Historical Buildings Potential to Power Urban Electromobility: State-of-the-Art and Future Challenges for Nearly Zero Energy Buildings (nZEB) Microgrids

Abstract

The growing need for electric energy is forcing the construction industry to greater integrate energy production systems based on renewable energy sources. The energy ought to be used not only to support functions of the building but also to charge electric vehicles, whose number has been increasing for the last few years. However, implementation of RES (Renewable Energy Sources) systems in already existing buildings is problematic. Basing on an example of a historical building, the article presents the conversion of a facility into a nearly zero-energy building, where energy surplus may be used to charge EVs (Electric Vehicles). Interdisciplinary research describes energy consumption of the EV in real driving conditions, taking into consideration changing weather conditions and an option of energy being produced by buildings operating in an urban agglomeration: it stipulates the time needed to charge the vehicle, depending on the charging We removed dot, according to email in submitting system, please confirm.method, as well as an energy potential of adapting the solution in selected periods of building operation. The summary presents how electromobility can be supported by the construction industry.

1. Introduction

1.1. Combining Architecture with Alternative Power Sources

The future of the electric vehicle (EV) market is closely connected with the development of the network of charging stations (both in cities, located by main roads, and small, private stations) as they guarantee the real usability of EVs. The technology of charging EVs with energy produced by photovoltaic panels is now perceived as a particularly attractive and forward-thinking solution [1]. Therefore, an interdisciplinary approach to research the possibility of charging EVs from photovoltaic (PV) systems is recommended.

Urban and architectural designing in European culture is an extraordinary challenge. Numerous existing cities are like documents proving their centuries-old traditions. Their past “provides invaluable lessons for the future” [2], which is created by actions we take today. Throughout the decades, architects and urbanists have been trying to find optimal solutions regarding urban planning and they agree that the historical nature of cities should be “given strict custodial protection” [3]. At the same time, it is important to keep balance between protection of historical values and of cultural heritage and the implementation of new technologies [2]. Pursuant to the Venice Charter [4], the conservation process should support functioning of historical buildings by allowing changes which are the result of custom and lifestyle evolution. Adding new functions to the historical building or area may not, however, significantly affect the historical urban layout or architectural arrangements.

European cities are in their major parts older than 50 years; over 40% of residential buildings were built before the mid-20th century. They were raised in accordance with the then valid construction rules but, obviously, ignored later detailed energetic regulations stipulated for the construction industry. At the same time, the construction industry is one of the key energy consumers in Europe [5]. The research shows that most historical buildings are ineffective in terms of energy, they generate great energy costs and CO₂ emission. Their proper modernisation that would simultaneously protect and highlight their historical, scientific and artistic values, which constitutes an important element in achieving European environmental goals [6].

At first, initiatives and procedures regarding energy efficiency, implemented in the United States of America, European Union and China, did not take into consideration historical buildings. However, the growing awareness that this part of the construction industry is culturally important and increasing in number, and can no longer be ignored, has resulted in the development of research on that area. Most available literature refers to attempts aimed at the decrease of energy consumption and improvement of thermal comfort inside the historical building, without prejudice to its historical value [6,7,8]. Most analyses have been conducted in 19th and 20th century buildings, as the level of their conservational protection is lower, and their modernisation is easier.

The article [9] presents an analysis of the historical building with a far more complicated structure of historical layers and much older provenance, which means also higher level of conservational protection. The tenement house at Wroniecka 23 in Poznań shows layers from the turn of the 14th and 15th century, superstructures from the end of the 16th century and reconstructions from the 19th and 20th century. Moreover, this building is a unique example of a historical building adapted to parameters of the nearly zero-energy building (nZEB).

The research included analyses of both real energy production in the tenement house and the possibility to use this historical, nearly zero-energy building to charge electric vehicles. This facility was chosen because of its location in the historical area of the Old Town but, what is most important, this is an old house that has become the nearly zero-energy building. Moreover, there is “extensive metering of exploitation processes, focusing on adopted new technologies” and “using innovative solutions improving the standard of the place by applying most effective technologies based on renewable energy” [10].

