What is the impact of thermal defects on solar power generation?
Solar modules are the primary units responsible for generating electricity in a solar PV system. Their function is to convert sunlight into electrical energy. When any anomaly occurs that affects the module’s conversion efficiency, less solar energy is converted into electricity. According to the principle of energy conservation, this unconverted energy manifests as additional heat — which we refer to as thermal defects. In other words, the presence of thermal defects directly impacts the system’s power generation. Referring to IEC 62446-3, thermal defects can be categorized into twelve types based on their causes and appropriate corrective measures.
| NO. | Thermal defect name | Impact of PV module power | Remark |
|---|---|---|---|
| 1 | Modules in open circuit | 100% | The module does not generate power |
| 2 | Modules in short circuit | 100% | The module does not generate power |
| 3 | Broken front glass | 15.47% (rough estimate) | Apply the upper limit of the hot spot power degradation |
| 4 | Substring in short circuit | 33.33% | 1/3 module does not generate power |
| 5 | One substring in open circuit | 33.33% | 1/3 module does not generate power |
| 6 | Two substring in open circuit | 66.66% | 2/3 module does not generate power |
| 7 | Single cell with difference in temperature | 8.15% (average) | Research indicates hot spot influence range on power: 0.83%~15.47% |
| 8 | Module with cells shaded | 8.15% (average) | Research indicates hot spot influence range on power: 0.83%~15.47% |
| 9 | Bird dropping or dust | 8.15% (average) | Research indicates hot spot influence range on power: 0.83%~15.47% |
| 10 | Transfer resistance at cell connections | 0.83% (rough estimate) | Apply the lower limit of the hot spot power degradation |
| 11 | Heated module junction box | 0.83% (rough estimate) | Apply the lower limit of the hot spot power degradation |
| 12 | Potential Induced Degradation | 50% (average) | Research indicates PID influence range on power: 30%~70% |
The table also lists the estimated power loss associated with each type of thermal defect in solar modules. The values are based on relevant international studies. For example, hot spots can cause a power loss ranging from approximately 0.83% to 15.47%, while potential-induced degradation (PID) can reduce module output by about 30% to 70%. When glass breakage occurs, it can lead to severe cell cracks. High resistance in cell interconnections or overheating of junction boxes can create lower temperature differentials similar to those of hot spots; therefore, their power loss estimates are modeled after the upper and lower limits of the hot spot power loss range. In the cloud-based visualization platform IRUAV APP by IRUAV Technology Co., Ltd., the inspection report clearly shows the detection rates of these thermal defects within the site and provides corresponding maintenance recommendations.
It is worth noting that the above calculation method does not take series–parallel connections of modules into account, making it a relatively conservative way to estimate power loss. In reality, any abnormal module will affect other modules in the same string. For example, a module with broken glass, in addition to creating hot spots, may pull down the current of the entire string or, due to insulation resistance issues, cause the inverter to trip or start up late. This impacts a wider range of modules and tends to worsen over time. Therefore, once thermal defects are detected, early remediation is the best course of action.