Executive Summary:Springtime post-winter inspections prevent annual production losses. Learn how infrared thermography detects hotspot delamination, how to test failed bypass diodes in junction boxes, and correct cleaning chemistry.
### The Post-Winter Inspection Checklist
Winter weather subjects rooftop and ground-mounted solar arrays to severe mechanical stress: heavy snow loads (often exceeding 2,400 Pa to 5,400 Pa), freeze-thaw expansion cycles around module frames, and animal nesting under racking conduits.
Conducting a rigorous spring maintenance inspection preserves factory warranty validity and restores peak array efficiency.
---
### 1. Infrared (IR) Thermography Inspection
Using a calibrated FLIR thermal camera during mid-day clear skies ($>700 \text{ W/m}^2$ irradiance):
- **Healthy Cell Temperature:** Uniform temperature distribution across all cells ($Delta T < 3^\circ\text{C}$).
- **Hotspot Cell Defect:** A single cell exhibiting a localized temperature spike ($Delta T > 15^\circ\text{C}$ to $30^\circ\text{C}$). Caused by micro-cracking from snow load or localized bird dropping shading.
- **Activated Bypass Diode:** An entire 1/3 string of cells operating significantly hotter or cooler than adjacent strings indicates continuous forward-biased diode conduction or a shorted Schottky bypass diode.
---
### 2. Testing Junction Box Bypass Diodes
Modern PV modules utilize three bypass diodes in the rear IP68 junction box. To verify diode integrity:
1. Disconnect the module MC4 connectors and place the panel face down on a soft surface.
2. Set digital multimeter to **Diode Check Mode**.
3. Forward bias measurement: Should read **0.3V to 0.45V** (Schottky barrier voltage drop).
4. Reverse bias measurement: Should read **O.L. (Open Loop)**.
5. If the multimeter reads 0.00V in both directions, the diode is short-circuited and must be replaced immediately to prevent irreversible back-sheet burn-through.