In this communication, a study is carried out to evaluate an annual thermal and exergy efficiency of a hybrid photovoltaic thermal (HPVT) air collector for different Indian climate conditions, of Srinagar, Mumbai, Jodhpur, New Delhi and Banglore. The study has been based on electrical, thermal and exergy output of the HPVT air collector. Further, the life cycle analysis in terms of cost/kWh has been carried out. The main focus of the study is to see the effect of interest rate, life of the HPVT air collector, subsidy, etc. on the cost/kWh HPVT air collector. A comparison is made keeping in view the energy matrices. The study reveals that (i) annual thermal and electrical efficiency decreases with increase in solar radiation and (ii) the cost/kWh is higher in case of exergy when compared with cost/kWh on the basis of thermal energy for all climate conditions. The cost/kWh for climate conditions of Jodhpur is most economical.
Increasing cost of fossil fuels has compelled scientists to look for different options to meet energy requirements keeping in view that such options are economical, abundant in nature and have low maintenance cost. Over the years, scientists have studied various options available such as nuclear energy, wind energy, bio mass, fuel cell, solar energy, etc. Studies have shown that amongst available sources of energy, solar energy appears to be freely available, more economical and truly environment friendly than other sources of energy available.
Solar energy can be utilized as electrical energy, thermal energy or a combination of both. Hybrid photovoltaic thermal (HPVT) air collector system can collectively generate electrical and thermal energy. Efficiency of photovoltaic (PV) system can be increased by withdrawing the thermal energy available at the bottom of the PV module.
The HPVT system can be used as air collector/water collector. A HPVT air collector consists of a PV module with an air duct mounted below the PV module. The air is passed through the duct by using a fan. The air gets heated by using the thermal energy available at the bottom of the PV module. In case of HPVT water collector, water is used in place of air. Thus, an HPVT system can be used as
(1)
Air collector: ( Hegazy, 2000; Infield et al., 2004; Tripanagnostopoulos et al., 2002; Prakash, 1994; Cartmell et al., 2004; Bhargava et al., 1991; Tiwari and Sodha, 2006 and Tiwari and Sodha, 2007; Chow et al., 2007a; Tiwari et al., 2006).
(2)
Water collector: ( Zondag et al., 2002; Kalogirou, 2001; Garg et al., 1994; Chow, 2003; Chow et al., 2006 and Chow et al., 2007b; Tripanagnostopoulos et al., 2002; Zakherchenko et al., 2004; Sandnes and Rekstad, 2002; Tiwari and Sodha, 2006)
Kalogirou (2001) observed an increase of mean annual efficiency from 2.8% to 7.7% with a thermal efficiency of 49% of an unglazed HPVT air collector under forced mode of operation for the climatic conditions of Cyprus. A similar study has been conducted by Zondag et al. (2002). They referred to an HPVT system as a combi-panel that converts solar energy into electrical and thermal energy and observed electrical and thermal efficiencies as 6.7% and 33%, respectively. Sandnes and Rekstad (2002) observed that the HPVT system concept must be used for low-temperature thermal applications and for increasing their electrical efficiency. Zakherchenko et al. (2004) have also studied unglazed HPVT system with a suitable thermal contact between the panel and the collector and then observed that the area of PV panel and collector in HPVT system need not be equal for high overall efficiency. Tripanagnostopoulos et al. (2002) studied an integrated unglazed HPVT system with a booster diffuse reflector with the horizontal roofing of a building and concluded that the system yields distinctly clear higher electrical and thermal outputs. Infield et al. (2004) derived an overall heat loss coefficient and thermal energy gain factor for a combination of a ventilated vertical PV module and PV facades. It is observed that the ventilated facades ensure that the electrical efficiency of PV module is improved on account of low temperature. Zondag et al. (2002) and Sopian et al. (2000) observed that thermal energy of a glazed HPVT system increases along with lower electrical efficiency due to higher operating temperature.
In this paper, an attempt is made to study life cycle cost analysis of an HPVT air collector incorporating the effects of interest rate, subsidy and life of the system (with and without consideration of balance of system (BOS)) for different climatic conditions.
It is observed from Fig. 2 that for a variation in solar radiation in the range 1025–1175 W/m2, the thermal and exergy efficiency drop by about 10% and 5%, respectively. It is also observed that the exergy efficiency is 40–45% lower than the thermal efficiency in the range of solar radiation mentioned above.
(ii)
Amongst the climatic conditions covered under the study, Jodhpur is the best for use of hybrid photovoltaic thermal (HPVT) air collector.
(iii)
The energy payback time (EPBT) of the HPVT air collector without balance of system (BOS) is about 2 years, which can further be reduced for higher solar radiation, longer sunshine hours and number of clear days in a year.
(iv)
There is marginal effect of the life of the HPVT air collector on life cycle conversion efficiency (LCCE) after 50 years. Thus, minimum period of 50 years of the present system is economical.
Appendix A. Derivation of capital recovery factor (Humphreys, 1991)
Considering uniform end of the year annual amount, R, (Unacost) for a period of n years. The diagram for this is as shown below
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Let P be a single present value at initial time (i.e. n=0):
equation(A.1)
View the MathML sourceP=R[11+i+1(1+i)2+⋯+1(1+i)n]orP=R∑1n1(1+i)n.
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The summation of geometric series in Eq. (A.1) can be evaluated as
View the MathML source∑1n1(1+i)n=11+i1-(1/1+i)n1-(1/1+i)=(1+i)n-1i(1+i)n.
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Thus, Eq (A.1) becomes
View the MathML sourceP=R(1+i)n-1i(1+i)norP=RFRP,i,n,
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where
View the MathML sourceFRP,i,n=(1+i)n-1i(1+i)n,
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which is referred to as the equal payment series present value factor or annuity present value factor. Thus, the expression for Unacost becomes
View the MathML sourceR=Pi(1+i)n(1+i)n-1orR=PFPR,
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where FPR,i,n is defined as capital recovery factor (CRF). Thus, the expression for CRF is given by
View the MathML sourceFPR,i,n=i(1+i)n(1+i)n-1.
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