Elevational Earth-Sheltered Buildings with Horizontal Overhang Photovoltaic-Integrated Panels—New Energy-Plus Building Concept in the Territory of Serbia

Abstract

The global scientific community is intensively promoting energy-plus buildings. Following the leading world trends, this paper presents a new energy-plus building concept—elevational earth-sheltered buildings with three different types of horizontal overhang photovoltaic-integrated panels: wooden support columns covered with clay tiles, steel pipes as support columns covered with sheet steel, and concrete support columns with concrete coverage. In this instance, the specific multi-numerical case study building model for the city of Kragujevac (located in central Serbia with favorable climatic conditions) was performed over 7 months (from 1 October to 30 April), taking into account the soil temperature, the effects of solar shading, the performance of the heating system—a ground source heat pump—and the characteristics of the artificial and automatic lighting control system. The simulation results show that the optimal depth of a horizontal overhang (energy-plus status) depends on the occupant’s habits, in addition to meteorological conditions. The presented methodology can be used for any other location, both in Europe and the world.

1. Introduction

The development of the concept of energy-efficient buildings (EEBs) arose from the need to bring the (primarily) residential sector closer to sustainable development [1]. However, certain studies for the year 2021 showed that the EU residential sector uses 24.7% of the total final energy consumption [2]. The greatest amount of this energy is used for heating (64.4% [3]). The Serbia residential sector, with a share of 35.8% [2], is in a more difficult situation, although several legal documents in the field of energy efficiency (for example, building energy ratings (BERs)) have been prescribed and adopted since the beginning of the 21st century [4]. As time goes on, it is certain that the EU energy community will be increasingly strict about final energy consumption in the residential sector and will work even more intensively to implement EEBs (Figure 1). The mentioned trends will not bypass Serbia either, so it is desirable to catch the connection as soon as possible because the existing buildings will be in an increasingly unfavorable position.

Today, great attention is paid to the shape of buildings [6,7], their orientation [8,9], the mutual distance between buildings and building density [10,11], vegetation use [12,13], maximization of daylight use [14,15], the use of modern construction materials [16,17], and shading devices, which will be chronologically (from 1998 to 2024) analyzed below. In [18], the effects of passive cooling using window overhangs for a building located in Shiraz (Iran) were investigated experimentally and theoretically. The results of a 1998 study showed that the annual final energy consumption for cooling can be reduced by over 12%. The paper also determined the optimal dimensions of overhangs for buildings located at latitudes of about 29.6° N. In 2005, Ossen et al. used a dynamic energy simulation program supported by the DOE2.2 calculation engine to determine the energy consumption for artificial lighting because the overhangs reduce the level of daylight [19]. In a review paper published in 2012, the effects of building shading and their importance for energy savings were analyzed [20].

Determining the optimal dimensions of overhangs above windows on the south facade wall of a building physically made in line with energy efficiency recommendations for the area of Souidania (Algeria) is presented in [21]. In addition to the experimental approach, numerical dynamic simulations (using TRNSYS 16 software EnergyPlus 7.1) were also used in this paper. In the same year (2014), the effects of window shading on high-rise buildings were published in two papers. The first high-rise building was located in Seoul (Republic of Korea) [22]. The second high-rise building was located in Taipei (Taiwan) [23]. For example, the results in [22] showed that the final energy consumption for cooling can be reduced by more than 20%. One more review paper (for different types of shading devices for windows [24]) was published in 2014. Two interesting papers [25,26] were published in 2016. In [25], the use of overhangs as a potential building facade for improving single-sided ventilation performance was analyzed. The influence of horizontal overhangs (HOs) and glazing with special spectral radiative properties on the annual thermal balance of buildings, as well as the thermal and visual comfort of the users, is presented in [26].

Research from 2017, available in [27], focused on the effects of passive cooling and the effects of passive heating. The authors concluded that the overhangs could, on the one hand, reduce the annual final energy consumption for cooling, but they could also increase the annual final energy consumption for heating on the other hand. In other words, the optimal dimensions of the overhangs should be carefully determined. Bojić et al. [28] used the Hooke-Jeeves algorithm and the EnergyPlus 7.0 software Google SketchUp 8 to numerically determine the optimal depth of HOs for a residential building located in Belgrade (Serbia). Concrete HOs were positioned on all facade walls. The simulations were performed during the summer period, so only cooling energy consumption was monitored. The optimization algorithm used takes into account embodied energy and primary energy. A review of energy savings using solar control techniques and optimal building orientation for the strategic placement of facade shading systems is presented in [29].

The possibility of using shading devices in the educational building in Madurai (India) was investigated in [30] in 2018.

Unlike most works, Liu et al. [31] paid attention to nontransparent facades and their shading to achieve energy savings (study from 2019). They used various types of horizontal and vertical shading devices, with different positional angles about the facade walls, to show that the greatest energy savings (up to 8%) are achieved by shading the western nontransparent facade walls. Rashid et al. investigated the redistribution of energy flows for three thermo-technical systems (passive cooling, artificial lighting, and mechanical cooling) for three types of external sun shading devices (one HO, multi-vertical fins, and an egg-crate device) [32].

The results of Sghiouri et al. (2020) showed that automated movable shading in the building located in Maroco is the most effective solution for passive cooling [33]. The research presented in [34] by Nikolić et al., in fact, is a continuation of the research presented in [28]. Here, the subject of numerical research (also using the Hooke-Jeeves algorithm and EnergyPlus software) was a building (also located in Belgrade, Serbia) with two floors. The shading devices were balconies (for the ground floor) and roofs (for the first floor). With optimal dimensions for the mentioned HOs, the annual total primary energy consumption (for heating, cooling, and lighting) can be reduced by over 7%.

In 2021, Krarty compared movable (with different working principles) and fixed window shading devices that would be applied to US buildings in Phoenix and San Francisco [35]. The advantage of movable shading devices over fixed ones depends on the size and type (number of layers, type of material, etc.) of the window, their orientation, and weather conditions (time of day and year). Mobile shading devices can save 45% more energy for air conditioning compared to fixed shading devices for buildings with a window–wall ratio of 30%. In [36], Krarti continued his research in the area of solar shading. He placed PV panels on movable superstructures with a horizontal axis. If such devices were placed above the windows on the southern facade walls, the energy savings would be up to 6% for overhangs without PV panels and up to 35% for overhangs with PV panels. In general, for locations with warm climates, the savings could be over 90%.

