The Use of Renewable Energy Sources in Road Construction and Public Transport: A Review

Abstract

The development and advantages of renewable energy technologies mean that their areas of application are constantly expanding. The development of roads, transport systems, and electromobility also increases the demand for electricity. Roads occupy a certain area that could be used to install wind turbines or photovoltaic systems that could be used to power, among others, electric vehicle charging stations and road technical infrastructure facilities (travel service areas, tunnel lighting, road signs). There are many examples around the world where such solutions have been used. This critical review of existing solutions and the possibilities of their application in new places may contribute to further development and research in this area. Particular attention was paid to the possibility of using renewable energy systems in Poland, which can be successfully transferred to other countries with a similar climate.

1. Introduction

The use and provision of access to green energy lead to sustainable development worldwide. The world is focused on renewable energy sources (RESs) for its economy and to achieve climate protection goals. Renewable energy sources such as solar and wind energy are widely recognized as suitable for powering roads and highways, their maintenance and management systems, lighting, signaling, information boards, etc. The integration of selected renewable energy technologies into highways reduces the number of installations and the costs of building power lines to power networks used on highways. At the same time, renewable energy sources do not emit carbon dioxide. Another reason for the use of renewable energy in the area of broadly understood road construction is the fact that approximately 2–5% of the Earth’s surface is covered by roads. It is estimated that by 2050, this percentage may increase by another 6%, which shows that up to 8% of the planet’s surface will be excluded from nature and will have a very strong impact on the natural environment. In turn, technological progress and new solutions regarding, for example, photovoltaic panels indicate their extraordinary mechanical strength. Photovoltaic roads could replace traditional asphalt roads, simultaneously becoming powerful energy generators, which, in connection with the development of electromobility, will be of key importance [1].

The implementation of various energy sources increases energy efficiency and also realizes the goal of smart cities, i.e., the use of clean energy with zero emissions of carbon dioxide and other gaseous and particulate air pollutants.

The aim of this article is to determine the current state of knowledge on the possibility of using road areas, usually undeveloped so far, for the installation of systems generating energy from renewable sources, especially photovoltaic and wind sources. Achieving this goal is possible by critically reviewing available solutions, with a particular emphasis on European countries. This review is intended to indicate possible directions of RES development for roads Poland.

Current changes in legal regulations and global and European trends (including European Commission directives) limiting the number of combustion cars in favor of electric vehicles are aimed at reducing the amount of environmental pollution. However, such actions will force an increase in the number of charging points for electric cars, especially on expressways and highways, which will translate into a significant increase in demand for electricity. Therefore, all actions enabling the generation of energy at the point of demand (road infrastructure) are desirable in order to reduce transmission losses and build expensive high-power transmission infrastructure. One way to achieve this effect is to design and install photovoltaic systems and/or wind turbines along roads, as well as integrate photovoltaic cells with acoustic screens.

The aims of this study are as follows:

• A multi-level analysis and presentation of potential solutions using selected renewable energy technologies in the road sector;
• An assessment of the potential of using renewable energy sources in road construction in terms of improving the energy efficiency of road infrastructure;
• The identification of best practices in the design of the above-mentioned systems based on case studies from various regions of the world.

The authors decided to review existing solutions for the use of solar cells and wind turbines installed in road areas, which have not been used so far and occupy a large area. Renewable electricity is used to power road infrastructure devices or can be used to charge electric vehicles due to the development of electromobility. This manuscript is organized as follows: (1) The use of photovoltaic devices of various versions (traditional photovoltaic panels, paths, roads, sidewalks, road roofs) is reviewed; special attention is paid to various available forms of integration of PV cells with acoustic barriers creating photovoltaic noise barriers, with many examples of the implementation of these types of solutions, mainly in Europe, cited. (2) The use of turbines with vertical and horizontal rotation axes installed in road areas are discussed. (3) The development of electromobility and the use of RESs for local electricity generation are described. (4) Information on the construction of the Trans European Transport Network (TEN-T) is provided. (5) The potential of using RESs in road construction in Poland, including photovoltaic and wind sources, is discussed. (6) A discussion and conclusions resulting from this review are provided.

2. Materials and Methods

A analysis of current solutions in the use of renewable energy generation systems in road infrastructure was carried out using desk research methods and a literature review. The scope of this research covers both the global context (China, USA, India, Australia) and the European context (Germany, Italy, Austria, Switzerland, Great Britain), including Poland. The main sources of data are databases of scientific journals (e.g., mdpi.com, ieeexplore.ieee.org, sciencedirect.com, taylorandfrancis.com), websites of industry portals (e.g., gramwzielone.pl, pvmagazine.com), and government offices containing press reports and descriptions of projects covering the renewable energy sector in the road area.

The research problem adopted in this work includes the analysis of the possibility of using available, previously undeveloped space for the installation of photovoltaic systems and wind turbines.

The cited examples of applications and uses of road areas are an interesting starting point for future scientific discussion, attempting to adapt the presented solutions in various countries with non-obvious environmental values (e.g., the use of low-power wind turbines in close proximity to the road, using the wind movement from passing vehicles, even in low-wind areas). In addition to the scientific community, this study can be used by public and private decision-makers, investor management boards, municipal and city authorities, and local communities. The considerations contained in this study provide information to enterprises, producers, and end users of roads, who, based on the development of a network of fast chargers along roads, may decide to switch to electric cars. It is also important to make state authorities aware of the need to adapt legal regulations to enable the economy to be fed with the latest scientific research results and technical proposals resulting from them in the area of using renewable energy sources in road infrastructure.

3. Solar Systems in Europe and around the World in the Context of Use in Road Construction

One of the difficulties in using photovoltaic systems to generate electricity on a large scale is the significant demand for free areas on which photovoltaic panels would be installed. Problems with surfaces for PV systems are particularly noticeable in highly developed countries, where, at the same time, road, railway, and air communication systems are highly developed. Road systems have particularly good properties for the development of photovoltaics. For this reason, photovoltaic noise barriers (PVNBs) are becoming more and more popular. They reduce noise while using existing road infrastructure and high-power receiving installations without occupying additional land, e.g., agricultural land. The first photovoltaic noise barriers of this type were installed in 1989 in Chur, Switzerland, along a highway [2,3].

3.1. Application of Photovoltaics

3.1.1. Roofs, Masts, and Canopies Made of PV

PV modules in road areas can be used to build roofs over roads (Figure 1). An example of such a solution is the DACH project implemented by three European countries, Germany, Austria, and Switzerland, in 2020–2021 and managed by the Austrian Research Foundation (FFG). The project goes beyond the current concept of using rest areas or powering tunnels from renewable sources used on roads in these countries. A PV installation in the form of a roof over traffic areas, in addition to generating energy and multiple use of the area, brings additional benefits for the road infrastructure operator, such as protecting the road surface against precipitation (rain, snow, ice formation) and overheating in the summer, which may lead to increased durability of the road surface. Moreover, such a roof provides additional protection against noise by shielding, thanks to the use of appropriate structures. When designing this type of solution, attention should be paid to additional elements such as drainage, wind and snow loads, the stability and impact safety of supports, maintainability, and road traffic safety [4]. In Germany, such structures are subject to the same requirements as bridges and tunnels, because a roof over communication routes over 80 m long is also considered a tunnel structure. Aspects related to its lighting, fire protection, and monitoring and the presence of escape routes should also be taken into account [5]. Due to the above limitations, the research project of the photovoltaic canopy over the federal highway was 80 m long. The first stage of the DACH project included conceptual phases, while as part of the second phase of the project, a demonstration of the installation was carried out in July 2023 on the A81 motorway in Baden-Württemberg (Figure 2). The roof demonstrator measures 12 × 14 m and 5.5 m high above the carriageway of the Hegau-Ost motorway service area. However, after the conceptual phase, a quick commercial implementation of the roof cannot be expected due to its high costs. Such solutions may be introduced in a sectoral and selective manner, especially in areas with increased demand for electricity, e.g., within tunnels, viaducts, and passenger service areas [5]. From approximately 170 m² of the PV roof area, the estimated electricity yield is approximately 40 MWh per year [6].

The Swiss Minister of Energy has commissioned the Federal Roads Office (Astra) to investigate the possibility of covering roads with roofs equipped with photovoltaic panels. According to a report by the Neue Zurcher Zeitung (NZZ), theoretically, 1300 of the 1500 km motorway network would be suitable. In addition to the use of roofs, the possibility of lining acoustic screens with PV panels is also being considered, the potential energy gain of which could amount to up to 55 GWh per year, which would constitute 0.05% of the total energy consumed in Switzerland [8]. For comparison, the installation of PV panels on acoustic screens in Poland would contribute to the production of electricity at the level of approximately 175,000 GWh per year, which would constitute approximately 0.03% of the country’s total energy production.

