Comparative study of monofacial and bifacial solar photovoltaic system performance in the built environment

Abstract

Recent advancements in solar photovoltaic (PV) manufacturing technology have witnessed the introduction of bifacial PV modules. The primary distinction lies in their energy generation capabilities, with monofacial modules producing energy solely from the front, while bifacial modules can generate electricity from both the front and back, resulting in higher power output per m². This study aims to analyse typical installation scenarios to determine which technology fits better for the purpose. It investigates whether placing bifacial modules close to the roof, as installers commonly do, is sensible. Furthermore, the contribution of the back surface energy production for different inclinations (15°, 30° and 90°) was assessed. Therefore, this dissertation provides answers to frequently asked questions that are commonly asked by building services engineers, given that all new and renovated buildings will need to achieve net zero-energy status after 2032, according to the forthcoming EU Energy Performance in Buildings Directive. A demonstration setup incorporating both monofacial and bifacial modules was designed and installed to serve as a test bed. Moreover, modelling using Polysun software was applied to further extrapolate the expected yield over a full year, providing valuable insights for conducting a cost-effectiveness analysis for both technologies. Results showed that as the angle of inclination increases, the energy production from the back side of bifacial modules increases, and this contribution becomes more prominent in comparison to frontside energy production on cloudy days, making bifacial modules an ideal candidate for use as sound barriers on arterial roads. Setting bifacial modules at very low angles such as 15° practically defeats the purpose of bi-faciality and this is also true for facade installations. On a micro-scale it was noted that most of the energy generated from the back occurs around solar noon. This means that the inverter needs to be sized accordingly to avoid shaving off the extra energy during peak sunshine hours. If the inverter was undersized, a practice that is widely used for monofacial PV modules, this issue can arise. In comparison, monofacial modules, showed lower overall energy yields under similar conditions, particularly when installed at higher tilt angles. Despite their higher initial costs, bifacial modules demonstrated a superior energy yield and potential for increased cost-effectiveness over time, especially in applications where space constraints and high reflectivity are factors. This highlights the importance of considering bifacial modules for installations where maximizing energy output is critical.