Friday, June 14, 2013

New PV Module Encapsulation Materials Led By New Cell Types

New PV Module Encapsulation Materials Led By New Cell Types

James Montgomery
June 12, 2013

Solar photovoltaic (PV) technology is a recipe of highly engineered materials and components, sandwiched with specific functions and working together to harness sunlight and convert it into electricity. One of those layers is the encapsulation film which protects the solar cell and ensures its performance and reliability; its role is to provide optical and electrical transmissivity and keep out moisture.

Ethylene vinyl acetate (EVA) has been the solar module encapsulant material of choice since the 1980s. It is as field-proven as any solar PV technology component.

EVA still commands the vast majority of solar module encapsulation today: it has a proven track record and is a low-cost option, notes Alison Bennett, global technology manager for PV encapsulants at DuPont. But the emergence of both thin-film and high-efficiency cells means a greater need for an alternative to EVA. As the market expands for more thin-film and higher-efficiency crystalline silicon solar cells, so too will the usage of alternative encapsulant materials.

Time and technology march on, and EVA's shortcomings have been revealed after years of evaluation. Additive materials to improve EVA's crosslinking and adhesion properties can generate "free radicals" which contribute to physical deterioration and degradation of properties, starting with yellowing or discolouration. Among these is generation of acetic acid.
This acid might not be fatal to most silicon-based solar modules, which will technically still function even if the metal becomes coated. For thin-film technology, in particular copper-indium-gallium-(di)selenide (CIGS), however, any acid generated would be terminal. "Companies that are making CIGS modules are using alternative encapsulants to EVA," said Fatima Toor, lead analyst for solar components at Lux Research.

Also encountering problems with EVA encapsulation materials are newer high-efficiency cells, which make more use of shorter wavelengths of light. Typically encapsulant materials have included UV blockers to protect them, but "that didn't matter because the cell couldn't use that light," explained Bennett. But as new cell designs utilise more of the light spectrum, those UV blockers need to be removed, and "for EVA that can create a real problem."

"Due to the inherent structure of the polymer, EVA does not have superior moisture resistance and electrical properties desired to protect the solar cell over the 25-year service life of the module," summed up Brij Sinha, global strategic market manager for photovoltaic films at the Dow Chemical Company. "People are looking for something other than EVA."

Comment by Anumakonda Jagadeesh

Excellent post.

Hitherto the main drawback for wider use of solar PV is its low efficiency and high cost. But as Toor says,what really has to happen – and this is in all areas of solar PV, not just encapsulants – is a change in the conversation from purely low cost vs output ($/W) to a more performance-based metric ($/kWh).

I am glad tremendous research is on in improving the materials and efficiency of Solar PV.

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