*3.6. Other Functions of PV Panels for Buildings*

In addition to the generation of electricity, PV modules are taking on more additional functions and are hence achieving numerous synergy effects—photovoltaic panels can provide protection from the weather, sun shading, and privacy functions, or, as insulating units, even constitute the thermal envelope. In addition, they can characterize the architecture [26] (p. 106). Some authors considered sun–shade systems, in addition to roof and facade systems, as one of the three basic photovoltaic systems [7] (p. 8). PV panels as sun protective devices, if they are strategically located, and due to adequate shading analyses, can effectively fulfill this role. There are many examples thereof. This strategy can lower the costs of construction through the dematerialization effect. Among such solutions, the shading role seems especially interesting due to the constantly increasing role of overheating in buildings. It relates mainly to office buildings, where this issue is important.

The southward-oriented building volume can be designed with a complementing facade module geometry. The overall irradiation of the building can be translated to a system of modules that allows external shading from solar radiation while permitting daylight entry and unimpeded views of the surrounding landscape from inside the building [40] (p. 3608). If the application of PV panels as shading systems on south-facing elevations is comprehensible, their use on other facades can be debatable, as is the case of conventional sun protective systems.

Sun shading on east or west facades is a difficult task. Solar radiation can be especially disturbing on office buildings with north–south orientations, with the longest facades exposed to low-angle of incident sunlight. The problem was illustrated with an example of an office building for which the incident solar beams and the shading pattern by PV modules were simulated (Figure 15). The set of diagrams presented below shows the path of solar rays and the resulting pattern of dark shadow patches on the elevation assigned to every hour between 7 a.m. and 12 p.m. (Figure 16). The simulation was carried out with the computer program Sketchup with a precisely defined geolocation and application CuricSun.

(**a**) **Figure 15.** *Cont*.

(**b**)

**Figure 15.** Study of the sun shading of an office building fitted with PV panels located on geographical coordinates 50◦5.118- N and 19◦56.096- E (author: P. Filipek). (**a**) building's location, (**b**) building model and its shading pattern.

**Figure 16.** Hourly sequential shading of an office building fitted with PV panels on the east façade (**a**) At 7.00 a.m.; (**b**) At 8.00 a.m.; (**c**) At 9.00 a.m.; (**d**) At 10.00 a.m.; (**e**) At 11.00 a.m.; (**f**) At 12.00 a.m. (by P. Filipek).

Photovoltaic solar systems are applied on buildings in the form of panels that come in glossy and shiny finishes and are either opaque or semi-transparent. Reflections on this surface may make the modules highly visible at a distance and occasionally cause undesirable glare. There are some reports of blinding people in their vicinity [41] (p. 70), [23] (p. 221) and [33] (p. 1). Blinding by the reflective surfaces of PV panels can be reduced by the application of an antireflexive layer on top, and this increases the panels efficiency. This problem can be neglected in the presented analyzed office building. The location, layout, and orientation of the two main facades facing the west and east could potentially be reflective enough to blind the drivers approaching the building from the west or east along the street. However, the regular and allover application of PV panels on these two facades and the rational arrangement at an angle resulting from the analysis of sun path diagram significantly reduce this problem. A possibility exists of blinding but only from the southern approach, which is impracticable for vehicles. There are methods of reducing the glare of glazed elevations. This effect can be achieved by a nonreflective film applied to panel surfaces [42] (p. 2). This method is practical for photovoltaic façade systems. Various designs were developed for prototypical applications to integrate PV systems into rooftop gardens, with a specific focus on retrofitting flat roofs. The concurrent integration of PVs and green roofs into the same surface area can be achieved with lightweight construction, which is particularly suitable for existing buildings. Such solutions for retrofitting existing roofs must be sought to transform the current building stock into energy generating green habitats [43] (pp. 1–2).

### **4. Discussion**

This research covered issues that are now rapidly changing due to new developments in the photovoltaic industry. Given the large discrepancies concerning the energy performance and material efficiency of these systems, systematic updates of designers' knowledge is required for choosing an appropriate option. Despite the novel third-generation systems offered by producers, conventional monocrystalline panels are still the most popular choice, especially for residential buildings. However, the second- and third-generation systems are becoming increasingly popular on the market, as they are more versatile in terms of their location on buildings or their components. They also offer more opportunities in terms of their variety—i.e., flexibility and colors. Along with their improved energy efficiency, they will be implemented more frequently. Their potential for retrofitting historic buildings seems especially promising. Although all the considered PV systems are on the market in a wide variety, they are undergoing constant improvements. This applies to increasing the economy and the options for architectural integration [44] (p. 68). The applied technology covers a wide range of problems pertaining to the technical durability of buildings. PV systems may conflict with other building systems in this regard. The potential problems of their longevity may appear in the case of BIPV. The materials or components can perform satisfactorily for a long time if they are autonomous within the structure, but coupled with other materials, they might form a new and less-stable system [45] (p. 21).