Koç et al. [37] created 1485 scenarios with fixed shading devices to reduce the final energy consumption for cooling an office building in Turkey (a study published in 2022). By using a comprehensive approach, they managed to reduce the annual final energy consumption for cooling by 70%. Mohammed et al. installed seven types of shading devices on the Darwin town hall building (Australia) and achieved savings of 15.5% [38].

In 2023, two interesting papers were published. Corti et al. [39] presented a review work of external integrated systems as photovoltaic (PV) shading devices, while [40] presented a design framework of an automatic shading device based on a sun path diagram.

Dong-Hyun et al. (a study from 2024) presented a paper [41] that proposes a high-precision methodology for optimizing dynamic shading device systems using the genetic optimization algorithm. Jiang et al. [42] analyzed energy consumption and daylighting control in office buildings using dynamic PV shading devices. Energy savings in office buildings can be achieved between 32.13–50.38%.

It is clear that in the future, EEBs will strive to maximize the passive use of renewable energy, primarily solar energy, geothermal energy, and wind energy. It can also be expected that the bioclimatic-passive strategy, which promotes the use of earth-sheltered buildings (ESBs) [43,44], again, becomes a subject of wider interest, although it has always been used in human civilization as a construction concept.

The scientific community is working hard to popularize ESBs. In the recent past, the energy, environmental, and economic performance of these buildings have been the subject of many studies and projects in different countries: Nigeria [44], China [45], Egypt [46], Russia [47], the USA [48], Brazil [49], Iran [50], etc. On the other side, the negligible presence of ESBs on the territory of Serbia (despite a certain number of works by Milanović [51,52] and Nešović [53,54]), both in traditional and contemporary architecture, has a multi-layered background: historical, cultural, sociological, economic, climatic, typological, and pedological. Although thermal comfort has been positively evaluated, high investment costs, problems with moisture, sound and visual effects, etc., have, in the past, created another negative background in terms of structural elements. The current rulebook on the classification of buildings in Serbia [4] does not recognize ESBs. The same applies to other accompanying legal documents.

In this paper, the subject of research is elevational earth-sheltered buildings (ESBs) with horizontal overhang photovoltaic-integrated (HOPVI) panels. The authors think that a bioclimatic-passive strategy combined with a passive solar shading device (HO), energy-efficient thermo-technical systems (PV panels, a ground source heat pump (GSHP), and an artificial and automatic lighting control system (AALCS)), as well as people’s responsible habits, can reach EPB status. In other words, drawing the attention of the scientific public to the great importance of ESBs using HOPVI panels as future EEB trends is the main motive of this research.

The work is based on numerical simulations. The EnergyPlus software uses the finite difference method (FDM) to determine energy flows in ESB with HOPVI panels, while the Siemens Femap 2020 software Siemens Femap 2020 uses the finite element method (FEM) to determine the degree of safety of shading devices (the first novelty in this research).

According to the comments given in [27], the potential EPB status of ESBs using HOPVI panels was investigated during the heating season (from 1 October to 30 April) in a moderate continental climate (the second novelty). Contrary to [28], a breakthrough was also made because three completely different types of HOs were considered (the third novelty): wooden support columns covered with clay tiles (first model), steel pipe support columns covered with sheet steel (second model), and concrete support columns with concrete cover (third model).

The energy and ecological indicators of ESBs using HOPVI panels were determined and are presented here: final energy consumption, primary energy consumption, CO₂ emission, embodied energy, and total energy consumption.

2. Description of the Elevational Earth-Sheltered Buildings

2.1. Construction Physics

The subject of the research is elevational ESBs (Figure 2). The length of the building is 20.5 m, the width is 5 m, and the height is 2.6 m. The total area is A_esb,gf,tot = 102.5 m². The form factor is A_esb,tot/V_esb,tot = 1.267 l/m, while the window–wall ratio (WWR) is A_esb,ww,tot/A_ebs,wl,tot = 0.16 for the south, free facade. An isometric view of an elevational ESB is shown in Figure 2.

A family of four lives in the elevational ESB all year round. The building consists of eight rooms, i.e., thermal zones (Figure 3): BDR1 (17.5 m²), BDR2 (9 m²), BDR3 (9 m²), BAT (6 m²), H (26 m²), LR (25 m²), K (6 m²), and SR (4 m²). BDR1 is intended for the parents, while each child has their room (BDR2 and BDR3). According to basic architectural principles, all rooms (except SR) are exposed to the Sun by the southern facade wall, so all transparent elements (windows and entrance door) are positioned on them.

The elevational ESB is modeled on the Rulebook on Energy Efficiency of New Buildings [4]. The adopted values for the air change for each thermal zone n_z [h⁻¹] are the following: n_z = 0.5 l/h (BDR1, BDR2, BDR3, H, LR, and SR) and n_z = 1.5 l/h (BAT and K). The adopted U_ad [W/(m²K)] and allowed, i.e., maximum U_max [W/(m²K)], values for all the construction elements of the analyzed building are presented in

Table 1. Heat transfer coefficients of construction elements.

Construction Element	Uad [W/(m2K)]	Umax [W/(m2K)]
Floor on the ground	0.3	0.3
Exposed facade wall
Facade wall in the ground		0.35
Flat roof above unheated space	0.15	0.15
Flat roof above heated space		0.3
Window	1.5	1.5
Entrance door	1.6	1.6

.

2.2. Performance of the Heating System

During the analyzed period (from 1 October to 30 April), 98.5 m² of the elevational ESB was thermally treated (SR is an unheated room, Figure 3).

The central heating system using a GSHP was selected (Figure 4). The coefficient of performance COP [-] of the GSHP is COP = 4.56. The nominal power of the condenser is 7.3 kW. The nominal power of the compressor is 1.6 kW. On the outside, the GSHP is connected to two geothermal vertical probes (GVPs). The depth of the GVPs is 73.2 m (each), so the total nominal power is 5.7 kW.

Each room (on the inside) is equipped with a suitable floor panel heater (FPH) and a thermostat (Figure 4). The thermostat regulates the mass flow rate of the working fluid (water) to maintain the desired internal ambient temperature (20 °C, valid for all heated rooms).

2.3. Performance of the Lighting System

Each room (except SR) is equipped with artificial lighting (AL). In this case, surface-mount lights (SMLs) were adopted. The technical characteristics of SMLs (according to the recommendations from [55]) are presented in

Table 2. Technical performances of SMLs.

Room (Zone)	(Pe,l)z [W]	(Le,l)z [lux]	RAF [-]	FR [-]	FV [-]	CHG [-]
BDR1	27	100	0	0.72	0.18	0.1
BDR2	18
BDR3
BAT	54	700
K
LR	36	100
H	18	50
SR	No lighting system

.