The building analysed in the presented research is the tenement house located in the Old Town, the historical, urban-architectural complex of Poznań, which is under conservation protection pursuant to the entry into the Register of Monuments (no. A-225/M, decision of 4 June 1979) [11]. This means that, pursuant to art. 36 of the Act of 23 July 2003 on the Protection and Preservation of Historical Monuments [12], any works affecting the outside look of the house, the landscape and the interior of the urban layout shall be conducted upon conservator’s permit. The decision on the permit is made by the Provincial Monument Conservator, and in case of Poznań, by the City Monument Conservator, upon agreement with the President of the City. The tenement house at Wroniecka 23 is also entered individually to the Register of Monuments (under no. A-133, decision of 25 April 1966) [11]. For designers, it means that any and all works, including those inside the building, shall be conducted under permits described hereinabove and may not negatively impact the historical value of the house; therefore, when they implement new technologies and relevant systems, they shall design their location in a way that does not infringe the historical essence of the place.

1.2. Electromobility in Urban Conditions

The specifics of vehicle traffic in city centres is mainly focused on vehicles’ dynamic speed changes, which results in increased fuel consumption and exhaust gas emissions, in particular, in case of vehicles with conventional drive [13]. Decreasing the impact of the transport industry on air pollution in urban conditions may be implemented by feeding internal combustion engines with e.g., compressed natural gas, using modern combustion systems or by using electrified driving systems, hydrogen or battery-powered systems [14,15]. A significant local decrease of emissions of harmful and toxic substances is possible through the application of drive systems working without internal combustion engines. Taking into account the aspect of the use of battery-electric means of transport, it is necessary to adapt the urban infrastructure, which involves many problems [16].

The conducted comparative analysis of direct and indirect methods of electrifying drive systems dedicated to private passenger transport proves that the direct use of electrical power in a car is more beneficial in terms of decarbonisation pace and energy consumption in energy transition [17]. The use of smaller means of transport like electric bicycles and scooters can be beneficial in reducing car traffic [18,19].

Energetical cooperation of a small household solar power station with a battery electric vehicle is an attractive trend in the development of electromobility [20,21]. In the recent years there has been a dynamic increase of power produced by photovoltaic panels: it reached the value of 633.7 GW in 2019 [22]; the number of LDV increased by 43% in 2020 compared to a previous year [23]. The development of the abovementioned branches of the transport industry and power supply is particularly essential in the face of planned restrictions regarding access of vehicles to city centres [24].

The variety of aspects and characteristics of the vehicle dynamics in urban conditions is subject to numerous analyses [25,26], which indicate the significant impact of types of streets, drivers and driving conditions. Taking into consideration the use of a battery-powered EV, Desreveaux et.al [27] indicated the lowest value of energy consumption in urban conditions per 100 km, compared to the use of the vehicle in extra-urban and motorway conditions. The comparison of an internal combustion engine (ICE) vehicle and an electric vehicle proved a reverse tendency in energy consumption per 100 km [28]. In urban conditions, the EV driving in accordance with RDE requirements consumed about 63% less energy than the ICE vehicle. The increased energy consumption in the case of EV is caused i.e., by the changing outside temperature. In research conducted by HAO et al. [29], the lowest energy consumption was registered at the temperature of 19 °C. This proved the negative impact of low temperatures on internal conductivity in the battery.

While examining energy consumption of the vehicle, it is important to select an adequate test for the drive system. The comparison of NEDC, WLTP and RDC test results obtained in simulated conditions [30] indicates significant discrepancies. The highest value of energy consumption was shown in RDC results.

Adding the photovoltaic infrastructure as a source of power significantly improves the power balance of urban areas which constitute 2% of the area on Earth but consume 2/3 of the produced energy [31]. In Berlin, the city authorities consider implementing an obligation to install photovoltaic panels in new buildings and include solar systems while renovating roofs. The aim is to achieve the result of 4.4 GW of installed power [32]. Optimal estimation of the potential regarding PV panels on roofs proves the possibility to obtain up to 87% power surplus that can be returned to the grid [33]. In urban conditions, where there is considerable housing density, the estimation of available roof area can be made on the basis of satellite or UAV images [34]. In Ibadan (Nigeria), estimation based on satellite images and other techniques gave proved that the total roof area is 49.54 km², out of which only 7.54 km² is suitable for PV panels [35].

The purpose of this article is to demonstrate the feasibility of powering electric vehicles through renewable energy installations, in this case photovoltaic panels without affecting the exterior architecture of the building. The article presents an interdisciplinary analysis showing the energy consumption of electric vehicles as a means of mobility, as well as the real benefits of PV installations enabling increased range in urban areas.

