A Novel Investigation and Comparative Study on Building Integrated Photovoltaic Thermal (BIPVT) System

An analysis of BIPVT system has been carried out in this paper based on arrays named as solar cell tile array and semitransparent array. Previously comparisons and performance analysis were carried out for opaque and semitransparent system in non-optimized way but in the present case it has been optimized to get better results. As far as energy efficiency and exergy is concerned semitransparent PVT has an edge as compared to others in all respect. Semitransparent PVT has higher useful energy gain by 2.5 KWH as compared to SCT. Further the electrical and thermal efficiency has been derived and a conclusion has been made that semitransparent PV cell has an edge in all respects as compared to SCT. The electrical efficiency has been increased to 17.17% from the previous 16% and overall exergy to 18.4% from previous 17.1%. i.e. an overall growth of 6.8% and 7.6% respectively. Keywords-SCT & semitransparent PVT array, Building integrated photovoltaic system (BIPVT), Photovoltaic (PV), Exergy.


Introduction
In recent times solar thermal systems are widely used, but PVTs are not used extensively. More than 80% of the incoming solar energy is either reflected or absorbed as heat energy. Loferski et al. (1998) studied and obtained few results related to the system with air circulation in a housing. Agrawal and Tiwari (2009) concluded that in terms of energy saving glazed hybrid gives better result as compared to normal PV module. Vats and Tiwari (2012) provided various data of the efficiency of different types of material out of which one can select. He et al. (2006) used the Hybrid Photovoltaic and Thermal (PVT) collector technology using water as the coolant as a solution for improving the energy performance. The BIPVT system designed by (Agrawal and Tiwari, 2010) have shown that the roof top placed in an effective area of 65 m 2 , is capable of producing the net electrical and thermal exercise of 16,300 kWh and 1550 kWh, respectively, at an overall thermal efficiency of 54.2%. Kim and Kim (2012) have studied simulation of air-type building-integrated photovoltaic-thermal system. Singh et al. (2015) described the modeling and optimization of single channel system by genetic algorithm. The scheme proposed by Singh et al. (2016) made a comparative study of exergy of different cities and concluded that there is an increment of 5.8 to 14.7% of exergy as compared to proposed by Agrawal and Tiwari (2012) using soft computing technique.

Thermal Modeling of BIPVT System
In the current paper research has been made on cold climatic condition of India by placing the designed model on the roof top of the building. Rajoria et al. (2012) described the overall energetic heat gain and exergy heat gain and overall efficiency of different city for summer condition.  Rajoria et al. (2013) made an attempt to analyse the performance of semi-transparent hybrid photovoltaic thermal double pass facades (HPVT-DPF) connected in series and parallel in terms of energy and exergy for four weather conditions of Srinagar. Figure 1 shows the prospective view of the designed model with specification of the proposed system. As Srinagar is located at 3401'N, 74 0 51'E due to which the propose systems is fitted in the south direction inclined at an angle of the latitude of that city i.e. 35 0 to the horizontal. With proposed area of 65 m 2 the present system has 48 PV Module in 6rows.  Table 2 gives the detail values of the design parameters of the proposed system.
To calculate electrical efficiency of any PV cell as Zondag et al. (2002) designed a theory is given by, Quantities ηref, Ta and φref are usually references to what the researcher has to set accordingly.

= * ( ) * *
(2) Equivalent thermal energy of electrical is given by Adding thermal gain of the proposed systems to equivalent thermal energy of electrical energy overall thermal energy of proposed system can be calculated as, The overall thermal energy of the proposed system can be derived by Overall thermal efficiency can be derived as, Energy balance equation of the proposed model is given by: For tedlar of proposed model, Energy balance can be derived as, Substituting Tc in Eq. (11) Energy balance of air flowing in the duct of the BIPVT system is given by, On substituting Tbs from Eqn (12) to Eqn (13) we have By Tair=Tar , Tair=Tairout.
The temperature at the output of duct for length L can be derived as, For ηpv row of the system the overall thermal energy can be derived as, For heating of space of the building the energy balance equation can be derived as, * [ Temperature of air inside the room can be derived as In case of semi-transparent PVT roof, the maximum room air temperature and maximum daily useful heat gain for a typical day of January is higher by 6.8 o C. The efficiency, exergy, thermal and electrical gain have been calculated from temperature at different places from Table 3 and  Table 4 after changing the parameters related to the system. The values have been compared with the previous one and percentage change is calculated with the use of "MATLAB-13". The air is blown at a pace of 1.5kg/sec inside the duct to get maximum efficiency.

Results and Discussion
 Figure 2 shows that even if the cell temp dies out at 5pm there is presence of duct temperature which indicates the efficiency of the module.  A comparison has been made between electrical efficiency and exergy efficiency which shows that after combining the electrical and thermal energy the net electrical efficiency increases from 17.1% to 18.4% which can be shown from Figure 3.  At 12.9% more outlet temperature of semi-transparent PVT it has an edge as compared to other system, which can be shown from Figure 4.  At 13.3 kWh, semi-transparent system has more daily useful heat gain as compared to SCT roof, which can be seen from Figure 6.  The Figure 7 shows the overall thermal electrical gain in KWH.  Figure 8 gives better idea that present system is best suited for Srinagar climatic condition as compared to Delhi.

Conclusion
Data shows that the solar intensity is maximum in Srinagar at 1pm in the month of January. If for the same system a comparison is made then it has been concluded that Srinagar gives better result as compared to Delhi, that is, almost 2% more efficient. Comparison has also been made to know about the room temperature, duct and the outlet in Table 3 and Table 4.
The present system produces almost 67KWh thermal energy per day as compared to 51KWh of previous system (Figure 7). As far as total electrical energy is concerned it produces 25 KWh per day from 8 to 5pm as compared to 23KWh of previous system. As far as efficiency is concerned this system produces 17.1% of electrical efficiency and overall exergy of 18.4% as compared to 16% and 17% of previous system. .

Conflict of Interest
The authors confirm that there is no conflict of interest to declare for this publication as the work is original.