Building Unifying with Concentrating Photovoltaic (BUC-PV) systems are seamlessly incorporated into building envelopes, replacing traditional construction materials while offering benefits such as on-site electricity generation, enhanced radiant efficiency, and improved thermal management. This research introduces an innovative empirical assessment of Phase Change Materials (PCM) to enhance the efficiency of less-concentrated BUC-PV systems through heat transfer mechanisms. Unlike previous studies, which focused primarily on transient and spatial temperature analyses of PCM within constructed systems, this experiment examines the impact of paraffin-based PCM on the electrical energy output of the current setup. Addressing the limitations of the initial system, an advanced evaluation model is proposed and validated through controlled indoor experiments. Wax-based RT42 (paraffin) was used in a custom PCM enclosure. An indoor test was conducted using a steady irradiance of 950 W/m². Results demonstrated a 7.57% increase in electrical energy efficiency with the integration of PCM. Additionally, the BUC-PV-PCM system exhibited a mean module temperature reduction of 4°C compared to a PCM-less outdoor system. The experiment also revealed that PCM performance varied with irradiance flux density, showing an efficiency increase of 1.4% at 600 W/m², 5.0% at 700 W/m², and 7.0% at 950 W/m².