2. Buildings under Research

2.1. A Nearly Zero-Energy Building (nZEB)—Wroniecka 23

During renovation the tenement house at Wroniecka 23 was equipped with all-new power system with photovoltaic panels of 4 kWp (Figure 1). Thanks to spatial orientation of this narrow building, slightly away from the east-west axis, it was possible to effectively benefit from the shape of the renovated, gable roof. The small width of the building (5.3 m in its widest part) resulted in a small area of the southern slope of the roof, so there was enough space for 16 polycrystalline panels of 1650 × 992 mm (Figure 2). Because of the long shape of the house and its horizontal location, the panels are installed in line, horizontally and vertically. The first twelve panels (from the western side) are placed vertically, another four—horizontally in the layout of two pairs, which increases the total area of the installation [9].

“The growing expectations regarding savings of non-renewable prime energy and decreasing impact of historic facilities on natural environment enforce changes in evaluation of the present state and possibilities of restoring them to functioning in contemporary reality which is based on sustainable construction” [36]. The location of this building and its PV panels in the very center of Poznań creates great potential in terms of EV charging. Changes proposed by the Ministry of Climate and Environment, regarding electromobility and zones of clean transport in cities over 100 K residents (JoL 2018, item 317 of 11 January 2018), shall require considerable infrastructural support, i.e., the possibility of quick and comfortable driving, parking and charging for EVs. Therefore, the availability of charging stations in the city center will have to improve significantly. An example of Wroniecka 23, where renovation was closely connected with the idea of sustainable designing, may become a starting point for discussions on an attempt to solve urban, ecological and transportation problems of Poznań by combining the historical value of existing buildings with effectiveness of new technologies. It is important, however, to bear in mind that there is a great need to respect the unique identity of the building that has witnessed the history of Poznań throughout centuries.

Pursuant to Resolution adopted in 2018, the area of Wroniecka Street and the Old Town with adjacent streets became the Culture Park [37]. The Resolution clearly defines the required aesthetics and functions of this part of the city (Figure 3). Paragraph 11 thereof stipulates requirements regarding location of technical devices of any kind exclusively in places which are not visible in the public area, e.g., from the perspective of streets, squares or parks. Fortunately, those restrictions do not include places that cannot be seen by city residents, i.e., fragments of roofs which can be used to install PV panels within the area of the Culture Park.

The historical part of Poznań, including Wroniecka 23, is characterized by the orthogonal urban layout. The grid of streets only slightly (about 10°) deviates from the grid of north-south and east-west axes (Figure 3). Such layout creates compact blocks of tenement houses whose fronts (perpendicular orientation) or ridges (parallel orientation) are directed towards the south, which is optimal for the functioning of PV panels. Moreover, most roofs in the Old Town are pitched, hidden behind decorative facades or simply invisible for pedestrians and thanks to the inclination angle, they may become a perfect surface for systems producing green energy.

The recently conducted analyses on the possibility to use existing buildings as carriers for PV systems clearly prove their huge power potential. Nevertheless, the calculations presented in the literature refer mainly to single buildings analysed theoretically [38,39] or bigger urban-geographic areas [40,41]. The research described hereunder presents an innovative approach as it combines the scale of the building block with its uniqueness, i.e., its undisputable historical value that is under protection of the conservator.

Throughout the year there are periods of surplus production at Wroniecka 23, when power is sold to the grid. Similar cases have already been described in the literature [39], that is why the decision was made to conduct theoretical research to calculate the value of energy generated by the whole block of historical buildings. According to analyses conducted by Bartosz Chwieduk and Hanna Jędrzejuk, a PV system made of crystalline silicon installed on a single-family building (heated with a heat pump) returns 400 kWh out of the produced 2870 kWh of power in a year [39]. This value is approximately 14% of a yearly production. A similar analysis was conducted for an industrial building of KOMAG Institute of Mining Technology [38]. Since there is a much larger PV system than in the case of a single-family house, yearly profit was estimated at the level of 144,904 kWh. The increased value, however, is also connected with a changed function of the building, which has a far greater energy consumption and thus, consumes 98.3% of the generated power. Pursuant to the tendency observed in cases described in literature, it was decided to conduct an analysis based on the agreed fragment of the building block and using the comparative methodology to combine actual data from the analysed tenement house at Wroniecka 23 and theoretical estimates.

