Thermal Cycling (TC200) in Solar PV Modules: Definition, Process, Importance & Impact on PV Reliability
Solar photovoltaic (PV) modules operate in environments where temperatures can fluctuate dramatically—hot afternoons followed by cold nights, or extreme seasonal variations. These temperature changes cause repeated expansion and contraction of module materials.
To ensure long-term durability, solar modules must undergo rigorous reliability testing. One of the most crucial tests is the Thermal Cycling (TC) test, and the industry often defines benchmarks like TC200, which is considered a strong indicator of module robustness.
This article explains everything you need to know about Thermal Cycling (TC200)—what it is, why it matters, the testing procedure, common failure mechanisms, and how it affects real-world solar performance.
What Is Thermal Cycling (TC200)?
Thermal Cycling (TC) is a reliability test defined under IEC 61215 standards for solar PV modules. It subjects the module to repeated cycles of extreme temperature changes to simulate decades of natural thermal stress.
TC200 specifically means the module undergoes 200 temperature cycles, typically between-40°C and +85°C.
Purpose of TC Testing
- To evaluate long-term module durability
- To identify material weaknesses under thermal stress
- To ensure reliable electrical connections
- To predict field performance over 25–30 years
Why Thermal Cycling Matters in Solar PV Modules
Solar modules experience daily heating (from sunlight) and cooling (evenings/nights). This leads to mechanical stress within the module layers.
Key Performance Aspects Affected
- Mechanical stability of solder joints
- Cell interconnect durability
- Encapsulation integrity
- Minimization of microcracks
- Reduction of moisture penetration risk
A module that passes TC200 is more likely to:
- Sustain long-term electrical performance
- Provide stable power output in harsh climates
- Achieve lower annual degradation rates
- Maintain a long operational lifespan
TC200 Testing Procedure: Step-by-Step
1. Temperature Cycling Range
- Low temperature: -40°C
- High temperature: +85°C
- Cycle duration: approx. 3–4 hours per cycle
2. Number of Cycles
- TC200 = 200 cycles
- TC600 / TC1000 may be used for extended “beyond-standard” tests (premium modules)
3. Module Condition Monitoring
During and after testing, fresh measurements are recorded:
- Power output (Pmax)
- Insulation resistance
- Visual inspection
- Electroluminescence (EL) imaging
- IV curve testing
What Happens Inside the Module During Thermal Cycling?
1. Expansion and Contraction
Different materials—glass, EVA, cells, ribbons, backsheet—expand at different rates.
2. Mechanical Stress on Solder Joints
Solder bonds between cells and busbars may fatigue.
3. Microcrack Development
Silicon cells may develop:
- Hairline cracks
- Partial fractures
- Complete cell breakage (rare but possible)
4. Encapsulant Behavior
EVA may:
- Delaminate
- Yellow
- Lose adhesion
5. Backsheet Wear
Some polymer backsheets may crack or become brittle.
Common Failure Modes Detected in TC200
1. Solder Joint Fatigue
One of the top reasons for power loss.
2. Microcracks in Solar Cells
Affect:
- Conductivity
- Current pathways
- Power output
3. Delamination in Module Layers
Reduces protection and increases moisture risk.
4. Ribbon Detachment
Can lead to significant power drop.
5. Hotspots
Arising from increased resistance at stress points.
Performance Criteria After TC200
According to IEC 61215 requirements:
- Power loss must not exceed 5% after 200 cycles
- No major visual defects
- No safety issues
- Electrical parameters must remain stable
Modules that pass TC200 demonstrate superior long-term reliability.
Benefits of Modules Passing TC200
1. Higher Reliability in Extreme Climates
- Desert regions
- Cold mountain climates
- Tropical and humid environments
2. Lower Annual Degradation
Often <0.5% per year for premium modules.
3. Better Investment Returns
- Higher long-term energy yield
- Lower maintenance costs
4. Enhanced Consumer Confidence
Useful for:
- Utility-scale projects
- Commercial & industrial (C&I) installations
- Residential buyers seeking durability
TC200 vs. Other Stress Tests
Thermal Cycling is part of a larger reliability suite:
%20-%20Solar%20PV%20Module%20Test.jpg "Thermal Cycling (TC200) - Solar PV Module Test")
A module strong in TC200 + DH + mechanical load is usually highly durable.
Applications That Benefit Most From TC200-Certified Modules
✔️ High-altitude and cold regions
✔️ Desert and hot climates
✔️ Utility-scale solar farms
✔️ Offshore and coastal areas
✔️ Battery-integrated PV systems (frequent temperature changes)
Conclusion
Thermal Cycling (TC200) testing is a crucial indicator of solar PV module quality, durability, and long-term performance. Modules that successfully pass TC200 are better equipped to handle everyday temperature fluctuations and extreme weather conditions, ensuring stable power production and a longer operational life.
For investors, installers, and project developers, prioritizing modules with strong TC200 performance is a smart strategy to maximize energy yield and protect solar investments.
