Joseph Kuitche

Investigation of Dominant Failure Mode(s) for Field-Aged Crystalline Silicon PV Modules Under Desert Climatic Conditions

The first step in developing a life prediction model for photovoltaic (PV) modules is the identification of dominant failure modes/mechanisms for given environmental and operating conditions. Although important, the literature is very scarce. The Jet Propulsion Laboratory (JPL) approach consists of identifying the weakest link in module construction and the failure modes or mechanisms susceptible to the link are considered dominant. The failure mode and effects analysis/failure mode and effects criticality analysis approach, proposed and tried by a few authors, provides a more analytical alternative. It uses the risk priority number (RPN) as a ranking metric for failure modes prioritization. The RPN is a product of three parameters: severity of a failure (S), occurrence of the failure (O), and detection of the failure (D). Typically, the values for S, O, and D are assigned based on qualitative analyses. As such, the values assigned for the failure modes to those factors are highly subjective, leading to considerable variations from one analyst or design team to another. The main objective of this study is to move as far away as possible from this traditionally subjective approach to a formal, objective, and data-driven determination of RPN. The approach described in this paper relies on quantitative measures and sizable datasets. For the hot and dry climatic conditions of Phoenix, Arizona USA, solder bond failures and encapsulant discoloration are found to be the dominant failure modes.

Failure analysis of design qualification testing: 2007 VS. 2005

The design/performance qualification testing is a set of well-defined accelerated stress tests with strict pass/fail criteria. ASU-PTL is an ISO 17025 accredited testing laboratory and has been providing photovoltaic testing services since 1992. This paper presents a failure analysis on the design qualification testing of both crystalline silicon (c-Si) and thin-film technologies for two consecutive periods: 1997–2005 & 2005–2007. In the first period, the industry was growing at a slower rate with traditional manufacturers and the qualification testing of c-Si technologies was primarily conducted per Edition 1 of IEC 61215 standard. In the second period, the industry was growing at an explosive rate with new manufacturers joining the traditional manufacturers and the qualification testing of c-Si was primarily conducted per Edition 2 of IEC 61215. Similar failure analysis according to IEC 61646 has been carried out for the thin-film technologies as well. The failure analysis of the test results presented in this paper indicates a large increase in the failure rates for both c-Si and thin-film technologies during the period of 2005–2007.

Evaluation of 12-year-old PV power plant in hot-dry desert climate: Potential use of field failure metrics for financial risk calculation

This paper provides a metric definition for the safety failures, reliability failures and degradation loss for the PV modules. These metrics are then used in real power plant evaluations to calculate the distribution among these three metrics which in turn could objectively be used to perform financial risk calculations. The results obtained on 2352 and 1280 modules in two of the evaluated power plants, aged 12 and 4 years, in a hot-dry desert climate are analyzed using these defined metrics. The results indicate that the mean and median degradations, respectively, are 0.95 and 0.96 %/year for the 12-year old, and 0.96%/year and 1%/year for the 4-year old power plants. The distribution between safety failures, reliability failures and durability loss is determined to be 7%, 42% and 51%, respectively for the 12 year old power plant.

Potential induced degradation of pre-stressed photovoltaic modules: Effect of glass surface conductivity disruption

Potential induced degradation (PID) due to high system voltages is considered as one of the possible degradation mechanisms of PV modules in the field. In the previous studies carried out at ASU-PRL, the surface conductivity of the entire glass was obtained using either conductive carbon layer (covering the entire glass surface and extending it to the frame) or humidity inside an environmental chamber. This study investigates the influence of disruption of glass surface conductivity on the PID. In this study, the conductive carbon layer was applied on the modules glass surface but without extending it to the frame and hence the surface conductivity was disrupted (no carbon layer) at 2 cm distance from the periphery of frames inner edges. This study was carried out on the modules of different manufacturers under dry heat conditions at multiple stress temperatures and voltages. To replicate closeness to the field-aged modules, half of the selected modules for the PID investigation were pre-stressed under damp heat for 1000 hours and the other half under thermal cycling for 200 cycles. When the surface continuity was disrupted, the degradation was found to be absent or negligibly small even after 35 hours of negative bias at elevated temperatures. This preliminary study appears to indicate that the modules could become immune to PID losses if the continuity of the glass surface conductivity is disrupted at the inside boundary of the frame. The surface conductivity of the glass, due to water layer formation in a humid condition, close to the frame could be disrupted just by applying a transparent hydrophobic layer near the inner edges of the frame or by attaching the frameless laminate with the conductivity disrupting mounting methods such as glue-on rail on the backsheet.

