Jim Joseph John

Visual Degradation in Field-Aged Crystalline Silicon PV Modules in India and Correlation With Electrical Degradation

This paper presents the analysis of visual degradation data collected during an All-India Survey of Photovoltaic Module Degradation conducted in 2013, in which 57 crystalline silicon modules were inspected in the five different climatic zones of India. Analysis of the data indicates that the highest percentage of modules suffered discoloration in the Hot and Dry climatic zone, with the Hot and Humid zone coming in second in the list. A higher percentage of modules have suffered corrosion in the Hot and Humid zone, as compared with other zones. The modules installed in the Cold climate suffered the least degradation. Both discoloration and corrosion have been seen in modules across all age groups, even in some of the modules installed less than five years ago. On the other hand, delamination and backsheet degradation have been seen only in modules more than a decade old. The visual degradation data have been correlated with the electrical performance data and reaffirm the direct relation between encapsulant discoloration and reduction in short-circuit current and output power, as well as that of series resistance with metal corrosion.

Performance degradation in field-aged crystalline silicon PV modules in different indian climatic conditions

A survey of field-aged crystalline silicon modules in various climatic conditions in India was carried out, focusing on modules, which show visible signs of degradation. Analysis of the survey data indicates that the power degradation rate is highest in the Hot & Dry climatic zone, followed by the Hot & Humid zone, while it is least in the Cold zone. The degradation in power output of crystalline silicon modules is primarily due to reduction in the short-circuit current, followed by decrease in fill factor while the decrease in open-circuit voltage is very small. Analysis of the survey data also indicates that degradation rate of multi-crystalline silicon is slightly higher than that of mono crystalline silicon.

Study of Soiling Loss on Photovoltaic Modules With Artificially Deposited Dust of Different Gravimetric Densities and Compositions Collected From Different Locations in India

Evaluation of soiling loss on photovoltaic (PV) modules in a geographical location involves collecting data from a fielded PV system of that location. This is usually a time-consuming and expensive undertaking. Hence, we propose collecting dust samples from various location of interest, preferably from the module surface, and use them as dust samples so that the soiling experiments can be conducted in the laboratory. In this work, a low-cost artificial dust deposition technique is utilized that could be used to deposit dust on a module surface in a controlled manner, which helps in predicting soiling loss associated with various dust properties, including densities, chemical compositions, and particle sizes. The soil samples covering diverse climatic conditions and six different geographic locations covering all of India were collected and investigated. Soiling loss on a silicon solar cell with Mumbai dust (17.1%) is about two times that of Jodhpur dust (9.8%) for the same soil gravimetric density of 3 g/m2. The dust collected from Mumbai showed the highest spectral loss, followed by Pondicherry, Agra, Hanle, Jodhpur, and Gurgaon. The worst affected module technology was amorphous silicon (17.7%), followed by cadmium telluride (15.7%), crystalline silicon (15.4%), and CIGS (14.5%) for the same density (1.8 g/m2) of dust from Mumbai.

Ashes to ashes, dust to dust: Averting a potential showstopper for solar photovoltaics

Soiling, especially the sedimentation of dust particles on the exposed surfaces of solar collectors, is critical to the operation of solar systems-even possibly a “showstopper” in many regions of the world. Historically, this important issue has received intermittent research attention over the past 7-decades, with studies mainly focused on the relationship of dust accumulation to performance. Significantly fewer studies relate to the mitigation using coatings and other physical mechanisms. Cleaning methods have also been limited in scope, primarily using solutions or techniques that are water-based. Recently, interest has been increasing with the growing markets and adoption of solar technologies in the MENA (Middle East and North Africa) and desert regions, where sand particles (1-μm to 500-μm) are problems. This becomes serious when combined with dew or other moisture forming cementitious coatings that can be difficult to remove. This paper provides a comprehensive review of past and recent research work on the impact of dust on solar-PV performance with a focus on issues relating to MENA/desert regions. This paper also reports on progress with dust mitigation approaches. We report our contributions in the microscopic and chemical composition analyses of the “dust samples” from various MENA and India-showing differences in composition, morphology that can affect accumulation and resulting performance. The focus is on PV (glass) surfaces. Alternative methods (mechanical, electrostatic, liquid, vibrational) for cleaning these surfaces are also examined. Some future research directions & technology requirements are cited.

