Exergoeconomic and Enviroeconomic Analysis of Photovoltaic Modules of Different Solar Cells

The exergoeconomic and enviroeconomic analysis of semitransparent and opaque photovoltaic (PV) modules based on different kinds of solar cells are presented. Annual electricity and net present values have also been computed for the composite climatic conditions of New Delhi, India. Irrespective of the solar cell type, the semitransparent PV modules have shown higher net energy loss rate (L en) and net exergy loss rate (L ex) compared to the opaque ones. Among all types of solar modules, the one based on c-Si, exhibited the minimum L en and L ex. Compared to the opaque ones, the semitransparent PVmodules have shown higher CO2 reduction giving higher environmental cost reduction per annum and the highest environmental cost reduction per annum was found for a-Si PV module.


Introduction
In this era of advanced technologies the demand of energy is increasing day by day.The sources of energy are very limited and are running out very rapidly.Emission of greenhouse gases from the fossil fuels is another major concern as it is causing the global warming [1].Therefore, the renewable sources of energy are developed which have no harmful effects on our delicate environment.To reduce the impacts related to processing of any energy source the efficiency of energy plants should be improved and such studies are done by exergoeconomic and enviroeconomic analysis.The exergoeconomic analysis is basically the exergy analysis along with the cost analysis in order to access the performance of the energy systems [2].It reveals the relative cost importance of each component and provides the ways to improve overall cost effectiveness [3,4].On the other hand, enviroeconomic analysis (also known as environmental cost analysis) identifies the options for reducing the environmental impact associated with the overall system [5].
Photovoltaic (PV) energy conversion is considered as one of the most promising renewable energy technology which has the potential to contribute significantly to a sustainable energy supply and to mitigate greenhouse gas emissions.PV systems are free from greenhouse gases emission.Badescu analyzed a heating system of an ecology building and found that a PV array can provide all the energy required to derive the heat pump compressor, if an appropriate electricity storage system is provided [6].Ozgener and Hepbasli investigated the capital costs and thermodynamic losses in a greenhouse heating system with solar-assisted groundsource heat pump and found a correlation between the capital cost and exergy loss but no relation was established between capital cost and energy loss [7].Caliskan et al. [8] performed the energy, exergy, environmental, exergoeconomic, enviroeconomic, and sustainability analyses of the novel air cooler considering the nine different dead state temperatures at constant environment temperature.They found the maximum exergetic cost rate of 0.0228 kWh/$year at a dead state temperature of 37.77 ∘ C. According to the enviroeconomic analysis, the novel air cooler has CO 2 emissions cost as 6.96$/year.Agrawal and Tiwari [9] have done the exergoeconomic analysis of a glazed PV thermal (PVT) module air collector and found that for energy saving point of view the glazed PVT module air collector is a better option compared to PV module.Prabhakant and Tiwari [10] have carried out an analysis of carbon credit earned by each district in India, for supplying minimum subsistence electricity to each family (energy security).
We present here the exergoeconomic and enviroeconomic analysis of semitransparent and opaque PV modules based on four different types of solar cells, namely, c-Si, a-Si, CdTe, and CIGS.The schematic designs of semitransparent and opaque PV modules based on c-Si and thin film solar cells are shown in Figure 1, where panel (a) corresponds to semitransparent c-Si, panel (b) corresponds to semitransparent thin film, panel (c) corresponds to opaque c-Si, and panel (d) corresponds to opaque thin film solar cells.The detailed performance analysis of the same systems has been presented very recently [11].For incidence of the maximum solar radiation, the PV modules in northern hemisphere were considered to be places south oriented, having inclination with horizontal surface (30 ∘ ) equal to the latitude of the system's station [12][13][14].The performance analysis was carried out for New Delhi which is located at 28.38N, 77.12E in India.We now present here the annual electricity and exergoeconomic and enviroeconomic computations of those PV modules having power 75 Wp by considering the following weather conditions [15]:

Modelling
The efficiencies and operating temperatures of PV modules are calculated using energy balance equations.To write the energy balance equations for PV modules, the following assumptions have been made: (i) the heat conduction is in one direction; (ii) the system is in quasi steady state; (iii) the ohmic losses in solar cells and PV modules are negligible.

Energy
where the expression for electrical efficiency of semitransparent c-Si PV module is given by [11] and   =   +   .
2.1.2.For Opaque c-Si PV Modules.The expression for electrical efficiency of opaque c-Si PV module is given by [11] where   =   +   .

