It has long been known that the efficiency of solar panels can decrease over time due to the voltage difference between the solar cells and the grounded frame – a phenomenon known as potential-induced degradation (PID). Most conventional photovoltaic modules today are designed to be PID-proof. However, with the voltage of new solar systems set to increase from 1000 volts to 1,500 volts, the question of PID is back on the agenda.

Anticipating this, the Centre for Solar Energy and Hydrogen Research (ZSW) in Baden-Württemberg, has developed an extreme test called NELL (“Novel Encapsulant for Long Lifetime high voltage resistant PV modules”) which can provide more detailed information about the resistance of various modules.

Within the framework of the European research programme SolarEraNet (funded by BMWi), the project compared the resistance of two solar cells embedded with different PID-resistant materials in a series of tests. First the cells were treated with the standard material EVA-1, then with an improved PID-resistant material EVA-2, and finally, they were embedded with a new material, polyolefin elastomer (POE).

Critically, it was found that after subjecting the modules to tests amounting to decades of operation and up to 2,500 volts, the EVA-1 suffered a performance drop of only 5 percent after two years, while the EVA-2 suffered a 5 percent loss only after 22 years, and the POE variant modules showed absolutely no sign of PID after 60 years.

Peter Lechner, head of the ZSW’s SOLAB, says in a German press release: “The embedding material of the solar modules has a great influence on PID resistance. Modules with POE are absolutely stable here”.

As more and more solar systems and inverters are designed for 1,500 volts – especially those used by solar parks and commercial roof systems – the results should provide reassurance for manufacturers, construction planners and investors alike.