Induced thermo-mechanical stress in CPV receivers with cycled high intensity light

CPV receivers are made of materials with very different lineal expansion coefficients. Strong variations in DNI due to the passage of clouds can cause sudden temperature changes that creates mechanical stress. For common solder and metal filled polymers the plastic limit could be reached causing substantial fatigue. The best forecast of receiver reliability is therefore achieved by applying an intermittent light source with nominal irradiance level and a number of cycles equal to the expected cloud passages for a given site. The UPM has developed specialized equipment, dubbed the LYSS (Light cYcling Stressing Source), for carrying out such experiments. The small thermal capacity of receivers allows simulating more than 25000 cycles per week. The number of deep transients expected for Madrid in 30 years operation, based on available data, is about 45000. We are currently using the system to cycle a ?Ge/Ag Epoxy/aluminum? receiver, which shows no degradation after 20000 cycles. The equipment can cast up to 200 and 70 W/cm2 on 0.1 and 1 cm2 cells, respectively.

Analysis of thermo-mechanical stress effects on CPV receiver under high intensity light cycles

After construction of the LYSS (Light cYcling Stressing Source) in early 2014, several CPV receivers, with and without secondary optical element (SOE) have been aged under fast transient illumination cycling,. The test plan for Madrid consisted of 50000 cycles. Receivers with poor heat spreaders showed low reliability but those with thicker metal layers passed the test well. The operation of LYSS along 8 months, after more than 250000 cycles, did not show any significant failure, except lamp reposition every 120 hours, in average. The equipment seems valid for unveiling weak receiver designs with respect to intensive illumination, in steady and transient modes.