Si PV Modules Research Articles

Multifunctional coatings for solar module glass

AbstractCurrently, single‐layer antireflection coated (SLARC) solar glass has a dominant market share of 95% compared to glass with other coatings or no coating, for Si PV modules. This antireflection coating (ARC) results in an efficiency gain of 2–3%. However, there are issues with these SLARCs: (1) solar cell warming due to increased sub‐bandgap light absorption (by +0.4 ~ 1.2 K), counteracting the cell current gain and accelerating the aging of the solar panels, and (2) poor durability due to the coating's porous structure (typically lasting ≤5 years). This paper aims to develop a non‐porous multilayer coating (MLC) that is more durable and will act as a spectrally selective filter for solar modules. Studies have been conducted on MLCs in terms of optical, microstructure, mechanical, and durability properties compared with commercial single‐layer AR coatings. The MLCs showed superior performance in durability and benefit in reducing parasitic heat absorption in the non‐usable wavelength range. Also, a techno‐economic analysis model based on the multifunctional coating specifically to evaluate economic benefits has been developed.

Defects and performance of Si PV modules in the field – an analysis

Photovoltaic installations will likely become one of the major power sources in the 21st century and we need photovoltaic modules to operate reliably. The map shows the average photovoltaic fleet age in Europe.

First principles modeling of polymer encapsulant degradation in Si photovoltaic modules.

An outstanding issue in the longevity of photovoltaic (PV) modules is the accelerated degradation caused by the presence of moisture. Moisture leads to interfacial instability, de-adhesion, encapsulant decomposition, and contact corrosion. However, experimental characterization of moisture in PV modules is not trivial and its impacts can take years or decades to establish in the field, presenting a major obstacle to designing high-reliability modules. First principles calculations provide an alternative way to study the ingress of water and its detrimental effect on the structure and decomposition of the polymer encapsulant and interfaces between the encapsulant and the semiconductor, the metal contacts, or the dielectric layer. In this work, we use density functional theory (DFT) computations to model single chain, crystalline and cross-linked structures, infrared (IR) signatures, and degradation mechanisms of ethylene vinyl acetate (EVA), the most common polymer encapsulant used in Si PV modules. IR-active modes computed for low energy EVA structures and possible decomposition products match well with reported experiments. The EVA decomposition energy barriers computed using the Nudged Elastic Band (NEB) method show a preference for acetic acid formation as compared to acetaldehyde, are lowered in the presence of a water solvent or hydroxyl ion catalyst, and match well with reported experimental activation energies. This systematic study leads to a clear picture of the hydrolysis-driven decomposition of EVA in terms of energetically favorable mechanisms, possible intermediate structures, and IR signatures of reactants and products.

Investigation of the potential induced degradation of on-site aged polycrystalline PV modules operating in Malaysia

On-site investigation of PID behavior of PV module has been carried out under typical Malaysian climate. A quantitative degradation measurement process of PV module through EL imaging has been introduced. PID has been observed only for the negative voltage stress in this p-type polycrystalline Si PV module. The negative end PV module degrades 42% due to 9 years field aging under a negative voltage stress from the 240 V string size. While positive end PV module is degraded near about 17% over the same period due to normal field aging. Shunt resistance of negative-end module has been found 75% lower than that of the positive-end module. Module crack propagation is found to be accelerated due to onsite cyclic high voltage stress. PID at higher string size has been estimated from the leakage current of brand new same PV module. The estimated PID of PV module under 600 V stress is 72.84%.

Technology Options for the Built Environment in Kenya: Dye-Sensitized and Amorphous Silicon Photovoltaics for Application in NZE Buildings

Background: The performance of a Dye-Sensitized Solar Module (DSSM) has been investigated under different outdoor air mass (AM), irradiance intensity and temperature conditions in Wajir, Kitui, Vihiga and Kajiado Counties in Kenya. Methods: The performance was thereafter compared with that of Amorphous Silicon (a-Si) devices undertaken under similar weather conditions in Nigeria. The DSSM's good response to short wavelength radiation made it perform better at increased AM values than what has been reported of a- Si PV modules. Results: Studies on a-Si showed that their performance favors low AM conditions. The DSSM generally performed better than what is reported of a-Si, based on irradiance and temperature dependence. Nonetheless, a-Si devices performed better at higher irradiance intensities. These results show that Dye-Sensitized and a-Si technologies complement each others’ performance when subjected to the outdoor field AM, irradiance and temperature conditions. Conclusion: These findings can be applied in PV sizing, especially for application in Building Integrated Photovoltaics (BIPV) in the tropics. Keywords: Amorphous silicon, building integrated photovoltaics, complimentarily, dye-sensitized, geo-thermal, solar PV.