All rooms with SMLs are equipped with day-lighting control systems (DLCSs). The DLCS measures the intensity of solar illuminance through a reference point. In Figure 5 (example for LR), it can be seen that the DLCS device (reference point) is located in the middle of the room and at a height of 800 mm (this applies to each room, except for H and SR).

The DLCS and SML are interconnected within each zone. When the solar illuminance is not sufficient to achieve optimal values, i.e., set values (Table 2), then the DLCD activates the SML, which supplements this difference artificially (with electricity consumption). The SML and DLCS together form the artificial and automatic lighting control system (AALCS). The working time of the AALCS during the analyzed period was from 06:00 to 22:00.

3. Description of the Horizontal Overhang Integrated Photovoltaic Panels

3.1. Performance of the Horizontal Overhangs

The following types of HOs are most often used in the city of Kragujevac: wooden support columns covered with clay tiles, steel pipe support columns covered with sheet steel, and concrete support columns with concrete coverage. Accordingly, in the following figures (Figure 6, Figure 7 and Figure 8), corresponding models of HOs were created: model HO-1 (Figure 6), model HO-2 (Figure 7), and model HO-3 (Figure 8), respectively.

In order to create the HO-1 model at a total height of 2.9, the following profiles were used (Figure 6): vertical wooden posts with hairpins (1) and horizontal wooden beams (2) with a square cross-section of 150 × 150 mm, horizontal slats with cross-sections of 100 × 50 mm (3) and 50 × 50 mm (4). The overhang is covered with clay titles (5) with a thickness of 25 mm.

The geometric characteristics of the HO-2 model are the following (Figure 7): vertical (1) and horizontal (2) steel pipes with a square cross-section of 40 × 40 × 1.5 mm, steel pipes (3) with a rectangular cross-section of 80 × 20 × 2.5 mm, steel pipes (4) with a square cross-section of 20 × 20 × 1.5 mm, and steel sheets (5) with a thickness of 0.5 mm.

The HO-3 model has the simplest design (Figure 8). The vertical concrete columns (1) have a square cross-section of 200 × 200 mm, and the horizontal concrete slab (2) is 100 mm thick.

The mechanical and thermal characteristics of the supporting columns and covers for the different models of HOs (HO-1, HO-2, and HO-3) are presented in

Table 3. Mechanical and thermal performances of HO models.

Model HO	HO-1		HO-2		HO-3
Construction	Supporting Columns	Cover	Supporting Columns	Cover	Supporting Columns	Cover
Material	Wood	Clay titles	Steel pipes	Sheet steel	Concrete
Ym,ho [GPa]	12.5	13.79	200	210	26.3
νho [-]	0.55	0.2	0.3		0.2
ρho [kg/m3]	700	1384	7850		2400
eho,emb [MJ/kg]	26.9	4.3	38.8	79.6	1.1
Source	[56]	[57]	[58]	[59]	[60]

.

According to the recommendations from [61], the production of steel sheets requires the greatest energy investment (97.6 MJ/kg; Table 3). In second place is the production of steel pipes (38.8 MJ/kg). In third place are the wooden elements (26.9 MJ/kg). On the other hand, HO-3 consumes the least amount of energy (1.1 MJ/kg, Table 3).

3.2. Performance of the Photovoltaic Panels

Solar radiation is incoming onto horizontally placed PV panels—according to the design of the HOs (Figure 6, Figure 7 and Figure 8). The PV panels cover the upper surface of the HOs (HOPVI design). The efficiency of the PV panels is 20% (adopted value), and the embodied energy is 585 kWh/m² [62].

4. Location Parameters

4.1. Meteorological Data

Serbia (with time zone + 1 h) is a continental country in the Balkans. The climate is moderately continental (central and southern regions) and continental (northern regions), with distinct seasons. The summers are hot and humid. On the other hand, the winters are cold and snowy [63]. On the website Climate.OneBuilding.Org [64], meteorological data are available for a large number of cities in Serbia, including Kragujevac, i.e., KG (Figure 9).

During the analyzed 7-month period (from 1 October to 30 April), the average monthly temperature (Figure 10a) ranged between 0.39 °C (January) and 13.39 °C (October). The average monthly wind speed was higher than 2 m/s in November and February (Figure 10b). South and southwest winds were dominant under the influence of the Mediterranean climate (Figure 10c), with an attack angle between 200° and 250° (180° is for the south wind, and 270° is for the west wind).

During the analyzed 7-month period (from 1 October to 30 April), the average monthly temperature (Figure 10a) ranged between 0.39 °C (January) and 13.39 °C (October). The average monthly wind speed was higher than 2 m/s in November and February (Figure 10b). South and southwest winds are dominant—the influence of the Mediterranean climate (Figure 10c) because the attack angle is between 200° and 250° (180° is for the south wind, and 270° is for the west wind).

According to the data of Pavlović et al. [65] and Đurđević [66], the annual average solar irradiance on the horizontal (ground) surfaces is between 1250 kWh/m² and 1450 kWh/m², which is 154–354 kWh/m² more than the European average (1096 kWh/m²). This indicator shows that the solar potential in central Serbia, i.e., Kragujevac, is underutilized; that is, there is a large potential for the additional installation of solar systems.

The individual components of incoming solar irradiance are weakest in intensity (I_dir < 100 W/m² and I_diff < 35 W/m²) in December and January (Figure 10d). Solar irradiance is strongest in April: I_dir > 200 W/m² and I_diff > 60 W/m². The total incoming solar irradiance on the horizontal (ground) surface can also be determined using Figure 10d as the sum of direct and diffuse solar irradiance (I_tot = I_dir + I_diff [W/m²]).

4.2. Soil Temperature

The ceiling, i.e., the roof of the elevational ESB is located at a depth of 2 m from the free surface of the soil. Soil temperature at this depth, according to [67], can be determined by Equation (1):

$$t_{s,d}=t_{s,avg(d=0)}-t_{s,amp(d=0)}{e}^{-d\sqrt{\frac{\pi }{365{\alpha }_s}}}\cos \left(\frac{2\pi }{365}\left(day-da{y}_{\min }-\frac{d}{2}\sqrt{\frac{365}{\pi {\alpha }_s}}\right)\right)$$

(1)

where t_s,d [°C] is the average daily soil temperature during the year at depth d, t_s,avg(d=0) [°C] is the average annual free soil surface temperature, t_s,amp(d=0) [°C] is the temperature free soil surface amplitude, d [m] is the vertical distance from free soil surface to the ceiling (roof) of the elevational ESB, day [-] is the day of the year, day_min [-] is the phase constant corresponding to the day of minimum free soil surface temperature, and α_s [m²/s] is the soil thermal diffusivity (for loam soil type α_s = 0.91 × 10⁶ m²/s [68,69]).