Determination of Dominant Failure Modes Using FMECA on the Field Deployed c-Si Modules Under Hot-Dry Desert Climate

The failure and degradation modes of about 5900 crystalline-Si glass/polymer modules fielded for six to 16 years in three different photovoltaic (PV) power plants with different mounting systems under the hot-dry desert climate of Arizona are evaluated. Based on the results of this evaluation, failure mode, effect, and criticality analysis, a statistical reliability tool that uses risk priority number is performed for each PV power plant to determine the dominant failure modes in the modules by means of ranking and prioritizing the modes. This study on PV power plants considers all the failure and degradation modes from both safety and performance perspectives and, thus, comes to the conclusion that solder bond fatigue/failure with/without gridline contact fatigue/failure is the most dominant failure/degradation mode for these module types in the hot-dry desert climate of Arizona.

A statistical analysis on the cell parameters responsible for power degradation of fielded pv modules in a hot-dry climate

One of the major factors influencing the power degradation rate of PV modules is the environmental condition of the power plant site. In a previous investigation conducted by ASU-PRL on about 1900 modules (from six different manufactures) aged between 12 and 18 years, we reported a power degradation rate ranging between 0.6%/year and 2.5% per year for the hot-dry climatic condition of Tempe, Arizona. Statistically analyzing the performance parameters (current, voltage or fill factor) responsible for the power degradation and determining the degradation modes responsible for the degradation of those performance parameters is of great importance to the industry, especially to design appropriate accelerated tests for the new modules with similar/same construction as that of the field aged modules. The statistical analysis of the results presented in this paper was obtained using the null hypothesis technique. This analysis indicates that the major degradation modes for the modules having glass/polymer construction are encapsulant discoloration (causing Isc drop) and solder bond degradation (causing FF drop due to series resistance increase).

Degradation analysis of solar photovoltaic modules: Influence of environmental factor

The degradation of solar photovoltaic module is associated with the outdoor weather condition at the products use location. In this paper we propose a practical method to integrate this auxiliary information into the reliability prediction. Multi-year field data of degradation measurements of PV modules installed in Mesa, Arizona, are analyzed. Temperature is found to be a significant factor that influences the PV degradation process.

Nominal Operating Cell Temperature (NOCT): Effects of module size, loading and solar spectrum

NOCT (Nominal Operating Cell Temperature) is defined as the cell temperature within an open-rack mounted (45° from horizontal) module in the following conditions: ➢ total irradiance: 800 W□m⁻² ➢ ambient temperature: 20°C ➢ wind speed: 1 m□s⁻¹ ➢ electrical load: open circuit This paper investigates if: • the NOCT value remains the same irrespective of module size; • the NOCT value remains the same irrespective of electrical loading configuration (short-circuit,open-circuit or resistive load) • the NOCT value remains the same irrespective of type of irradiance sensor used (pyranometer or reference cell) • the low energy infrared photons of sunlight contribute to NOCT

Performance degradation of grid-tied photovoltaic modules in a hot-dry climatic condition

The crystalline silicon photovoltaic (PV) modules under open circuit conditions typically degrade at a rate of about 0.5% per year. However, it is suspected that the modules in an array level may degrade, depending on equipment/frame grounding and array grounding, at higher rates because of higher string voltage and increased module mismatch over the years of operation in the field. This paper compares and analyzes the degradation rates of grid-tied photovoltaic modules operating over 10-17 years in a desert climatic condition of Arizona. The nameplate open-circuit voltages of the arrays ranged between 400 and 450 V. Six different types/models of crystalline silicon modules with glass/glass and glass/polymer constructions were evaluated. About 1865 modules were inspected using an extended visual inspection checklist and infrared (IR) scanning. The visual inspection checklist included encapsulant discoloration, cell/interconnect cracks, delamination and corrosion. Based on the visual inspection and IR studies, a large fraction of these modules were identified as allegedly healthy and unhealthy modules and they were electrically isolated from the system for currentvoltage (I-V) measurements of individual modules. The annual degradation rate for each module type is determined based on the I-V measurements.

An Evaluation of 27+ Years Old Photovoltaic Modules Operated in a Hot-Desert Climatic Condition

Identification of failure mechanisms from the long-term field deployed modules is of great importance to the photovoltaic industry. This paper investigates the modules removed from a water pumping array operated over 27+ years in a hot-desert climatic condition, Arizona. Thirty-two modules were evaluated in this investigation. Each module is comprised of silicone rubber superstrate/encapsulant, mono-Si cells, fiberglass-like substrate, potted junction box and neoprene cable. Ten of these thirty-two modules were either non-functional or near non-functional with less than 30% of the original power. The other twenty-two functional modules showed an average power degradation of 1.08% per year over 27 years of operation. After the damp-heat (1000 hours of 85degC/85%RH), thermal cycling (two-hundred cycles of 90degC/-40degC) and hot-spot stress tests the modules lost about 11%, 9.8% and 3.5% of power, respectively