Project data

Summary of the project

Photovoltaic modules are continuously exposed to the elements during their 20-year service life. In addition to UV radiation, temperature changes, humidity and wind, snow and extreme weather conditions lead to severe stress on the individual components in a photovoltaic module. Specifically with regard to module ageing, in.RET offers ageing and stress tests to check suitability for long-term operation prior to product launch. Tests can also be carried out to analyse damage that occurs during operation. Standard tests in accordance with the type suitability and type certification of photovoltaic modules in accordance with IEC 61215, IEC 61646 and IEC 61730 can also be carried out and analyses of load scenarios and damage patterns specially adapted to customer requirements.

Experimental set-ups can be realised quickly and easily in the in.RET laboratories. Below you will find a small selection of the test options:

Climate chamber tests: 

In the climate chamber (temperature range: -60 °C...+100 °C; rH: 0%...95%, UV irradiation: up to 250W/m²), modules can be subjected to accelerated ageing tests under reproducible conditions. Individual test variations are also possible here, such as bias vapour heat tests to investigate potential-induced degradation (PID) on crystalline photovoltaic modules or TCO corrosion of thin-film photovoltaic modules. By applying a voltage of up to 2000V between the front glass and the short-circuited connecting leads of the module, a negative potential is built up. In combination with temperatures of 85 °C and a high relative humidity, an accelerated diffusion of Na⁺-ions from the front glass in the direction of the solar cells.

Sun simulator: 

To improve the quality of research and teaching, a continuous light solar simulator was procured and put into operation at in.RET in 2011. The solar simulator can be used to test PV modules with a constant irradiation of 200 to 1200 W/m² and an adjustable temperature. The spectrum of the artificial solar radiation corresponds to the standard spectrum AM1.5, whereby the solar simulator fulfils the BBA classes. The sun simulator is used to carry out hot-spot tests and to investigate ageing effects.

The rated power under standard test conditions is determined using a class AAA flasher. The current-voltage characteristic curve measured with this under STC conditions is used to determine underperformance and enables the determination of individual model parameters for analysing ageing mechanisms.

Hot spot tests: 

During the long service life of 20 years, PV modules are repeatedly completely or partially shaded by plants, buildings or the photovoltaic system itself. If a cell is shaded, it is operated in the blocking range and the cell may be destroyed if the breakdown voltage is exceeded. Furthermore, localised temperature increases, so-called hot spots, can occur due to shading. Hot spots pose the risk of delamination and thermal overload of the cell. To counteract the destruction of the cell, manufacturers must take appropriate protective measures.

During the tests in the solar simulator, the temperature distribution is recorded and analysed. This allows faulty contact points, defective cells and hot spots to be detected. Furthermore, the current-voltage characteristics are determined both before and after the hot-spot tests to assess the module performance. The tests are also used to check and adapt protective measures against this effect.

Reverse current tests: 

Reverse currents can occur when several PV modules are connected in series in parallel. In this case, the current flows in the forward direction and the PV module operates as an electrical load. Depending on the current strength, this can result in high thermal loads, which can lead to delamination and destruction of the cells. Furthermore, mechanical stresses caused by temperature differences in the PV module can cause the glass to break. The high temperatures that occur and any arcing caused by glass and cell breakage can lead to fires. The primary aim of these tests is therefore to protect people and the environment.

In order to ensure the most economical operation of PV systems, a maximum reverse current load capacity is determined as a result of the tests, on the basis of which a maximum string fuse rating can be determined. The temperature profile is recorded and analysed during the test using an infrared camera. The images can be used to draw conclusions about faults in the contacting of the individual cells as well as faults in the cells themselves.

Electroluminescence: 

Solar cells convert radiant energy into electrical energy by absorbing photons. If an electrical voltage greater than the open-circuit voltage is applied to a solar cell or a photovoltaic module, the absorption process is reversed. In the near infrared range, the solar cells emit photons in the invisible range. These emissions can be recorded with the aid of special cameras. The intensity of the emitted photons can be used to localise inefficient areas of the solar cell and detect microcracks and cell fractures. Electroluminescence images are particularly important in the field of accelerated ageing tests to detect incipient, visually imperceptible signs of degradation. The institute has a measuring station for analysing solar cells and photovoltaic modules.