Farrukh Ibne Mahmood

Hotspots pose a significant long-term reliability challenge in photovoltaic (PV) modules that can have a detrimental impact on the efficiency, safety, and financial viability of a PV system. This paper aims to evaluate the endurance of hotspot stress in pristine and prestressed glass–glass (GG) modules. The accelerated prestressing was conducted for 600 thermal cycles (TC600) to represent decades of field exposure. GG modules are quickly becoming an alternative to the traditional glass–backsheet (GB) modules that have been the industry standard. Unlike other conventional studies that subject only pristine modules to hotspot stress, this paper evaluates the performance of an accelerated/simulated field-aged GG module (using TC600) and a pristine GG module. Pre- and post-characterizations were performed before and after each test to determine changes in electrical performance and observe any defects in GG modules. During the hotspot test, an approximately 200 °C maximum cell temperature was observed with a cell shading of 25% (the worst-case shading ratio). After the hotspot test, electroluminescence imaging indicated that most cells in the prestressed GG module exhibited severe damage whereas no significant defects were evident in the pristine GG module where the prestressed GG module degraded 8.2% and the pristine GG module degraded 1.5% in maximum power. These findings are critical for the industry, considering that GG bifacial modules will dominate the market.

Potential induced degradation (PID) is a reliability issue affecting photovoltaic (PV) modules, mainly when PV strings operate under high voltages in hot/humid conditions. Polarization‐type PID (PID‐p) has been known to decrease module performance quickly. PID‐p can be reduced or recovered under the light in some cases, but this effect, as expected, would be less pronounced on the rear side of bifacial PV modules receiving lower irradiance. As bifacial PV modules are projected to dominate the PV market within the next 10 years, it is crucial to understand the PID‐p issue in bifacial modules better. In this study, we performed indoor PID testing to induce PID‐p on 14 commercial bifacial p‐PERC modules with three different module constructions from three manufacturers. Four rounds (+ve and −ve polarities for front and rear sides) of PID testing are done at 25°C, 54% relative humidity (RH) for 168 h using the aluminum foil method. Each module side (front cell side and back cell side) is tested individually under both negative and positive voltage bias. The results show that the highest degradation of 32% in maximum power (Pmax) at standard test conditions (1000 W/m²) and 51% at low irradiance (200 W/m²) has been observed in some cases. Recovery under sunlight is also done, and outcomes show a near‐complete recovery in Pmax. This study presents an extensive experimental methodology and a detailed analysis to systematically and simultaneously/sequentially evaluate multiple construction types of bifacial modules to the PID‐p susceptibility and recovery.

Hotspots can be a detrimental reliability issue that can adversely affect the long-term performance of (PV) modules in the field. The endurance of hotspot stress is usually evaluated on pristine modules, which do not represent the hotspot issues related to long-term field-aged modules. PV modules can become vulnerable to hotspots when exposed to long-term field operating conditions. Hence, in this study, we evaluated the endurance of hotspot stress of a fresh half-cell glass-backsheet (GB) module along with a prestressed half-cell GB module that was subjected to 600 accelerated thermal cycling stress. The maximum power (Pmax) of both GB modules (fresh and prestressed) experienced a negligible decrease of approximately 1% after the sequential thermal cycling followed by the hotspot stress test. This indicates that GB modules having half-cell GB configuration can potentially endure the hotspot stress even after being exposed to the field for over 30 years. However, these findings were derived from a sample size lacking statistical significance and, therefore, should not be generalized to encompass all half-cell GB modules.

