New model for predicting moisture penetration into photovoltaic modules

A research team led by TU Delft in the Netherlands simulated moisture penetration into photovoltaic modules to better understand moisture-induced degradation. It analysed the influence of the choice of encapsulation material and back sheet and of climatic conditions.

To analyse moisture penetration into photovoltaic modules, the team simulated devices made from three different encapsulation materials and four different back sheets over a period of 20 years, as well as modules located in eight cities in four climate zones.

The Peck model, which is an acceleration model for evaluating temperature and moisture during IC failures caused by moisture in epoxy moulded components, was used to calculate the normalised power over the module's lifetime.

The team selected ethylene vinyl acetate (EVA), thermoplastic polyolefin (TPO) and polydimethylsiloxane (PDMS) as encapsulation materials. Polyethylene terephthalate (PET), tedlar-PET-tedlar (TPT), tedlar-PET-SiOx (TPSiOx) and polyamide (PA) were selected as back sheets. Their properties were obtained from published sources.

The reference photovoltaic module used EVA as the encapsulation material and PET as the back layer.

Eight cities were divided into four climate zones: tropical zone represented by Manaus in Brazil and Jakarta in Indonesia; temperate zone represented by Los Angeles in the USA and Freiburg in Germany; arid zone represented by Dubai in the United Arab Emirates and Almeria in Spain; and continental zone represented by Portland in the USA and Oslo in Norway.

The researchers verified the model using indoor experiments and outdoor simulations from the literature.

‘In our research, we found that the climate in which a photovoltaic module is installed has a much greater influence on moisture penetration than the choice of materials for encapsulating the rear layer,’ said Blom. ‘This suggests that it may be advantageous to have different photovoltaic module designs tailored to specific climates, rather than one global design solution.’

The researchers then developed a ‘simple analytical equation that can be used to predict moisture penetration’ without the need for time-consuming and computationally intensive simulations. ‘This equation contains only four unknown parameters that can be obtained from the climatic conditions of the installation site,’ explained Blom.

The less computationally demanding analytical model used empirical parameters derived from FEM simulations and achieved an accuracy deviation of less than 0.05. The researchers concluded that it can effectively predict moisture penetration in new locations without the need for computationally intensive FEM simulations.

Blom added that his team plans to conduct further simulations to analyse lifetime simulations, additional degradation mechanisms and their impact on photovoltaic modules.