# Status of BIPV and BAPV System for Less Energy-Hungry Building in India--A Review
## 3 Building Integrated and Applied Photovoltaic (BIPV/BAPV) Technologies  
BAPVs are an addition to the traditional or new PV system, on an existing or new building whereas BIPVs replace the existing traditional building envelope, such as window, roof, and wall [74]. Hence, BIPV has a greater impact on the building's indoor environment. BIPVs are often transparent or semi-transparent by nature, which allows incident daylight and solar heat to pass through, thereby directly modifying the indoor ambiances. Additionally, it also has a variety of capabilities like control solar heat gain or loss, daylight glare and offset the window, roof or wall material cost [75]. On the other hand, BAPVs have no such contribution to the building environment other than the production of green power. Currently, available BIPV products include BIPV tile, foil and glazing [76; 77]. BIPV foils and tiles are primarily applied on the roof while BIPV glazings are mostly employed for vertical semi-transparent and transparent windows, facade and wall applications. Presently, 80% of the BIPV market contributes to rooftop-mounted and only 20% of it is in accord for facade-mounted [78; 79; 80; 81; 82]. Generally, rooftops, standing without any hindrance from nearby tall buildings or trees, are the ideal solutions to harvest the best energy when pitched at certain elevation angles. BIPV foil products are best suited for building applications due to their flexibility and light-weight properties. PV cells for BIPV products are mostly thin films, which possess low power generation due to the high electrical resistance of the thin film. However, due to a low temperature coefficient of thin-film BIPV foil, power degradation is comparatively less at high temperatures to silicon types. Alwitra GmbH and Co, which uses amorphous silicon cells and Uni-Solar cells are the present manufacturers of BIPV foil. Next, BIPV tiles are most prominently used as roof integration, which includes covering the entire roof or selected part of the roof with BIPV tiles. Some of these tiles also appear to be similar to that of a ceramic curved tile, which might be aesthetically pleasing but are not effective in terms of power generation, due to its curved surface area [76; 77]. SRS Energy, Solar Century, Luma solar, Suntegra and, Sunflare Tesla are few of the present BIPV tile manufacturers. Figure 1 shows the presently available BIPV and BAPV products. BIPV windows are one of the most fascinating applications, responsible for maintaining visual comfort between the external world and building interior, modulating available daylight and heat. Crystalline silicon [83; 84], amorphous silicon [85; 86; 87; 88], CdTe [89; 90], DSSC [91; 92] and perovskite [44] are the few materials, which when intensely investigated for BIPV window applications (shown in Figure 2), have found impressive possibilities towards building integration. \begin{table}
\begin{tabular}{|c|c|c|c|} \hline
**Solar cell** & \multicolumn{2}{c|}{**Advantages**} & \multicolumn{2}{c|}{**Disadvantages**} \\ \hline Perovskite solar cells [71; 72; 73] & \(\bullet\) & Perovskite uses smaller & \(\bullet\) & Not stable at \\  & & quantity of material to absorb & ambient condition. \\  & & the equivalent amount of & \(\bullet\) & Not fully \\  & & light in comparison to c-Si. & matured technology. \\  & \(\bullet\) & Perovskite materials, like & \(\bullet\) & Thermal performance of this \\  & & methylammonium lead & technology is not well. \\  & & halides are cheap and easy & \\  & & to produce. & \\  & & Semi-transparent/transparent & \\  & cells are possible, which & & \\  & makes it suitable for aesthetic & & \\  & building application. & & \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._Concentrator-based BIPV windows are also very attractive for less energy-hungry building integration. Low concentrating compound parabolic concentrator (CPC) [94] and luminescent solar concentrators (LSC) [95] are now dominating the major building-integrated concentrating photovoltaic research activity.