Hielkema Testequipment 1 article published in JoVE Engineering In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for Cu(In,Ga)Se2 Solar Cells Mirjam Theelen1, Klaas Bakker1, Henk Steijvers1, Stefan Roest2, Peter Hielkema3, Nicolas Barreau4, Erik Haverkamp5,6 1TNO Solliance, Thin Film Technology, 2Eternal Sun, 3Hielkema Testequipment, 4Institut des Matériaux Jean Rouxel (IMN)-UMR 6502, Université de Nantes, CNRS, 5ReRa Solutions BV, 6Institute of Molecules and Materials, Radboud University Two 'Combined Stress test with in situ measurement' setups, which allow real-time monitoring of accelerated degradation of solar cells and modules, were designed and constructed. These setups allow the simultaneous use of humidity, temperature, electrical biases, and illumination as independently controlled stress factors. The setups and various experiments executed are presented.