Study Tests Reliability of Photovoltaic Materials When Exposed to UV Light

In an article published in Energies, researchers analyzed optical stability properties and conducted an ultraviolet test on several lightweight polymer material front sheets. A photovoltaic (PV) module with a front sheet made of polymer material rather than glass was built. Both a character analysis and an ultraviolet test for stability were carried out. 

photovoltaics

Study: The Influence of UV Light Exposure on the Reliability of Various Front Materials for Lightweight PV Module. Image Credit: Thongsuk Atiwannakul/Shutterstock.com

The need for new designs and polymer materials is rising for many types of photovoltaics installation in building integrated photovoltaics, floating systems, and agriculture. The weight of the photovoltaics module must be minimized to make the photovoltaics module as applicable as possible in these applications. Instead of tempered glass, the front surface must be constructed of a polymer material to make the photovoltaics effective. 

Following the ultraviolet test for stability, the polycarbonate (PC) front sheet's transmittance dropped by just 3%, and the module manufactured with PC showed only a 6% power loss. The PC was suitable for use in the photovoltaics module sector. 

Understanding the Prospects of Photovoltaic Modules

Due to its environmental friendliness and minimal impact on air pollution, PV energy production has attracted significant interest, including agro-PV, floating PV, and building integrated PV (BIPV) systems.

The most common of these is BIPV systems. However, most of them are based on a typical photovoltaics module architecture and have several flaws, such as being heavy because of one or more glass layers.

Acrylic and other polymer material are used in lightweight crystalline-silicon photovoltaics modules to replace the glass. Since glass makes up around 70% of the photovoltaics module weight, the module's weight can be significantly reduced if the front sheet is composed of polymer material rather than glass. Compared to conventional architectures, polymer material provides less expensive alternatives.

It is necessary to evaluate the output and stability of the photovoltaics module when a polymer material is utilized as the front surface material rather than glass since it has different qualities from low-iron tempered glass.

The front sheets of photovoltaics modules can be made from various lightweight materials. Films made of ethylene tetrafluoroethylene (ETFE) have relatively high melting temperatures and excellent corrosion and temperature resistance. They are thin, flexible, and have a high transmittance. 

Polyethylene terephthalate (PET) has excellent mechanical and chemical resistance and great transparency. It has been applied in many different contexts, from producing electronic components to packaging food and beverages. 

Polymethyl methacrylate (PMMA) is a transparent polymer material with improved mechanical and scratch resistance qualities. PMMA has enhanced environmental stability than most other polymer materials. It has a variety of uses, including contact lenses, transparent panels, and industrial parts, as well as in the fields of ballistic protection, medicine, and the auto industry.

As a result, it is essential to consider a material's light transmittance and ultraviolet qualities, as well as the resulting weight reduction of the photovoltaics module. Therefore, if the light transmittance is significantly reduced after the ultraviolet test, even polymer material with a high light transmittance cannot be used as the front sheet of the photovoltaics module.

The primary goals of this study were to investigate new lightweight polymer material and to create a lightweight photovoltaics module resistant to UV light's effects. For this reason, the impact of UV irradiation on the front sheets of lightweight photovoltaics modules made of ETFE, PC, PET, and PMMA polymer material was researched.

The difference between the materials' yellowing index (YI) and optical transmittance before and after the ultraviolet test was also examined. A photovoltaic module's electrical characteristics were assessed before and after the ultraviolet test for stability, which was conducted utilizing lightweight polymer material. The results revealed how lightweight polymer material worked in actual settings.

Conducting the Experiments

A front cover sheet made of a lightweight polymer material and an N-type crystalline silicon solar cell was utilized to construct a single-cell module. The solar cell adhered to the PV module's top cover sheet and backside due to the ethylene-vinyl acetate (EVA) copolymer encapsulants utilized during manufacture.

All layers, including the EVA, solar cell, and back sheet, were laminated, employing a solar module laminator to create the PV module. The entire lamination process was conducted at the recommended temperature of 140 °C. Finally, the finished PV module was constructed in a total lamination time of 1060 s. A spectrophotometer with low scattered light, high sensitivity, and an expandable wavelength range of 185-3300 nm was used to test transmittance.

The ultraviolet test was carried out in a specially designed closed chamber for 150 hours at 30 kWh. Field emission scanning electron microscopy was used to investigate the high-resolution morphology of the EVA film. The energy dispersive X-ray (EDX) investigation was also carried out to learn about the chemical makeup of EVA before and after the ultraviolet test for stability on the module.

The goal of the ultraviolet test was to confirm each material's stability and discoloration. Since UV light severely discolored the polymer material, the module's light trapping and transmittance side decreased, reducing the PV module's performance. Consequently, the transmittance impact after exposure to the ultraviolet test was a crucial metric.

A temperature of 46 °C and 30 kWh of irradiance were present during the ultraviolet test. The front material's transmittance was evaluated between 300 and 1200 nm wavelengths. It was discovered that PMMA, PC, and PET turned yellow after being exposed to UV light. An essential element that characterized how a sample transitioned from white to yellow was the yellowness index (YI). The yellowing happened due to prolonged exposure to harmful environmental factors such as temperature, UV radiation, and dust.

Future of Polymer Materials in PV Modules

This study evaluated various lightweight polymer front sheets' optical and UV stability characteristics. After conducting the ultraviolet test for stability, it was discovered that the transmittance of ETFE, PC, PET, and PMMA fell to roughly 2.65%, 2.98%, 15.01%, and 4.16%, respectively.

A PV module's electrical characteristics and ultraviolet stability were also examined after it was fabricated, utilizing PC and ETFE as the front cover sheet. For the PC and ETFE-based modules, Pmax decreased by 6.11% and 54.85%, respectively. The findings revealed that PC material was a good choice for applications requiring lightweight PV modules.

Reference

Zahid, M.A., et al. (2022). The Influence of UV Light Exposure on the Reliability of Various Front Materials for Lightweight PV Module. Energies, 15(19), 6894. https://www.mdpi.com/1996-1073/15/19/6894/htm

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Pritam Roy

Written by

Pritam Roy

Pritam Roy is a science writer based in Guwahati, India. He has his B. E in Electrical Engineering from Assam Engineering College, Guwahati, and his M. Tech in Electrical & Electronics Engineering from IIT Guwahati, with a specialization in RF & Photonics. Pritam’s master's research project was based on wireless power transfer (WPT) over the far field. The research project included simulations and fabrications of RF rectifiers for transferring power wirelessly.

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