Equation (1) does not take into account soil precipitation and soil heterogeneity properties at different locations and depths. The soil thermal diffusivity is based on prior knowledge of the soil density (ρ_s [kg/m³]), soil thermal conductivity (k_s [W/(mK)]), and soil specific heat capacity (C_s [J/(kgK)]).

Average monthly soil temperatures at a depth of 2 m for Kragujevac are 12.61 °C (October), 11.73 °C (November), 10.29 °C (December), 9.58 °C (January), 11.07 °C (February), 12.34 °C (March), and 12.95 °C (April).

5. Numerical Analysis

5.1. Google SketchUp

Google SketchUp 8 software is intended for the 3D modeling of buildings and other objects [70]. The interface provides faster and simpler work compared to other CAD softwares CAD—Catia V5R20. Models with a large number of details can be created in this software. It also provides many other possibilities, such as integration with Google Earth services and EnergyPlus software (Legacy OpenStudio 1-0-11 (Legacy OpenStudio 1-0-11) and Legacy OpenStudio Rendering tool palettes). It also has a database with a large number of ready-made 3D models.

5.2. EnergyPlus

The EnergyPlus software is a useful tool for numerical investigations of energy flows in a building and its impact on the environment [71]. It was developed by Lawrence Berkeley, the National Laboratory, the US Army Construction Engineering Laboratory, and the University of Illinois [72]. The calculation algorithm uses the finite difference method (FDM). When combined with a large number of implemented mathematical models and appropriate weather files [64], different thermo-mechanical systems can be simulated (the calculation algorithm uses FDM): heating, cooling, air conditioning, ventilation, electrical devices, gas devices, solar systems, water supply, and sewerage, occupants, artificial lighting, etc.

5.3. Siemens Femap

Siemens Femap is a software application used for engineering numerical simulation and (structural and thermal) the analysis of objects, buildings, complex systems, plants, and production lines [73]. By using the FEM, it is possible to determine the degree of safety of constructions, their mechanical properties, and places with critical loads, from 1D beam models and thin-walled shell element modeling to 3D tet-dominant or hex-dominant meshing.

5.4. Scenario Simulation

5.4.1. EnergyPlus Preparations

The initial simulation model (Figure 2 and Figure 3), modeled according to the Rulebook on Energy Efficiency of New Buildings (Table 1), is an elevational ESB that passively uses geothermal (soil natural thermal insulation) and solar (the windows and the entrance door are positioned on the south facade wall) energy (Figure 11).

The elevational ESB is equipped with smart heating (GSHP, Figure 4) and lighting (AALCS, Table 2) thermo-technical systems. The thermal performance of the mentioned building was analyzed for 7 months (from 1 October to 30 April), depending on two variables (Figure 11): HOPVI type (first variable; three simulation models) and HOPVI depth (second variable; a total of 10 simulation models). The analyzed period (from 1 October to 30 April) includes the heating season (from 15 October to 15 April) and two transitional periods when there are sometimes needs for cooling and sometimes for heating, depending on the outside temperatures. The first transitional period lasts from 1 October to 14 October. The second transitional period lasts from 16 April to 30 April.

The first variable (HOPVI type; Figure 11) has already been mentioned (HOs performance—Section 3.1; PV performance—Section 3.2). The following figures show examples of elevation ESBs with different HOPVI types (for 2.5 m deep): type HO-1 (Figure 12), type HO-2 (Figure 13), and type HO-3 (Figure 14).

The second variable is very important. The depth of the HOPVI panels affects the energy (final and primary) consumption for heating and artificial lighting (with a negative direction), as well as electricity production (with a positive direction). Unlike other studies, in this case, the vertical supporting columns are taken into account. The number of and mutual distances depend on the depth of the HOs (Figure 15). Vertical supporting columns additionally influence the shading effects of an elevational ESB, so they must not be neglected.

All cases of combining the types and depths of the horizontal overhangs were analyzed separately with the appropriate simulation flows. In order to achieve the optimal depth for the horizontal overhangs, 31 simulation scenarios were conducted (one for the initial building model—without horizontal overhang—and 30 for the rest of the simulation scenarios).

5.4.2. Siemens Femap Preparations

A static structural analysis of all HOs in the HOPVI panel construction was performed within some boundary conditions (Figure 16).

The loads due to the PV panels are, on average, F_pv = 11 kg/m² (field research of available PV panels on the local market). This value was used as one of the boundary conditions. According to recommendations in [74], the load due to snow (F_sn = 0.8 kN/m²) can be determined using Equation (2):

$$F_{sn}=f_{sn}\cdot K_{ex}\cdot K_t\cdot K_o$$

(2)

where f_sn [N/m²] is the specific load due to snow (f_sn = 1 kN/m²), K_ex [-] is the exposure coefficient (K_ex = 1), K_t [-] is the thermal coefficient (K_t = 1), and K_o [-] is the overhang shape factor (K_o = 0.8).

The static structural analysis took into account the mass of the HOs (according to Table 3 and Figure 15), the mass of the PV panels, and the load due to snow cover for locations with a moderate continental climate.

The third component could have been neglected because of the continuous production of electricity from the PV panels during the analyzed period, which, in itself, implies that the HOPVI panels should always be cleaned, but this does not have to be a required practice.

5.5. Energy Balance

5.5.1. Final Energy Balance

Depending on the total final energy balance, each building can be classified into a certain BER (Figure 1). The same applies to elevational ESBs. For elevational ESBs to be in the EPB category (objective function) during the analyzed period (from 1 October to 30 April), the total final energy balance during this season must be negative (E_f,tot < 0 kWh), which is described by Equation (3):

$$E_{f,tot}=\left\{\begin{array}{cc}{E}_{f,tot}>0\mathrm{kWh}\hfill & E_{f,tot}=\left\{\begin{array}{cc}{E}_{f,tot}>7175\mathrm{kWh}& ESB\to NEEB\\ 1537.5\mathrm{kWh}<E_{f,tot}\le 7175\mathrm{kWh}& ESB\to LEB\\ E_{f,tot}\le 1537.5\mathrm{kWh}& ESB\to PB\end{array}\right.\\ E_{f,tot}=0\mathrm{kWh}\hfill & ESB\to AB\mathrm{or}ZEB\\ E_{f,tot}<0\mathrm{kWh}\hfill & ESB\to EPB\end{array}\right.$$

(3)

where E_f,tot [kWh] is the total final energy balance in an elevational ESB during the analyzed period.

