Exergy analysis on daylighting with a single-paned glass window and PV-based electric lighting

Abstract

This study aims to evaluate two representative pathways for utilizing solar radiation in a building for indoor lighting using exergy analysis: (1) direct daylight utilization through a window system and (2) indirect utilization through electric lighting powered by photovoltaic (PV) systems. While both pathways contribute to reducing fossil fuel consumption and advancing sustainability goals, their thermodynamic performance in terms of exergy has not been well studied. Using a case study of a 15 m 2 floor area with a 4 m 2 south-facing window, the exergy flows associated with daylighting and PV–LED (light-emitting diode) lighting were evaluated. Exergy analysis was applied to calculate the solar exergy input, exergy consumption, and visible light output for each pathway. The results show that the engineering-based PV–LED pathway consumes more than 90% of the incoming solar exergy. Path A, the PV–LED system, exhibited higher exergy consumption due to the conversion of solar radiation into electricity and subsequently into visible light. In contrast, Path B, daylighting, avoids multistage electrical conversion losses. Ultimately, most of the solar exergy is converted into low-quality thermal exergy. These findings support prioritizing passive lighting strategies in architectural design from an exergy perspective.