The DACH concept also presented canopies over tunnels or parking lots from other places around the world (Figure 3), which can also be adapted to Polish conditions and the modernization of existing roofs, such as tunnels in cities over expressways (Figure 4).

There is also basic road infrastructure in Poland that could be used to develop a similar solution (Figure 4).

The German Altes Neuland Frankfurt foundation presented the idea of using road space with photovoltaic solutions. The project assumes the erection of steel masts every 15 meters along the roadsides of highways, between which a structure for the installation of PV panels would be mounted (Figure 5). Assuming the construction of such installations along 80% of highways and 65% of federal roads, the total length of which is approximately 45,000 km, energy generation could amount to 200 TWh per year. However, the implementation of this concept would require additional investment outlays, for example, laying 110 kV cables underground along roads, while the cable connections would have to be located 9 to 87 km apart, depending on the conditions [10].

Reference [12] presents a concept of canopies over dual carriageways in India (Figure 6). A photovoltaic roof over the approximately 207 km long NH47 highway between Ahmedabad and Rajkot could reach a power of 104 MW and generate 163 GWh of energy per year. The second analyzed highway was the NE1 road between Ahmedabad and Vadodara, approximately 93 km long, where the system power was 61 MW and the energy generation was 96 GWh. By changing the single-layer roofing system to a double-layer one, the generated energy would increase by over 40% and would amount to 229 GWh and 140 GWh, respectively, for the analyzed roads. Additional benefits resulting from the construction of a photovoltaic roof were also indicated, such as no additional costs of use and purchase of land, improved vehicle traffic efficiency and reduced energy consumption (reduced need for vehicle air conditioning), and longer vehicle tire and road life (due to the lack of direct solar radiation and lower road temperature).

By using the green belt separating the highway lanes running in opposite directions, it is possible to build high-power photovoltaic installations, an example of which is the concept presented in [13] for a highway in India. The width of this strip of land is approximately 4.5–5 m. The installation height of PV panels above the ground was assumed to be 1 m; the vertical arrangement of the panels was at an optimal angle, where they were directed to the south. The length of the road is 2.9 km, which would translate into the possibility of obtaining an installation with a power of 1.2 MW, generating approximately 1.824 GWh per year. Analyzing the longer sections of the highway between Ahmedabad-Rajkot (202 km) and Ahmedabad-Vadodara (114 km), it is possible to build PV systems with a power of 67 MW (generating 101 GWh) and 39 MW (generating 58.5 GWh per year), respectively.

Reference [14] presents prospects of solar-powered road and rail transport in China. In 2008, the first-ever solar power plant with a power of 220 kW, using silicon thin-film cells, was installed in Beijing South on the roof of a railway station with an area of approximately 14,000 m². Its energy production is approximately 223.6 MWh per year [15,16]. In 2013, a PV installation was built on the roof of the Hangzhou East railway station with a capacity of 10 MW, using crystalline silicon panels, on an area of approximately 79,000 m². The annual energy yield from the installation is 10.4 GWh [17]. Further PV systems were built on the roofs of the Shaling depot in 2016 with a power of 2.4 MW, the Xizhaotong depot in 2016 with a power of 1 MW, and the Yuzhu depot in 2018 with a power of 5 MW [18,19,20]. PV panels are also installed on the roofs of railway platforms (e.g., in Tokyo with a power of 453 kW from 2011) [14]. In 2017, an electric vehicle charging station was built in Shanghai, integrated with 1002 photovoltaic generators that can generate approximately 500 kWh of electricity per day, enough to charge over 400 cars per day. A similar solution was used on the Jingjintang Expressway. The power of the PV system was approximately 290 kW, and an additional energy storage with a capacity of 230 kWh was used [21]. The 1080 m long Jinan Bypass Highway also uses solar energy to power road facilities [22]. Similar solutions for integrating PV systems with electric vehicle charging stations have been developed in other countries. In the United States, an autonomous renewable EV charger (ARC) was developed, consisting of an independent charging and energy storage system (32 kWh battery). In California, some EV ARC charging stations are not connected to the power grid at all [23,24].

3.1.2. Photovoltaic Roads, Paths, and Sidewalks

Figure 7 illustrates photovoltaic roads developed in the USA that are intended to harvest solar energy, which will be possible to walk and drive on in the future [25].

However, the results of the tests carried out in France are not satisfactory in this respect. The photovoltaic road built by Colas in Tourouver au Perche in France with a rated power of 420 kW, covering an area of 2800 m², cost as much as EUR 5 million, which means that the unit cost of 1 kW of installed power was EUR 11,905. It was assumed that the photovoltaic road would generate, on average, approximately 800 kWh of energy per day, but the research conducted shows that the actual yield is 409 kWh/day, i.e., approximately 150 MWh per year. Therefore, the cost of a PV road is as much as 10 times higher than that of a traditional free-standing PV installation, and its energy yield is almost three times lower. The disadvantages of this solution include horizontal arrangement (i.e., non-optimal angle of inclination of PV cells), high susceptibility to shading (dirt, dust, moving objects on the road), the use of thick glass (due to increased mechanical strength, limiting the penetration of sunlight for PV cells), and higher cell temperature (due to lack of air flow) [26]. Similarly, in 2016, a kilometer-long section of a photovoltaic road in Normandy generated only half of the expected amount of electricity [27].

The Sandpoint, Idaho-based startup Solar Roadways Incorporated has developed solar panels to replace asphalt road surfaces. The top glass layer is rough enough to ensure the proper grip of vehicles and transparent enough to ensure the proper operation of PV cells. According to researchers [28], solar roads could replace the surfaces of residential roads, parking lots, driveways, and even highways. However, attention was paid to their effectiveness and the availability of sunlight only for a specific time of the day or year.

In 2014, the first photovoltaic bicycle path in the Netherlands (Krommen) was built, and then in 2016 near Amsterdam, while in 2020, the longest path was built in Utrecht, measuring 300 m in length (Figure 8), in cooperation with the TNO Research Institute and Strukton Prefab Concrete. It uses special prefabricated PV modules with 5 mm thick glass with an anti-slip coating for the safety of travelers and silicon PV cells. Also, in the Netherlands, in Groningen, a photovoltaic pavement was built with an area of approximately 400 m², composed of 2544 photovoltaic cubes produced by the Hungarian company Platio. The sidewalk generates approximately 53 MWh of energy per year, which is used to power the city hall. The casing of the photovoltaic paving stone is made of recycled plastic, and on its top, there is tempered glass, protecting the PV cells against mechanical damage. The surface of the tile is not smooth, but textured, to ensure greater pedestrian safety, and can be available in several colors. The paving stones have their own cable outlets, which can be connected from 16 to 21 pieces into one chain, connected to an inverter or battery charging controller [29].

In the Dutch province of North Brabant, along the M285 road, a 500-meter photovoltaic bicycle path was recently built on an asphalt surface. The system, composed of 600 solar modules, is to be tested for the next 5 years in terms of the mechanical strength of PV modules loaded by pedestrians and cyclists, system maintenance costs, and its efficiency. Two similar systems have also been installed on the N395 in Oirschot and the N324 in Grave [30]. Also, in Germany, in the city of Freiburg, photovoltaics were used, not on the surface of the bicycle path but as its roof (Figure 9), on a 300 m section. The system, intended to generate 280 MWh of electricity per year, was created in cooperation with three partners: Badenova WARMEPLUS, the Institute Fraunhofer, and the city of Freiburg. The function of the project, in addition to generating green energy, especially in densely populated agglomerations, is also to protect people from the sun and rain. Glass–glass PV modules were used, and the entire system is still waiting to be connected to the power supply system of the Fraunhofer Institute, which will use the energy to power its laboratories [31]. A similar roofing of the bicycle path, using double-sided PV modules, was carried out at the first installation in Switzerland in the commune of Satigny in the canton of Geneva (Figure 10). The roofed photovoltaic part is 200 m long, has an area of 860 m², and generates 200 MWh of energy per year. It consists of 468 double-sided translucent PV modules that can generate 5–15% more energy compared to conventional PV modules. The cost of building the path was CHF 1.5 million [32].

Figure 8. Photovoltaic bicycle path in Utrecht [33].

Figure 8. Photovoltaic bicycle path in Utrecht [33].

3.2. Photovoltaic Noise Barriers (PVNBs)

Noise screens are commonly used elements of road infrastructure. They are made of various materials; their main part is usually made of steel elements placed on a concrete foundation. Filling materials used in the construction of screens, such as wood, concrete, glass, plastics, aluminum, or their combination, are characterized by good sound-reflecting or -absorbing properties [34,35].