The presented analysis aims at verifying the potential of historical blocks in the Old Town and opportunities to use them as power generators supporting electromobility solutions in the city. Researchers focused on two conditions: an analysis of roof exposure to the sun, which is necessary to provide effective work of the system, and testing visibility of roofs from the perspective of public places in the Old Town to protect the unique historical identity of the block, so that aesthetic value of the buildings in the Culture Park is not violated.

2.2. Electric Vehicle—Skoda Citigo

According to the report on the volume of EV sales on the European market in the first half of 2021, the greatest result was achieved by Tesla Model 3 (50,222 pcs), which is twice as many as the second car in that ranking (Renault Zoe—24,616 pcs) [23]. The top ten of bestselling EVs also includes Volkswagen e-Up, which is equivalent to the tested vehicle, ŠKODA CITIGOeiV (presented in detail on Figure 4). The vehicle of this class is also widely used in car sharing [42].

When presenting vehicles in their offers, producers declare their range on the basis of WLTP tests, which, despite increased precision of measurement in comparison with NEDC tests, do not take into consideration variables of real driving conditions. Therefore, testing EVs’ energy consumption in real driving conditions is essential for real calculation of the vehicle’s range and time needed to charge it to the level providing the assumed range. Figure 5 presents the declared range of selected vehicles and shows two relations:

• The vehicle’s range increases along with the increasing capacity of the high voltage battery;
• The vehicle’s range for different vehicles with the same battery capacity may vary even up to 50% or more, depending on the type of the vehicle and its drive.

Taking into consideration the above, the EV energy consumption tests in real drive conditions should be continued and should include both changing weather conditions and driving modes.

The article presents an interdisciplinary analysis showing energy consumption of EVs as means of transport, energy consumption of the charging process and power from renewable energy sources produced by the building. The research includes the range in accordance with Figure 6 hereinunder.

3. Energy Analysis

3.1. Energy Production by the Building

3.1.1. Analysis of Insolation Time of the Roof—Research Method

Power efficiency of the applied renewable energy source is mainly conditioned by insolation, that is why the analysis of the amount of time the building is exposed to sunlight was conducted. A 3D model of the building block was made in Rhino 6.0. and became the basis for testing the roof exposure to the direct sunlight. As roofs are not accessible, conducting a detailed survey including minor construction elements, such as dormers, chimneys or technical equipment, was not possible. Based on generally available elevation data and background maps, the 3D model assumed the detailed representation on Level of Development 200 and included basic information regarding the general shape of the building blocks and approximate location and orientation data (Figure 7). The model was then analysed with the use of Grasshopper engine 1.0.0007, used for visual programming (VPL), and Ladybug Tools 1.3.0. which allow analysis and visualisation of weather conditions, as well as testing the complex geometry.

Weather measurements made by Instytut Meteorologii i Gospodarki Wodnej (Institute of Meteorology and Water Management) and located at Ławica Airport in Poznań served as basic data for the conducted analysis of insolation. Weather data collected in Energy Plus Weather (EPW) file format was implemented to the algorithm used to analyse exposure time (Figure 8) The date of vernal equinox, on 20 March 2021, between sunrise (5:55 CET) and sunset (18:06 CET) was agreed as the measurement time; such time span allowed complete analysis of insolation for average day length.

In order to provide the graphic visualisation of analysis results, an orthogonal grid with equal areas of 0.5 × 0.5 m was placed upon the solid model. Next, the precision of the marking scale was defined and equalled 1 h, with the assumption that the legend range is from 0 to 12 h of insolation. Colours presented on Figure 9 below show the time of direct exposition of the given fragment of the grid to the sun. Bearing in mind the basic rule of how polycrystalline panels work and the fact that their efficiency mostly depends on amount of direct sunlight shining on the surface of the panels, the survey proved a huge power potential of roof areas in the analysed building block. In accordance with the legend below the Figure, we can see that most roofs in the block are exposed to direct sunlight for minimum 7 h a day (assuming the precision of the analysed model, which does not take into account minor construction elements, such as dormers, chimneys or technical equipment, that might decrease efficiency of PV panels by their partial shadowing).

The analysed block takes the area of 4844 m², out of which 3456 m² is covered by the existing buildings. The red color indicates the area in discussion. When analysing the built surface, we can see a considerable diversity of roof geometry; it gives the total roof surface area of about 4471 m², which is quite similar to the total area of the whole building block (Figure 10).

