The National Renewable Energy Laboratory (NREL), a US-based research institution on renewable energy, studied n-PERT PV modules deployed for six years in a 3 MW plant. NREL found that these modules had an average annual power loss of 2.4%, primarily due to surface recombination and high series resistance. Diagnostic methods including IV curves, electroluminescence, photoluminescence, external quantum efficiency, and thermography confirmed recombination in the blue spectrum and resistance increases from metallization composition. According to NREL, accelerated stress testing reproduced field failures, where UV exposure of 67.5 kWh/m², exceeding IEC 61215-2 standards, induced significant recombination losses. Extended UV exposure of 6,000 hours resulted in nearly 6% power decline, consistent with observed degradation from field conditions. Additional damp heat exposure of 1,000 hours at 85% relative humidity and 85°C worsened resistance, as acetic acid from encapsulant degraded silver gridlines. NREL concluded module susceptibility was strongly influenced by passivation properties and metallization paste composition, rather than the silicon cell type itself.