## 4 Discussion  
This study has encapsulated 24 BIPV modelling projects in terms of design features, energy consumption, and cost aspects. Three typical building types are analyzed: residential, office, and historical BIPV projects. Model-based design and analysis enabled estimations of costs and energy balance benefits, along with their compliance with regulations. The 24 analyses related to the 12 separate countries by indicating incentives, electricity tariffs for production and consumption, as well as specific regulations. More modeling and synthesis were required to make an overview of BIPV projects, which was the study attempt. The data availability was one of the primary concerns in building selection, such as their 3D sketches and their consumption profiles and other characteristics. Country-specific incentives and the fame of the building also played a role. Consequently, the majority of the projects investigated were located in the EU or other developed countries due to data availability (20-55\({}^{\circ}\) N, except one in Sydney, Austria). Some outliers appeared, as the feed-in tariffs were too low or employed expensive modules. After excluding outliers (5/24), the payback time ranged between 6 and 18 years, with a mean value of 13 years overall, and 10 years for residential and office buildings. Many residential building cases obtained high levels of self-sufficiency (110%). Out of seven residential buildings, the majority (five) were NZEB from the perspective of electrical demand. However, none of the office buildings, and only two of historical buildings, were able to attain NZEB and 100% (or above) self-sufficiency. This could be argued to be due to offices' high energy demands--greater even than residential buildings. For historical buildings, the design features to be respected led to occasional non-optimized energy yields on BIPV. These two types of buildings could become more energy efficient in the near future through the use of isolation materials of BIPV that could contribute to air conditioning or heating of the building, and light management of the interior--all of which were outside the scope of our study. Another solution to increase self-sufficiency would be to install more capacity over more areas, such as parking spots, etc. Certain technical aspects, such as degradation of the PV modules or cables, are typically assumed to be included in the maintenance cost, yet a yearly degradation output of 0.5% could be applied--a figure which will not significantly affect the results. The ROI was based on the LCOE approach, Capex and Opex, as described in Section 2. Assuming that the Capex would already be possessed, loan rates were therefore ignored. Net present value was also investigated for some cases, reaching 8-10 years for a return on investment. In favorable conditions, subventions and government incentives could be used to decrease the projects' initial costs. For certain projects, the costs were very high, even with mild assumptions. Additionally, the projects calculated the module installations themselves, and do not consider the avoided material costs of replacing building materials. However, the cost per kWp was typically assumed to be low (300 \(\text{\text{\text{\text{\text{\text{\text{$\epsilon$}}}}}}/\text{m}^{2}\)), hence BIPVs are likely to be less expensive in the near future when the niche market moves to the mass market [59]. Limitations concerning the software tools for round geometries also restrained certain designs. Figure 7 shows how the students would have liked to create BIPV modules to be installed and that those visually specific modules demanded too much computational power or were not supported by BIMsolar. Since the present study was done on existing architectural objects, it is important to stress a need for every solution to be examined from an architectural perspective.