Highly Resolved Spectral Responsivity for PV Modules

Accurate spectral responsivity (SR) measurements are crucial for evaluating and improving photovoltaic (PV) module performance. This work presents a refined approach derived from the Differential Spectral Responsivity (DSR) technique pioneered at PTB, extended by incorporating a tunable laser source and a laser beam homogenizer (LBH). Spanning 280 nm to 1320 nm, the system offers a highly monochromatic irradiance that enables detailed SR characterization across the entire active area of small PV modules. A central challenge in measuring SR for PV modules—rather than individual cells—is the series connection of cells and larger total size, requiring uniform illumination and proper signal detection at various operating conditions. To address these requirements, the proposed method employs a chopped laser beam, lock-in detection, and impedance converters in tandem with a bias light from an LED-based solar simulator, ensuring consistent short-circuit current monitoring and precise SR measurement. Experimental results on a 1 m × 0.75 m module confirm reliable performance across a broad wavelength range, though some deviation appears between 900 nm and 1050 nm with or without bias irradiation, while the LBH design—though not free of non-uniformity—remains essential for achieving the required beam quality.