• Energy Research

AbstractThe 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 2× 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.

In this study, the impact of pollen as a PV soiling agent is investigated. The performance data of five utility-scale PV plants in North Carolina, USA, was collected and analyzed using two soiling extraction methods. Satellite and environmental data, including pollen counts, cropland, and vegetation, was also collected and analyzed to identify impacts to soiling losses. During the spring peak pollen season, performance losses of >15% were observed at all five sites. Partial performance recoveries following the pollen season were slow, with lack of correlation with rainfall. This means that the statistical soiling estimation methods that assume abrupt performance recovery from rain are not appropriate for pollen-impacted solar sites. When manual cleanings were performed on site the performance recovery ranged from 5% to 11% indicating persistent soiling impacts are present in this region. The results of this work provide new insights into the phenomenon of pollen deposition on PV systems, demonstrating that 1) soiling can also affect systems located in rainy locations and 2) that its effects cannot be determined using the current estimation methodologies.

Several models have been presented in the recent years to estimate the magnitude of soiling from environmental parameters. However, these models are often based on data from a single site, or at most a few sites, and only limited data are, as of yet, available on their uncertainty. The present work aims to present a first comparative analysis of soiling estimation models, using measured soiling data from various locations in the USA. The study also investigates the impact that the source of the input data can have on the estimation. The results show that the model selection is only one of the factors that can affect the evaluation. Indeed, the use of satellite-derived or ground-mounted particulate matter data can lead to the generation of different soiling maps, with factors greater than 2× between the modeled losses. The current challenges and the unanswered questions that can bias soiling estimation are discussed. Additionally, potential research directions to improve the quality of soiling modeling are identified.

This study analyses the consequences of an extreme dust storm that occurred in March 2022 on the Spanish national photovoltaic (PV) energy supply. This event, indeed, substantially raised the particulate matter concentrations and the aerosol optical depths across the country, seriously affecting the surface radiation and posing a substantial threat not only to individual PV systems but also to the national electricity grid. The research, based on the analysis and the forecast of weather, environmental and electrical data, reveals that such event halved the capacity factor of the national PV fleet over a period longer than two weeks. A peak drop as high as 80% was registered, at national level, on the worst day. This underperformance also affected the market share of PV in the national electricity mix, whose monthly average value fell from the predicted 10.9% to 7.1%. Despite the expectations, however, no significant difference in soiling was found compared to the typical losses, thanks to the occurrence of heavier-than-usual rainfall events. This facilitated the recovery of the national PV capacity, which returned to the expected performance factors as soon as the sky cleared.

Hybrid renewable systems increase electricity production by reducing the randomness of sources without greenhouse gas emissions. Literature indicates that further research is still required for large systems connected to the grid. The energy storage capability of hydroelectric plants provides an opportunity to develop new renewable energy generation. This work presents the results of a hybrid preliminary design between an existing hydropower plant (HPP) in Brazil, Santa Branca, and a simulated floating photovoltaic plant (FPV), occupying only 2.8% of reservoir's surface. The study analyzed 20 years of HPP historical data, the methodology proposed the injection of the FPV full power into the system during daytime and the HPP adjusting the production. As this process changed the HPP generation profile, operational limits such as reservoir level needed to be verified. In the period, while HPP generated about 4 TWh, the FPV could add 2 TWh without significantly changing the daily generation of HPP. This increase of 50% in production was possible since there was space available in the reservoir to store water during the day and use it during the night, working as a free virtual battery for the FPV. A 50% increase of the grid connection capacity factor was also observed.

Soiling is the process whereby dirt, dust, and organic/inorganic contaminants deposit on the surface of a photovoltaic (PV) module. It causes significant economic losses and can have a substantial impact on the expansion of photovoltaic technologies for energy generation. The first step to address soiling adequately is monitoring, as soiling mitigation has to be tailored to the specific conditions of each PV system and no universally valid strategy exists. The main focus of this study is to assess the current state of the art in soiling monitoring, in order to help the community better understand the needs and the challenges in this area. The potentials and the limitations of each monitoring method are discussed thoroughly in the paper, with the support of original experimental data. An estimation of the future soiling monitoring market trends is also presented, with a forecasted need for tens of thousands of new soiling monitors every year.