Zoning plans, as a rule, do not consider the prospective use of solar systems in buildings despite such applications not being new. Their impact on planning procedures has not yet been noted or recognized. Given the analyzed spatial configurations of buildings and access streets, as well as other elements of various arrangements, this problem should be raised and broader discussions among specialists and architecture authorities responsible for planning should be inspired. Some design-established procedures practiced among professionals in the field exhibiting a traditional and meaning-limited scope of analyzed aspects during their work on zoning plans should be modified and supplemented with energy-related issues. This means that the building location on the lot and a multitude of parameters related to buildings and their parts should be an indispensable part of plans, as well as other regulations related to energy. So far, this is not the case and no serious discussions are being conducted related to this subject. The reasons for this may be the complexity of the issue, the diversity of urban grids, difficulty in properly fitting the buildings, and the building orientation. Another meaningful cause is property colliding with the optimum vegetation patterns. Harmonizing all these factors is hardly a feasible task. Discussions must be undertaken if a sustainable building and land use are to find logical solutions.

Conventional black photovoltaic panels installed on red, brown, or similar roofing materials are a frequently seen picture in landscapes. The replacement of red tiles or steel panels on existing buildings to harmonize them with the color of modules is rarely performed. New buildings offer opportunities to achieve satisfactory outcomes in this regard, as the option can be selected during the design stage. Matching the roof and panel, both in color and texture, is considered the most desirable solution from the esthetical point of view. However, when comparing the energy-related parameters of monochromatic black monocrystalline panels with the next-generation systems, which offer an increased esthetic potential, unavoidably a trade-off must be considered. As indicated earlier, monocrystalline panels are still the best option in terms of the ratio of electrical energy yield to costs. When a typical investor is faced with such a dilemma, they would, in most cases, opt for a less expensive and more efficient solution. This situation mainly refers to residential buildings. Only this segment of construction is responsible for the aforementioned controversies. The buildings of other functions are, in most cases, covered with flat roofs, which make photovoltaic roof installation invisible from the ground level. Small houses pose yet some other related problems. The more articulated the layout and roof form of a building, the less appropriate it is for the installation of PV panels, as fewer plane roof surfaces are offered, making the investment less rational. The color integration of panels and roof coverings can be considerably improved once more efficient and more affordable photovoltaic systems appear on the market and gain popularity. This could substantially contribute to an increased harmonization of the built landscape and improvement of its esthetic values.

Photovoltaic systems applied as sun protection modules, as analyzed earlier, are steadily appearing on more office buildings. They generate the most energy when exposed and inclined to the south. This occurs both on roofs and facades. East and west elevations are less efficient as their insolation is reduced merely to the half of the incident on the south-exposed walls. However, it does not make such applications useless. A reduction in the heat load due to the use of solar protective PV panels could at least partly compensate for the extra expenditure on the panels. This disadvantageous orientation of a building from the analyzed point of view, as an alternative installation of solar systems on flat roofs characteristic of office buildings, is not an encouraging solution. The reason for this is the longitudinal roof layout extended along the north–south axis, which is disadvantageous due to the limited amount of PV modules that would fit in the space given the necessary long distancing of adjacent panels in the space-consuming row arrangement mentioned earlier. A remaining question is the installation of PV panels on facades of multistory buildings. They are not yet economically feasible, as was calculated for a commercial building in the 10- to 20-story range (USA) [7] (p. 104).

The problem of blinding in the case of large glazed facades is potentially important when they are perpendicular to the direction of pedestrian or driver movements. Therefore, installed exterior sun protective systems can be an effective solution to reduce glare. A reasonable proportion of PV panels play that role, provided they are mounted on facades in the configuration depicted in Figure 15.

Findings from surveys on public educational barriers showed various reasons for a poor public understanding of the cost perceptions of BIPV systems and their financial benefits, and a lack of enough knowledge by clients and the public in general. Additionally reported was a high negative perception of the system price and costs associated with aesthetic BIPV options. The lack of knowledge on how to ensure the most efficient choice of BIPV design was also noted [46] (p. 5). All of this highlights the need for further relevant written contributions. The application of BIPV systems will progress in the near future, but some practical barriers remain, such as investment costs and the payback times of the solar energy technology, which are highly important for real estate developers.

### **5. Conclusions**

Photovoltaic systems are an indispensable part of contemporary low-energy buildings. Their increasing popularity is linked to them being the cheapest and easiest method of making new and existing buildings at least partly sustainable due to using a renewable source of energy (solar energy), hence the financial support offered for their installation in special state programs in many countries. Their application requires specific knowledge from designers and building specialists. The systemic approach to the issue of suitable design decisions, which was presented in this study, entails the need for analyses of factors like: the spatial and technical parameters of a building, an in-depth study of site features including the orientation of building and its relation to the access street and other built structures on the building lot, as well as the position and type of vegetation. This broad view facilitates the choosing of the optimal solution to obtain the desired energy efficiency of the applied PV system.

Another problem of increasing significance is the esthetics concerning features such as building materials and their color and texture in terms of their harmony with PV panels, which are frequently considered inconsistent with buildings' traditional esthetic values. Building designers and investors have offered various systems that feature different characteristics covered in this research. This study was designed for architects to enhance their knowledge on this subject and to systematize the knowledge, providing a step-by-step process with the proposed procedure of suitably coupling designed buildings with photovoltaic systems. Notably, obstacles remain on this path, including an insufficient and obsolete knowledge of these systems, potential problems with their implementation, and mistrust of investors wary of potential excessive costs. However, some positive experiences with photovoltaics and imaginative thinking would help further the application of photovoltaic solutions in building developments and related industries. This promising vision should encourage further studies on the subject.

**Author Contributions:** The co-author contributed actively to the illustrations, discussion of this research and in reviewing the article. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