Potential induced degradation (PID) mode is one of the most critical degradation modes in the photovoltaic (PV) modules. The PID issue is highly dependent on the conductivity of the materials (especially encapsulant and glass surface) and the adhesion strengths of interfaces (glass/encapsulant, encapsulant/cell and encapsulant/backsheet). In the field-aged modules, the material conductivity typically increases due to aging of materials, weakened interface and cemented soiling of glass surface. Currently, the PID tests are performed on the fresh modules as per IEC standards' requirements. In the fresh modules, the encapsulant conductivity is very low (compared to the field-aged modules) and the adhesion strengths of interfaces are high. Therefore, the PID loss in the current tests represent only the loss which would happen in the fresh modules and young modules, not in the long-term field-aged modules. In the current work, we have used two pre-stressed modules to represent the long-term field-aged PV modules. The pre-stressing was done on two glass/polymer modules for 2000 hours at 85°C/85%RH according to IEC 61215 standard. After the damp-heat prestressing, these two modules were subjected to PID (+ve PID on one module; -ve PID on the other module) in an environmental chamber at 1000 V, 60°C, and 85% RH, according to IEC 62804-1. These modules experienced 6.3-7.5% power degradation which is beyond the allowed limit of 5% by the standard. Based on these results, we believe that the PID tests may need to be performed on the unstressed/fresh and pre-stressed modules to appropriately represent the PID issue corresponding to the short-term and long-term field-aged modules, respectively.

The solar photovoltaic (PV) industry often experiences module damage during transportation. PV modules stacked horizontally and strapped on wooden pallets may develop failures impacting their efficiency (glass shattering, cracks, frame indentation, etc.), especially when modules are not packed by professionals. The appearance of failures during the shipment from one laboratory to another can be detrimental to research studies. In this study, we tested a reusable plastic pallet designed to ship modules vertically. Five technologies of commercial PV modules were shipped together from Arizona to Florida including: glass/glass bifacial modules (framed and frameless), glass/transparent backsheet bifacial modules and glass/white backsheet modules (framed). Each module technology has a different physical size. Some modules had pre-existing cell-cracks allowing for the study of cell-crack formation and propagation during shipment. Dark current-voltage (I-V), light I-V and electroluminescence characterization were performed before and after shipment. A datalogger was used to monitor shocks and ambient temperature throughout the shipment and identify when the modules were more susceptible to damage. The modules were tilted upon receipt and the pallet were damaged but with no shattered modules. Time series shock data provided by the datalogger were used to determine potential responsible events. Our results reveal a few new post-transportation cracks for some modules. Modules parameters before and after shipment are also compared regarding the module constructions and their position in the pallet.

Potential induced degradation of the polarization type (PID-p) can reduce module performance in a relatively short period of time. PID-p can occur at both voltage polarities, but most studies are focused on degradation under a negative bias. This paper uses commercial bifacial passivated emitter and rear contact (PERC) cells within a monofacial glass-backsheet module construction to evaluate the impact of PID-p under a positive bias on the front side. Using the aluminum-foil (Al-foil) method, the module was stressed for PID in an environmental chamber. After the stress, the maximum power (Pmax) showed a decline of 3.1% at 1000 W/m ² and 6.2% at 200 W/m ² . Recovery under light was also investigated. Complete recovery was observed at high irradiance, while a partial recovery was seen at lower irradiance. The outcomes of this study can help in understanding PID-p degradation under a positive bias and its recovery under the light.

Investigation and Comparison of DC and AC Nanogrid Networks using MATLAB/Simulink

The energy crisis in Pakistan has crippled the country’s economy with an energy shortfall reaching up to 6000 MW. Fortunately, Pakistan lies close to the Sun Belt and therefore receives very high irradiation. To this end, in the beginning of 2014 the Pakistani government sanctioned a solar photovoltaic project namely Quaid-e-Azam Solar Park which was rated at 1000 MW. In this study, a cost benefit analysis for the Quaid-e-Azam Solar Park has been developed. The model uses RETScreen software. In fact, a literature review pointed out that most of the previous research work with reference to cost benefit analysis for solar projects has been mainly carried out on smaller power plants. The outcome of the study shows promising results with the simple payback period coming out at 5.6 years. Furthermore, this analysis can serve as guideline for future solar photovoltaic projects in Pakistan and can help in the development and utilization of the huge solar potential of the country, thus aiding in the reduction of energy shortage. In its proposal, our research is unique and innovative in the Pakistani context. The results aim to serve as a guideline for decision makers and researchers interested in this topic.