The graph presented below shows dependence between the time of sun exposure of roof fragments and their share in the total roof area. The major part of the roof, 72.1%, is exposed to the direct sunlight for minimum 7 h, which creates optimal conditions for functioning of PV panels (Figure 11).

The tenement house at Wroniecka 23 is equipped with photovoltaic panels SF156X156-60-P produced by Sunowe Photovoltaic. The declared maximum power of a single panel is 240 W in STC (Standard Test Condition), where values for insolation equal 1000 W/m², for the temperature of surrounding of the lit panel +25 °C and for spectrum of radiation for air mass AM = 1.5. Having calculated the given value per one m² of the panel, the maximum power is 146.63 W.

Installing PV panels with exactly the same parameters as in case of Wroniecka 23 on all roofs of the building block was the basic assumption for analysis of power potential of the block. Other facilities such as roads and parking areas are also analysed in a similar manner [47,48,49]. The next step included calculations to define how much energy could be generated by the block in question in optimal STC. Based on data obtained at earlier stages of the analysis, researchers recalculated the maximum power products, insolation time and surface area of the roofs corresponding to the selected time value (Figure 11). This resulted in defining the amount of energy that would be generated throughout the whole day on particular analysed roof surfaces (Figure 12). Then, the results were summed to collect the power produced on the total surface area of the roofs in the whole period of insolation (1):

$$E_{max}={\displaystyle \sum }_{h=1}^{12}\left[146.63\frac{W}{m^2}\ast h\ast P\left(h\right)\right]=5202.05 kWh$$

(1)

where E_max—Maximum amount of energy produced by the building block in test conditions [kWh]; 146.63 W/m²—Maximum power of installed solar panels calculated per 1 m² of surface area; h—Time of roof insolation [h]; P(h)—Roof surface area corresponding to the time of insolation [m²].

That is how researchers calculated the value of the maximum amount of energy that can be generated by the block during vernal equinox (21 March), which was the reference time of the analysis. The obtained result, 5202.05 kWh, proves great potential of the building block. This outcome, however, is not precise as calculations were simplified. They did not include factors such as, loss of surface area related to roof geometry and limited possibilities to install the panels. In order to precisely evaluate opportunities to generate power on roofs of the whole block, the researchers adopted the comparative analysis. Based on calculations described hereinabove, the scope of the analysis was narrowed by limiting the analysed area to the roof of the tenement house at Wroniecka 23, which is equipped with PV panels. This allowed comparison of theoretical calculations based on the assumed test parameters with real values generated by the existing and parameterized system. Using data collected continuously as of 21 May 2019, an average amount of power produced within one day of work of the panels was calculated: 9.61 kWh. Then the obtained value was compared with theoretical calculations, defining the maximum possibilities of the analysed system. Assuming that there are 16 polycrystalline panels exposed to sunlight for 11 h during the vernal equinox, it was calculated that the average maximum efficiency of the system is 42.24 kWh a day. Having confronted theoretical calculations with an average real daily value, the real efficiency of the panels was defined at the level of 22.75%.

The % value obtained in this way served to calculate the real amount of power which might be produced by PV system installed on the roofs of the whole building block located at Wroniecka Street. Having excluded 22.75% of the value obtained in calculations equalling 5202.05 kWh, the real value was calculated at the level of 1183.47 kWh of power that might be generated in the analysed location.

The comparative summary of data allowed including variables of weather conditions that have a direct impact on the efficiency of work of PV panels. The authors of another paper [46] also reported the impact of ambient conditions on energy generation. Accepting average realistic values of the power generated every day of the panels’ work allowed for the avoiding of a measurement error connected with significant amplitudes of clouding or insolation during a single measurement period (Figure 13); it also included the changing sun ray incident angle, which directly affects the system’s efficiency [50,51]. One must bear in mind, however, that the character of the analysis is purely estimated as it did not take into account the incident angle of the roof, and thus, the incident angle of PV panels themselves. Nevertheless, the simplified version of the analysis allows us to say that conditions on roofs of the historical building block bring huge potential to be used in the context of PV systems and generating green power meeting both direct needs of the building and its users and supporting electromobility by charging EVs during periods of generating power surpluses (Figure 14).

