What Material Protects Solar cells from Harsh Environmental Conditions in PV modules

What Material Protects Solar cells from Harsh Environmental Conditions in PV modules

Introduction

All conventional crystalline silicon-based solar panels consist of 5 layers. These layers are

  • glass
  • front encapsulant layer
  • matrix-cell/solar cells
  • rear encapsulant layer
  • backsheet

[1,2]. Silicon solar cells have been embedded in the middle of the other four layers. Although the process of putting silicon solar cells into these layers leads to different optical and electrical power losses, they play a crucial role in protecting PV modules from diverse environmental, electrical, thermal, and mechanical damages. As an example, both encapsulation layers should provide structural and mechanical support for solar cells and their circuit components.

Both encapsulant layers and backsheet not only have the responsibility for the protection of solar panels from harsh environmental conditions but also have an impact on the aesthetic aspect [2]. This article, first of all, will focus on the protective aspect of encapsulation layers. Then, it will describe different encapsulation materials that have been used by PV module manufacturers, and finally, outline the current status and future directions of this segment of the solar PV industry.

Why Encapsulation Layers?

Both the reliability of PV modules for mass production and the durability of them for long service lifetime up to 25-30 years are depending on the careful choice of materials for the encapsulant layers [1,3,4]. It is worth mentioning that the performance analysis of PV modules in the near and long-term is usually referred to as reliability and durability in the literature [1,5-7].

As a matter of fact, the new annual added solar capacity accounted for more than 48% of the total installed renewable energy capacity in 2020 and raised to more than 65% in 2021 [8,9]. Moreover, it is expected that the annual solar capacity will increase to 214GW and 222GW in 2022 and 2023 respectively [8]. Thus, this industrial dominance brings the reliability and durability of PV modules and encapsulant layers into the central focus [1].

What are the material of an encapsulation layer?

The low cost, lightweight, flexibility, and easier assembly of polymeric materials have made them the most widely used material in the PV module encapsulation [1]. First of all, Polyethylene (PE) was initially chosen as a polymeric encapsulant because of its simple structure and low cost. However, the main drawback was its opaque and translucent appearance [10,11]. After that, PE-based materials in which PE was the backbone along with different side groups were chosen to solve transparency challenges and keep PE advantages. One of these PE-based polymeric materials is Ethylene-vinyl acetate (EVA) in which vinyl acetate (VA) was added to PE to form a copolymer. EVA has become the mainstream material for commercial use due to its low cost, adequate transparency, and flexibility from 1981 up to now [1,5,10].

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There is a famous Golden triangle in the PV module production that scientific researchers and PV module manufacturers consider to assess the technical feasibility and commercialization capability of encapsulants in the destination market: Price, Performance, and solar panels Efficiency [12-14].

EVA as the dominant solar panel’s encapsulation material is good at two out of three items, i.e. price and efficiency. Although its performance has been acceptable, some deteriorating factors of EVA functionality including 

  • Acetic Acid Formation
  • Moisture ingression
  • Temperature
  • UltraViolet (UV) radiation

Sometimes lonely and usually along with each other during the period of field operation lead to different time-dependent failures [1]. Common time-dependent failures in EVA are

  • Turned EVA to yellow/brown color (discoloration)
  • Delamination and bubble formation
  • Potential-induced degradation (PID)
  • Snail trails
  • Hot spots  [1,15,16].

Therefore, the introduction of a new non-EVA type encapsulant with low-cost, high-performance, and high

durability could provide a solution to discoloration, delamination, and PID problems.

Current status and future perspective of encapsulation market 

As a dominant type of PV modules, crystalline silicon (c-Si) modules with more than 90% market share are embedded in polymeric encapsulant layers [17,18]. Today, EVA is the most popular polymeric encapsulation material with more than 80% market share [1,19].

Non-cross-linking thermoplastic polyolefin or TPO is a newly emerged encapsulation material which has four distinct advantages over EVA and overcomes the challenges which EVA has faced during field installation. We will deeply dive into time-dependent failures of EVA as well as advantages of TPO over EVA in the second part of this paper.

It is estimated that TPO will reduce the dominant share of EVA in the market and grab close to 20% share within the next 10 years, however, other materials will have kept their low market shares for niche applications [1,20].

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Did you know?

Solar Edition publishes the top 10 solar panels monthly since 2019. In addition to this, we also publish a top 10 72 cells solar panels for industrial-scale every quarterly (Q1,2,3,4).

