Overview and Perspective of Integrated Photovoltaics with a Focus on the European Union

Abstract

The global cumulative installed PV capacity is anticipated to surpass 2 TWp by the end of 2024, which is an increase in three orders of magnitude from the 1 GWp at the end of 2004. Depending on the energy transition scenarios, up to 8 kWp per capita have to be operational by 2050 globally. In Europe, this capacity could even be 50% higher, and this will have consequences on the decisions regarding where to install this capacity; thus, these decisions will be significantly impacted. This paper gives an overview of the technology options for installing PV systems in areas already used for other human activities as well as integrating them into ships and vehicles without the acquisition of extra land. The focus of this paper is on the situations within the European Union, such as land competition, and presents innovative solutions.

1. Introduction

Although the modern solar cell was invented at Bell Labs in 1954, it took 68 years to install the first 1 TWp of solar photovoltaic electricity capacity. However, the second terawatt will be installed in less than three years, when the global PV capacity will exceed 2 TWp by the end of 2024 (Figure 1).

In 2023, global cell production was estimated to be in the range of 580 to 630 GWp [1]. As new, global installations are expected to exceed 600 GWp in 2024 [2,3], the cell production could soon be over 700 GWp.

Solar cell production capacities are defined as the following:

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In the case of wafer silicon-based solar cells, only the cells.

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In the case of thin-films, the complete integrated module.

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Only those companies which actually produce the active circuit (solar cell) are counted.

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Companies which purchase these circuits and make cells are not counted.

Despite this strong market growth in solar photovoltaic generation capacity, the addition of new manufacturing capacity along the solar value chain is outpacing it. According to Bloomberg New Energy Finance, the six largest silicon module manufacturers alone, which accounted for almost two thirds of Tier 1 manufacturing capacity in 2023, will increase their manufacturing capacity from 552 GWp in 2023 to 621 GWp in 2024 [3]. This indicates that for the time being, the situation of manufacturing overcapacity will not ease, and the downward price pressure will continue for some time.

At the end of 2023, the total global PV capacity surpassed 1.6 TWp and the world average of cumulative installed PV capacity reached 200 Wp per capita (Figure 2). According to progressive energy transition scenarios, solar photovoltaic power generation capacity could increase up to 80 TWp globally and up to 8.3 TWp for Europe (EU + Albania, Kosovo, Island, North Macedonia, Norway, Moldova, Serbia, Turkey, Ukraine, and United Kingdom) [4,5]. The United Nations (UN) predicts a global population of about 10 billion and 675 million in Europe by 2050. This can be translated to 8 kWp operational per capita globally and 12.3 kWp per capita in Europe by 2050.

Figure 1. Cumulative installed photovoltaic capacity from 2010 to 2024 (data source: [3,6] and own analysis).

Figure 1. Cumulative installed photovoltaic capacity from 2010 to 2024 (data source: [3,6] and own analysis).

Figure 2. Countries with a cumulative photovoltaic capacity of at least 500 Wp per capita in 2023 and the world average value (the order is according to 2023 capacity). For comparison, the values of 2022 are presented as well. (Data source: [3,6] and own analysis).

Figure 2. Countries with a cumulative photovoltaic capacity of at least 500 Wp per capita in 2023 and the world average value (the order is according to 2023 capacity). For comparison, the values of 2022 are presented as well. (Data source: [3,6] and own analysis).

From a global perspective, there is no lack of available area for the installation of solar photovoltaic systems. However, in some densely populated countries and regions, the needed land can compete with other land use options and related policies. Some examples of this include agriculture, hydropower, infrastructure needs, natural land protection, or recreation.

Integrating photovoltaics with various already existing land use options as well as vehicles and ships opens access to PV potentials that are so far unused [7] and will help to overcome real as well as perceived area limitations [8,9,10]. The following sections will give an overview about the different technology options and where available the theoretical potential in the EU to combine photovoltaic systems with already existing land use options.

2. Market Segmentation

The market segments of rooftop PV and utility scale (The Solar Energy Industry Association defines a solar PV plant with more than 1 MWp as “utility scale”) were globally reasonably balanced in 2023. Approximately 40 to 45% of new capacity was installed on rooftops [6]. The range is mainly due to the uncertainty in the Direct Current (DC) to Alternating Current (AC) ratio of utility scale installations in China.

