Performance evaluation for PV systems to synergistic influences of dust, wind and panel temperatures: spectral insight Khadija K Khanum, Abhishek Rao, N. C. Balaji, Monto Mani*, Praveen C Ramamurthy Indian Institute of Science, Bangalore, 560012, India Abstract — Dust is a ubiquitous occurrence influencing PV performance, primarily by cutting the solar radiation reaching the PV cell. Since the PV cell is always encapsulated, the dynamics of light reaching the cell involves a complex interplay of scattering, absorption and reflection of light starting from surface of glass till it reaches the cell. Dust settling on the glass adds to this complex interplay and alters the way both direct and diffused radiation reaches the PV cell. The impact of dust thus far has always been understood to be detrimental, which may not be valid under all conditions. Dust on PV (panel) glass could be studied as optical filters determining which wavelength of light reaches the PV cell. While few studies on dust have dealt with the spectral-band of light necessary for PV output, they have overlooked the fact that the remainder of the spectra is absorbed by the PV system, and could influence its output. It is possible that dust actually absorbs the unwanted IR that would otherwise increase cell temperature, degrading its output. Preliminary study concurs that certain kind of dust deposition at specific settlement densities could be beneficial for PV performance by absorbing unwanted IR. The current study deals with Si based PV which is known to predominantly operate on the visible part of the solar spectrum, and is easily affected by temperature (IR absorption) and dust. Index Terms – PV, dust, spectral absorption, temperature, Si I. INTRODUCTION Harnessing solar energy directly as electricity is already seeing massive worldwide installation and commissioning of PV systems, from 5W panels to power rural lighting to MW system to power modern cities. However, massive adoption of new technologies brings forth problems hitherto invisible and unaddressed. Large shares of the PV systems today are Si based, and the current study remains focused on this technology (particularly mono and poly Si cells). PV systems operate at best efficiencies if they are directly face the sun with minimal/no obstruction and are maintained at lower temperatures (25 °C). The geography of installation (latitude, longitude and altitude) primarily determines the solar potential available for a fixed PV system. The terrain, exposure, and prevalent climatic conditions also strongly influences the performance of the PV system - with dust having the most pronounced influence on degrading system efficiency [1] [2]. The geometry of the PV system and the prevalent wind regimes would determine whether wind aggravates (negative pressure zones) or alleviates (positive pressure zones) dust settlement, in addition to aiding heat dissipation from the system. Contrary to popular belief, preliminary experimental studies have revealed that depending on the type of dust, even positive pressure winds could actually force dust particles to adhere stronger and more uniformly over PV panels. This however requires careful further scrutiny and not within the scope of this paper. Dust once settled on the top glass of the PV panel, generally hinders the light from reaching the cell, thereby lowering the overall efficiency. Earlier studies cited in [3] have restricted their observation on impact of dust to wavelengths required for the PV cell and have overlooked the remainder of the wavelength which could very well be absolved by the dust. Most Si based panels convert only the visible spectrum into electricity, with the rest contributing to system heat (and thereby lowering efficiency). A uniformly distributed dust, could very well act like a filter, selectively absorbing bands of the solar spectrum - which could actually aid in lowering system temperature, thereby increasing system efficiency. The thresholds for dust settlement, the nature of dust and its spectral response needs further investigated. The current work provides preliminary insight into salient observations made in discerning the interplay between dust settlement, solar spectra and system temperatures. II. INSTRUMENTS Reinhartd MWS 9-5 weather station was used to record the weather conditions during the measurements. Amprobe Solar- 500 module analyzer was used to record the IV characteristics. Fluke thermal imager TiR32 was used to measure the soiled PV panels. Center IR non-contact thermometer and Brainchild 8TC datalogger module (K type thermocouple) was used to monitor the temperature of the experimental system. FieldSpec® 3 Spectroradiometer has been used to measure the solar spectra and its impact on the role of dust. III. RESULTS AND DISCUSSIONS Here to understand performance of the PV due to the interplay of dust, solar spectra and temperature, commercially available 37W p and 230W p Si type panels were used. Dust samples and deposition densities were under out-door conditions, with laboratory slides also maintained under identical exposure conditions such as to have similar (in not identical) deposition (type and density) of dust. These slides were used for spectroradiometer studies to understand the absorptivity of the specific dust involved, and possible investigation on the temperature of the panel. 978-1-5090-2724-8/16/$31.00 ©2016 IEEE 1715