automatic estimation of soiling losses from PV data and validated it against the results obtained with traditional measurement systems. Figgis et al. (2017) reviewed the different approaches to measure and evaluate the impact of soiling in PV systems. Micheli et al. (2020a) introduced a method to extract the soiling profile and quantify the seasonal variation in soiling using PV and precipitation data. The most common soiling monitoring solutions are the so-called soiling stations. These consist of two PV devices: one of them must be regularly cleaned and the other is left to naturally soil. Soiling losses are calculated by the comparison of the electrical output of both devices through the soiling ratio (SR) index, as stated in the IEC 61724-1 Standard (International Electrotechnical Commission, 2017). It is expressed as:
The exponential growth of global capacity along with a reduction in manufacturing costs in the last two decades has caused photovoltaic (PV) energy technology to reach a high maturity level. As a consequence, currently, researchers from all over the world are making great efforts to analyse how different types of degradation impact this technology. This study provides a detailed review of the impact of different optical degradation mechanisms, which mainly affect the transmittance of the top-sheet encapsulant, on the spectral response of the PV modules. The evaluation of the impact on the spectral performance of PV modules is evaluated by considering the variations of the short-circuit current since this is the most widely used parameter to study the spectral impact in outdoors. Some of the most common types of optical degradation affecting the performance of PV modules worldwide, such as discoloration, delamination, aging and soiling have been addressed. Due to the widely documented impact of soiling on the spectral response of modules, this mechanism has been specially highlighted in this study. On the other hand, most of the publications analysed in this review report optical degradation in PV modules with polymeric encapsulant materials. Furthermore, an innovative procedure to quantify the spectral impact of degradation on PV modules is presented. This has been used to analyse the impact of two particular cases of degradation due to soiling and discoloration on the spectral response of different PV technologies.
The present paper evaluates the soiling losses of a 3.25-MW photovoltaic (PV) system installed in central Chile, 200 km north of Santiago, and analyzes the nonuniform soiling deposition between the various strings for a period of 3 years. A robust methodology is developed to extract, in the most systematic way, 142 reliable soiling profiles from the 256 PV power time series recorded on site. It is found that, if unmitigated, soiling would reduce the annual DC energy generation by 8%, with a factor of 2Â between the losses of the most and least affected strings. Most of the losses are registered on the edges of the plant, closer to traffic and unpaved roads.The most soiling intense months are in summer, result of the infrequent rainfalls and of the high concentrations of suspended particles that characterize this season. The revenues and the costs of different manual cleaning frequencies are evaluated and compared to identify the optimal soiling mitigation strategy for this site. Three cleanings per year are found to return the highest profits for the economic conditions considered in this study. However, a sensitivity analysis shows how different cleaning costs and electricity prices would affect the soiling mitigation strategy. In addition, in light of the nonuniform soiling deposition distribution, the possibility of cleaning only selected strings rather than the full PV plant is discussed.
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