

Under normal operation, a solar panel converts sunlight into electricity and runs only slightly warmer than the ambient temperature. When a cell is damaged or a bypass diode fails, that cell or group of cells stops producing power and instead dissipates the incoming solar energy as heat. This creates a temperature difference that a thermal camera can detect — often 10-30°C above the surrounding panel area.

Common Thermal Anomaly Patterns

Different thermal patterns indicate different underlying problems. Learning to read these patterns helps you prioritize field actions.

• Single-cell hotspot: One cell glowing brighter than its neighbors — typically indicates a cracked cell, degraded cell, or internal interconnect failure.
• Half-panel pattern (one column of cells): An entire sub-string of cells showing elevated temperature — usually a failed bypass diode that causes the entire sub-string to be bypassed and dissipate heat.
• Patchy, irregular hotspots: Multiple cells at different temperatures — often caused by partial shading, soiling, or cell mismatch from degradation.
• Junction box hotspot: Heat concentrated at the junction box on the back of the panel — indicates a loose or corroded internal connection, or a failing bypass diode at the box.
• Uniform panel overheating: An entire panel running hotter than its neighbors — can indicate a panel with very low efficiency due to PID (potential-induced degradation) or extensive cell degradation.

Ground vs. Aerial Thermal Imaging

Ground-based thermal imaging involves scanning panels from below or at ground level with a handheld thermal camera. It's effective for accessible arrays (ground-mount, flat roof) but limited for rooftop systems. Aerial thermography uses a drone-mounted thermal camera to scan entire solar farms quickly, producing a thermal map of every panel. For utility-scale sites, drone thermography is the most efficient method — a single flight can identify dozens of anomalies across thousands of panels.

Best Practices for Thermal Scanning

• Scan during peak production hours (10am-2pm) when irradiance is above 600 W/m² for maximum contrast.
• Avoid scanning on windy days — wind cools panels unevenly and reduces thermal contrast.
• Set the camera's emissivity to 0.85-0.90 for glass-fronted PV panels.
• Capture both the thermal image and a visible-light reference image for each anomaly for documentation.
• For drone surveys, maintain a consistent altitude and angle across the entire site for comparable results.

What to Do When You Find a Hotspot

Not every hotspot requires immediate action. Prioritize based on severity:

• Mild hotspot (5-10°C above surrounding area): Document and monitor. Schedule a follow-up scan in 3-6 months to check for progression.
• Moderate hotspot (10-20°C above surrounding area): Investigate further. Check the panel's IV curve and compare its output to neighboring panels.
• Severe hotspot (20°C+ above surrounding area): Schedule replacement. High-temperature hotspots can cause backsheet burn marks, arcing, and fire risk.
• Junction box hotspot: Investigate immediately. Junction box overheating can lead to arcing and fire. De-energize the affected string if the hotspot is severe.

When to Call for Remote Support

If you have thermal images but aren't sure what they indicate, or if you need help prioritizing which panels to replace across a large site, remote support can help. Share your thermal scan results and monitoring data, and a specialist can help you build a prioritized remediation plan based on severity, location, and warranty status.