Introduction
India’s solar capacity crossed 90 GW in 2024 and continues expanding at over 15 GW per year. Every megawatt contains thousands of photovoltaic modules, each capable of developing thermal faults that reduce generation without triggering any alarm on the SCADA system. In our field experience across 50+ solar projects, the average underperforming plant loses between 3% and 8% of its generation potential to thermal defects that have been present for months or years without detection.
Traditional inspection methods — visual walkdown, IV curve tracing string by string, or manual thermography with a handheld camera — are either too slow, too superficial, or too disruptive at scale. A 10MW plant has approximately 30,000 modules. Checking each with a handheld thermal camera takes three weeks. Our thermal drone covers the same 10MW in a single day, at operating temperature, with GPS-tagged anomaly records for every finding.
Drone thermography detects hotspot cells, bypass diode failures, PID, and soiling on solar panels by capturing 640×512 resolution thermal images during operating conditions. In India, a 1MW solar farm inspection takes 4 to 6 hours and follows IEC 62446-3 Level 2 standards. Elion has conducted drone inspections on solar assets across Rajasthan, Gujarat, Maharashtra, Karnataka, and 12 other Indian states.
What Drone Thermography Detects in Solar Panels
1. Hotspot Cells
A hotspot occurs when a single cell or group of cells within a module is shaded, cracked, or degraded while the rest of the module continues to generate. The degraded cell becomes a load rather than a source, dissipating energy as heat. Hotspot temperatures can reach 60 to 90 degrees Celsius above ambient, creating a clearly visible signature in thermal imaging. IEC 62446-3 classifies hotspots by delta-T above the mean module temperature: Class 1 is below 10 degrees (monitor), Class 2 is 10 to 20 degrees (plan maintenance), Class 3 is above 20 degrees (urgent action required).
2. Bypass Diode Failures
Each solar module contains 3 bypass diodes, one for each sub-string of 20 cells. When a diode short-circuits, the entire sub-string stops generating and the module shows as a thermal anomaly approximately one-third the size of the module. Both failure modes — short-circuit and open-circuit — are clearly visible in thermal imaging as distinctive rectangular thermal signatures matching the sub-string geometry.
3. PID — Potential Induced Degradation
PID is a degradation mechanism driven by voltage differences between the module frame and the cell circuit, typically affecting modules at the high-voltage end of strings in large plants. It appears as a characteristic thermal pattern: modules near the grounded terminal show lower temperatures than neighbours, indicating reduced generation. PID is prevalent in humid climates and in plants where earthing arrangements are not optimised. In our inspections of plants in coastal Maharashtra, Tamil Nadu, and Kerala, PID has been among the most common findings.
4. Soiling and Bird Dropping Contamination
Soiling creates a non-uniform temperature pattern across module surfaces. Soiled areas prevent light from reaching cells below, causing localised cooling in thermal images. Localised contamination such as bird droppings on specific modules causes hotspotting and is clearly identifiable and actionable from drone thermal data.
5. String-Level Open-Circuit Faults
An open-circuit string — caused by a failed string fuse, loose MC4 connector, or broken cable — appears as a full string of modules running colder than surrounding strings. String-level faults are among the easiest to identify in thermal imagery and among the highest-priority to fix, since each idle string represents a full loss of generation from that section.
6. Delamination
Delamination occurs when the encapsulant separates from the cell or backsheet, often due to moisture ingress or thermal cycling. Delaminated areas show thermal non-uniformity across the module surface. In our experience, delamination is more common in plants over five years old and in regions with high humidity or large day-night temperature swings.
The Elion Process — IEC 62446-3 Compliant
| Stage | What Elion Does | IEC 62446-3 Requirement |
| Pre-inspection | Irradiance check minimum 600 W/m2, wind check below 7 m/s, ambient temperature log, drone calibration | Minimum 600 W/m2, stable conditions |
| Timing | Inspection conducted between 10 AM and 3 PM IST | Optimal sun angle, avoid dawn/dusk |
| Sensor | 640×512 thermal sensor, NETD below 50mK, calibrated within 12 months | Minimum 320×240, calibrated sensor |
| Coverage | 100% of modules covered in systematic flight path | Full array coverage |
| Classification | Class 1 monitor, Class 2 plan, Class 3 urgent based on delta-T above mean | 3-class severity classification |
| Report | GPS-tagged thermal and RGB image pairs, anomaly table, priority list, summary | Traceable report with GPS coordinates |
Solar Panel Inspection Cost and ROI — Indian Market
| Plant Size | Typical Inspection Duration | Estimated Annual Yield Loss from Undetected Faults* | Payback Period |
| 1 MW | 4 to 6 hours | INR 3 to 8 lakhs per year | Under 1 month after repair |
| 10 MW | 1 to 2 days | INR 30 to 80 lakhs per year | Under 1 month after repair |
| 50 MW | 3 to 4 days | INR 1.5 to 4 crores per year | Weeks after repair |
| 100 MW | 5 to 7 days | INR 3 to 8 crores per year | Weeks after repair |
| 500 MW | 3 to 4 weeks | INR 15 to 40 crores per year | Weeks after repair |
*Based on average tariff of INR 2.80 per unit, CUF 20%, and average yield loss of 4 to 10% from thermal faults. Actual values depend on tariff, plant age, and operating conditions.
When to Inspect — Frequency Recommendations for Indian Plants
- Newly commissioned plants: Inspect within 3 months to identify manufacturing defects before warranty expires
- Plants under PPA: Annual inspection before PPA performance review is standard for large IPPs
- Underperforming plants: If generation is below P90 by more than 5%, inspect immediately
- Post-monsoon: September to October is best in most of India — modules are clean after rain and the next high-generation season begins
- Pre-sale due diligence: Any acquisition or refinancing of a solar asset above 10MW should include drone thermography as part of technical due diligence
What Your O&M Team Receives — The Elion Report
- Executive summary: plant overview, total anomalies found, classification breakdown, estimated generation impact
- Anomaly table: each finding with module ID, GPS coordinates, delta-T, anomaly type, and severity class
- Thermal and RGB image pairs: for each anomaly, showing thermal signature alongside the visible image for precise location
- Annotated aerial map: full plant aerial with each anomaly marked by GPS location
- Priority maintenance list: ranked by severity with recommended action for each finding
- Inspection conditions log: irradiance, wind, temperature recorded at start, midpoint, and end
FAQ — Solar Panel Drone Thermography India
Q: Can drone thermography find faults in all module types?
Yes. Drone thermography works on all crystalline silicon module types — mono, poly, half-cut, MBB. Bifacial modules can be inspected from the front face. Thin-film modules (CdTe, a-Si) require adjusted temperature thresholds. We have inspected thin-film plants and adjust analysis parameters accordingly.
Q: What irradiance level is required?
A minimum of 600 W/m2 is required for thermal anomalies to appear clearly. In practical terms, inspection must be conducted on clear or lightly hazy days between 10 AM and 3 PM IST. Post-monsoon inspection windows (September to October) are preferred across most of India.
Q: Does the plant need to be shut down?
No. Drone thermography requires the plant to be operating at normal conditions. Shutting down eliminates the thermal contrast needed to identify faults. Our drones operate at planned altitudes that do not interfere with plant operations or personnel.
Q: Is Elion’s report accepted by insurance companies?
Our IEC 62446-3 compliant reports have been accepted by O&M contractors, EPCs, asset management firms, and lenders across India. For insurance claims, coordinate with your insurer in advance to confirm their documentation requirements. We can provide supplementary thermal data files if required.