Final Energy Consumption

All energy flows in elevational ESBs are based on the use of electricity. In order to fulfill the condition E_f,tot < 0 kWh in Equation (3), electricity production must be greater than electricity consumption, as per Equation (4):

$$E_{f,tot}=E_{f,tot,e}={\left(E_{f,tot,e}\right)}_{cons}-{\left(E_{f,tot,e}\right)}_{prod}<0\mathrm{kWh}$$

(4)

where E_f,tot,e [kWh] is the total final (electricity) balance, (E_f,tot,e)_cons [kWh] is the total final (electricity) consumption (Equation (5)), and (E_f,tot,e)_prod [kWh] is the total final (electricity) production.

$${\left(E_{f,tot,e}\right)}_{cons}={\left(E_{f,tot,e}\right)}_h+{\left(E_{f,tot,e}\right)}_l+{\left(E_{f,tot,e}\right)}_{eq}$$

(5)

where (E_f,tot,e)_h [kWh] is the total electricity consumption for heating, (E_f,tot,e)_l [kWh] is the total electricity consumption for lighting, and (E_f,tot,e)_eq [kWh] is the total electricity consumption for electric equipment.

Heating System

Total electricity consumption for heating in Equation (6) is equal to the sum of electricity consumption for GSHP E_gshp [kWh] in Equation (7), electricity consumption for circulation pump 1 (CP1) E_cp1 [kWh] (the primary heating connection between GSHP and GVPs), and electricity consumption for circulation pump 2 (CP2) E_cp2 [kWh] (the secondary heating connection between the GSHP and the FPHs):

$${\left(E_{f,tot,e}\right)}_h=E_{gshp}+E_{cp1}+E_{cp2}$$

(6)

$$E_{gshp}={\displaystyle \sum _{z=1}^7{\left(E_{fph}\right)}_z}$$

(7)

where (E_fph)_z [kWh] is the electricity consumption for the FPH zone heater.

Lighting System

Since seven thermal zones (rooms) are equipped with SMLs (Table 2), then (E_f,tot,e)_l is determined by Equation (8):

$${\left(E_{f,tot,e}\right)}_l={\displaystyle \sum _{z=1}^7{\left(E_{sml}\right)}_z}$$

(8)

where (E_sml)_z [kWh] is the electricity consumption for the SML zone lighting.

Final Energy Production

Total final (electricity) production in Equation (4) from HOPVI panels can be calculated as per Equation (9):

$${\left(E_{f,tot,e}\right)}_{prod}=E_{hopvi}=E_{pv}=I_{sun,tot}{A}_{pv}S{C}_{pv}{\eta }_{pv}{\eta }_{inv}$$

(9)

where E_hopvi [kWh] is the electricity production from HOPVI, E_pv [kWh] is the electricity production from PV panels, I_sun,tot [kWh/m²] is the total solar irradiance incident on the PV panels, A_pv [m²] is the area covered by the PV panels, SC_pv [-] is the area fraction with active solar cells (SC_pv = 0.85), η_pv [-] is the efficiency of the PV panels (η_pv = 0.2), and η_inv [-] is the efficiency of the DC/AC inverter (η_inv = 0.85).

Value I_sun,tot (Figure 17) is determined by the following components in Equation (10):

$$I_{sun,tot}=I_{sun,dir}+I_{sun,diff}+I_{sun,refl}$$

(10)

where I_sun,dir [kWh/m²] is the direct solar irradiance incident on the PV panels, I_sun,diff [kWh/m²] is the diffuse solar irradiance incident on the PV panels in Equation (11), and I_sun,refl [kWh/m²] is the reflected solar irradiance incident on the PV panels in Equation (12).

$$I_{sun,diff}=I_{sun,diff,cr}+I_{sun,diff,sd}+I_{sun,diff,sh}$$

(11)

$$I_{sun,refl}=I_{sun,ref,s}+I_{sun,ref,ob}$$

(12)

where I_sun,diff,cr [kWh/m²] is the diffuse solar irradiance incident on the PV panels from the circumsolar region, I_sun,diff,sd [kWh/m²] is the diffuse solar irradiance incident on the PV panels from the sky dome, I_sun,diff,sh [kWh/m²] is the diffuse solar irradiance incident on the PV panels from the sky horizon, I_sun,refl,s [kWh/m²] is the reflected solar irradiance incident on the PV panels from the soil, and I_sun,refl,ob [kWh/m²] is the reflected solar irradiance incident on the PV panels from the obstacles.

5.5.2. Primary Energy Balance

Primary energy consumption, E_p,tot = E_p,tot,e [kWh], depends, in this case, on the primary energy transformation coefficient for electricity R_p,e [-]. If R_p,e = 2.5 [4], then Equation (13) holds:

$$E_{p,tot}=E_{p,tot,e}={\left(E_{p,tot,e}\right)}_{cons}-{\left(E_{p,tot,e}\right)}_{prod}=R_{p,e}\left[{\left(E_{f,tot,e}\right)}_{cons}-{\left(E_{f,tot,e}\right)}_{prod}\right]$$

(13)

where (E_p,tot,e)_cons [kWh] in Equation (14) and (E_p,tot,e)_prod [kWh] can be calculated for Equation (15):

$${\left(E_{p,tot,e}\right)}_{cons}=R_{p,e}{\left(E_{f,tot,e}\right)}_{cons}$$

(14)

$${\left(E_{p,tot,e}\right)}_{prod}=R_{p,e}{\left(E_{f,tot,e}\right)}_{prod}$$

(15)

5.5.3. Greenhouse Gases Balance

Analogously, Equation (13) for CO₂ emission can be used to calculate Equation (16):

$$M_{co2}=M_{co2,e}=m_{co2,e}\left[{\left(E_{p,tot,e}\right)}_{cons}-{\left(E_{p,tot,e}\right)}_{prod}\right]$$

(16)

where M_co2 = M_co2,e [kg] is the total CO₂ emission, and m_co2,e [kg/kWh] is the specific CO₂ emission (m_co2,e = 0.53 kg/kWh [4]).

