**1. Introduction**

Among the few methods of gaining energy from renewable sources set in the paradigm of sustainable architecture, it is the photovoltaic (PV) modules (further termed PV panels) which have become the most promoted and used in contemporary buildings. Of the solar electric systems currently available, photovoltaic technology is the most advanced and mature [1] (p. 75). The relative simplicity of installation, skyrocketing electric rates and a comfortable accessibility of generated electrical power for household appliances make PV technology a reasonable option for homeowners as well as for an array of facilities to solve energy problems. Solar panels are becoming gradually more popular as their costs are falling, and this form of electricity generation is growing fast [2] (p. 260). Another reason for the increasing use of this technology in the building market is because solar thermal electricity costs more than PV electricity [3]. The green electrical generating systems, because of their sustainable and ecological nature, are classified as a nonmaterial tecnofact [1] (p. 68). They bring many ecological advantages not only for using renewable energy, but also for reducing carbon dioxide emissions and fostering a recommended decentralized electrical power production, which thereby achieves a higher security level, e.g., because of an increased resilience to power outages.

Architecture based on a solar energy concept is sometimes called regenerative. A regenerative system provides the continuous replacement, through its own functional process, of the energy and materials used in the operation [4] (p. 10). The energy is replaced primarily by incoming solar radiation; thus, photovoltaic systems make buildings ecological. The processes for converting solar energy to

electrical power are the most efficient regenerative energy-conversion processes. Most regenerative technologies are modular in nature, just like photovoltaic cells [4] (p. 74).

Given the constant increase in thermal requirements, PV panels have become an indispensable element of nearly zero-energy buildings (NZEBs), which will shortly be a pervasive standard model. However, the application of photovoltaic systems to buildings requires in-depth analyses to make this energy option perform well in terms of its energy efficiency, economic issues, spatial effects, as well as the esthetic values of buildings, their components, and even the plot layout.

The basic and detailed knowledge of solar systems is ample and constantly increasing. New solar technologies concerning PV panels and other electricity generating systems are extensively covered in publications. However, the complexity of the related problems is rarely considered in publications in a way that is useful for architects. Therefore, architects' viewpoints, hardly present therein, were the main reason for this research. This is what makes this paper covering these issues significant. Many other professionals analyze the problem of photovoltaic systems in a sectional scope of view, adding to the knowledge but missing the overall image of this multidisciplinary issue. A relatively complex, however, incomplete, picture of these systems can be found in some larger publications, like "*Building-Integrated Solar Technology: Architectural Design with Photovoltaics and Solar Thermal Energy*" [5] or [6]. This deals with the historical aspects of PV systems and contains a series of study cases. There are also some other published papers related to the issue [7–12], to mention a few, but none are of full practical use for architects. The purpose of this work is to enhance the knowledge of the designers of architecture by issuing a research-based study, which would encourage them to approach their creative activity in a less intuitive way, in terms of solar electricity generation. This is important as the relations between the building components and installed PV panels must be analyzed at the first concept sketches for designed buildings. To do this in a competent way, an architect should possess an appropriate knowledge before he eventually analyzes the problem with specialists in the field, who, in turn, are less knowledgeable on spatial and esthetic issues. Contributing to improvements in architects' competence makes this study purposeful.

### **2. Materials and Methods**

This research is by its nature, and the character of targeted professionals, a complex task. Its scope is closely linked to the consecutive stages of architectural design to be of practical use for designers. Therefore, the method and structure of the paper were determined, by the design procedures, as outcomes of every consecutive step; this philosophy has a very distinctive impact on the next stage and related analysis. The idea underlying the design procedure usually consists of the gradual passage from large-scale decisions to small-scale solutions. In order to deal properly and systematically with the matter of this research, which is PV panels, the first step was to carry out an analysis of a wide range of accessible PV components offered on the market. Among many solar electricity-generating systems, the technology using PV panels is crucial, as it is the most popular and frequently opted for among building investors. It also requires in-depth analyses of multiple aspects of their installation. This is the reason for which this study has been overwhelmingly focused on this technology. The study is mainly concentrated on PV panels installed on roofs, as this location is presently more exigent for them in some positions, i.e., mainly facades.

The purpose of this research is to define the conditions assuring a rational choice of devices, and a method of their use to achieve the optimum energy and esthetic efficiency, coupled with the best spatial results. Large-scale considerations, being the next stage of this procedure, are the multifaceted analyses of the location characteristics aiming at the formulation of proposals for the optimum energy generation-related layout of a given land plot. This initial task is not an easy problem because of different spatial and some other restrictions comprised within zoning plans for defined areas of cities or villages.

The determination of the mutual spatial configuration of PV panels mounted on buildings, and their position in relation to incident solar radiation assuring their efficiency, is the subsequent

stage of this logical procedure. A method of deciding on the location of these devices on buildings and their parts is the next consideration. Esthetical issues are usually not considered a scientific domain. However, in the case of architectural discussions and analyses, it cannot be excluded from the relevant research. It also makes a significant consecutive part of this study. Finally, the research deals with some other functions that the PV panels used in architecture take on, and thus contribute to a better energy efficiency of contemporary buildings. A chart with the energy yield of an analyzed house was generated by sunnyportal.com. A simulation of the insolation and shading by PV panels was made with the use of Sketchup program and the application CuricSun.

The presented multifaceted and multistaged method permits the logically interrelate subsequent stages of research-based approaches to design buildings fitted with PV panels. The use of other PV technologies has been mentioned in these considerations, but they require a somewhat different approach.