Based on data collected by BMS installed in the house at Wroniecka 23 (Figure 15), researchers analysed the energy work of the building during the whole week. The testing period lasted from 6 September 2021 to 21 November 2021 and brought average values of power produced by PV panels, power taken from the grid and power returned to the grid on particular weekdays (Figure 14). At present, the building functions as an office, and thus, it is mainly used from Monday to Friday and needs power supply for typical office activities, such as computer work, lighting, heating or ventilation (Figure 15 and Figure 16). That is why there is a significant decrease in power taken from the grid during weekends. Logically, the decreased need for power at the time employees are absent results in higher amount of power returned to the grid on Saturday and Sunday.

In the analysed period, the power surplus generated at weekends was at average 5.12 kWh, which is 2–3 times more than the average power gain within a working week (Figure 14). The diagrams below show the flattening line of energy consumed by the building, which is caused by the decreased need of energy on Sundays, in regard to the presented needs. The diagrams are prepared on the basis of values that are averaged because of the changing weather conditions which affect the actual effectiveness of the system. Characteristics presented in this way indicate the positive tendency observed by the authors of this article. Certainly, there might be periods when weekend insolation will be far less effective than the total insolation within the working week, which will result in the decrease of power gains. The data presented on the diagram prove the power potential of the tenement house in the context of installing the EV charging station, which might also be supplied with the use of power surpluses generated by the photovoltaic installation. Figure 16 presents the average maximum values of power generated by the installation with rated power of 4 kWp; this indicates that the capacity of the installation stands at 87% (for the maximum power generated at the level of 3.49 kW in summer).

3.1.2. Analysis of Visibility of Building Block’s Roof Surfaces, in Accordance with Requirements of Old Town Culture Park in Poznań

Another important aspect conditioning the location of PV panels within the Culture Park is their visibility in the public area of the city. The historical character of the streets and buildings surrounding the Old Market cannot be disturbed by uncontrolled placing of elements of technical equipment. The diagram below shows the view range from the perspective of people present in public spaces and is based on the example of Wroniecka Street. Taking into account the proportion of width of space between buildings to their height, the visibility of roofs is practically close to zero (Figure 17). This allows using insolated roof areas without violating aesthetics and historical value of the district.

The analysis presented below was conducted on the basis of pictures made by a UAV which show the share of “hidden” roof areas in the total area of the building block. The layout of tenement houses and architectural details, such as decorative facades, effectively block the view on systems and elements placed on the roofs. The roofs marked blue are the only fragments that are exposed to the public within the analysed building block and thus, they cannot be used for installation of PV panels (Figure 18).

3.2. EV Energy Consumption

Measurement of energy consumption in electric drive was conducted in accordance with RDC procedures (Real Driving Conditions), with initial battery charge status 100% (according to the app SKODA CONNECT linked with SKODA CITIGO e IV). While driving, the following parameters were recorded: recording time [s], vehicle’s speed [km/h], rotational speed of the engine [rpm], charge/discharge current in a high-voltage battery [A], current value on electric engine [A], tension value on electric engine [V], power taken/recovered from the high-voltage battery [W], state of charge of the battery (SOC) [%], EV engine torque [Nm]. Then, based on the author’s work on driving parameters, the requirements to be met during driving tests were stipulated in accordance with RDE procedures (Real Driving Emission); it led the researchers to calculating the EV power demand at selected stages of the test. The RDC test was divided into three sections with speed ranges, 0–60, 60–90 and above 90 [km/h], that resemble speeds on urban roads, rural roads and motor ways, respectively (test results will refer to these ranges, in particular, an extended analysis of EV power consumption in urban areas will be conducted).

The measurement was conducted in two seasons of the year to consider changing weather conditions affecting power consumption of the drive system. The measurement in winter conditions was conducted in March, with average day temperature +3 °C; the measurement in summer conditions was conducted in July 2020, with average day temperature +23 °C. Meeting test requirements in accordance with the procedure [52,53,54,55] is presented on a diagram on Figure 19. Because of different driving conditions, the time of conducting both tests was different but they met the requirements of the RDC test, which made the analysis possible.

Both rides are characterised by comparative driving parameters. Moreover, the routes were summarised and presented in the comparative matrix with regard to the time share of constant speed (Figure 20a) and convergence of battery charging and discharging on a particular fragment of the route (Figure 20b); this shows that the summary levels of charging and discharging in terms of frequency of occurrence are similar for both rides. The analysis of values of power consumption and recovery shall be presented in another stage. The greatest power recovery, over 25% of driving time, is obtained in urban areas. The higher speed (as the route changes), the bigger power consumption.