In the European Union, utility-scale PV plants were more dominant with a 65% share of the market, followed by rooftop installations (approx. 30%). Building-integrated photovoltaics, agrivoltaics, and floating photovoltaics accounted for only 5% all together [11]. The 2024 International Technology Roadmap for Photovoltaics reports a projected decrease in utility-scale and rooftop applications (55% and 25%, respectively) in favor of the building-integrated photovoltaics (5% share), floating photovoltaics (5% share), and agrivoltaics (10% share) that will account for the remaining 20% in the EU market in 2034 [11].

3. Integrated Photovoltaics Options

In this section, the various options to integrate photovoltaic power systems, either in buildings or vehicles as well as combining it with existing infrastructure or land use options are described. The diversification of PV applications described in this chapter would lead to more balanced production patterns that would reduce the market integration costs and anomalies that are being increasingly caused by uniform PV array deployments [12].

3.1. Agrivoltaics

Agrivoltaics are a multi-use land application enabling the production of food and energy at the same time and on the same piece of land [13,14]. Policies on clean energy, energy transition, sustainable agriculture, food security, biodiversity, rural development, and research and innovation, that are directly supporting the goals of the European Green Deal (EGD) [15,16], are strongly associated with agrivoltaics.

Currently, the installed capacity of agrivoltaic systems is 2.8 GWp in Europe [17] and 14 GWp globally [18].

Agrivoltaics in the EU have a notable potential. Considering an installed capacity per land area equal to 0.6 MWp/ha and deployment on only 1% of Utilized Agricultural Area (UAA), the agrivoltaic potential installed capacity in the EU can reach roughly 944 GWp, (half of the approx. 1809 GWp that can be achieved by traditional ground-mounted PV systems). The EU’s agrivoltaics potential of 944 GWp is close to four times more than the EU installed capacity in 2023 and the electricity generated could cover over 42% of the EU’s total electricity consumption in 2023. As far as Technology Readiness Level (TRL) (Technology Readiness Level (TRL) is a type of measurement system used to assess the maturity level of a particular technology) is concerned, agrivoltaic applications stand between TRL 3 and 8, depending on the agricultural context [19]. Further studies regarding the crop suitability identification and implementation of water management optimization will substantially contribute to the application’s development.

3.2. Floating Photovoltaics

Floating photovoltaics (FPV) consist of the deployment of PV modules on water surfaces [20]. The most common surfaces envisaged for this application are man-made water surfaces such as irrigation dams, industrial basins, water treatment plants or hydropower reservoirs. Floating photovoltaics have also been deployed on natural waters like lakes and offshore sea locations (mostly at low wave categories). This PV application takes advantage of the cooling effect coming from the water beneath the PV modules [21,22] and easy installation while contributing to water evaporation and algae growth reduction [23]. The current installed capacity in Europe is close to 0.5 GWp, while global installations have reached 2 GWp.

In addition to the multiple benefits of FPV, they can exploit the already established grid connection when coupled with hydropower (or installed on dam surfaces) or wind energy [24]. In the case of earthen dams, the PV installation can protect the surface and minimize erosion caused by rain [25]. The coverage of only 10% of the EU’s reservoir (i.e., man-made) area can generate approximately 140 TWh (160 GWp), which corresponds to approx. 7% of the EU’s total electricity consumption in 2022 [26].

Currently, most FPV system designs are optimized for low wave categories (TRL 6–8 for wave categories 1–2) [19]. The design and development of FPV systems for high wave categories (TRL 3–4 for wave category 3–4) is still a challenge and ongoing. The overall lifetime of FPV systems and reliability aspects are another issue, which are under investigation and need further development.

3.3. Building-Integrated Photovoltaics and Rooftop Photovoltaics

3.3.1. Building-Integrated Photovoltaics

Building-integrated photovoltaics are well-known and have been established PV applications for many years now. They consist of the replacement of conventional building materials with materials incorporating PV technologies so as to have a double function, acting like an energy-producing building component. The generated electricity is consumed close to where it is produced, thus excluding potential grid investments.

According to a recent study, when considering a building skin to building net surface area ratio of 0.78 and a building skin glazing ratio of 30%, buildings could cover their electricity consumption using building-integrated photovoltaics systems by 2030 in the EU [27].

More technology details can be found in the dedicated paper in this Special Issue.

3.3.2. PV Systems on Rooftops

PV on rooftops offer grid integration opportunities due to their proximity to the point of consumption. The utilization of solar PV electricity on rooftops can also reduce the distribution losses, which in 2021 accounted for 6% or 170 TWh [28,29].

