What Are the Hot Recent Discussions on the Material of the PV Module Encapsulation

The PV module price has had a sharp decline since 2010 so that it has dropped more than 80% over the last decade [1]. This drastic decline is partly due to the constant pressure on PV module manufacturers to reduce the Levelized Cost of Electricity (LCOE) of solar power plants, especially photovoltaic ones. Such cost pressures have resulted in a drive to develop and implement new module designs, which either increase the performance and/or the lifetime of modules or decrease the cost to produce them [2]. Introducing new encapsulation materials is a measure leading to the two above-mentioned results at the same time.

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 [3,4]: Price, Performance, and Efficiency. The low cost, lightweight, flexibility, and easier assembly of polymeric materials have made them the most widely used material in PV module encapsulation.

Ethylene-vinyl acetate (EVA) is the mainstream encapsulation material for commercial use due to its low cost, adequate transparency, and flexibility since 1981 [5, 6, 7]. Although EVA has had a long-established history in PV module manufacturing, it is prone to acetic acid formation and having a high water vapor transmission rate. They lead to several serious failures and degrade the PV module performance during service life including discoloration, corrosion of metallization on top of the solar cells, delamination, and bubble formation [8, 9, 10].

PV modules have been designed for being on operation for 25-30 years while such deteriorating failures jeopardize the PV module performance and lifetime during the first years of their operation and bring them to their end of life sooner than expected. Therefore, there is an emergent need to develop and implement new encapsulants not only to guarantee the specified service life of PV modules but also to reduce the cost of production of them more than before.

As two alternatives for EVA, researchers have focused on thermoplastic polyolefin (TPO) and polyvinyl butyral (PVB). TPO is more famous than PVB for its better results under accelerated aging tests comparing to EVA  [2]. Moreover,  TPO has become one of the mainstream materials for glass-glass PV modules which is fit for hot and humid installation locations, thanks to its higher thermal stability and lower water vapor transmission rate as compared to EVA and PVB. These three and sometimes a combination type of EVA and TPO are under hot debate as encapsulation materials for PV modules.

It is important to note that each of the alternative materials for EVA has its own advantages and disadvantages. But there is an unwritten checklist for comparing different encapsulants and choosing the better ones in this segment of the industry, as we said about glass-glass PV modules. In other words, using a general bill of material (BOM) for PV module manufacturing is gradually faded away, oriented and specific BOM for PV production has found its position instead.

The story is continued in the next part.

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  10. Swonke, Thomas, and Richard Auer. “Impact of moisture on PV module encapsulants.” In Reliability of Photovoltaic Cells, Modules, Components, and Systems II, vol. 7412, p. 74120A. International Society for Optics and Photonics, 2009.