5.5.4. Embodied Energy Balance

In order to determine the total embodied energy of HOPVI panels E_emb,tot = E_emb,hopvi [kWh] in Equation (17) during the exploitation period of 25 years (the adopted working life), the embodied energy for HO E_emb,ho [kWh] in Equation (18), and the embodied energy for PV panels E_emb,pv [kWh] in Equation (19) must be calculated separately, as per Equation (17):

$$E_{emb,tot}=E_{emb,hopvi}=\frac{E_{emb,ho}+E_{emb,pv}}{25}$$

(17)

$$E_{emb,ho}=\left\{\begin{array}{cc}\mathrm{wooden}\mathrm{support}\mathrm{columns}+\mathrm{clay}\mathrm{tiles}& E_{emb,ho-1}=E_{emb,wsc}+E_{emb,ct}\\ \mathrm{steel}\mathrm{pipes}+\mathrm{sheet}\mathrm{steel}& E_{emb,ho-2}=E_{emb,sp}+E_{emb,ss}\\ \mathrm{total}\mathrm{concrete}\mathrm{construction}& E_{emb,ho-3}=E_{emb,cc}\end{array}\right.$$

(18)

$$E_{emb,pv}=e_{emb,pv}{A}_{pv}$$

(19)

where E_emb,wsc [kWh] is the embodied energy for wooden support columns in Equation (20), E_emb,ct [kWh] is the embodied energy for clay tiles in Equation (21), E_emb,sp [kWh] is the embodied energy for steel pipes in Equation (22), E_emb,ss [kWh] is the embodied energy for sheet steel in Equation (23), E_emb,cc [kWh] is the embodied energy for concrete construction in Equation (24), and e_emb,pv [kWh/m²] is the specific embodied energy for the PV panels (Table 3):

$$E_{emb,wsc}=e_{emb,wsc}{\rho }_{wsc}{V}_{wsc}$$

(20)

$$E_{emb,ct}=e_{emb,ct}{\rho }_{ct}{V}_{ct}$$

(21)

$$E_{emb,sp}=e_{emb,sp}{\rho }_{sp}{V}_{sp}$$

(22)

$$E_{emb,ss}=e_{emb,ss}{\rho }_{ss}{V}_{ss}$$

(23)

$$E_{emb,cc}=e_{emb,cc}{\rho }_{cc}{V}_{cc}$$

(24)

where (Table 3) e_emb,wsc [kWh/kg] is the specific embodied energy for the wooden support columns, ρ_wsc [kg/m³] is the density for the wooden support columns, V_wsc [m³] is the volume of the wooden support columns, e_emb,ct [kWh/kg] is the specific embodied energy for the clay tiles, ρ_ct [kg/m³] is the density for the clay tiles, V_ct [m³] is the volume for the clay tiles, e_emb,sp [kWh/kg] is the specific embodied energy for the steel pipes, ρ_sp [kg/m³] is the density for the steel pipes, V_sp [m³] is the volume for the steel pipes, e_emb,ss [kWh/kg] is the specific embodied energy for the sheet steel, ρ_ss [kg/m³] is the density for the sheet steel, V_ss [m³] is the volume for the sheet steel, e_emb,cc [kWh/kg] is the specific embodied energy for the concrete construction, ρ_cc [kg/m³] is the density for the concrete construction, and V_cc [m³] is the volume for the concrete construction.

5.5.5. Total Energy Balance

In the end, the total energy balance E_tot [kWh] is the sum of E_p,tot, and E_emb,tot, as per Equation (25):

$$E_{tot}=E_{p,tot}+E_{emb,tot}$$

(25)

6. Results and Discussion

6.1. Static Structural Analysis

Analogous to Figure 6, Figure 7 and Figure 8, the following figures (Figure 18, Figure 19 and Figure 20) show characteristic displacement fields for the limiting case of depth (5 m) for all three HOPVI panel types: HO-1 (Figure 18), HO-2 (Figure 19), and HO-3 (Figure 20).

All HIOPV types (HO-1, HO-2, and HO-3), in addition to their weight, were tested for loads due to PV panels in snow conditions (Section 3.1). The results of the static calculations are shown in

Table 4. Results of the static structural analysis.

GHO [kg]	Material	HO-1	HO-2	HO-3
Supporting columns	Wood	2875.60	-	-
	Steel pipes	-	1507.20	-
	Concrete	-	-	4492.8
Cover	Clay titles	3667.60	-	-
	Sheet steel	-	400.35	-
	Concrete	-	-	24,600
PV panels		1127.5
Snow		8358.82
Total		16,029.52	11,393.87	38,579.12

.

The maximum displacements (deformations) in the case of HO-1 (16.03 t, i.e., 157.25 kN) are 32.171 mm (Figure 18). The maximum displacements for HO-2 (11.4 t, i.e., 111.77 kN) amount to 34.619 mm (Figure 19). Finally, for HO-3, the maximum displacements are 3.4001 mm (38.6 t, i.e., 378.46 kN; Figure 20). In all analyzed cases, the degree of certainty is within the allowed limits (<0.7%): 32.171/5000 = 0.0064 (0.64%) for HO-1, 34.619/5000 = 0.0069 (0.69%) for HO-2, and 3.4001/5000 = 0.00068 (0.068%) for HO-3.

6.2. Final Energy Consumption

6.2.1. Heating System

The final (electricity) energy consumption for heating (GSHP) in the elevational ESB during the analyzed period (from 1 October to 30 April) for all scenarios (Figure 11 and Figure 15) is presented in Figure 21.

For the first type (HO-1, Figure 6 and Figure 12) of elevational ESB with HOPVI, electricity consumption for heating is (Figure 21) 1400.5 kWh (without HOPVI), 1419.66 (D_ho-1 = 0.5 m), 1482.7 (D_ho-1 = 1 m), 1797.69 (D_ho-1 = 1.5 m), 1914.05 (D_ho-1 = 2 m), 2023.84 (D_ho-1 = 2.5 m), 2113.13 (D_ho-1 = 3 m), 2173.23 (D_ho-1 = 3.5 m), 2187.3 (D_ho-1 = 4 m), 2205.43 (D_ho-1 = 4.5 m), and 2215.18 (D_ho-1 = 5 m).

Since the HO-1, HO-2, and HO-3 overhangs are characterized by an identical design for D_ho = 0 m, D_ho = 0.5 m, and D_ho = 1 m (Figure 15), electricity consumption for the considered cases is the same (Figure 21): 1400.5 kWh (D_ho-1 = D_ho-2 = D_ho-3 = 0 m), 1419.66 (D_ho-1 = D_ho-2 = D_ho-3 = 0.5 m), and 1482.7 (D_ho-1 = D_ho-2 = D_ho-3 = 1 m).