Author: Hesam-Edin Hayati Soloot & Amir Hayati Soloot

References

[1] Multi-criteria Analysis Method to Evaluate Different Encapsulation Materials for PV Modules and Proposing a Suitable Candidate

[2] Solar Edition, “Harmony & Beauty, an Aesthetic Aspect of Solar Panels use in the Buildings”, written by Shahab Moghadam.

[3] Yang, H., Wang, H., Cao, D., Sun, D., & Ju, X. (2015). Analysis of power loss for crystalline silicon solar module during the course of encapsulation. International Journal of Photoenergy, 2015.

[4] Mansour, D. E., Barretta, C., Pitta Bauermann, L., Oreski, G., Schueler, A., Philipp, D., & Gebhardt, P. (2020). Effect of Backsheet Properties on PV Encapsulant Degradation during Combined Accelerated Aging Tests. Sustainability, 12(12), 5208.

[5] Oreski, G., Omazic, A., Eder, G. C., Voronko, Y., Neumaier, L., Mühleisen, W., … & Edler, M. (2020). Properties and degradation behaviour of polyolefin encapsulants for photovoltaic modules. Progress in Photovoltaics: Research and Applications, 28(12), 1277-1288.

[6] Ishii, T., & Masuda, A. (2017). Annual degradation rates of recent crystalline silicon photovoltaic modules. Progress in Photovoltaics: Research and Applications, 25(12), 953-967.

[7] Kurtz, S., Sample, T., Wohlgemuth, J., Zhou, W., Bosco, N., Althaus, J., … & Kondo, M. (2015, June). Moving toward quantifying reliability-the next step in a rapidly maturing PV industry. In 2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC) (pp. 1-8). IEEE.

[8] PV-Tech, “Solar deployment to reach 191GW in 2021 but fall far short of 2030 ambitions, BloombergNEF says”, written by Sean Rai-Roche.

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[9] Taiyangnews, “Rystad Energy Forecasts Global Renewable Energy Capacity In 2022 To Exceed 270 GW”.

[10] Hsu, H. Y., Hsieh, H. H., Tuan, H. Y., & Hwang, J. L. (2010). Oxidized low density polyethylene: A potential cost-effective, stable, and recyclable polymeric encapsulant for photovoltaic modules. Solar energy materials and solar cells, 94(6), 955-959.

[11] Kempe, M. D., Jorgensen, G. J., Terwilliger, K. M., McMahon, T. J., Kennedy, C. E., & Borek, T. T. (2007). Acetic acid production and glass transition concerns with ethylene-vinyl acetate used in photovoltaic devices. Solar energy materials and solar cells, 91(4), 315-329.

[12] Solar Edition, “What Are the Hot Recent Discussions on the Material of the PV Module Encapsulation”.

[13] Meng, Lei, Jingbi You, and Yang Yang. “Addressing the stability issue of perovskite solar cells for commercial applications.” Nature communications 9, no. 1 (2018): 1-4.

[14] Yeo, Jun-Seok, and Yeseul Jeong. “Pathway toward market entry of perovskite solar cells: A detailed study on the research trends and collaboration networks through bibliometrics.” Energy Reports 6 (2020): 2075-2085.

[15] de Oliveira, M. C. C., Cardoso, A. S. A. D., Viana, M. M., & Lins, V. D. F. C. (2018). The causes and effects of degradation of encapsulant ethylene vinyl acetate copolymer (EVA) in crystalline silicon photovoltaic modules: A review. Renewable and Sustainable Energy Reviews, 81, 2299-2317.

[16] Adothu, B., Bhatt, P., Chattopadhyay, S., Zele, S., Oderkerk, J., Sagar, H. P., … & Mallick, S. (2019). Newly developed thermoplastic polyolefin encapsulant–A potential candidate for crystalline silicon photovoltaic modules encapsulation. Solar Energy, 194, 581-588.

[17] Polman, A., Knight, M., Garnett, E. C., Ehrler, B., & Sinke, W. C. (2016). Photovoltaic materials: Present efficiencies and future challenges. Science, 352(6283).

[18] Fraunhofer Institute for Solar Energy Systems, “Photovoltaic report,” 2020.

[19] Cattaneo, G., Faes, A., Li, H. Y., Galliano, F., Gragert, M., Yao, Y., … & Perret-Aebi, L. E. (2015). Lamination process and encapsulation materials for glass-glass PV module design. Photovoltaics International, 27, 1-8.

[20] International Technology Roadmap for Photovoltaic (ITRPV), 2020 Results, 2021.







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