Advances in the operating condition design analysis of air based photovoltaic thermal solar roof systems

Air based photovoltaic thermal (PV/T) solar systems combine the technologies of electricity generating PV cells and active solar energy to supplement the electricity and heating loads of buildings and potentially reduce energy consumption. There has been a significant amount of research on these systems over the past 30 years in which many researchers have investigated the merits of these systems. However, there is a lack of research on the energy efficiency of the proposed air based PV/T solar energy system when applied to buildings in various climates. This study provides information on the analysis of the energy efficiency of an air based PV/T solar roof system when integrated with a building’s existing HVAC system in various climates within the United States. Specifically, this study utilizes a computational and numerical analysis program that incorporates computational fluid dynamics (CFD) to investigate detailed fluid flow and heat transfer. The CFD simulations were carried out over a wide range of conditions to compute the inlet mass flow rate, momentum fluxes, fluxes of energy, and ultimately the thermal effectiveness of the solar roof system. The results showed that thermal conversion efficiency greater than 70% can be achieved with proper air channel depth, air mass flow rate, and a longer air channel length. Additionally, the results showed that performance of the proposed air based PV/T solar roof system eventually hits a maximum and that the level of incident solar radiation does not play a significant role once the system’s thermal efficiency is near the maximum range. Together, the findings suggest that the proposed air based PV/T solar roof system can be effective in various climates. In addition to the CFD simulations, this study performed whole-building annual energy simulations, using the EnergyPlus program, to obtain comprehensive insight in the understanding of the performance of an air based PV/T solar roof system for various climates within the United States. Two computational case study models, a small commercial office building and a quick-service restaurant were selected for this study. These were chosen because they are both designed with a Gable roof which can potentially expose half of the roof area to the sun depending on the roof configuration and orientation. Six different climatic zones within the United States were developed based on by the amount of insolation and the need for space heating. Local weather information of 28 cities was used in the simulations and analysis. The findings from the annual building energy simulations demonstrated that climatic Zones 1 and 2, which have the highest mean daily total insolation, achieved the highest energy savings. In Zones 1 and 2, the small commercial office building showed an average of 31.1% in heating gas consumption savings and an average of 277.4 GJ in annual PV electricity production. As for the quick-service restaurant, an average of 40.7% of heating gas consumption was saved and an average of 230.9 GJ in PV electricity was produced in Zones 1 and 2. Results further show that the gas energy savings is proportional to the mean daily winter insolation and that energy saving of gas and electricity can be achieved in various climates within the United States using the air based PV/T solar roof system. It is also important to note, however, that the air based PV/T solar roof system is not able to handle the entire heating load of a building but rather can supplement the existing HVAC system. Finally, a cost benefit analysis was also performed to evaluate the economic merit of the proposed air based PV/T solar roof system. Calculations showed that the estimated payback period in Flagstaff, AZ (Zone 1), Atlanta, GA (Zone 3), and Minneapolis, MN (Zone 6) are all less than six years