Determination of the best air space value for installation of a PV façade technology based on 4E characteristics

Impact of changing the air gap, as the main geometrical characteristic of a PV façade (BIPV/T) system, is investigated to find the optimal value. It is done by considering annual CO₂ emission reduction and annual useful exergy from the environmental and exergy sides, while annual electricity production and annual recovered heat are also investigated as representatives of energy aspect. In addition to the mentioned performance criteria, three key economic indicators, namely the overall fund saving, levelized cost of electricity, and payback time, are investigated, which results in conducting a comprehensive energy, exergy, environmental, and economic (4E) analysis. The conducted 4E analysis demonstrates that BIPV/T performance is heavily dependent on the air gap. Based on the results, for the investigated building, located in Tehran, Iran, 5.45, 5.68, 19.89, and 37.86% changes in the total fund saving, annual useful exergy, annual CO₂ emission reduction, and annual heat recovered are seen when air gap varies from 0.05 to 0.25 m. Payback time is also found to be in the range of 2.2–3.5 years, which reveals that the system is completely economically viable. In addition, the conducted 4E analysis shows that the optimum value of the air gap is around 0.15 m.