Optimal Design of PV Module with Bypass Diode to Reduce Degradation due to Reverse Excess Current

In this paper, we present an economical and practical standard to install a bypass diode in a thin-film PV module. This method helps to reduce heat generation and to prevent module degradation due to excess current from reverse bias. The experimental results confirm that for different numbers of solar cells, there is a relation between the excess reverse current and the degradation of solar cells in a-Si:H modules. The optimal number of solar cells that can be connected per bypass diode could be obtained through an analysis of the results to effectively suppress the degradation and to reduce the heat generated by the module. This technique could be expanded for use in high power crystalline Si PV modules.

Degradation Effects in sc -­‐ Si PV Modules Subjected to Natural and Induced Ageing after Several Years of Field Operation

This paper presents ageing effects observed in sc-Si PV modules operating in field conditions for 18 and over 22 years. The effects of both natural ageing processes and induced ageing by external agents, causing partial or total shading of cells for a prolonged period of time, are examined. Optical degradation effects observed through visual inspection include discoloration of the EVA, degradation of the AR coating, degradation of the interface between the cell and encapsulant, corrosion of busbars and fingers, and tears, bubbles and humidity ingress at the back surface of the modules. Thermal degradation effects examined via IR thermography reveal the existence of hot cells, hotspots on the busbars, and colder bubbles. Modules' power and performance degradation is assessed through I-V curve analysis. Results show naturally aged modules to exhibit milder ageing effects than modules subjected to induced ageing, an outcome also supported by their power degradation ratio.

The Experimental Performance of an Unglazed PV-thermal Collector with a Fully Wetted Absorber

In general, there are two types of PVT collector, glazed and unglazed, depending on the existence of glass in front of the PV module. On the other hand, water-type PVT collectors can be classified into two types according to absorber type: the sheet-and-tube absorber PVT collector and the fully wetted absorber PVT collector.The aim of this study is to analyze the electrical and thermal performance of a water-type PVT collector with a fully wetted absorber. For this study, a prototype of an unglazed PVT collector with a fully wetted absorber was designed and built, and both the thermal and electrical performances of the prototype PVT collector were measured in outdoor conditions. A conventional mono-crystalline Si PV module was tested alongside the PVT collector in order to compare their electrical performance

CdTe photovoltaics: Life cycle environmental profile and comparisons

We discuss the emissions of cadmium throughout all the life stages of CdTe PV modules, from extracting, refining, and purifying the raw materials to producing, using, and disposing or recycling of the modules. Then, we compare these emissions with those in the life cycle of three different types of crystalline Si PV modules. The energy requirement and energy pay back times (EPBT) of CdTe PV modules are considerably shorter than that of crystalline Si modules, although the latter exhibit higher efficiencies. This difference is primarily due to the energy used to process silicon, a fraction of which is derived from fossil fuels, inevitably producing Cd and many other heavy-metal emissions. The lower energy requirement of CdTe PV results in lower emissions of all pollutants, including cadmium.

PV module dynamic impedance and its voltage and frequency dependencies

The paper presents a derivation of the dynamic impedance of a PV module. At each bias voltage, the general form of the impedance describes a semicircular locus in the complex impedance plane. Intercepts of each impedance locus yield series, shunt and dynamic resistance of a module. Determinations of the dynamic impedance of a x -Si PV module in the dark with five reverse bias voltages and over a frequency range of 1 Hz to 60 kHz are made. The experimental results validate the derived general form of dynamic impedance.

A Search for Degradation Mechanisms of CdTe/CdS Solar Cells

AbstractCdTe/CdS solar cells have demonstrated stability over thousands of hours of field testing, but have not yet established the same track record for reliability achieved by crystalline Si PV modules. In order to identify potential degradation mechanisms, this paper describes a series of experiments in which CdTe/CdS solar cells are subjected to combinations of temperature, voltage and illumination levels intended to stress the devices beyond levels which would be experienced in the field. During this process the devices display decreases in Voc and FF which are tentatively attributed to chemical changes at the low resistance contact to the CdTe and to changes in the electrical transport properties of the CdTe. Two thermally activated effects were observed depending upon stress bias. Reverse bias appears to degrade bulk CdTe electrical properties while forward bias strengthens a reverse diode which most likely is located at the back contact. Chemical analysis of the back contact region of the devices using XPS reveals strong oxide peaks in all stressed samples. Evidence of Cd diffusion into the Mo contacts is observed by SIMS and Auger. Mo diffusion into the CdTe is promoted by reverse bias stressing. Cu migration consistent with positively charged ions was indicated by SIMS.