Effect of tilt angle on soiling of photovoltaic modules

Soiling on PV modules is known to reduce PV system performance, mainly in dry arid climatic conditions. Cleaning with water or other means may become an expensive solution to the problem. For the highest annual energy production from a fixed tilt PV system, the modules are typically installed at tilt angle close to latitude angle of the systems location. Soiling loss is an interplay between terrain of the installation, tilt angle, rain frequency and rain intensity. For un-cleaned arrays in certain dusty locations, it would be better to optimize the tilt angle for maximizing transmitted radiation to the cells by adjusting the tilt angle slightly higher which would in turn minimize the soiling loss. In this work, we have developed an inexpensive soiling station which evaluates soiling loss at different tilt angles (0°, 5°, 10°, 15°, 20°, 23°, 30°, 33°, 40°). For Mesa, Arizona (a hot-dry climate), the 0° tilt angle showed a 2.02% loss whereas 23° and 33° showed soiling loss close to 1% during the first three months of 2011.

Influence of soiling layer on quantum efficiency and spectral reflectance on crystalline silicon PV modules

Reduction in transmittance of glass superstrate due to soiling on PV modules is studied by various groups throughout the world. However, the soil layer changes not only the irradiance level but also changes the spectral distribution of the incoming solar radiation. In this work, we have selected three solar cells within a commercial module covered with different thickness of soil layer. These soiled solar cells within a module are used to study the spectral reflectance and quantum efficiency changes at various wavelengths. Heavily soiled solar cell (~74.6gm/m2) showed a very high reflectance loss and very low quantum efficiency at all wavelengths with respect to after-cleaning. The three soiled solar cells were then cleaned using three different cleaning techniques - 60psi compressed air clean, brush assisted 30psi compressed air clean and water cleaned. Short circuit current, spectral reflectances and quantum efficiencys dependence on wavelengths is studied before and after each cleaning steps.

Angle of incidence effects on soiled PV modules

The transmission level of the incident light on the photovoltaic (PV) modules depends on the angle of incidence (AOI) and air/superstrate interface. The AOI dependence for the air/glass interface has already been well established. When the glass superstrate is covered by a soil/dust layer, the air/glass interface is altered and thereby changes the AOI dependence to air/soil/glass interface. In this work, PV modules retrieved from the field that had different dust densities have been measured for the dependence of the AOI curves on the dust gravimetric densities. It was determined that the AOI curve is inversely related to the soil density. The critical AOI for the air/glass interface is about 57° and it shifts dramatically as the soil gravimetric density (g/m2) increases. The measured AOI curves were then fitted and validated with the analytical/empirical models reported in the literature.

Novel PV module cleaning system using ambient moisture and self-cleaning coating

Soiling is a major concern for PV modules installed in field with power losses ranging from 15% to 65%. In current work, we propose an improved design for a PV module cleaning system based on absorption of ambient moisture and making the module glass super-hydrophilic by TiO2 coating. Initial studies indicate uniform and continuous fibers of diameter of approximately 250nm deposited throughout the sample. A complete prototype design with an automated water delivery system is implemented.

Quantification and Modeling of Spectral and Angular Losses of Naturally Soiled PV Modules

Spectral and angle of incidence (AOI) losses on naturally soiled crystalline silicon photovoltaic (PV) modules have been investigated in this study. The test modules designated as “moderately soiled (3 g/m2 )” and “heavily soiled (74.6 g/m2)” showed short-circuit current (Isc) losses of about 10% and 41%, respectively. The spectral reflectance and quantum efficiency (QE) losses were also quantitatively determined. In the wavelength range of 350-1100 nm, the average reflectance of moderately and heavily soiled modules increased (as compared with the clean surface) by 58.4% and 87.2%, respectively. In the moderately soiled module, the 26.3% (average) reduction in QE is mainly because of 23% of absorption and 5.5% of reflection in the dust. In the highly soiled module, the 75.3% (average) reduction in QE is mainly because of 62% of absorption and 31% of reflection in the dust particles. It is also seen that the typical critical AOI of 57° for cleaned PV modules decreased to 38° for the moderately soiled module and 20° for the heavily soiled module. This influence is crucial for fixed tilt modules as they experience a wide range of AOI during daily operation, and a significant fraction of energy is generated at higher AOIs.

Linking performance of PV systems in India with socio-economic aspects of installation

A survey of PV modules in the field for more than 5 years in India has been conducted The analysis revealed that module degradation rates are linked with the social and behavioral issues of the end users. The appropriateness in system installation, maintenance and hence the degradation depends on the type of ownership of the system, the financial model for the installation and the end purpose. We found that whenever there are cash flows associated with the installations in terms of savings or income generation, the maintenance activities are properly done, irrespective of the type of ownership of the system. Community owned PV installations were found to be better installed and maintained than individual systems because of the presence of institutionalized mechanisms for operation and maintenance.