According to conservative estimates, the EU’s rooftop solar potential stands at a minimum of 560 GW, capable of generating 680 TWh of electricity annually [30]. Harnessing this vast potential, a significant portion of the installations will need to be undertaken by individuals, either through rooftop systems on single-family homes or collectively owned systems on multi-unit apartment buildings [31,32]. Moreover, there is growing interest among citizens in harnessing solar energy for self-consumption, both with and without energy storage, as well as in installing solar systems on shared apartment buildings [33].

The revised Energy Performance of Buildings Directive, which includes the concept of Nearly Zero-Energy Buildings (NZEBs), was published in May 2024 [34]. Once implemented by EU Member States, it is expected to further boost the adoption of rooftop solar energy systems. Furthermore, various municipalities are either considering or have already introduced regulations mandating the installation of renewable energy systems in new constructions. If each of the 2 million new residential buildings constructed annually in the EU were equipped with 4 kWp of rooftop PV, approximately 8 GWp of additional capacity could be added every year [35]. This could lead to an additional 48 GWp of rooftop PV capacity by 2030.

The full upscaling of the building-integrated photovoltaics market requires actions related to PV module and Balance of System (BoS) technology development, business models, design, and energy integration (TRL 4–8) [19]. In addition, clarity regarding PV in building regulations at the regional, national, and EU level are essential to avoid fragmentation (TRL 8–9).

As of 12 March 2024, the European Parliament has implemented the EU Solar Standard [36]. This regulation requires the installation of rooftop solar energy systems in all new public and commercial buildings exceeding a floor area 250 m² by 2026. In addition, this includes the installation of rooftop PV in existing buildings of the same size undergoing renovations by 2027, and all new residential buildings by 2029.

3.4. Infrastructure-Integrated Photovoltaics

The multi-use of various existing infrastructure offers the opportunity to add additional PV capacity either without additional land use or through making use of otherwise unused land. In the majority, these sites are already connected to the electricity grid or close to a place with electricity use.

A number of case studies have already been conducted and are mentioned in the following subsections, but to better understand the available potential for renewable electricity generation with photovoltaic systems, more studies in a larger variety of geographical regions have to be conducted. Therefore, the following sections only give some examples.

3.4.1. Closed Landfill Sites

Landfills are brownfields and need supervision or even maintenance. Their use of PV plants will not affect sensitive ecosystems or protected areas but they offer an opportunity to offset the maintenance cost by income from selling PV electricity [37]. As far as closed landfills are concerned, the potential for the EU can reach 13 GWp. This EU estimate is a pretty conservative one as it is based on Corine Land Cover (CLC) characterization. Two case studies used in a 2017 analysis contained 15% (by area in UK) and 3% (by number in Hungary) of the available national characterization of landfill sites. Site identification by using national cadasters would result in multiple time higher potentials of landfill PV. Second, closed landfills are often connected to the electricity grid and in the case of landfill gas use, the PV system can improve the load factor of the plant.

3.4.2. Irrigation Channels

In many agricultural regions, canal irrigation is a widespread method, especially particularly in regions with either an extensive river network or large artificial water reservoirs or lakes. In general, these canals are open and a water evaporation source.

Especially in arid regions, irrigation canals not only offer a potential for solar PV installations with channel top PV (channel top PV: CTPV) but can help to reduce water evaporation and offer more water for farming purposes [38,39]. India has been a pioneer country using this technology [40]. A recent study by the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) estimates that CTPV could account for 3% or 24 GWp of total PV installation by 2024 [41]. In 2022, Romania announced that it was looking into the possibility to invest EUR 1.8 billion for a total of 1700 km irrigation channel projects with the help of the European Recovery Fund [42].

3.4.3. Parking Lots and Individual Carports

A huge untapped potential for the installation of PV systems and accelerating the transition towards electromobility are PV systems on the numerous parking lots and individual parking canopies. The idea is not new, but so far only limited applications have been realized [43,44]. The reason is that this kind of installation still has a number of hurdles to overcome. These structures are classified, as buildings, thus the applicable standards as well as the planning time can be considerably longer than conventional roof-mounted PV systems. As the PV system is not just an add-on, the necessary roofing structures have to be included in the cost calculation.

In a number of EU countries, an increasing number of car parks are being equipped with PV systems. It is assumed that this trend is driven by the increase in electric vehicles. In France and in six German federal states, it has become a legal requirement to equip car parks over a certain size with solar PV systems [45,46,47,48,49,50,51]. The main difference is that the French Renewable Energy Acceleration Act (loi ApER), adopted in 2023, applies to all car parks with more than 80 parking lots or an area of 1500 m², whereas the obligations in the six German federal states applies only to new car parks with over 35 parking lots.

