Thermal and optical properties of semi-transparent amorphous silicon BIPV for building application

A new type of poly-crystalline amorphous thin film photovoltaic module with high visible light transmittance was developed for use in a building. The method of PECVD (Plasma-enhanced chemical vapor deposition) was applied to produce satisfactory high color rendering index (HCRI) BIPV module of good quality with visible light transmittance as high as 26.9%, solar radiation absorptance below 60% and shading coefficient equal to 54%. The thermal and optical properties of HCRI BIPV module are studied in some detail and the results reported. The thermal conductivity and diffusivity of HCRI BIPV module are less than that of Si-based BIPV. The HCRI-BIPV module appeared to be effective in improving the visible transmittance and reducing the absorptance, but the value of SC of HCRI-BIPV module was higher than that of Si-based BIPV. This indicates that there is still a trade-off between day lighting and thermal insulation for designing an optimal BIPV module. Further thermal performance work conducted by a small-sized hot-box with a solar simulator lamp revealed that heat is mostly absorbed by the HCRI-BIPV and a small amount of heat is conducted into building. The surface temperature on both sides of Si-based BIPV reached a steady state is faster than that of HCRI-BIPV due to the higher thermal diffusivity. This can have important practical implications on the fabrication of low-cost, high visible light transmittance of BIPV module.