Enhancing Bifaciality Factor for Building Integrated Bifacial PV in a Double Skin Façade System

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The British University in Dubai (BUiD)
On a global scale the move towards renewable energy is at its highest rates, new technological developments aiming to increase efficiency of energy production and reducing overall cost, making renewables viable on all scales. United Arab Emirates is one of the countries that are pioneering in the area of renewable green energy, with the goal is to increase the contribution of green energy up to 50% by the year 2050 and reduce the carbon footprint by 70 % by increasing consumption efficiency and introducing versatile energy sources that are more sustainable. Considering that the region solar energy provides prospects in terms of energy yields and project scalability. Specially within the building sector, which is an energy demanding sector, lies the opportunity to cover the energy requirements through implementation of localized solar energy generating schemes in the form of standalone PV panels and building integrated photovoltaics. Moreover, applying novel innovations in solar power to maximize energy yields. One of these technologies is bifacial photovoltaic panels, which is a type of PV panels that produce electricity from both sides compared to regular Monofacial PV that utilize the front surface only. Studies shows that bifacial panels produce 25-40% more electricity than Monofacial panels in all installation schemes. This research examines the application of bifacial PV integrated within building elements, specifically double skin façade, where the Bifacial PV presents the second outer façade in a double skin façade configuration. The study objective is to analyze the bifaciality factor under different façade material and façade gap distances using ray tracing computer simulation software (TracePro). Bifaciality factor is the ratio of irradiance hitting the rear of solar panel to the total irradiance, which is a parameter to evaluate the performance of bifacial PV panels. The optical performance of the façade envelope directly affects the value of bifaciality factor (bifacial back side irradiance to bifacial front side irradiance). Bifaciality factor significantly impacts electrical energy production of bifacial PV cells, and it is the main factor when comparing different bifacial PV technologies. To answer the question of which façade material provides the highest bifaciality factor, therefore, the highest electrical yields of bifacial BIPV as part of a double skin system, computer simulations for optical performance were analyzed. The simulation matrix applied in this study consists of four façade materials: clear glass, reflective glass, white paint cladding and diffused white paint cladding. Each façade material was simulated for four different gap distance (0.5, 1, 2 and 3 m). The ray tracing simulation applied a solar emulator specifically for Dubai UAE solar profile. Simulation results were provided as Irradiance maps with data like façade incident irradiance, bifacial back surface incident irradiance, bifacial front surface incident irradiance and number of rays exiting each surface. Bifaciality factor was calculated using Excel for all simulation scenarios. The simulation with the highest bifaciality factor is Scenario No.13, which is the scenario of diffused white paint cladding for a façade gap distance equal to 0.5m. With bifaciality factor of 14.32%, followed by S5, Bifaciality factor of 13.74%, presenting reflective glass façade with 0.5m gap distance. It was noticed that across the same façade material increasing the gap distance reduced the Bifaciality factor, that reduction was the highest between gap distance of 1m and 2m, almost half for all façade materials.
BIPV, TracePro, bifacial photovoltaics, ray tracing, double skin facade, renewable energy