【Objective】To address the high lighting energy consumption of high-rise buildings and the thermal problem caused by the infrared spectral band during full-spectrum solar energy utilization, this study proposes an integrated transmission illumination photovoltaic system, namely the ITIPV system, cooled by composite phase change materials. The proposed system aims to improve the comprehensive utilization efficiency of solar energy, reduce building lighting energy consumption, and enhance the thermal stability and power generation performance of photovoltaic cells. 

【Methods】In the proposed system, a Fresnel lens is used to concentrate incident solar radiation, and a beam splitter is employed to divide the solar spectrum into visible light and near-infrared light. The visible-light component is transmitted through optical fibers for indoor lighting, while the near-infrared component is utilized for photovoltaic power generation. To control the temperature rise of the photovoltaic cells under concentrated solar irradiation, a nanographite/paraffin composite phase change material combined with cooling fins is adopted for thermal management. The addition of nanographite improves the thermal conductivity of the paraffin-based phase change material, while the cooling fins enhance heat dissipation and temperature uniformity. Geometrical optical analysis is carried out to determine the optimal arrangement of the three-lens unit and the relative positions of the optical components. Based on this analysis, visible-light and near-infrared-light transmission models are established. In addition, an indoor multi-light-source simulation experiment is conducted to evaluate and verify the photoelectric performance and temperature control characteristics of the system under different irradiation intensities. 

【Results】The results show that, under an irradiation intensity of 800 W/m², the average light transmission efficiency of the system reaches 18.9%, and the average photovoltaic power generation efficiency reaches 9.5%. With the composite phase change material cooling strategy, the stable temperature of the photovoltaic cells is reduced to 43.5 ℃, which is approximately 25 ℃ lower than that under natural convective air cooling. Moreover, within the irradiation intensity range of 200–1000 W/m², the photovoltaic cell temperature remains below 50 ℃. This indicates that the proposed cooling method can effectively suppress temperature rise, reduce heat accumulation, and ensure stable electrical output of the photovoltaic cells during operation. 

【Conclusion】Through the synergistic design of spectral splitting and composite phase change material cooling, the proposed ITIPV system realizes the efficient utilization of different solar spectral bands. Visible light is used for indoor illumination, while near-infrared light is converted into electricity by photovoltaic cells. Meanwhile, the nanographite/paraffin composite phase change material coupled with cooling fins effectively maintains the photovoltaic cells at a relatively low operating temperature, thereby supporting efficient and stable power generation. Therefore, the proposed system provides a promising energy-saving solution for buildings such as underground garages and other spaces with high lighting demand. The system exhibits stable performance, broad application potential, and practical significance for improving solar energy utilization efficiency in buildings.