The integration of photovoltaic modules with sound-absorbing screens can essentially be achieved in two ways: by mounting PV panels on the top or sides of existing acoustic screens or by mounting them directly into sound-absorbing barriers (integrated systems) [36]. In the case of PV panels, it is extremely important to properly adjust their inclination and orientation in order to optimize electricity generation. Their proper installation influences whether barriers maintain adequate noise attenuation effectiveness. You can often come across taps equipped with additional inclined plates, placed on top of the vertical part of the barrier, which serve to additionally reduce noise when it is necessary to use a lower sound-absorbing barrier [36,37]. Figure 11 shows selected methods of mounting PV modules on acoustic screens.

Integrated PVNB board configurations can be in a vertical, vertical bifacial (double-sided modules), zigzag, or cassette configuration (Figure 12), depending on the PV modules used and the orientation of the screen towards the world. Integrated systems have better sound-absorbing properties than vertical or inclined structures mounted on top of barriers in terms of sound absorption. More insulating materials are needed to build a cassette module, but it is a highly effective solution in terms of noise protection. The cassette absorbs sound very effectively, and its upper surface is well suited for mounting photovoltaic modules [34].

Unlike regular photovoltaic systems, the orientation of PVNBs is determined by the direction of the road. Therefore, a solar sound barrier does not always have the optimal spatial position for energy generation purposes. The vertical double-sided system (Figure 12B) uses bifacial solar cells that can absorb solar radiation reaching from two sides (e.g., from north/south or east/west) and convert it into electricity, thanks to which the energy yield is less dependent on the orientation of the barrier. The theoretical two-plane prototype showed that PVNB generation could be 6% higher than that of a south-oriented installation. Tests of a 10 kW bifacial PVNB installation conducted in Switzerland showed that it produces approximately 17% less electricity than expected. Lower electricity production could be caused by losses resulting from the orientation of the PV installation along the highway (running in an arc), oversizing of the photovoltaic inverter, or the photovoltaic conversion efficiency of the PV module [2,34].

Due to the large selection of photovoltaic cells on the market, the period of failure-free operation and the energy efficiency of screens may vary. For monocrystalline cells, manufacturers provide a warranty of approx. 25 years. On the other hand, if the barrier has a sufficiently good base and is made of high-quality materials, its durability is approx. 20–25 years [39]. Hence, it is possible to integrate these elements to ensure appropriate acoustic and electricity generation properties for the assumed period of operation. The properties of PVNBs concern not only electrical and acoustic aspects, but also safety, visual impact, and the possibility of uninterrupted maintenance and servicing [2]. Therefore, in the process of designing systems with PVNBs, possible car accidents should be taken into account, which entails the need to meet standards and regulations regarding the safety of road users.

The world’s first installation of photovoltaic panels mounted on acoustic barriers was the PVNB barrier in Switzerland in 1989 on the A13 motorway (Figure 13). Solar panels with a total power of 100 kW were attached to the 2 m high acoustic barrier structure, in its upper part, at an angle of 45°, with a 25-degree deviation towards the east. The length of the photovoltaic acoustic barrier is 800 m. Polycrystalline solar panels increased the barrier area by 968 m² and generated approximately 100 MWh of electricity per year [40]. In 2000–2001, several inverter failures occurred (after 11–12 years of system operation), but the system continues to operate properly to this day, and despite the lack of cleaning of the PV modules, no significant deterioration in system performance was noticed. In 2019, the installation was modernized and the installed power was increased by another 262 kW, thanks to which the system currently generates over 330 MWh of electricity per year [41].

In 1995, the Swiss authorities, after 6 years of proper operation of the PVNB installation, announced an international competition for new alternative PVNB solutions, thanks to which six more installations were built in 1997–1999, with a capacity of 10 kW each (three in Switzerland and Germany) [3].

There are currently approximately 35 PVNB projects in Europe with capacities ranging from several kilowatts (small test installations) to several megawatts [40]. All installations located adjacent to road, rail, or industrial infrastructure are presented in

Table 1. List of available and planned photovoltaic acoustic barriers in Europe [2,3,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77].

Country	City	Highway Number	System Power [kW]	Angle [°]		Year	Cell Material	Owner/Designer	View
				Inclination	Azimuth
Switzerland	Chur	A13	100 + 262	45	25	1989/1995	c-Si	TNC AG
Austria	Seewalchen	A1	40	n.d	160	1992	n.d	Oberöstereichische Kraftwerke	n.d
Germany	Rellingen	A23	thirty	n.d	200	1992	n.d	TST (DASA)	n.d
Switzerland	Gordola	Rail	103	n.d	200	1992	n.d	TNC AG	n.d
Germany	Saarbrücken	A620	60	n.d	n.d	1995	n.d	Stadtwerken Saarbrücken	n.d
Switzerland	Giebenach	A2	104	45	n.d	1995	n.d	TNC AG/Canton Basel
The Netherlands	Utrecht	A27	55	50	245	1995	c-Si	RWS
The Netherlands	Ouderkerk a/d Amstel	A9	220	50	200	1996	c-Si	Shell and ENW/EU Commission
Germany	Inning am Ammersee	A96	thirty	n.d	n.d	1997	n.d	TNC GmbH, Bayernwerk, BMFT	n.d
Switzerland	Zurich (Aubrugg)	A1	10	90	80	1997	c-Si	Uitbreiding door TNC in 2004
Switzerland	Zurich (Walliselen)	Rail	9.6	45	200	1998	c-Si	TNC	n.d
Switzerland	Zurich (Brütisellen)	A1	10	90	140	1999	a-Si	TNC	n.d
France	Fouquières-lès-Lens	A21	63	45	170	1999	c-Si	n.d	n.d
Germany	Sausenheim	A6	100	n.d	n.d	1999	n.d	n.d	n.d
Austria	Gleisdorf	A2	101	n.d	n.d	2001	n.d	n.d	n.d
Switzerland	Safenwil	A1	80	45	170	2001	c-Si	IG Solar Safenwil	n.d
Germany	Emden	A31	53	90	180	2003	n.d	many owners
Germany	Freising	A92	718	45	180	2003	c-Si	n.d
Germany	Vaterstetten	Rail	180	n.d	210	2004	a-Si	Phoenix Solar	n.d
Germany	Freiburg	B31	365	n.d	n.d	2006	n.d	TNC, aluminum: Van Campen	n.d
Germany	Grossbettlingen	313	28	n.d	n.d	2006	n.d	n.d	n.d
Germany	Töging am Inn	A94	1000	45	210	2007	n.d	n.d	n.d
Switzerland	Melide (Lugano)	A2/rail	123	45	220	2007	c-Si	Suntechnics Fabrisolar AG	n.d
Switzerland	Münsingen	Rail	12	90	80	2008	c-Si	TNC	n.d
Germany	Schwabisch Hall	Reinhold-Würth- Airport noise barrier	75	n.d	n.d	2008	n.d	n.d	n.d
Italy	Marano d‘Isera (Trento)	A22	730	n.d	140	2009	c-Si	IrisLab/Autobrennero A22
Germany	Aschaffenburg	A3	2650	45	150	2009	c-Si	Evergreen solar GmbH
Italy	Oppeano (Verona)	SS434	833	45	210	2010	c-Si	n.d
Germany	Bürstadt	B57	283	60	150	2010	n.d	n.d
Germany	Biessenhofen (Bayern)		90	45	180	2010	n.d	Rau Lärmschutzsysteme	n.d
Germany	Muhlsdorf	A4	3000	n.d	n.d	2012	n.d	n.d	n.d
Germany	Munich	Rail/road	7544	90	n.d	2013	bifacial c-Si	Kohlauer
Switzerland	Zumikon	Road	89	45	n.d	2014	c-Si	TNC	n.d
Germany	Bollberg	A4	1000	n.d	n.d	2015	n.d	n.d	n.d
Germany	Neutting	B12	52	n.d	n.d	2016	n.d	n.d	n.d
Germany	Wallersdorf	A92	1000	45	150	2017	n.d	Apfelböck Ingenieurbüro GmbH	n.d
The Netherlands	Pijnacker-Nootdorp	N470	thirty	n.d	n.d	2017	n.d	n.d	n.d
Germany	Reundorf	Rail	95	n.d	n.d	2020	n.d	n.d	n.d
Systems implementation plans
The Netherlands	Bathmen	A1	1000	n.d	180	n.d	n.d	RWS	n.d
The Netherlands	Tiel	A15	300	n.d	n.d	n.d	n.d	n.d	n.d
Germany	Michendorf	A10	4500	n.d	180	n.d	n.d	n.d	n.d
Great Britain	Swindon	A419	n.d	n.d	n.d	n.d	n.d	n.d	n.d
Great Britain	Buckinghamshire	M40	n.d	n.d	n.d	n.d	n.d	n.d	n.d
The Netherlands	Rotterdam	A20	n.d	n.d	n.d	n.d	n.d	n.d	n.d

. The table summarizes the technical data of the installations, such as rated power, orientation, slope, location, and type of solar technology used, as well as information about the contractor, owner, and operator of existing or planned barriers.