In order to calculate power consumption of the drive, an analysis was conducted to check power flow in speed sections referring to the types of routes: urban, rural and motorway. Power consumption maps presented on Figure 21 show significant momentary power flows in winter, particularly in the range of average loads of the drive system at the level of 75–180 Nm. Most probably, it is caused by switching on the system keeping temperature inside the car. Summary power consumption during the winter season for the whole route of RDC test in urban conditions was by 0.6 kWh bigger than in summer. It is connected with both characteristics of the ride (more frequent stops and accelerations in comparison with summer) and additional load of the drive by the vehicle’s heating system. Since the vehicle in winter is started more often, the bigger share of power recovery was also noted at the moment of braking. The biggest differences in power consumption were observed in the speed range of 60–90 km/h in the rural route, it is over 50% more power consumption in rural areas in winter than in summer. The presented analysis shows the possibility of using RES to charge EVs in urban areas, that is why its further part exclusively includes EV power consumption when driving in urban areas. Taking into consideration the proportional share of the distance in urban ride, the total EV power consumption in urban areas was calculated at the level of 13.73 [kWh/100 km] in winter and 11.43 [kWh/100 km] in summer. Thus, the summer season brings a 20% lower power consumption in case of the tested vehicle, taking into account conditions occurring during the tests. The average value (12.58 [kWh/100 km]) shall be the basis for stipulating ride distances with the use of renewable energy sources.

3.3. Methods of Charging Electric Vehicles

When solving communication and energy problems, we should not forget about the significance of the presence of charging stations on Wroniecka Street, where the analysed tenement house is located. Pursuant to the abovementioned provisions of Resolution on creating the Old Town Culture Park (Resolution no. LXII/1151/VII/2018 of the City Council of 27 February 2018), all technical devices, such as elements of charging stations, shall be placed in a way making them invisible to the public (Figure 22). This restriction, however, does not hinder the location of EV charging stations within Culture Park. The developing sector of electric vehicles offers the possibility to use innovative technology of inductive charging. This form of the station allows complete covering of technical devices under the top layer of the street, respecting high aesthetics of the solution and effective power transfer at the same time. Moreover, the construction andinstallation works necessary to install the charging station might contribute to launching renovation works of the whole street, which, despite being a witness of many centuries of the Poznań history, is now in a very poor technical condition. Another option of the invisible installation of the charging station would be a connection point hidden in the street when not used. Such a solution would not interfere with aesthetics of the street permanently and provide high effectiveness of vehicle charging by applying a conventional connection.

A WiTricity system may serve as an example of inductive charging, where applied technology of wireless charging allows charging from grid to battery at the level of 90–93% [48]. This system is applicable to most EVs because the distance between the charger and the receiver, which the vehicle must be equipped with, may not exceed 10 to 25 cm. Unlike prototype solutions, this system is not sensitive to precision of parking, the location correction corrects (or compensates) the misalignment or parking. According to the presented assumptions, the charging system is also highly effective in case of installing it under the floor surface or in winter, under the layer of snow. Security systems like FOD (Foreign Object Detection), LOD (Live Object Detection) and PD (Position Detection) offer advanced security and simplicity of use. In accordance with the present tendency of integrating EVs in V2G (Vehicle-to-grid) [57], the WiTricity system allows the two-direction power transfer. The concept of Smart Grid has a positive impact on the integration of decentralised generation, i.e., mainly small wind and solar farms, with the power system. In this aspect, it creates new trends in the development of electromobility by enabling effective implementation of energy from those farms to the power system via vehicle-grid technology. The two-direction power transfer allows consumption of power by the vehicle in periods of low consumption or intensive production from RES, and then power transfer in the reverse direction at the time of peak energy consumption. The system presented above shows numerous advantages of the concept of integrating the building block in the city centre with the possibility to charge EVs. In the following stages of the research, the authors are going to obtain resources to implement the presented system.

The other proposed solution regarding the charging system that does not interfere with the public space is a hidden charging station with the type-2 socket offered by the British company Urban Electro [48]. It allows for the charging of the EV with an alternating current 7.2 kW. The key advantage of this solution is its invisibility in infrastructure of the surrounding when the EV is not being charged. Moreover, this option does not make car owners buy additional equipment to their vehicles.

