During our research period the difference in thermal expansion coefficients of individual layers in the PV panel and their effect on the whole panel were investigated. For our largest panels which are approximately 2m long we observed 1mm expansion across this length in the temperature range from -20 to 100 °C. Layers which have the largest thermal expansion coefficients are the tempered glass and metal sheet. However, between these, there are several layers of elastomer encapsulant which are accommodating the thermal stresses between temperatures from -40 to 100°C. At around 100°C it was observed that the polyolefin elastomer starts to reach its hardening point.
In addition, the product has passed the thermal cycling test which is performed according to IEC 61215:2005. The purpose of this test is to determine the ability of the PV module to withstand the effects (material fatigue, temperature stresses etc.) of rapid temperature changes from 85°C to -40°C.
This test puts a strain on PV module which, as a result of different thermal expansion coefficient of PV layers, is shown up as defects (poor soldering, cracked cells, delamination, performance reduction and insulation resistance etc). In the case of our panels, there were no significant observable and measurable differences in the panel between before and after thermal cycling. The tests include visual inspection, electroluminescence testing, electrical health checks and adhesion tests.