The smallest installation with a power of 7.5 kW is located in Germany in Munich, while the largest (also German) installation with a power of over 2 MW is located in Aschaffenburg. There are plans to build a 5.5 km 4.5 MW PV acoustic barrier in Michendorf near Potsdam, Germany [40]. It can be seen that most of the barriers face south, with an inclination ranging from 140° (southeast) to 220° (southwest). Most photovoltaic planes are tilted at a given elevation angle, although a few are vertical at 90°, including those in Brütisellen in Zurich and in Emden and Munich in Germany. Most systems use silicon cells (c-Si); however, three systems (Vaterstetten, Melbourne, and Emden) use cells based on amorphous silicon (a-Si). In Zurich and Münsingen in Switzerland, the installed systems are equipped with bifacial solar cells, which enables the use of solar energy arriving from both sides of the barrier. These barriers are set at an angle of 90° to the horizontal. The world’s first such barrier with double-sided cells was built on the highway viaduct in Aubrugg with a power of 8 kW. The panels also act as sound-reflecting elements.

A European study [2] conducted by seven partners from six countries determined the energy potential of PVNBs, taking into account current and planned road and rail systems. A detailed summary of the results obtained is presented in

Table 2. Technical potential for electricity generation along the road and rail systems surveyed in six European countries (copyright publisher: John Wiley & Sons Publishing, 2004, from [2]).

Technical Potential	Switzerland	Germany	The Netherlands	Great Britain	Italy	France	SUM
PVNB [km]
Roads	303.8	1525	475.9	204	50.7	352.2	2911.7
Railway lines	94.7	600	444.6	16.5	7	139	1302.1
System power [MW]
Roads	58.5	293.8	114.6	39.3	9.8	67.9	583.9
Railway lines	14.9	+4.5	82.4	2.6	1.1	21.9	217.4
SUM	73.4	388.3	197	41.9	10.9	89.7	801.3
Energy generated [GWh/year]
Roads	53.4	247.5	91.8	29.9	10.3	63.7	496.6
Railway lines	13.6	82.4	65.6	2	1.2	21.4	186.1
SUM	67.0	329.9	157.3	32	11.5	85.1	682.8

. In the analyzed countries, it is possible to install a PVNB system with a power of 800 MW and an annual electricity generation of approximately 680 GWh. Due to the different stages of planning and implementation of noise protection measures in Great Britain, Italy, and France, only existing noise barriers were taken into account, which makes the actual potential of these countries much higher.

Moreover, three pilot research installations with powers between 8 kW and 10 kW were built in Germany and Switzerland (Figure 14). Detailed data of these systems are summarized in

Table 3. Examples of pilot PVNB installations in Germany and Switzerland (copyright publisher: John Wiley & Sons Publishing, 2004, from [2]).

Country	Installation	Year	Type	Power [kW]	Annual Energy Yield [kWh/kW]	PV Cell Temperature [°C]
Germany	Fabrisolar	1998	Cassette	8.77	751	40.9
	Zueblin	1998	Shingles	9.13	814	43.9
	DLW Metecno	1998	Zigzag	10.08	794	27.0
Switzerland	Bruettisellen	2000	Cassette	8.2	446	34.8
	Wallisellen	1998	Zigzag	9.65	497	43.9
	Aubrugg	1997	Bifacial	8.27	681	26.5

.

In the UK, a hybrid system of noise barriers and PV panels was designed for the A419 road in Swindon. It was calculated that the profit from electricity generated over 25 years by the PVNB barriers would cover the total costs of building the screens (an amount of GBP 3.2 million for 1.7 km of acoustic barriers to the west of the road and a 2 km section of PVNB screens for the village to the east). Moreover, the construction of acoustic screens and reducing the noise level could contribute to increasing the amount of land available for residential development and increasing their value. Although PV panels are capable of reflecting sound, when mounted on top of acoustic screens and positioned at an angle of 35º (for optimal energy yields), they can reflect sound from the road towards homes. In turn, it was also shown that the use of a 4 m high PVNB barrier would provide better noise attenuation effects than an earth embankment of the same height [78].

Two pilot 54-meter sections of a photovoltaic acoustic barrier were built on an existing earth slope near junction 9 of the M27 motorway in the UK (Figure 15). At the top of the slope, there is a 2 m high screen with forty PV panels inclined at an angle of 68° (Figure 16a), and that at the bottom of the slope is 2.5 m high with ten photovoltaic laminates inclined at an angle of 60° (Figure 16b). The power of each installation was 5.12 kW. The total annual energy yield was 6.4 MWh, and both installations generated a comparable amount of energy. The existence of the barrier did not distract drivers. The results of the noise study showed that the existing photovoltaic barriers increased the road noise level on the opposite side of the highway by 0.3 dB(A), without exceeding the permissible values [79].

In 2007, VicRoads in Melbourne, Australia, installed a 24 kW PVNB installation on Road 40 (at the motorway junction near Tullamarine Airport), in which PV panels were mounted vertically on top of noise barriers over a length of 500 m (Figure 17). The photovoltaic portion of the barrier consists of 210 opaque amorphous silicon solar panels, each weighing approximately 106 kilograms, installed vertically on top of a 4-meter-high acoustic barrier. Due to the thickness of the tempered glass in the panels, the acoustic tape installed between the panels, and the additional meter of barrier height, the photovoltaic panels act like conventional acoustic walls. It has been shown that photovoltaic panels of appropriate weight can be an equally good solution, performing functions similar to those of acoustic screens, assuming that the acoustic screen is a sound-reflecting surface. The reduced solar efficiency of a vertical panel compared to an angled panel is at an acceptable level. The vertical orientation of PV panels minimizes the risk of dirt accumulation and facilitates self-cleaning of the surface and does not distract drivers (does not blind drivers). Unfortunately, low energy prices in the feed-in tariff system with energy generation during the day and lower demand at night result in the lack of economic profitability of this type of solution in Australia [37].

Scientists from Turkey took into account a section of a highway in Istanbul running through a city with dense buildings [80]. Various heights and widths of photovoltaic barriers were analyzed to check noise reduction. Energy issues were not subject to optimization, only acoustic ones. In this respect, the best angle of inclination of the highest acoustic module was 58°, and the worst attenuation was achieved at an angle of 27°. Using a different angle for photovoltaic modules results in lower electricity yields. However, for noise attenuation reasons, PVNBs had similar properties to traditional acoustic barriers. Researchers indicated that the use of PVNBs in densely populated places could also contribute to the development of electromobility, due to energy generation in places of significant energy demand. In further research [81], the authors also took into account energy aspects, which made it possible to estimate energy yields using PVNBs and obtain optimal installation conditions. However, energy aspects and noise attenuation were considered and analyzed independently in different simulation programs, which also causes errors in the obtained results. The authors point out the lack of appropriate simulation tools for a comprehensive analysis of integrated photovoltaic acoustic screens.

4. Wind Systems in Europe and around the World in the Context of Use in Road Construction

Areas located close to expressways and highways enable the kinetic energy of natural air movements and the use of its increased potential resulting from vehicle movements. For this purpose, wind turbines placed in the central part of the road and in its side sectors can be used. The use of a VAWT (vertical-axis wind turbine) instead of an HAWT (horizontal-axis wind turbine) does not require their orientation. As stated in [82,83,84,85], the appropriate selection of parameters for VAWTs with a height of up to 1.5 m, placed on concrete protective barriers separating traffic lanes on highways in the USA (Figure 18), enables the generation of mechanical and electrical energy from the kinetic energy of the flow air. The indicated kinetic energy of air masses depends on the speed of moving vehicles, their number, and their distance from the wind turbine rotors. In this respect, there are still unexplored aspects related primarily to the safety of road users [86,87,88,89,90]. Studies are being conducted to investigate the instantaneous speed values of the induced air flow, such as along highways in North Carolina, where the North Carolina Department of Transportation (NCDOT) has provided funding to the Clean Energy Technology Center (NCCETC) to investigate the potential for generating electricity in high-intensity traffic corridors using wind technologies (Figure 19) [91].