Both solutions presented hereinabove use alternating current, 7.2 kW for Urban Electric system and 3.6 to 11 kW for WiTricity. In case of charging with alternating current, the maximum power of charging is controlled by a factory-fitted converter which transforms alternating current into direct current. In SKODA CITIGOe IV the maximum charging power for alternating current is 7.2 kW. Taking into account the registered charging courses of the vehicle for all available methods of charging, the charging time from 0% SOC, read from the vehicle can bus, to 100% SOC was presented (Figure 23). Real parameters were tested with the use of the diagnostic tester reading absolute values of the battery charging status. The charging time in case of 7.2 kW was 4 h 48 min. Including up to 10% of maximum loss during wireless charging, the time will be 5 h 16 min, which still gives a reserve when compared with the working time of an employee. In their previous article, the authors indicated that there is no need for a potential EV user to charge the high-voltage battery every day from 0 to 100% SOC. Most EV users who took part in a survey (almost 70%) declared that their daily travels on level S1 do not exceed 15 km. In such case the charging time necessary to travel that distance, including power consumption of the tested vehicle on urban routes, shall be in accordance with data presented in

Table 1. Time necessary to charge battery for 100 km range in urban area [54].

SEASON	Energy Consumption in Urban Conditions [kWh/100 km]	Charging Time Depending on Charging Method [min]
		7.2 kW AC	7.2 kW AC Wireless	2.3 kW AC	2.3 kW AC Wireless
winter	13.73	114	126	358	394
summer	11.43	95	105	298	328
average	12.58	105	115	328	361

.

Knowledge on how the EV functions creates opportunities to manage power used to drive EV in selected conditions. On the basis of the equation presented below, the user may calculate the time necessary to charge the EV for a planned distance.

$$estimated charging time=\frac{planned distance\ast energy consumption on the road}{charging power}$$

Another stage of calculating the possibility to charge the EV is defining a rate that informs about charging exclusively with energy coming from renewable sources, RES rate (2). RES rate 100% means total use of renewable energy to charge the EV. As time of the day changes, clouding increases and power consumption by the building grows, the rate will be of lower values to indicate consumption of power coming from the grid.

$$RESrate=\frac{REpower}{chargingpower}[\%]$$

(2)

4. Summary

The article aims at presenting the possibility of including a nearly zero-energy building (nZEB) in the process of supporting electromobility, with particular focus on charging EVs travelling in urban areas. The growing need of power in both architectural equipment and cars create an opportunity to use renewable energy sources to provide power for buildings and electric vehicles. Apart from the initial stage of integration of a PV system in the presented building block in Poznań, the potential of the system in producing power surpluses was also proven. The power, which is at present transferred to the grid, may be transferred directly to a particular EV charging station without the necessity to be transferred to the power plant (avoiding losses). The growing potential of power used to charge EVs at weekends is significant here, because the building decreases its power consumption on Saturdays and Sundays, as it operates mostly on working days. The increase of returned power is then 2–3 times bigger than in the period from Monday to Friday (which is presented on Figure 13). The nominal parameters of the presented PV system at the level of 4 kWp, which results in the operation at the level of 87% and the recorded real average power gain (Figure 14) have led to calculating the possibility to use 100% RES rate to increase the range of the EV at the level presented on Figure 24 below.

Assuming that only RES is used to generate power needed to charge the EV, the present PV system is able to charge the EV for the range of 7 km in weekdays and about 20 km at weekends. Although those values are not big, they may be sufficient for almost 70% of users who declared during the survey that their daily distance is up to 15 km [8].

In future, if PV systems develop according to the presented plan, it will be possible to gain power at the level of 1183.47 kWh/day, which will enable charging for a far larger range of about 9407 km for a vehicle tested in the urban area or simultaneous charging of 164 vehicles with power of 7.2 kW. Those estimates shall be evaluated at consecutive stages of works. The work at the present stage aims at indicating the direction of modernization for other buildings in the block and transforming them into nZEBs.

The above work has some limitations due to the simplifying assumptions of the simulation of renewable energy production, or the consideration of a single vehicle, but due to the rapidly developing transportation and architecture in line with the integration of these systems, this work sets the stage for further research both by the authors and other research institutions.

In their further research, the authors are going to conduct analyses of power consumption of vehicles from other segments and create the data base of power consumption in real driving conditions for a larger number of vehicles. They are also planning to carry out analyses of implementing PV panels in the presented building block. When considering the implementation of charging stations, the authors will also consider current trends in applied charging stations and their management for effective energy supply control [58].