# Status of BIPV and BAPV System for Less Energy-Hungry Building in India--A Review
## 3 Building Integrated and Applied Photovoltaic (BIPV/BAPV) Technologies
Low concentrators are static which reduces the cost of the expensive solar tracker. The thermal effect is lower than a high concentrator, due to a low concentrator on PV cells, which reduces the necessity of a cooling system and makes a low concentrator a suitable candidate for building's window and facade application [96; 97; 98]. For northern latitude location, diffuse solar radiations are higher, CPC and LSC both work efficiently. Concentrating PV came into a scenario to reduce the usage of the costly silicon material by replacing low-cost material, which concentrates a  
Figure 1: Major BIPV and BAPV products [79]. Figure 2: Window integrated with different types of PV cell materials [93]. higher amount of incident solar light on a lesser PV material [99]. For crystalline silicon-CPC-based BIPV window, regular distribution of spacing between PV cells offer semi-transparency (silicon solar cells are opaque), as shown in Figure 3. Different geometries of CPCs were investigated for BIPV window and facade application [100; 101; 102; 103]. Recently, the performance of DSSC and perovskite solar cells was also investigated, using low concentrating CPC, which enhanced the PV performance than non-concentrating counterpart [104; 105]. A typical LSC consists of a glass or plastic-based square/rectangular-shaped waveguide luminophores, which absorbs a short-wavelength photon and convert them into long-wavelength. Further, due to total internal reflection, these photons finally reach the PV cells attached at the edge of the waveguide [106; 107; 108; 109; 110], as shown in Figure 4. The advantage of LSC-BIPV system is that the PV cells are placed at the edge, which does not create an obstacle for viewing. Also, this waveguide plate can be made semi-transparent to fully-transparent or different colors, which is aesthetic for building application and suitable for building window integration [111; 112; 113; 114]. Promising results, using LSC-thin film integration, was also reported by [115]. LSC does not possess any thermal effect on PV cells, which is an added advantage over low concentrating CPC. The performance degradation of both BIPV and BAPV is possible at higher ambient temperature and exposure to higher incident radiation, which increases the PV cell's temperature. Crystalline silicon and thin-film both work, with poor efficiency, at higher PV cell temperature. Thermal regulation BAPV  
Figure 4: Working principle of inkjet-printed luminescent solar concentrator and photograph of a printed A4 sized luminescent solar concentrator [109]. Figure 3: (a) CPC based BIPV, (b) Semi-transparent building blocks using CPC-silicon PV (image courtesy Build Solar). system is possible by employing forced water flow, forced airflow or phase change material (PCM) at the back of the system [116; 117]. At the back of the BPAV system, copper pipes are integrated to flow the air [118; 119; 120] or water [121; 122]. This typical BAPV is also known as BAPV-thermal (BAPV/T) water or air collector, where water or air will extract the additional heat energy from the PV system and allow PV system to operate efficiently. Hot air or water can be used by building purposes [123]. Notably, researchers often misuse the BIPV term [121; 122; 124; 125; 126; 127; 128; 129; 130]. As BIPV is attached as a building envelope, natural airflow and PCM are the only two available and investigated options to diminish the elevated PV cell temperature [131; 132; 133]. The inclusion of collector to BIPV was forced to compromise with buildings aesthetic. For a system which is BAPV/T system is most often referred to as BIPV/T in the articles. Hence, care should be taken when referring to a PV/T system as BAPV/T or BIPV/T. A typical BAPV/T with a water flow system is shown in Figure 5. Details of BIPV and BAPV are listed in Table 2.