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Elena Lucchi
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Lindsay Dong
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Marchwiński, J.; Milošević, V.; Stefańska, A.; Lucchi, E. Flexible Photovoltaics. Encyclopedia. Available online: https://encyclopedia.pub/entry/49431 (accessed on 09 July 2024).
Marchwiński J, Milošević V, Stefańska A, Lucchi E. Flexible Photovoltaics. Encyclopedia. Available at: https://encyclopedia.pub/entry/49431. Accessed July 09, 2024.
Marchwiński, Janusz, Vuk Milošević, Anna Stefańska, Elena Lucchi. "Flexible Photovoltaics" Encyclopedia, https://encyclopedia.pub/entry/49431 (accessed July 09, 2024).
Marchwiński, J., Milošević, V., Stefańska, A., & Lucchi, E. (2023, September 20). Flexible Photovoltaics. In Encyclopedia. https://encyclopedia.pub/entry/49431
Marchwiński, Janusz, et al. "Flexible Photovoltaics." Encyclopedia. Web. 20 September, 2023.
Flexible Photovoltaics
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This entry is adapted from the peer-reviewed paper 10.3390/en16165945

Flexible PVs encompass the second and third generations of photovoltaic (PV) materials. Both perovskite (PSCs) and organic PV (OPV) can be integrated into PV textile membranes, which benefit from their flexibility and easy production techniques, similar to textile processes, and this has created new markets for PV applications. The flexibility of solar cells mainly depends on the substrates used. They can be divided into (i) plastic and (ii) metallic substrates. Plastic ones are composed of polymeric materials (e.g., PEN, PET, PTFE, ETFE). These substrates are characterised by low cost, high optical transparency, chemical stability, and favourable bendability.

photovoltaics PV Flexible PVs

1. Introduction

Energy production from renewable energy sources (RESs) [1][2][3] is essential to address the energy dependency of European countries on other nations [4], both for new and existing buildings. The European legislative framework calls for the widespread application of RESs to tackle energy dependency and climate change, aiming to reduce energy needs, environmental emissions, and economic costs [5]. Furthermore, the implementation of RESs can lead to human comfort, security, well-being, and social engagement and stimulate economic growth, investments, and property values [6][7]. Among RES options, photovoltaic (PV) systems show significant promise due to continuous improvements in PV cell designs and performance, along with their reliability [8][9], versatility [9], and scalability [9][10]. Otherwise, unlike other solar technologies, such as solar thermal (ST) and hybrid systems (PVTs), they support the energy transition towards supply-side strategies, guarantying on-site production [10][11], self-consumption coverage [9][10], and energy peak shaving [9]. Promoting energy autarky [12], “users” transform into energy-independent “producers”, receiving remuneration for energy production and selling to the national energy grid [1]. Hence, they are also “prosumers”, a term combining “producers” and “consumers”.
PV systems can be applied directly to buildings in two primary ways: building-attached PVs (BAPVs) and building-integrated PVs (BIPVs). In the first case, PV modules are mounted on the building envelope with mechanical elements that can be easily removed [13]. In contrast, BIPVs involve replacing conventional building elements with PV materials, creating a construction product with both energy and building functions [13][14][15][16]. It is important to note that dismantling BIPV products requires replacing the entire building element [14].
Despite a high potential from an environmental standpoint, PVs face various constraints and uncertainties. The constraints mainly involve applications in sensitive areas, where limitations mainly concern the PV cell’s aesthetic appearance and the system’s reversibility [8]. Additionally, policy [17][18][19][20][21], economic [17][18][19][22], information [18][19], human resource [7][18][23], and technical [17] issues have been identified as hindrances. The complexity of the legislative framework [17][18][19][20][21] and the economic costs of PV systems [17][18][19][22] are recognised as the industry’s main problems. Moreover, technical stakeholders’ insufficient knowledge of innovative approaches is a particular concern, especially in undeveloped countries [7][18][23]. Technical uncertainties revolve around the energy and aesthetic performance of innovative PV cells [10], as well as life-cycle assessment (LCA) and the sustainability of the manufacturing process [7][11]. Critiques have also arisen regarding the difficulties in integrating rigid PV systems into building envelopes because the structures need high mechanical resistance to sustain these systems [24]. This limitation confines the application of rigid PVs mainly to roofs, curtain walls, and regular façades, reducing electric production because of shading in high-density cities and lowering irradiation on vertical elements [24]. In this context, PV textile membranes offer new possibilities by integrating PV modules into the textile structure via sewing or bonding [25]. PV membranes allow for tailored aesthetic designs thanks to the flexibility and adaptability of their shapes, geometries, colours, and patterns. As a result, this technology holds significant potential for the building sector. The background of flexible PV systems depends mainly on solar cells and substrates. 

