Browsing by Author "Valerino, Michael"

The efficiency of solar panels is significantly reduced by dust and air pollution deposition. This issue (known as soiling) is a roadblock to a renewable future and can only be mitigated by informed cleaning decisions. Globally, there is a lack of reliable soiling data. Furthermore, observed soiling losses are often poorly correlated with ambient air quality, making predictions and planning around mitigation difficult. To address the research and industry needs surrounding soiling, this work addressed the following aims: 1: Develop and validate low-cost soiling monitoring and sample collections systems 2: Deploy monitoring and sample collection systems as well as new analysis methods in a comprehensive study into the soiling processes of Western India 3: Develop an interactive platform that combines a soiling, photovoltaic, and economic model to determine optimized maintenance schedules for photovoltaic installations globally 4: Develop and assess a novel cleaning method using ultrasonic acoustic waves For the first aim, a sensor using a small clean (reference) and a dirty (test) photovoltaic panel was developed and tested in the field against a Campbell Scientific SMP100 Soiling Station. The sensor was shown to accurately quantify soiling to within ± 1.5 % soiling at an order-of-magnitude lower cost than available to the industry. A digital microscope system was then tested for the ability to estimate soiling from image analysis applied to microscopy images of deposited dust. The digital microscope sensor and mass loading estimation from a custom image analysis procedure showed a high correlation (R2 between mass loading and measured soiling loss). Calibration of the system allows for soiling estimations with an accuracy of ± 1.1 % soiling. Aim two first quantified soiling impacts throughout the year in Western India at a test site in Gandhinagar India. Significant seasonality was observed with high soiling rates in the dry season (0.45 ± 0.10 % day-1) and monsoon rains keeping soiling losses < 5 %. The threshold for removal from rainfall was found to vary from 0.5 mm to 8 mm per day and is likely impacted by meteorological conditions impacts particle adhesion prior to the rain event. A new method for analysis of deposited PM size distribution using light microscopy was developed. Size distribution of deposited PM displayed a bi-modal distribution with peaks in the 0.5-1 µm and the 16-30 µm diameter range. Monsoon rains shifted size distribution, cleaning off 89.8% of particles with a diameter > 10 µm in diameter. High humidity in the monsoon season created a buildup of more than two times (123%) the mass of particles smaller than 2.5 µm in diameter despite lower ambient concentrations – likely due to increased capture efficiency and lower particle rebound. This is also evident in effective particle deposition velocity being 5 to 10 times higher during periods of high (>80% humidity). The light microscopy method was also used to develop a novel method of determining soiling non-uniformity on the millimeter scale, deemed milli-scale non-uniformity (MSNU). Rainfall and high humidity leading to dew formation caused significantly higher MSNU on the surface. Building on the light microscopy method, a new method of estimating size-resolved soiling impacts was developed by applying Mie Theory to the particle size distribution. Despite making up less than 10% of the mass on the surface, particles smaller than 5 µm in diameter contribute to > 50% of the soiling impacts, highlighting the importance of small particles to energy losses. Scanning electron microscopy combined with energy dispersive x-ray spectroscopy was then performed on ~700 individual deposited particles to quantity particle composition. A majority of the deposited mass was found to be crustal mineral dust likely transported over long distances. A range of precipitation products highlight the chemical and physical reactions that take place on the panel surface over periods of wetting and drying. Cementation impacts were dominated by carbon-heavy precipitation masses, deemed carbonaceous caking masses (CCMs). It is likely CCMs are a concern for energy losses and cleaning difficulty in many regions of the world that experience dry periods with dew formation. Fungal growth was observed to be present and spore-producing after just 3-weeks – the smallest time period over found for fungal growth on solar panels. Building off the efforts of Bergin et al. 2017, an improved global model for estimating soiling losses throughout the year was developed. The model is shown to accurately estimate soiling losses over orders-of-magnitude at 16 locations across the world. This soiling loss model was combined with models of energy generation and economic optimization. Hosted in an interactive web platform, Solar Unsoiled INC. was formed and offers a first-of-its kind tool for the solar industry to prioritize, plan, budget, manage, and optimize panel cleanings. Finally, a transducer system using surface acoustic waves was developed and tested for deposited particle removal. The system is the first study that used surface acoustic waves (SAWs) to remove particles in the size range relevant to soiling. The system was shown to remove and average of 70% of deposited mass from a glass surface. These promising results indicate a potential for a new method to prevent and remove soiling buildup from solar panels.