In France, the car parking owners now have five years to comply with this obligation and the French government expects a new PV capacity of 11 GWp on these parking lots.

As the German obligation applies only to new car parks, it is difficult to estimate how much new capacity will be installed. However, the Fraunhofer ISE has conducted a study calculating that 59 GWp could be installed on the largest 300,000 parking lots alone in Germany [52].

3.4.4. Roads and Railroads

Photovoltaics can be integrated into the transport infrastructure, e.g., noise or crash barriers along roads, highways and railroads, road pavements, dikes, flyovers, road roofing, and rest areas. The infrastructure element in these applications, in addition to its main functionality (like noise or crash protection), incorporates PV modules for the simultaneous generation of electricity. The most common infrastructure applications are on noise barriers and rest areas.

Research on PV on transport infrastructure (roads and railways) has shown that the potential installed capacity in the EU is 401 GWp, translated into 280–391 TWh depending on the PV technology employed (monofacial vs. bifacial PV modules). The above-mentioned electricity generations cover between 11% and 16% of the EU’s total electricity consumption in 2022 [53]. In the Netherlands, the potential installation capacity on dikes has been identified to be 11 GWp [54].

Depending on the specific application, TRLs vary between 6 and 7 for landfills, road roofing, and noise barriers, and 4–5 for crash barriers and dikes. Infrastructure-integrated photovoltaics are set to ramp up when the designed integrated solutions become more mature in terms of performance and safety as well as cost effectiveness [19].

3.5. Photovoltaics Integrated in Vehicles and Ships

The reduction in PV costs and higher penetration of EV are the main driving forces behind vehicle-integrated photovoltaics developments. However, this application can have several variations depending on the (i) type of vehicles (light-duty, heavy-duty, camper, etc.), (ii) use of energy (for extended range, refrigeration, etc.), and (iii) PV technology (Si, III-V, organic, etc.).

Apart from the above-mentioned parameters, the climatic conditions also play a significant role in vehicle-integrated photovoltaics. A recent study performed on a commuter car and a light delivery van, even though it does not take into account shading, suggests that the average annual solar range (mileage) of a photovoltaic electric vehicle with 454 W_p vehicle-integrated photovoltaics can amount between 12% (worst climatic conditions for PV) and 35% (best climatic conditions for PV). The respective range for a delivery van with 649 W_p vehicle-integrated photovoltaics is between 9% and 23% (considering a 51% higher annual mileage versus the car driving pattern) [55]. A crucial parameter requiring extensive research is the shading patterns and effects for vehicle-integrated photovoltaics [56].

Vehicle-integrated photovoltaics applications are expected to reach TRLs between 6 and 8 by 2025 [19]. More technology details can be found in the dedicated paper in this Special Issue.

The tightening of environmental standards, especially in costal regions, has increased the interest of the maritime transport industry for the use of renewable energy sources [57]. The use of a PV system in combination with battery storage and a conventional diesel engine can reduce the CO₂ emissions of the maritime transport sector, especially during port times, when the overall energy demand is considerably reduced [58,59]. This application is still in a demonstration and research phase.

4. Conclusions and Outlook

For the complete utilization of the potential of solar photovoltaic power for a sustainable energy transition, along with additional adaptation measures in the power sector, diversified integration approaches are necessary, due to the variable nature of solar photovoltaic electricity generation. Intelligent permitting processes with local authorities having a good understanding of the risks and benefits of PV installation in a multifaceted land use manner calls for the EU-level training of administrators, similar to the EU Battery and PV academy. Different regions of the world will require different shares of the different renewable energy sources, combined with a range of different storage options, demand management, and sector coupling. However, this paper focuses on presenting different PV applications that have the potential to install PV systems on areas already used for other human activities.

Energy transition scenarios that foresee extreme high solar photovoltaic power share predict an installed PV capacity of up to 8 kWp per capita globally and 12.3 kWp per capita in Europe. This is feasible, assuming that the conversion efficiency of solar modules will increase to 25% in the coming years. This corresponds to an area requirement of 32 m² per capita globally for the solar modules. Depending on the mounting structures, the area for the global capacity per capita can reach up to 50 m² when using free standing systems. Due to the higher capacity per capita, these numbers would increase by over 50% in Europe. Thus, it is essential to identify applications that can offer multiple benefits and uses when installing PV, thereby creating energy–land synergies without requiring additional land.