Asynchronous daylight luminescence obtained without programmable power sources

Abstract

Daylight Electroluminescence and Photoluminescence techniques (dEL/dPL) have rapidly advanced in recent years and are now well-established tools for the characterization of photovoltaic (PV) Si solar modules in the field. Performing dEL/dPL requires cameras capable of working in the near IR region of the light spectrum (such as InGaAs cameras) and sophisticated filtering procedures to distinguish the weak luminescence emission coming from the PV module from the more intense ambient light. Effective filtering of the weak luminescence requires specific acquisition schemes, both synchronous and asynchronous methods can be used for this purpose. Asynchronous schemes are more convenient, but they usually rely in expensive programmable power sources that produce high quality square or sinusoidal waveforms for the controlled current injection into the PV modules. When paired with fast InGaAs cameras (600 fps), dEL images can be obtained using very short (sub-second) acquisition times. However, the requirement for these programmable power sources may be a significant barrier to rapid in-field deployment of the technique. In this work we show the results of using asynchronous daylight luminescence inspections obtained without programmable power sources, using external control to modulate a DC signal from any power source, including the neighbor panels, or even without the use of a power source but using the Sun as the light source, in the dPL case. We specifically study the shape of the generated current and voltage signals, comparing the external control case with the case of using a programable power source. We also study the impact of varying the modulation frequency and camera speed on image quality and how these acquisition parameters influence performance. This approach broadens the applicability of the dEL technique, enabling effective filtering and identification of panel defects under self-powered or sunlight-driven conditions.