Attenuation of Irradiance by Water for Potential Solar Photovoltaic Systems Applications

Abstract

This study explores the feasibility of submerged photovoltaic (PV) systems as a supplementary energy source for autonomous underwater vehicles (AUVs), which are widely used in ocean exploration, remote sensing and marine monitoring. Given the limited operational durations of conventional energy sources like lithium-ion batteries and piezoelectric propulsion, the integration of PV systems offers potential for extended deployment by harnessing solar irradiance in the upper water column. The research combines theoretical modeling and experimental analysis to investigate irradiance attenuation through water samples with varying densities (1036, 1025 and 1000 kg/m^3), represented by attenuation coefficients of 0.2,0.1 and 0.04 m^(-1) respectively. A submerged polycrystalline photovoltaic (PV) system was tested under these conditions, and water properties for all samples, including pH (7.65), salinity (0.03 psu), total dissolved substances (TDS) (25.6 ppm), conductivity (51.3 μS/cm), and resistivity (19.3 kΩ.cm) - were measured for their influence on irradiance attenuation as it propagates through the media. Potassium and sodium concentrations were inferred as 2.8 ppm and 12 ppm using emission intensity calibration. Results showed a notable irradiance drop from 1000 W/m^2 (air mass AM 1.5) to 450 W/m^2 at the surface and 360 W/m^2 at 18 cm depth, with a maximum power output of 37 W, which is sufficient for many shallow-water AUVs requiring 20-200 W. These findings highlight the critical role of water composition and depth in optimizing underwater solar energy harvesting, supporting the advancement of sustainable power solutions for persistent marine operation.