In photovoltaic (PV) systems, hotspots are localized regions on a solar module where temperature rises significantly above the nominal operating cell temperature (NOCT). This occurs when individual cells or sections within a module are electrically stressed due to shading, defects, or damage. Over time, these thermal anomalies can degrade module materials, reduce energy yield, and pose safety hazards.

Mechanism: What Exactly Is a Hotspot?
A solar panel consists of multiple interconnected cells arranged in series. When one cell is partially shaded or defective, it cannot generate current at the same level as adjacent cells. Because of the series connection, current from the unshaded cells is forced through the impaired cell, driving it into reverse bias.
In reverse bias, the cell behaves like a resistive load instead of a power generator.
The dissipated electrical energy is converted to localized heat, forming a hotspot.
Thermal imaging typically shows these hotspots exceeding 20–80°C above surrounding cells, accelerating material breakdown.

Impact: Why Hotspots Are Critical

1. Efficiency Loss
   Hotspots create electrical mismatch, reducing the overall module current and causing system-wide energy losses. Even one defective cell can reduce the power output of an entire string.
2. Permanent Module Damage
   Localized heating can degrade encapsulants (EVA), discolor the backsheet, and cause delamination or solder joint failure. Repeated stress leads to irreversible efficiency loss and reduced service life.
3. Safety Hazards
   In severe cases, hotspots exceed critical temperature thresholds (>150°C), increasing the risk of burn marks, insulation failure, and fire in large-scale PV arrays.
4. Economic Impact
   Loss of energy yield, coupled with replacement and maintenance costs, directly impacts Levelized Cost of Energy (LCOE) and return on investment (ROI).

Root Causes of Hotspots

• Soiling (dust accumulation, bird droppings, leaves): Creates partial shading and non-uniform irradiance.
• Micro-cracks: Caused by mechanical stress, hail impact, or improper handling during transportation/installation.
• Manufacturing defects: Inherent weaknesses such as poor soldering, cell misalignment, or lamination voids.
• Aging and degradation: PID (Potential-Induced Degradation) and thermal cycling over time.
• Improper array design or installation: String mismatch, bypass diode failure, and uneven loading conditions.

Detection and Diagnostics

• Infrared (IR) thermography: Identifies temperature anomalies under load conditions.
• Electroluminescence (EL) imaging: Detects micro-cracks and inactive cell areas.
• IV curve tracing: Reveals mismatch losses and abnormal reverse currents.

Mitigation and Prevention Strategies

1. Robotic or Automated Cleaning
   Deploy water-efficient solar cleaning robots to remove soiling without micro-scratching modules, especially in arid and desert climates.
2. Optimized Site Design
   Conduct shading analysis pre-installation (using tools like PVsyst or Helioscope).
   Avoid nearby obstructions and ensure uniform irradiance across arrays.
3. Use of High-Quality Modules and Bypass Diodes
   Select IEC 61215/61730-certified modules with proven thermal cycle endurance.
   Ensure functional bypass diodes to limit reverse bias stress on shaded cells.
4. Scheduled Thermographic Inspections
   Perform annual or semi-annual IR inspections to locate early-stage hotspots.
   Correlate findings with maintenance actions (cleaning, rewiring, module replacement).

Conclusion
Hotspots are a critical reliability concern in utility-scale and commercial PV systems. They compromise energy yield, accelerate module degradation, and pose operational risks. By integrating preventive cleaning, real-time soiling monitoring, and thermal diagnostics, operators can significantly reduce hotspot occurrence, optimize plant performance, and extend module service life, ultimately improving the overall ROI of solar assets.