Legal regulation still requires many aspects, e.g., repairs and inspections of wind turbines, which should be carried out at night, with the traffic lane in the immediate vicinity closed. It would also be necessary to develop new rules for snow removal from roads to prevent damage to wind farms, as well as to limit the use of salt for road de-icing, as it could accelerate the corrosion of turbine structural elements [82].

Wind power plants are rarely used directly in road construction, but they can be used in some aspects of road infrastructure or in accompanying applications, playing a supporting role and providing energy for various devices and systems while promoting sustainable development and the use of renewable energy. Potential applications of wind sources in the context of road construction may include powering road lighting in areas where there is no access to the power grid, powering measuring devices, monitoring and controlling road traffic, or implementing intelligent energy systems; wind turbines can complement other electricity generators used in the vicinity of road infrastructure. Figure 20 shows vertical-axis wind turbines that are designed by “TAK Studio” [92] and used to power highway lighting.

Simulation studies on the possibility of using small wind turbines with a vertical axis of rotation were carried out for a highway in Ohio (USA) [93]. They include simulation of the wind speed indicated by passing vehicles using CFD analysis. For a sedan car, the highest values of induced wind speed of 1.7 m/s were recorded at a height of 1 m above the road and at a lateral distance of 1 m from the vehicle. For VAN and SUV vehicles, the wind speed was approximately 2 m/s, while for trucks, the wind speed generated at a height of 2 m was as much as 8 m/s. Wind speed values recorded by continuous vehicle movement were also checked. A repeatable sequence of vehicles (sedan, SUV, VAN, truck) spaced 80.4 m apart and moving at a speed of 60 mph was assumed. The obtained research shows that the wind speeds generated by individual vehicles decreased slightly in the direction of travel, but increased slightly in other directions, and turbulent flows appeared in the direction opposite to the direction of travel. The obtained conclusions clearly indicate the possibility of generating electricity by small VAWT turbines and, in combination with electrochemical storage facilities, powering highway lighting.

Similar research is being conducted by the Turkish company Deveci Tech, which has developed intelligent wind turbines (Figure 21) that use natural wind and gusts of wind generated by passing vehicles. The tested turbines are additionally equipped with sensors allowing the determination of air quality, including CO₂ levels and temperature, and are also able to detect earthquakes. The turbine is also equipped with a small photovoltaic panel, which increases the total generation of electricity obtained. These turbines can be installed not only on highways, but also along other communication routes or in metro tunnels [94].

Another solution that can be used in similar conditions is the Alpha 311 roadside wind turbine developed by John Sanderson and Barry Thompson. The device can be integrated with any lighting pole to convert the energy of the air stream into mechanical energy from any direction of its inflow. The turbine is made of carbon fiber and polyethylene terephthalate. It is a mechanical solution without a shaft. Its purpose is to install it next to expressways or railway lines in order to use the generated convective air flows [95]. The solution view is shown in Figure 22.

A new design of the Darrieus VAWT three-blade helical turbine model, designed specifically for use on highways to generate electricity, is shown in Figure 23. The turbine was placed on a light pole located along the King Fahad Bin Abdul Aziz Highway in Kuwait. The generated electricity was measured and stored in an electrochemical energy storage tank. Test results indicated that the power plant generated up to 46 W of electrical power based on the air movement induced by moving vehicles, and this value was recorded at a wind-induced air mass movement speed of 4.4 m/s. Based on short-term measurements, its efficiency was found to be 34.6% [96].

Studies on the possibility of using small wind turbines to generate electrical power, supplemented with measurements of the induced wind speed, were presented in [97] for the area in the immediate vicinity of the highway in Lebuh SPA (Sungai Udang–Paya Rumput–Ayer Keroh) in Malaysia. In order to determine the appropriate positioning of wind turbines, three parameters were analyzed: the lateral distance from the roadside, the height from the ground, and the orientation of the wind turbines in relation to the road. The results of the CFD analysis indicate that the optimal location of the wind turbine is at a distance of 1.0 m and the same height above ground level. It has been experimentally confirmed that large vehicles such as trucks and buses produce higher wind speeds compared to smaller ones.

Reference [98] indicates problems related to the operation of wind farms when they are installed in close proximity to highways due to strong turbulence fields resulting from the changing nature of vehicle traffic. In order to reduce unfavorable phenomena, a hybrid wind power plant was designed and manufactured in which Darrieus and Savonius rotors were combined. The indicated connection enables the generation of high initial torque and rotational speed at, respectively, low and high wind speeds from all inflow directions. The solution uses a DC generator (24 V) with a rated speed of 300 rpm. The solution is characterized by almost 3 times higher energy efficiency than the Savionius wind farm and over 1.5 times higher than the solution equipped only with a Darrieus rotor. The prototype of a two-rotor wind farm is shown in Figure 24.

The use of a gearless three-blade wind turbine with a screw rotor (Figure 24b) for installation on lighting poles located along communication roads is also discussed in [99]. The Gorlov helical turbine was developed by Professor Alexander M. Gorlov. The solution is equipped with a permanent magnet generator located in the lower part of the structure. The structural strength of the solution was confirmed at a wind speed of 116 km/h, which resulted in a linear speed of the blades of 52 km/h.

Turbulent air flow caused by the movement of vehicles on highways is one of the sources of energy that can be used to power highway lighting and telecommunication signaling. The use of induced air movement resulting from the movement of vehicles on expressways using wind turbines with a vertical axis of rotation, marked “E-wind”, is presented in [100]. The author predicts that the gained electricity will power emergency lighting, information boards, and emergency telephones located along the road. Figure 25 shows the concept of the arrangement of individual units in the area of motorway lane separation.

A design solution with a similar technical version of the rotor was presented in [102], where the authors envisage the possibility of installing wind turbines in the area of highway lane separation in order to generate electricity by using the dynamic reverse two-way air movement generated by high-speed vehicles. It was assumed that the movement of air hitting the turbine blades tangentially would be used to initiate the rotational movement of the rotor of a wind power plant with a vertical axis of rotation (Figure 26). The generated electricity will be stored in batteries. The aluminum and steel generating unit was designed to operate at wind speeds in the range of 5 m/s is 30 m/s.

5. Development of Electromobility and Renewable Energy Sources (RESs) in Road Construction

The European Parliament and the Council of Europe have reached a provisional agreement on the deployment of electric charging stations every 60 km for passenger cars along the TEN-T core network (i.e., the EU’s main routes) by 2026 (Figure 27 and Figure 28). Charging stations for trucks are to be deployed at a distance of 120 km by 2026, while hydrogen charging stations are to be deployed every 200 km by 2031. The agreement also includes arrangements to enable easy and convenient payments at recharging or refuelling points (payment cards, proximity devices or QR code) for users of vehicles powered by alternative fuels. The price of fuels is to be given in terms of kWh, minutes/session, or vehicle weight. MEPs assured that the Commission will create an EU database of alternative fuel stations by 2027 to provide consumers with information on availability, waiting times or prices. It continues to wait for the official approval of the agreement by the Standing Committee of the Council’s Representatives and the European Transport Committee, and then by the entire Parliament and the Council of the Union [103].

The General Directorate for National Roads and Motorways (GDDKiA) has leased fragments of areas at MOP (passenger service place) facilities (type I—basic) for electric vehicle charging stations to external operators. In 2022, nine roadside charging stations were set up, equipped with a total of nine charging points [105]:

(a)

A1, Kuyavian-Pomeranian Voivodeship—MOP Ludwinowo North and Ludwinowo South: two stations;

(b)

A2, Łódź Voivodeship—MOP Niesułków, Kozanki and Zaborów: three stations;

(c)

A1, Silesian Voivodeship—MOP Wieszowa North and Wieszowa South: two stations;

(d)

S7, Warmian-Masurian Voivodeship—MOP Lutek and Majdany Wielkie: two stations.

According to GDDKiA’s plans, in 2023, it was planned to launch another 38 electric vehicle charging stations, equipped with a total of 82 charging points. A detailed overview is provided in

Table 4. List of planned charging stations for electric vehicles on GDDKiA roads [105].

