The stability and durability of photovoltaic modules directly affect the efficiency and life of the solar power generation system. Long-term reliability testing of photovoltaic modules can ensure the life of photovoltaic modules. Photovoltaic modules withstand various stress factors such as different humidity, temperature, light, wind, dust, etc.

Follow the IEC standard process to perform accelerated damp heat testing on modules to ensure that photovoltaic modules can still operate normally under various extreme environments. Damp Heat Test Chamber from Millennial Solar is an essential tool and equipment.

Accelerated Damp Heat Test

The damp heat test is one of the key tests in IEC61215. Photovoltaic modules are placed in an environmental chamber at 85°C/85%RH for 1,000 hours to evaluate their heat and moisture resistance. Moisture penetration is the core cause of photovoltaic module degradation. Then polymer encapsulants such as ethylene vinyl acetate (EVA) react within the penetrating water molecules and decompose through the hydrolysis mechanism, causing the encapsulant to delaminate, thereby accelerating the entry of moisture. And the corrosion of metal electrodes. Corrosion is caused by the reaction of metal electrodes with water molecules, and the acetic acid produced by the hydrolysis of vinyl acetate monomer in EVA will accelerate the corrosion of metal electrodes, ultimately by increasing the contact resistivity and reducing the fill factor (FF ) causes the output power of photovoltaic modules to decrease.

First, all photovoltaic modules were subjected to a 1000-hour damp heat test at 85°C/85%RH as the initial results. Subsequently, distributed stress tests were conducted under three different temperature conditions while keeping the RH constant. The test conditions of module 1 are 85℃/85%RH, module 2 is 100℃/85%RH, and module 3 is 120℃/85%RH.

Table 1 shows the heat and humidity exposure conditions, test temperature, relative humidity, total duration, and measurement intervals. During the entire test process, the I-V curve and EL imaging of each module were acquired at set time intervals to track the aging process.

Table 1. Summary of measurement intervals for damp heat tests

Accelerated Damp Heat Test Results

During the damp heat test, the photovoltaic modules were taken out of the test chamber every 300-400 hours, and their electrical parameters and I-V characteristics were measured and compared. All photovoltaic modules passed the IEC standard test, which requires a 1000-hour damp heat test at 85°C/85%RH. The accelerated test showed a large difference.

Module performance evaluation at 85°C/85%RH

Table 2 and Figure 1 show the statistical analysis of the degradation characteristics of performance parameters such as Voc. Voc, FF and Pmax after 1000 hours of damp heat testing at 85°C/85%RH with measurement intervals of 300 and 400 hours. The Pmax value of the tested PV module remained at 90% of its initial value (i.e. the loss was less than 10%) until 1000 hours. Through the 1000h damp heat test, the encapsulant effectively prevented moisture penetration as the FF only dropped <2.6%. In order to reduce the Pmax of the module, the damp heat test should be extended to at least 3000 hours to see a significant reduction.

Table 2. Module performance parameters and time changes under 85°C/85%RH damp heat test

Figure 1.a) Changes in photovoltaic module performance parameters over test time. b) I-V curves at different test intervals at 85°C/85%RH.

Module performance evaluation at 100°C/85%RH

Table 3 and Figure 2 show the performance parameters of the module after 1000h testing at 100℃/85%RH with measurement intervals of 300h and 400h. The Pmax value of the tested photovoltaic module remained at 90% of its initial value until 600 hours. As shown in Figure 2, Voc gradually decreased by less than 5% throughout the test period, indicating that the p-n junction characteristics were not significantly affected. Most Pmax drops occur due to FF drops. A drop in FF of more than about 10% indicates that moisture may have corroded the metal electrodes and resulted in increased contact resistance and FF degradation.

Table 3. Module performance parameters and time changes under 100°C/85%RH damp heat test

Figure 2.a) Changes in PV module performance parameters over test time. b) I-V curves at different test intervals at 100°C/85%RH.

Module performance evaluation at 120°C/85%RH

Table 4 and Figure 3 show the performance parameters of the module after 600 hours of testing at 120°C/85%RH with a measurement interval of 300 hours. The Pmax value of the tested PV module remained at 90% of its initial value until 300 hours. As shown in Figure 3, Voc was reduced by less than 5% over the entire 600 hours of accelerated testing, demonstrating that p-n junction performance is not significantly affected even at higher temperatures. After 600 hours, Isc decreased by approximately 30% and FF decreased by approximately 40%, resulting in complete failure of the PV module (approximately 65% of Pmax loss). Therefore, accelerated hygrothermal testing can check reliability by replacing advanced materials.

Table 4. PV module performance parameters and time changes under 120°C/85%RH damp heat test

Figure 3.a) Changes in PV module performance parameters over test time. b) I-V curves at different test intervals at 120°C/85%RH.

The trial proposes an effective accelerated testing method for PV modules, where temperatures up to 120°C are applied to accelerate degradation mechanisms. The experimental results show that the environmental stress observed after 600h at 120°C/85%RH is equivalent to the results of the 85°C/85%RH damp heat test for about 5000h, saving a lot of time and resources. This accelerated testing is suitable for crystalline solar cells and EVA encapsulation materials, which account for more than 85% of the market share, and is helpful in determining the conditions for degradation mechanisms.

Damp Heat Test Chamber

E-mail: market@millennialsolar.com

Introduction:

Solar modules will withstand various harsh weather tests during their application. Among them, the performance of PV modules such as their ability to withstand high temperatures, high humidity, and long-term moisture penetration needs to be evaluated. Hot and humid environment simulation tests are used to verify and evaluate the reliability of modules or materials, and to identify manufacturing defects early through thermal fatigue-induced failure modes.

Fulfill the standard:

IEC61215-MQT13; IEC61730-MST53

Features:

Continuous operation for more than 1,000 hours at 85°C and 85%RH requires ultra-high stability, both in terms of manufacturing process and reliability of electronic equipment.

•Built-in circulating air duct and long-axis ventilator for effective heat exchange, making the temperature inside the environmental box uniform and stable

•Adopt imported temperature controller to realize multi-stage temperature programming with high precision and good reliability

•Can operate in continuous high temperature and high humidity environment, and can also conduct high and low temperature interactive tests according to the plan

•With a Potential Induced Degradation Tester, the module can be visually observed

Potential Induced Degradation Tester

E-mail: market@millennialsolar.com 

Long-term leakage current will cause changes in the state of the cell carriers and depletion layer, corrosion of the contact resistance in the circuit, electrochemical corrosion of the packaging materials, etc., resulting in cell power attenuation, increase in series resistance, light transmittance, etc. Degradation, delamination and other phenomena that affect the long-term power generation and life of PV modules.

As one of the indispensable equipments in the solar energy industry, Damp Heat Test Chamber plays an important role. By simulating high-temperature and high-humidity environments and conducting performance tests on photovoltaic modules, it can help the solar industry continue to improve product quality and promote the development and application of solar technology. With the continuous advancement of technology and the rapid development of the solar energy industry, the Damp Heat Test Chamber developed by Millennial Solar can help you optimize energy production and obtain the best return.