## 1 Introduction  
A considerable amount of energy is consumed in buildings; this sector is responsible for 40% of total energy consumption and 36% of the greenhouse-gas emissions in the European Union [1]. These numbers are expected to increase further due to the growing use of energy-intensive devices, efforts to expand energy access in developing countries, the prevalence of coal-fired power plants, etc. [2]. However, there is a proven potential to increase energy independence and reduce greenhouse gas emissions by adopting strategies such as energetically efficient buildings, renovations, energy performance standards, and measuring the embodied carbon of buildings, as emphasised by the European Commission's Energy Performance of Buildings Directive, which aims to double the retrofitting rate of existing buildings and enhance energy efficiency to support climate neutrality and energy independence goals [3]. On the basis of data from the EEA (European Environment Agency), it is important to attain climate neutrality in the EU by 2050 [4]. To this end, zero-energy buildings and renewable energy technologies play a pivotal role. A technology that successfully addresses the requirements mentioned above by generating \"green\" energy in an efficient way is known as building-integrated solar technology [5; 6; 7]. These systems are designed to integrate seamlessly with building structures, providing renewable energy in situ while contributing to the architectural design and sustainability in buildings. Various types of building-integrated solar systems exist, each offering distinct advantages (from an energetic point of view as well as from an environmental point of view). For example, photovoltaic (PV) modules can be incorporated into roofs, facades and windows by means of semi-transparent PV modules/systems, enhancing both functionality and aesthetics, and offering eco-friendly solutions for buildings, greenhouses, etc. By way of illustration, [PERSON] et al. [8] investigated dot-matrix patterned photovoltaic (PV) modules for building integration, underlining the importance of building-integrated PV systems due to the high energy conversion efficiency and the aesthetic versatility. The use of the smallest possible dot size was presented as a solution to cope with the problem of losses. Bearing in mind that space availability is a limiting factor in buildings, hybrid photovoltaic-thermal (PVT) collectors stand out due to their interesting geometrical and architectural characteristics (e.g., in the case of building-integrated applications [9]) and on-site cogeneration of electricity and heat with global efficiencies of around 70% (with an electrical efficiency about 20% and thermal efficiency around 50%) [10]. In addition to this, PVT systems occupy less space than conventional solar energy systems (i.e., PV modules and solar thermal collectors), which produce the same amount of energy using separate devices for production of electricity and thermal energy [10]. Furthermore, PVT technologies offer numerous options (active systems; passive systems, etc.) for various applications in the building sector [11]. On the other hand, PVT systems can reduce cost and environmental impacts while increasing the efficiency by using solar concentration, known as concentrating photovoltaic-thermal (CPVT) systems. In this case, expensive solar cell material is partly replaced with lower-cost optical elements, concentrating light onto a smaller area [5; 6; 7]. Nonetheless, effective temperature management is crucial since the energy flux received by the cells is proportional to the concentration ratio, and high cell temperatures may cause considerable efficiency losses, depending on the PV technology [5]. In this regard, there are different cooling strategies, active or passive [12; 13; 14; 15; 16], but among them, direct immersion of PV cells in dielectric liquids offers additional advantages. PV-cell efficiency is enhanced due to a reduction in Fresnel losses (compared to a bare PV cell).