2. Flexible PV

PV technology’s aesthetic appearance, technical quality, and energy performance have improved drastically in the last twenty years. The first generation of PV solar cells (SCs) was based mainly on silicon wafers (e.g., monocrystalline, polycrystalline, amorphous, or hybrid silicon cells), low-iron glass-cover sheets, and encapsulants. Monocrystalline and polycrystalline cells are the most frequently used thanks to their higher energy efficiency (19–25%), longer-lasting duration, and reduced costs [26]. Their aesthetic appearance is not appealing because of the presence of blue colours, square shapes, and high thicknesses. Other drawbacks are the absence of flexibility, low geometrical adaptability, and reduced efficiency with high environmental temperatures (>25 °C). Conversely, amorphous cells have improved flexibility thanks to the adaptation of curved subphases, manufacturing cost reductions, and better performance with low light levels. The disadvantages are low energy efficiency (≅10%) and complex production methods that hinder their architectonical application. Thus, hybrid silicon cells try to combine the advantages of crystalline and amorphous silicon cells. The second generation of PV cells is composed mainly of thin films made by low-thickness semiconductors composed of amorphous silicon and non-silicon materials, such as cadmium–telluride and copper indium gallium diselenide. Their advantage is a cost reduction due to eliminating silicon wafers, higher dimensions, and improved energy efficiency (15–20%) [26]. The most recent innovation in PVs refers to the third generation, which is composed of several materials, including dye-sensitised (DSSCs), copper–zinc tin sulphide (CZTS), quantum dot (QDSCs), perovskite (PSCs), and organic PV (OPV) solar cells. They have very different energy, technical, and aesthetic performances because of their physical–chemical structures. For example, DSSCs use synthetic dyes to replace chlorophyll in plants to reproduce a photosynthesis scheme [27]. They have high flexibility in shape, colour, and transparency; low cost; and an environmentally friendly manufacturing process [27], but on the other hand, they have low energy efficiency (≅7.1%) and high environmental sensitivity (liquid electrolytes may freeze or evaporate at low or high temperatures). CZTSs and QDSCs are less exploited because of complicated fabrication processes, relatively low energy efficiency (CZTs ≅ 13% and QDSCs ≅ 10%), high costs [25][27], and the presence of toxic elements (such as the presence of particle sizes that are hard to control) [28]. PSCs are structured compounds composed of organic and inorganic materials (e.g., methylammonium lead halides, inorganic caesium lead halides, and tin-halide-based materials) [28]. They have high flexibility, a low cost, a high power-to-weight ratio (≅19.5%), and involve facile fabrication techniques but, conversely, reduced mechanical robustness, low long-term stability (particularly relative humidity, which can generate degradation issues), high-efficiency drops, and high manufacturing costs [25][29]. Finally, OPVs have environmentally friendly manufacturing processes, low weight (especially ultrathin OPVs), high mechanical performance, and geometrical flexibility [25][27]. The disadvantages are decay risks at high temperatures, low energy efficiency (≅10%), and performance instability over the passage of time [25].
Flexible PVs encompass the second and third generations of PV materials [24]. Both PSCs and OPVs can be integrated into PV textile membranes, which benefit from their flexibility and easy production techniques, similar to textile processes, and this has created new markets for PV applications [29]. The flexibility of solar cells mainly depends on the substrates used. They can be divided into [25] (i) plastic and (ii) metallic substrates. Plastic ones are composed of polymeric materials (e.g., PEN, PET, PTFE, ETFE). These substrates are characterised by low cost, high optical transparency, chemical stability, and favourable bendability [25]. However, they have certain disadvantages, including high deformation, reduced mechanical resistance, and limited tolerance to high temperatures [25][30]. Metallic ones are manufactured using copper or stainless-steel foils. These substrates offer advantages like good thermal stability, high corrosion resistance, and charge conductivity. However, they are less transparent, resulting in their opacity being a drawback [25].
After the first studies referring to the chemical composition of PV cells for improving their performance [24], studies on the design and calculation of PV performance arose. Early studies investigated the compatibility between PV designs and advanced parametric models to research the technical, aesthetic, and energy possibilities of tailored BIPV tensile membrane structures [27]. The most widely used parametric tool is the Grasshopper parametric plug-in for Rhino, known for its ability to optimise multiple environmental parameters [24]. Concurrently, numerical simulation software such as ANSYS, EASY, and ABAQUS is employed for structural designs [24]. For instance, Zanelli et al. [31] developed a prototype for integrating ethylene-tetra-fluorine-ethylene (ETFE) with OPVs. They discussed the fabricating approach, the printing techniques, and the pattern possibilities thanks to the support of Grasshopper. Ibrahim et al. [32] assessed the PV layout and daylighting patterns of a BIPV tensile membrane using the Grasshopper software. This method predicted structural performance and payback time under different mechanical and environmental conditions. An important topic is related to form-finding processes to optimise the shape of PV tensile membrane structures using dynamic relaxation [33], finite element [34], and force density [35], methods. Dynamic structural analyses are preferred for understanding the structural feasibility of the curved shapes of inflatable membrane structures [35].
Indeed, given the complex challenges and the potential of PV tensile membrane structures, there is a clear need for optimisation studies that encompass various aspects such as geometrical design, structural integrity, energy efficiency, and electrical performance. These studies should be conducted under different climatic conditions to gain insights into how irradiation affects different building shapes and orientations. By conducting such comprehensive optimisation studies, it is possible to better understand and harness the potential of PV tensile membrane structures, paving the way for the more efficient and effective integration of PV tensile membranes in the built environment.

References

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  9. IEA-SHC T41. Solar Energy and Architecture. Available online: http://task41.iea-shc.org (accessed on 13 July 2023).
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  14. Berger, K.; Cueli, A.B.; Boddaert, S.; Del Buono, S.; Delisle, V.; Fedorova, A. International definitions of “BIPV”, Report IEA-PVPS T15-04: 2018. Available online: https://iea-pvps.org/wp-content/uploads/2020/02/IEA-PVPS_Task_15_Report_C0_International_definitions_of_BIPV_hrw_180823.pdf (accessed on 13 July 2023).
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Subjects: Construction & Building Technology
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Janusz Marchwiński
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Vuk Milošević
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Anna Stefańska
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Elena Lucchi
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Revisions: 2 times (View History)
Update Date: 22 Sep 2023
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