What is the impact of thermal defects on PV plant's power generation?
Solar module is the main unit of solar electric system to generate electricity, its function is to convert sunlight into electricity, if there is an abnormality that affects the conversion efficiency of the solar module, the conversion of light energy into electricity will become less, according to the principle of conservation of energy, this time will produce additional thermal energy, which is what we call thermal defects. In other words, the existence of thermal defects will affect the power generation of the system. With reference to IEC 62446-3, thermal defects are categorized into the following twelve types according to the causes of thermal defects and their subsequent treatment:
| 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 above presents estimated impacts of thermal defects on PV module power output, based on relevant research. For example, hotspots can reduce module power by approximately 0.83% to 15.47%, while Potential-Induced Degradation (PID) may lead to losses ranging from 30% to 70%, depending on severity.
The above calculation does not account for the series and parallel connection effects of PV modules, making it a relatively conservative estimate of power generation losses. In reality, any abnormal module can influence the performance of others within the same series. For example, a module with broken glass may not only develop hotspots but also reduce the current of the entire string. Additionally, insulation resistance issues can lead to inverter shutdowns, further amplifying power generation losses. Over time, these effects compound, significantly impacting overall system efficiency. Therefore, early detection and timely intervention in thermal defects are essential to minimizing power losses and ensuring stable system operation.