Voivodeship	MOP	Route No.	Number of Charging Points
Kuyavian-Pomeranian Voivodeship	Kałęczynek East	A1	2
	Kałęczynek Zach.	A1	2
Lubuskie Voivodeship	Marwice East	S3	2
	Marwice Zach.	S3	2
Lodz Voivodeship	Main-East	A1	2
	Głowno Zach.	A1	2
	Skoszewy East	A1	2
	Skoszewy Zach.	A1	2
	Graves	A2	2
	Bolimów	A2	2
Lesser Poland Voivodeship	Swamp	A4	2
	Mokrzyska	A4	2
	Podłęże	A4	2
	Zakrzów	A4	2
Masovian Voivodeship	Budykierz	S8	3
	Let us assume	S8	3
Opole Voivodeship	Mill Pond	A4	4
	Rzędziwojowice	A4	4
Subcarpathian Voivodeship	Bratkowice	A4	2
	Oak trees	A4	2
	Kaszyce	A4	2
	Zamiechów	A4	2
	Javorník	A4	2
	Hawk	A4	2
	Mills	A4	2
	Shacks	A4	2
Podlaskie Voivodeship	Cautious	S8	2
Silesian	Dobieszowice East	A1	2
	Dobieszowice Zach.	A1	2
	Knurów East	A1	2
	Knurów Zach.	A1	2
Świętokrzyskie Voivodeship	Występa Zach.	S7	2
Warmian-Masurian Voivodeship	Grabin East	S7	2
	Grabin Zach.	S7	2
Greater Poland Voivodeship	Sobótka	A2	2
	Tsikhemian	A2	2
West Pomeranian Voivodeship	Kunowo East	S3	2
	Kunowo Zach.	S3	2

.

The issue of locating charging stations along expressways and motorways is very important and has a significant impact on the development of electromobility, especially if the user of a BEV vehicle will mainly travel long distances. Increasing the number of fast charging points (FCSs) increases the satisfaction of electric car users by reducing the charging time, but it must be correlated with the development of the power grid (high and medium voltage lines), which leads to a significant increase in the cost of infrastructure investments (212% in [96]). One of the solutions under consideration is the use of renewable energy sources (RESs), particularly solar and wind, in the vicinity of charging points in order to improve grid performance with reduced capital expenditure (18%) [106].

Currently, an important trend among the conducted research related to electromobility is the analysis of wireless dynamic charging systems for electric vehicles while driving, using special infrastructure built into the road (coil system). Currently, test stages are being built in many European countries (Germany, France, Norway, Italy) [107,108]. In [107], the main objective of the research was to carry out an analysis of the influence of various factors on the SoC of the battery in the vehicle and, on this basis, to develop optimal mounting points for the elements of the wireless charging system for cars. During the analysis, the different speeds at which the vehicles move were taken into account, alongside, among others, terrain, charging technology, and the vehicle’s energy consumption model (Figure 29). The presented issue is important and may contribute, among other things, to reducing the battery capacity of BEV cars, which is currently an important problem due to their high weight. Distributed charging systems can work very well with RESs installed along expressways and motorways, which can significantly improve the legitimacy of the investment and, above all, the efficiency of energy use, especially during the day, when street lighting is switched off and the number of energy consumers of the road infrastructure is small at that time [107].

In [108], it was noted that dynamic (while driving) wireless charging systems for electric vehicles can contribute to increasing carbon dioxide emissions when the only source of power for them is the classic power grid, using fossil fuels. During the analysis, an attempt was made to reduce this effect through the appropriate use of renewable energy sources. In the cited case, the charging system supported by the wind turbine system was analyzed (Figure 30). The optimal operation of this type of systems depends primarily on predictive models, which allow for an estimation of the intensity of vehicle traffic, including electric vehicles, power demand, the generation capacity of RES systems, and the location of the wireless charging system. As you can see, the development of electromobility and the energy transition should be considered together, especially taking into account the increasing percentage share of RES sources in the overall production of electricity.

The best results were achieved for the autumn and winter months (Figure 31). During this period, 100% of the energy demand was covered by renewable sources (wind turbines) (Figure 31d). This is mainly due to two factors, reduced traffic volume (Figure 31a) and the increased average wind speed during this period (Figure 31b). According to the calculations of the predictive algorithm, the price of energy for vehicle charging will reach low values, so the demand for its purchase will increase and the number of charging coils currently used will be higher than assumed in the original case (Figure 31c).

Unfortunately, this optimistic trend is not maintained in the spring and summer months. During this time, the average wind speed for the study site reaches much lower values and is less stable (Figure 32b), while the traffic intensity increases (Figure 32a). This results in a decrease in the stability of the wind system and reduces its generation capacity. Therefore, it is necessary to support the wireless charging system of vehicles with energy from the power grid (Figure 32d). With such a system configuration and power supply parameters, the price of energy will increase, which will clearly translate into demand, which will be lower than originally anticipated (Figure 32c).

Ultimately, the analyses allowed us to estimate that the solution proposed in the paper provides a reduction in CO₂ emissions at a level of 63%. However, the study did not take into account the possibility of using photovoltaic modules, which could significantly improve the efficiency and stability of energy production in the summer months. Such hybrid systems, combined with local energy storage, could provide a stable power supply to wireless vehicle charging systems.

An important issue influencing the development of electromobility around the world is the need to modify the existing power grid. What is certain is that the traditional approach to the operation of the power system is not able to provide adequate resources to charge the growing number of electric vehicles (BEVs). It is necessary to change the approach to the issues of electricity generation, transmission, and storage [109]. In order to improve the balancing of the grid and make better use of energy from RESs, energy storage is used in the system. However, their installation and operation are very expensive, which is why their development is still limited. An alternative approach is the introduction of a V2G (vehicle-to-grid) system, in which electric car batteries become part of the system as full-fledged storage devices. This solution is based on Internet of Things (IoT) technology, where an important role in the proper functioning of the entire system is the quick transfer of information on predictions concerning, among others, the consumption and generation of energy by vehicles and the entire power system, particularly renewable sources; weather conditions; user behavior (travel hours, distances); current and expected energy prices; and storage capacity for the area in question. These calculations are carried out using different types of machine learning algorithms, but for their proper operation, it is necessary to obtain the appropriate amount of input data necessary to conduct the learning and verification process. The advantage of the V2G system is the mobility of the warehouses installed in the vehicles. A charged electric car can travel many kilometers, using energy from RESs to recharge along the way, thus delivering it to other locations without the use of a classic power grid [109].

An important direction of this research is to ensure the stability of the power system in its current form. One of the factors that make it possible to control the behavior of electric car users, which is related to the creation of demand for energy at the desired points of the network, is the appropriate regulation of the prices of energy used to charge electric vehicles (Figure 33). Reference [110] proposes an analysis of the impact of the price of energy and, among others, the distance of alternative chargers on the choice of a place to charge an electric car battery, using the example of the Dublin Agglomeration.

The conducted analyses showed that for the presented example, it was possible to increase the value of the average self-consumption of energy from renewable sources by about 30% for energy from both wind turbines (89% at the peak) and photovoltaic farms (59% at the peak) [110]. These results show how important the price of electricity is for the operation of the entire power system. The proposed solutions will be possible to implement only with the introduction of appropriate legal regulations.

Increasingly, the idea of mass motorway traffic of electric trucks is being considered. Various ways of supplying them are considered, but all of them lead to problems related to the very high demand for electricity in this area. By superimposing mass charging systems for electric passenger vehicles on the above-mentioned solutions, the demand for electricity within the road infrastructure, especially expressways, is very high. The transmission of energy over longer distances exposes the currently unprepared power system to numerous technical problems. Distributed generation of energy, especially renewable energy sources, combined with road infrastructure may, to some extent, reduce these problems.

In Sweden, over a distance of 21 km of the E20 motorway (between Hallsberg and Oerbro), pilot installations for charging electric vehicles during traffic have been carried out. There are three technical solutions to choose from: inductive charging and two wired charging methods. The indicated methods have already been tested: on Gotland, coils have been built into the road in order to test the wireless inductive charging while driving. In Lund, southern Sweden, a system with a conductor rail on the road, reminiscent of the subway and S-Bahn, was tested between 2020 and 2022, where vehicles could charge their batteries using a current collector. The second method of wired power supply uses an overhead line (Figure 34), just like locomotives, trams, or trolleybuses; the vehicle must be equipped with a pantograph. The disadvantage of this solution is that it can only be used for trucks, while the first two do not limit the type of powered vehicle. The Swedish e-motorway is expected to be commissioned in 2025 [111].

Research from the German state of Hesse confirms that it is possible to use overhead lines to charge trucks. A study was conducted over a period of 4 years on the A5 motorway, between Langen and Weiterstadt (Figure 35). Similar projects are also being implemented in Schleswig-Holstein and Baden-Württemberg. Detailed results of the study, covering more than 500,000 kilometers driven by hybrid trucks, should be known later this year [112].

