In-Field Energy Performance of Solar PV Module Made of UMG Silicon

Upgraded metallurgical grade silicon (UMG-Si) PV modules have failed to make their space in the PV market, which was partly to the uncertainty on their in-field performance that brings the wide disparity of results published over the years. The most-recently developed UMG-Si PV modules have demonstrated similar initial degradation and efficiencies under standard test conditions (STC) to those obtained with conventional solar grade silicon (SoG-Si). Nevertheless, their performance under operating conditions other than STC and its impact on the energy production are key aspects that have not yet been properly characterized in the literature. This article analyzes the in-field performance of a PV generator comprised of recently developed UMG-Si modules. This performance was compared to that of another PV generator comprising standard polysilicon modules. The cells and modules of both types of generators were made by the same manufacturer in the same period and on the same production lines, which guarantees that performance differences encountered are exclusively due to the silicon employed. Contrary to the previous experience, this article reveals that UMG-Si modules do not necessarily present a better temperature performance than today's conventional modules. The analyzed UMG-Si modules presented 1.6% less efficiency under low irradiance conditions, but this different irradiance performance led to an insignificant difference (less than 0.5%) in their energy production. No significant degradation was measured in both UMG-Si and SoG-Si modules during the two-year analyzed period, being the final energy performance of both types of modules essentially the same. These results can be considered as highly representative of the current state-of-the-art of UMG-Si technology.