For other HO-2 depths, electricity consumption in the elevational ESB with HOPVI panels is (Figure 21) 1649.97 (D_ho-2 = 1.5 m), 1780.91 (D_ho-2 = 2 m), 1914.17 (D_ho-2 = 2.5 m), 2012.88 (D_ho-2 = 3 m), 2095.88 (D_ho-2 = 3.5 m), 2128.12 (D_ho-2 = 4 m), 2171.84 (D_ho-2 = 4.5 m), and 2186.93 (D_ho-2 = 5 m).

In the end, electricity consumption for the HO-3 type is (Figure 21) 1736.99 (D_ho-3 = 1.5 m), 1846.42 (D_ho-3 = 2 m), 1968.13 (D_ho-3 = 2.5 m), 2056.03 (D_ho-3 = 3 m), 2136.53 (D_ho-3 = 3.5 m), 2164.95 (D_ho-3 = 4 m), 2199.93 (D_ho-3 = 4.5 m), and 2220.97 (D_ho-3 = 5 m).

The biggest differences between the considered overhang types can be observed when D_ho = 1.5 m. As the overhang surfaces increase with their depth, the differences decrease, so at a depth of 5 m, they are the smallest.

Figure 22 shows that the monthly electricity consumption for heating in elevational ESBs with HOPVI panels during the analyzed period is the highest in January (for all scenario simulations), from 381.07 kWh (D_ho-1 = 0 m) to 502.52 kWh (D_ho-1 = 5 m) for HO-1 (Figure 22a), from 381.07 kWh (D_ho-2 = 0 m) to 496.61 kWh (D_ho-2 = 5 m) for HO-2 (Figure 22b), and from 381.07 kWh (D_ho-3 = 0 m) to 500.75 kWh (D_ho-3 = 5 m) for HO-3 (Figure 22c).

On the other hand, electricity consumption is the lowest in October, from 20.41 kWh (D_ho-1 = 0 m) to 129.35 kWh (D_ho-1 = 5 m) for HO-1 (Figure 22a), from 20.41 kWh (D_ho-2 = 0 m) to 126.71 kWh (D_ho-2 = 5 m) for HO-2 (Figure 22b), and from 20.41 kWh (D_ho-3 = 0 m) to 129.05 kWh (D_ho-3 = 5 m) for HO-3 (Figure 22c).

Electricity consumption for circulation pumps (CPs) in elevational ESBs with HOPVI panels during the analyzed period for HO-1, HO-2, and HO-3 is presented in Figure 23.

For HO-1, circulation pumps consume between 20.28 kWh (without overhang) and 27.15 kWh (deep 5 m). The highest electricity consumption in the rest cases is 26.96 kWh (HO-2) and 27.24 kWh (HO-3), both for D_ho = 5 m.

From the diagram in Figure 23, three characteristic zones can also be observed: the overlapping zone (0 m, 0.5 m, and 1 m), the zone of intense changes (1.5 m, 2 m, 2.5 m, and 3 m), and the zone of slow changes (3.5 m, 4 m, 4.5 m, and 5 m).

Electricity consumption for heating in an elevational ESB (Figure 21, Figure 22 and Figure 23) depends on solar gains (Figure 17). The shading effects increase with increasing overhang depth, and the solar gains are reduced, so the temperature of the free (southern) facade is lower. Figure 24 shows the daily (for 7 January) surface outside temperature for LR in an elevational ESB with HOPVI, depending on the type and dimension of the overhangs: HO-1 (Figure 24a), HO-2 (Figure 24b), and HO3 (Figure 24c).

Regardless of the HO types, the biggest temperature changes in the reference case (building without overhangs) can be observed in the period from 09:00 to 16:30. For example, at 12:45 pm, t_lr,sr,out = 4.02 °C (for ESB without HOPVI). In the same period, this temperature is lower by 1.65 °C for D_ho-1 = 5 m, 1.56 °C for D_ho-2 = 5 m, and 1.61 °C for D_ho-3 = 5 m.

Figure 24 also shows that in the early morning hours and late evening hours, the temperature of the south facade increases with the increase in the depth of the overhangs. This can be explained by the solar elevation angle (very small), so the diffuse and reflected components increase the total solar gains, following Equation (10).

6.2.2. Lighting System

Electricity consumption for the adopted lighting system (AALCS) in an elevational ESB with HOPVI panels during the analyzed period for HO-1, HO-2, and HO-3 is presented in Figure 25.

Regardless of HO types, AALCS electricity consumption is the same for D_ho = 0 m (440.63 kWh), D_ho = 0.5 m (441.31 kWh), and D_ho = 1 m (443.79 kWh). The following discontinuities (drops in AALCS electricity consumption) can be seen in Figure 25: HO-1 (3 m, 3.5 m), HO-2 (3.5 m, 4 m), and HO-3 (3.5 m, 5 m). The discontinuities are explained by the different numbers, shapes, and dimensions of the vertical supporting columns (Figure 26—daily AALCS electricity consumption for LR: Figure 26a for HO-1, Figure 26b for HO-2, and Figure 26c for HO-3). The green line (Figure 25) shows the AALCS electricity consumption for different overhang depths in the variant without vertical columns (reference case). The highest AALCS electricity consumption is for D_ho = 5 m: 560.22 kWh (HO-0), 607.63 kWh (HO-1), 582.33 kWh (HO-2), and 574.06 kWh (HO-3).

6.2.3. Electricity Production

All HOPVI panel types (HO-1, HO-2, and HO-3) are characterized by the same production of electricity (77.31 kWh/m²; Figure 27), which depends on the surface of the upper side of the overhangs, i.e., their depths: 792.44 kWh (A_hopvi = 10.25 m²), 1584.89 kWh (A_hopvi = 20.5 m²), 2377.33 kWh (A_hopvi = 30.75 m²), 3169.77 kWh (A_hopvi = 41 m²), 3962.22 kWh (A_hopvi = 51.25 m²), 4754.66 kWh (A_hopvi = 61.5 m²), 5547.1 kWh (A_hopvi = 71.75 m²), 6339.54 kWh (A_hopvi = 82 m²), 7131.99 kWh (A_hopvi = 92.25 m²), and 7924.43 kWh (A_hopvi = 102.5 m²).