6. The Potential of Using RES in Road Construction in Poland

6.1. Possibilities of Using Photovoltaic Cells

The CEFRABID project [113], implemented in 2018–2020 as part of the European ERA-SOLAR.NET program, concerned the possibility of using photovoltaic modules in the system of noise and railway screens for Poland, Austria, Cyprus, and Spain. Poland’s participation in the project indicates the involvement of the domestic market in the development of PVNB technology, emphasizing the importance and topicality of the issue.

At the disposal of the General Directorate for National Roads and Motorways (GDDKiA) in Poland, there is a network of national roads with a total length of 17,800 km, of which 3804 km is highways, with 1247 km of motorways and 2557 km of expressways [114]. As indicated in [115], only along national roads, there is a 1700 km stretch of noise barriers. The estimated area available for development with the use of photovoltaic modules is about 7 million m², which, compared to other European countries, determines the competitiveness of Poland in the use of photovoltaics integrated with road barriers. However, detailed analyses are required to determine the appropriate communication sections, taking into account solar conditions (insolation value, number of sunny days, distribution of solar radiation components, and air temperature), technical conditions (condition of existing noise barriers, geometrical dimensions, installation possibilities, spatial angles), and directions of roads. Although the temporal distribution of insolation in Poland (900–1160 kWh/m²/a) is similar to the distribution observed in other developed countries of Central and Eastern Europe, it is difficult to clearly determine the potential of Polish roads in terms of the use of photovoltaic modules. It is assumed that the average insolation in Poland is 1000 kWh/m²/a. The number of hours of sunshine is about 1600 hours, which gives 66 days of sunshine per year, with most of them also falling in the summer period. This is a problem related to the mismatch between the load characteristics of GDDKiA road facilities (e.g., lighting) and the generation characteristics of photovoltaic systems.

Table 5. Summary of the energy potential of PV acoustic barriers in Poland [117].

Application of Existing Acoustic Barriers	Length of Photovoltaic Installations [km]	Installation Area [m2]	Energy Generated at 14% Module Efficiency [GWh/a]	Energy Generated at 15% Module Efficiency [GWh/a]	Energy Generated at 16% Module Efficiency [GWh/a]
25%	425	1,700,000	238	255	272
50%	850	3,400,000	476	510	544
75%	1275	5,100,000	714	765	816

shows a three-part analysis of the feasibility of existing screens. The analysis assumed 25%, 50%, and 75% use of 1700 km of currently existing noise barriers for PV module development. The efficiency of photovoltaic panels is 14%, 15%, and 16%, respectively [116].

Analyzing the results obtained, it can be concluded that the use of photovoltaic installations along roads may be justified, assuming the replacement or reconstruction of noise barriers. However, it is necessary to carry out a comprehensive technical and economic analysis that will clearly indicate all aspects of the use of this type of construction, especially in the context of the development of electromobility.

The issue of the integration of cadmium telluride photovoltaic modules and acoustic barriers for Polish climatic conditions is discussed in [118], where the energy analysis of a vertical installation using DDS-Cad software and life cycle assessment (LCA) is presented. The designed photovoltaic system, with a capacity of 3.56 kW and consisting of eight PV modules, is located along the expressway in Warsaw (52°27′ N 20°98′ E, altitude 130 m above sea level). The LCA analysis showed a statistically insignificant impact of the considered photovoltaic installation on the natural environment, and the concept may contribute to the implementation of the policy of sustainable energy development in Poland.

6.2. Possibilities of Using Wind Turbines

Along rights of way in Poland and in the areas directly adjacent to them, for several years, it has been possible to find low-power wind turbines of several hundred W. These are structures usually integrated with a PV panel of similar or lower power and a battery mounted on roadside lighting poles (Figure 36). Such solutions were originally used in areas far from the el-en grid. These types of hybrid (off-grid) installations are also used as power sources for road signs or traffic lights, especially portable ones. However, their number and total rated power are small, so it can be concluded that the energy potential available in this area is probably not adequately used.

The possibilities of using low-power wind turbines in the vicinity of roads in Poland seem to be significant, provided that there are favorable wind and terrain conditions (low roughness of the terrain). Service areas often allow for the placement of wind turbines of lower power—both with a horizontal and vertical axis of rotation—on their premises. Turbines can be installed on unused land or on roofs such as toilets or other buildings, as long as the strength of the roofs allows it. At the same time, it should be remembered that safety rules must be observed when designing generation systems due to the presence of a large number of travelers in the MOP areas. The moving parts of the turbines must not be accessible, and the distance from pedestrian and traffic routes should be greater than the height of the entire turbine. Placing turbines in the immediate vicinity of traffic lanes (between carriageways or on the shoulder) requires additional safety studies for road users, e.g., in terms of reduced visibility or dazzling drivers due to light reflection.

It has been statistically estimated that if at least one wind turbine with a capacity of approx. 5 kW was installed at each MOP in Poland, it would give an annual yield of 2–2.4 GWh on a national scale. In the current legal situation, there are restrictions on the location of wind turbines in the area of MOP II and III categories, i.e., leased to external entities. In addition, not every MOP is subject to wind conditions, terrain, and/or local buildings to achieve satisfactory electricity yields. However, the above calculation assumes that these limitations could be compensated for, for example, by placing more wind turbines in more “favorable” areas.

The project of an innovative and highly efficient wind turbine with a vertical axis of rotation for use in small power systems, also in places located in close proximity to communication routes, is being implemented by the Lodz University of Technology, cooperating with the Polish companies Enerwis and Ergos and a partner from Turkey. The starting point for this research is a Turkish design created by the start-up Devecitech. The wind turbine being developed by the Polish–Turkish team will be called Ninlil. The total budget of the project is over EUR 300 thousand and was awarded in a competition organized by the National Centre for Research and Development and the Turkish Council for Scientific and Technological Research. Lodz University of Technology will design a generator for the turbine and will test the turbine prototype in urban conditions.

The latest Polish research results on the possibilities of using the potential of the air stream induced by traffic with the use of model wind turbines with vertical and horizontal axes of rotation are presented in [113], where the authors from the Poznań University of Technology conducted a detailed analysis of the Darrieus and Savonius power plants and their numerous modifications (Figure 37). On a specially developed test stand, the torque, power, wind power utilization factor, and take-off speeds of wind turbines were measured. It was shown experimentally that the wind speeds obtained from passing vehicles did not exceed 9 m/s. It was found that among the tested models, under the test conditions, the Savonius screw turbine has the highest efficiency (0.2047 at a wind speed of 5.8 m/s) and should be considered for further analysis.

7. Discussion

The analysis of materials (scientific articles, technical reports) indicates a great interest in the use of renewable sources in areas related to road infrastructure. It consists of the following:

• A very large and constantly growing total length of expressways;
• A large number of passenger service facilities and their increasingly better technical equipment;
• A significant demand for electricity for road infrastructure (e.g., lighting, water heating);
• The development of electromobility and the necessity (legal requirements) to locate electric vehicle charging systems in road infrastructure facilities;
• The current structure of power systems (striving to reduce energy transmission over long distances and thus reduce transmission losses);
• The necessity to fulfil obligations with respect to specific shares of the capacity of RES sources in the total installed capacity of electricity sources.

The analysis of the current road infrastructure indicates that it is possible and interesting from the technical and economic point of view to use photovoltaic sources and wind turbines of lower power (especially with a vertical axis of rotation).

An extremely interesting aspect of electricity generation is the integration of PV modules with sound-absorbing screens. PVNB systems have been around in Europe for more than 30 years and mostly use existing noise barriers. Currently, the possibilities of using noise barriers to generate electricity in integrated PV systems are evaluated at the beginning of the planning of new projects. Nevertheless, existing and undeveloped noise barriers have significant potential in this regard. The German Federal Highway Research Institute (BASt) has modernized its system for finding the most advantageous locations with high solar potential. By using GIS analysis, which combines information about the location and orientation of existing infrastructure such as noise screens, roads, buildings, and levees, with natural features such as topography, land cover, and sunlight levels, it is possible to locate potential sites for new installations across the country. In addition, 3D modelling is used to help develop infrastructure more accurately and provide sites with the highest energy potential [120,121].

The payback time of such an investment depends on the price of electricity and the amount of the subsidy, but in sunny regions of Germany, such as the southwest, investments are particularly worthwhile. The screens are not a problem in terms of noise reduction or safety, and the PV technologies available on the market do not exceed the German guidelines for noise reduction. The same applies to the safety of barriers, which must meet certain regulations and safety standards, regardless of whether they contain PV technology. Maintenance of the system mainly involves visual inspection, and the panels are not usually cleaned. This is due to the fact that cleaning the plant is more expensive than the gains from a small increase in efficiency [40]. The construction of noise barriers is also relatively common in the Netherlands. Due to the country’s high population density, motorways and railways are usually located in close proximity to homes and businesses, which often requires the use of noise barriers [77].

