Evaluation of indoor photovoltaic power production under directional and diffuse lighting conditions

Abstract

This work proposes a detailed method to estimate the amount of power produced by photovoltaic energy harvesting in realistic indoor conditions, not only featuring artificial light sources and low levels of irradiance (0.1–1 mW/cm2) but also oblique directional and diffuse lighting. The method is based on a model of performance of a commercial silicon and an organic solar cells under diffuse and oblique light and on simulations of indoor light in a rectangular room of various dimensions. It is found that the solar cells absorb diffuse light almost as efficiently as if it were direct normal light. Diffuse light accounts for 30% to more than 70% of the total illuminance in the indoor configurations investigated. Indoor, the angle of incidence at the point of maximum illuminance on a wall depends solely on the directivity of the source and is usually comprised within 30o-60°, representing 15%–50% of power loss compared to normal incidence. The organic cell can achieve a power generation of up to 27 μW/cm2 under 600 lux in a 4 m2 room, and at least 7 μW/cm2 under a typical indoor illuminance of 200 lux. The performance of the organic cell is found superior to the commercial silicon cell used in this study (7 μW/cm2 under 600 lux), even if the power conversion efficiency of the silicon cell under one sun (12.7%) is higher than the one of the organic cell (5.4%).