6.3. Primary Energy Flow and Greenhouse Gas Emission

Considering the results shown in Figure 21, Figure 22, Figure 23, Figure 24, Figure 25, Figure 26 and Figure 27, as well as the corresponding Equations (13)–(16), the following diagram (Figure 28) shows the primary energy flows and CO₂ emissions in an elevational ESB with HOPVI, depending on the overhang types with depth, as well as electricity consumption for water heating, electrical equipment, cooking, etc.

$$E_{f,tot,avg}=\frac{E_{f,tot,ho-1}+E_{f,tot,ho-2}+E_{f,tot,ho-3}}{3}$$

(26)

$$E_{p,tot,avg}=\frac{E_{p,tot,ho-1}+E_{p,tot,ho-2}+E_{p,tot,ho-3}}{3}$$

(27)

$$M_{co2,avg}=\frac{M_{co2,ho-1}+M_{co2,ho-2}+M_{co2,ho-3}}{3}$$

(28)

One member of the household in Serbia consumes nearly 151.61 kWh/month of electricity [75] (for water heating, electrical equipment, cooking, etc.), which means that a family of four consumes 4245 kWh of electricity (final energy consumption) during 7 months (Figure 28a). The average primary energy consumption in an elevational ESB without HOPVI panels is 15,266.03 kWh (Equation (27)), and the CO₂ emissions are 8090.99 kg (Equation (28)). A HOPVI panel system with D_ho = 4.5 m provides EPB status because the primary energy consumption is between −141.9 kWh (for HO-1) and −297.575 kWh (for HO-2), while the CO₂ emissions are between −75.21 kg (for HO-1) and −157.71 kg (for HO-2).

Figure 28b shows that the optimal dimension of the horizontal overhangs could be 4 m (average primary electricity consumption is −180.49 kWh, and the average CO₂ emissions are −95.03 kg), with reduced electricity consumption for water heating, electrical equipment, cooking, etc., in an ESB with HOPVI panels on 3500 kWh.

Analogous to Figure 28a,b, the optimal dimension of the horizontal overhangs for an ESB with HOPVI panels could be 3.5 m if electricity consumption for additional needs is <3000 kWh (Figure 28c).

In the end, if the same indicator (people’s habits) reaches a value of 2500 kWh, the optimal depth of the overhang tends to reach a value of 3 m because the production of electrical energy that is delivered to the electrical network for D_ho = 3 m is greater than the others (the average value is −922.86 kWh).

6.4. Embodied Energy and Total Energy Flow

The diagram in Figure 29 shows total embodied energy and total energy flow in an elevational ESB with HOPVI, depending on the overhang types and depths and electricity consumption for water heating, electrical equipment, cooking, etc.

Total embodied energy (Figure 29) is the lowest in the case of concrete HOPVI panels (HO-3). This applies to all analyzed cases. In second place are the steel HOPVI panels (HO-2), and HO-1 represents the most unfavorable type (from the point of view of embodied energy). The types and depths of the overhangs, in combination with the appropriate number of vertical support columns, caused the differences between HO-1 and HO-2 to be greater for depths ranging from 0 m to 1 m. For greater depths (1.5–5 m), these differences are much smaller, and a slight advantage is on the side of HO-2 (Figure 29).

When a comprehensive analysis of energy flows (the construction physics of the building, meteorological data, heating system, lighting system, people’s habits—electricity consumption 4245 kWh—and electricity production from PV panels) in an ESB with HOPVI panels is carried out while taking into account the final, embodied, and primary energy (for the adopted primary energy transformation coefficient for electricity; R_p,e = 2.5), the ESB with HOPVI panels is unable to reach EPB status (Figure 29a). Additionally, it can be concluded that an ESB with concrete HOPVI panels is the most favorable solution for reaching EPB status.

It can also be concluded that a reduction in electricity consumption to 3500 kWh provides EPB status for D_ho = 5 m (the average total energy consumption for all overhang types is −805.82 kWh). A reduction in electricity consumption to 3000 kWh enables an ESB with HOPVI panels to reach the desired goal (goal function), even for 4.5 m deep horizontal overhangs (E_tot = −409.16 kWh).

Interesting results are achieved when electricity consumption is reduced to 2500 kWh (89.29 kWh/month/person). Then the EPB status for all types of horizontal overhangs (HO-1, HO-2, and HO-3) is reached for D_ho = 4.5 m (average total energy consumption is 1659.16 kWh) and also for D_ho-3 = 4 m (E_tot = −486.93, for HO-3). Precisely because the mentioned data values for the embodied energy for HO-3 are the smallest, a solution should be found for them.

However, when taking into account the trend of damaging the environment on a global level, as well as the current global political, economic, and social conditions, energy flows can no longer be viewed selfishly only from the human perspective (final energy consumption). The problem must be approached comprehensively, taking into account the reaction of the environment, which, despite a large number of legal norms, agreements, and other documents, is persistently ignored.

7. Conclusions

In this paper, the subject of the research is elevational earth-sheltered buildings with horizontal overhang photovoltaic-integrated panels. The authors combined a bioclimatic-passive construction approach, energy-efficient thermo-technical systems (ground source heat pump, geothermal vertical probes, floor panel heaters, circulation pumps, artificial and automatic lighting control systems, and PV panels), shading devices (three types of overhangs: wooden support columns covered with clay tiles, steel pipe support columns covered with sheet steel, and concrete support columns with concrete coverage) and the habits of tenants to determine the moment of reaching the energy-plus status regarding a building located in Kragujevac (Serbia); this was considered during the 7-month winter period (from 1 October to 30 April) because this time domain is very sensitive in terms of energy.

A static structural analysis was performed using the finite element method in the Siemens Femap software. Energy flow analysis was performed using the finite difference method in the EnergyPlus software (with the support of the Google SketchUp software).

The results showed that the energy-plus building status of such an architectural concept can be reached at a horizontal overhang depth of 3.5 m (for primary energy consumption) and 4.5 m (for total energy consumption). It was also concluded that the building energy rating of an ESB with HOPVI panels is greatly influenced by the habits of the ocupants, in addition to the construction physics of the building, meteorological data, heating system, lighting system, and electricity production from PV panels.

Modern architectural and construction design should not bypass such buildings, especially when taking into account the following facts: final energy consumption in the housing sector of the Republic of Serbia is still quite high, an increasing number of people live in cities, rural settlements are closing down, and the agricultural sector is collapsing.

The presented methodology can be applied to other locations in Europe and the world but with a very careful approach to assessing applicability. The specifics of climatic and geographical conditions, the specific production of electricity from PV panels, people’s habits, local differences in the field of energy efficiency in buildings, and other sensitive variables must be taken into account.