A study by Highways England has shown the impact of installing PVNB screens on safety and driver distraction [122]. The study consisted of recording the passage of vehicles approaching the PVNB and the passage after passing the barrier, using two cameras. No significant differences were observed in vehicle speed, braking, or sideways movement between the area upstream and downstream of the sign. There were also no behaviors that would indicate the negative effects of distraction on drivers [37]. Another study in Australia found that panels inclined at an angle of about 60° from the horizontal plane caused drivers to complain of glare, so the photovoltaic panels were covered with an anti-glare film. This slightly worsened the energy efficiency of the PV installation, but effectively improved the safety of drivers. Driver distractions and glare can also be minimized by placing PVNB panels high on noise barriers and/or away from the roadway, as well as ensuring that the panels are at the correct angle. However, it has not been confirmed in the literature that PVNB panels with a vertical structure cause glare. In addition, solar panels are designed to absorb rather than reflect light. Therefore, PVNBs are not expected to cause operational difficulties when placed behind a protective barrier [37].

Wind turbines, especially those with a vertical axis of rotation, have a high potential for electricity generation in areas related to road infrastructure. However, due to the presence of moving, rotating structural elements, there are many more location constraints here than in the case of PV systems. With the detailed location of turbines in the areas of passenger service facilities, there is a need to take into account their safety (fencing off turbine installation sites, moving turbines away from communication routes, etc.). The particularly high potential of wind turbines with a low specific power is related to the use of air mass movements induced by passing vehicles. Including rail vehicles, the possibilities of energy generation are significantly expanded. However, in this area of RES application, there are the greatest gaps in terms of the results of scientific research and the implementation of legal solutions (vehicle safety, maintenance or repairs).

The actual possibilities of using RESs to generate so-called green energy in the areas of road infrastructure are determined by technical and, of course, economic considerations. The legal possibilities of the possible sale of surplus energy and the allocation of the funds obtained in this way for the purposes of exploitation and investment in new road facilities may become an important factor in the development of RES technologies in the area under consideration.

Currently, not all the problems related to the generation of energy from renewable energy sources in the areas of road infrastructure have been identified yet. Therefore, further research is necessary, especially in which a group of technically optimal RES systems will be selected using multi-criteria optimization methods. Further extension of the functionality of optimized generation systems from RESs is possible through the use of energy storage facilities with selected energy capacity. From the group of pareto-optimal solutions, depending on other (objective and subjective) criteria, the experts should determine the final solution, taking into account local conditions in each case. Such activities should be carried out with the use of other methods of supporting multi-criteria decisions, e.g., AHP.

8. Conclusions

The implementation of photovoltaic and wind systems in the road and transport sector can bring a number of benefits, including ecological, economic, and social, contributing to a more sustainable development of road infrastructure, but may also involve certain challenges. The expected benefits of using renewable energy sources in Poland’s road infrastructure include the following:

• The effective use of wasteland: areas along expressways and noise barriers are often unused or have little value;
• Generating energy at the point of use: locating the installation of renewable energy sources in close proximity to roads allows electricity to be generated on site, which reduces the need for its transmission and potential energy losses;
• Sustainable transport: the use of renewable energy to power street lighting, road signs, traffic control systems, and electric vehicle charging stations may contribute to the sustainable development of transport and the implementation of the policy objectives of the European Commission;
• A reduction in greenhouse gas emissions and environmental protection: wind and photovoltaic power plants do not emit greenhouse gases during operation (generation of electricity), which contributes to improving the air quality around roads. The use of areas for photovoltaic installations and wind farms can reduce the need to cut down trees, which contributes to the protection of the natural environment;
• Improving energy security: local renewable energy sources can increase the region’s energy independence, reducing its dependence on imported fossil fuels;
• A positive image of technology among the public: the use of renewable energy in close proximity to roads may be perceived positively by the community, increasing the green image of a city or region;
• Potential financial profits: depending on local conditions and energy policy, photovoltaic installations and wind turbines may generate additional income from the sale of excess electricity.

The use of photovoltaic installations and wind turbines may also be associated with certain problems (not all of them may occur in a given location, country, or region):

• Reduced road safety: there is a risk that the installations may potentially increase the risk to road safety, especially when placed near roads with heavy traffic. Reflection of light from infrastructure elements may be confused with road signals or limit the correct perception of the situation;
• Negative impacts on the landscape: high wind systems and large photovoltaic installations may change the character of the landscape and the aesthetics of roadside areas, which may result in opposition from residents and local authorities;
• Land conflicts: the use of land for photovoltaic installations and wind turbines may lead to conflicts with other land users or investors, especially if the land is already used in another way;
• The protection of bird and animal species: wind farms may pose a threat to animals due to the rotating blades. However, this impact can be minimized with properly planned construction designs and locations. These solutions may also affect local ecosystems, e.g., by losing habitats for plants and animals or changing the landscape;
• Integration into existing infrastructure: integrating photovoltaic installations and wind farms with existing road infrastructure and acoustic barriers may be technically complicated and require adaptation of existing structures.

However, it should be emphasized that proper planning, environmental impact assessment, and involvement of local communities may be key to minimizing the above-mentioned problems.

The implementation of renewable energy sources (RESs) in road construction on a large scale may require the use of various methods and strategies, which include the following:

• Introducing appropriate regulations and policies, such as energy efficiency standards, requirements for the use of renewable energy in new road projects, and the creation of financial incentives, e.g., through subsidies or tax breaks for investors;
• Modern spatial planning involving the inclusion of renewable energy technologies in spatial planning strategies at both local and national levels by designating areas dedicated to the installation of photovoltaic panels, wind farms, or other renewable energy technologies along roads;
• Public–private partnership consisting of establishing cooperation between the public and private sectors to jointly develop and implement projects related to renewable energy in road construction, taking into account innovative financing and management models;
• Investing in the research and development of new technologies and methods of producing energy from renewable sources adapted to the specific nature of road infrastructure, such as integrated photovoltaic systems in sound-absorbing barriers;
• The development of quality standards and certification for products and services related to renewable energy in road construction, which may increase investor and user confidence in these solutions;
• Implementing integrated strategies that take into account both the use of renewable energy sources and energy efficiency, e.g., by designing intelligent road lighting systems or traffic management based on sustainable development.

Based on the presented characteristics of the selected and most promising RES solutions introduced and developed in various countries around the world in close proximity to road infrastructure and the analysis of the effects obtained in this respect, important conclusions can be formulated that can be further used in other locations to improve investments, including in Poland:

It is possible to effectively, safely, and efficiently install photovoltaic modules on acoustic screens, although there are a number of factors that should be taken into account in the design and installation phase, such as the direction of exposure (the acoustic screen should be properly directed in relation to the path of the sun; deviation from the optimal azimuth in the range of 20° does not lead to significant drops in electricity production while limiting the angle of inclination of PV modules), the angle of inclination necessitates the design and use of non-standard and often specific photovoltaic module technology supporting structures (the problem is particularly important in the case of the use of double-sided glass–glass PV modules, regarding the number of mounting supports required by the manufacturer), maintaining the original function of acoustic screens with the additional presence of PV modules, protecting the modules against mechanical damage caused by passing vehicles.

It is possible to use wind farms with a vertical axis of rotation in traffic separation areas to generate mechanical and electrical power; however, several key technical and practical challenges are identified that may hinder the implementation of these solutions on a large scale, such as technical considerations resulting from the fact that that wind farms are designed to use wind energy, not energy induced by the movement of air vehicles, which means that the design of the rotor, its shape, and the operational parameters described by the mechanical power curve must be thoroughly considered, as indicated in [113]. However, the use of classic designs also allows them to be adapted to new working conditions. Also, the installation of wind farms near roads may also reduce safety due to flares generated by rotating blades, which requires further research into the safety of using these solutions.

The development of electromobility can be intensified by increasing the availability of charging points for electric vehicles, where the integration of electric vehicle chargers with renewable energy sources (mainly photovoltaics) enables the installation of charging points in places where traditional power sources may be unavailable or too expensive to use, for example, in rural areas or in remote places (large road arteries, expressways, and highways run through these areas). Using electricity generated by renewable energy sources to power electric vehicle charging points can reduce charging costs for users, especially in the case of long-term use of electric vehicles.

The use of renewable energy generation In broadly understood road construction in European countries brings long-term financial benefits resulting from reduced costs of operation and maintenance of road infrastructure and reduced fuel costs.

Developments in technology and advances in engineering may help overcome some of these obstacles in the future.