Annual Electricity.
The hourly electricity of a PV module can be given by  el,hourly =   ×   × () [18].And the daily electricity in kWh is obtained by  el,daily = ∑  1 =1 ( el,hourly, /1000), where  1 is the number of sunshine hours per day.The monthly electricity for the clear days (condition (a)) in kWh is calculated by the following expression: where  1 is the number of clear days in a month.Now the annual electricity is calculated by

Net Present Value (NPV)
where present capital cost of the PV system includes the cost of PV panel with stand, charge controller cost, battery cost, inverter cost, and wiring cost. 5,1 ,  10,2 ⋅ ⋅ ⋅  , are the battery replacement costs that occurred every five years.We have

Exergoeconomic and Enviroeconomic Analyses 2.4.1. Exergoeconomic Analysis.
From the well-known first law of thermodynamics, "energy can neither be created nor be destroyed, " therefore, due to irreversibility of a process the exergy is consumed during the process.The energy balance equation for the components of a system was given by Lozano and Valero [19] as From (10a), (10e), and (10f) the energy and exergy loss rates for PV module can be given as follows.
(i) For semitransparent c-Si PV module, (ii) For opaque c-Si PV module, (iii) For thin film PV modules (a-Si, CdTe, and CIGS): where  ex (t) is the Petela-Landsberg-Press factor [20] and can be calculated as Following Rosen and Dincer [21], a new parameter R is defined as the ratio of loss rate.For energy loss rates, For exergy loss rates, 2.4.2.Enviroeconomic Analysis.Carbon dioxide (CO 2 ) emission trading is an administrative approach used to control the environmental pollution by providing economic incentives for achieving reductions in emissions of pollutants.So, the calculation of the cost associated with CO 2 emission is important to make an environmental assessment.The enviroeconomic (environmental cost) analysis is based on carbon price (or CO 2 emission price) and emitted carbon quantity.Establishing a carbon price is one of the most powerful mechanisms available to reduce national greenhouse gas emissions.The carbon price is an approach imposing a cost on the emission of greenhouse gases.Paying a price for carbon (CO 2 ) released into the atmosphere is a way of motivating people and countries to reduce carbon emissions.It also provides an incentive to invest and deploy renewable energy technology that does not emit carbon to the atmosphere.Also, the pricing method discourages people to generate electricity by the use of relatively more polluting coal, gas, and oil fired stations.Following Caliskan et al. [8], the enviroeconomic analysis based on CO 2 emission reduction and CO 2 emission reduction price can be given as where  co 2 is the environmental cost reduction parameter,  co 2 is CO 2 emission reduction price per tCO 2 , and  CO 2 is reduction in CO 2 emission per year (tCO 2 /year).If unit power is used by a consumer and the losses due to poor domestic appliances are around 20%, then the transmitted power should be 1 (1 − 0.2) = 1.25 units.If the transmission and distribution losses are 40%, which is common in Indian conditions, then the power that has to be generated in the power plant is 1.25 (1 − 0.4) = 2.08 units.The average CO 2 equivalent intensity for electricity generation from coal is approximately 0.98 kg of CO 2 per kWh at the source.Thus, for unit power consumption by the consumer the amount of CO 2 emission is 2.08 × 0.98 = 2.04 kg.We have The carbon dioxide emission reduction per annum Den Elzen et al. [22] mentioned the international carbon price between 13$/tCO 2 and 16$/tCO 2 for the low and high pledge scenario.So, this value is taken on average to be 14.5$/tCO 2 .Therefore, Environmental cost reduction per annum = Carbon dioxide reduction per annum × 14.5$.

Methodology
The climatic data for the solar radiation I(t) on horizontal surface, ambient temperature (  ), and the number of days for the weather conditions (a), (b), (c), and (d) for Delhi were obtained from the Indian Metrological Department (IMD), Delhi.The following methodology has been used for the exergoeconomic and enviroeconomic analysis of the PV module.Step 1.The hourly solar radiation on the PV modules (75 Wp), at the 30 ∘ inclination from the horizontal, was calculated using the Liu and Jordan method [23,24].
Step 2. The designed parameters, for all the PV modules, used for calculations have been tabulated in Table 1.
Step 3.For the known climatic conditions and designed parameters, the electrical efficiencies of the PV modules of c-Si and thin film (a-Si, CdTe, and CIGS) have been evaluated using ( 2), (3), and (5), respectively.
Step 4. The monthly electricity for clear days (condition (a)) has been evaluated using (6) and the same process was adopted to calculate the monthly electricity for other climatic conditions (b), (c), and (d).The total electricity for each month was obtained by adding the electricity generations in the climatic conditions (a), (b), (c), and (d) in that month.
Step 5.The annual electricity was calculated using (7).
Step 6.Net present value (NPV) has been calculated by (8).Operational and maintenance cost has been considered to be 10%, whereas salvage value has been taken as 5% of the present capital cost (P) of the modules.Interest rate i has been taken as 8%.
Step 8.For each PV module  en and  ex have also been calculated using ( 15) and ( 16).
Step 9.For each PV module carbon dioxide emission reduction per annum and environmental cost reduction per annum were calculated using ( 18) and ( 19), respectively.

Results and Discussion
To solve the mathematical equations, a computer program MathCad 8 has been used.The hourly variations of I(t) at 30 ∘ inclination to the horizontal surface and ambient temperature (  ) throughout the year are shown in Figures 2 and 3, respectively.The annual electricity for different semitransparent and opaque PV modules has been shown in Figure 4.For all the solar cell types, the semitransparent PV modules have shown higher annual electricity compared to the opaque ones.The maximum annual electricity is observed for a-Si to be 139 kWh for semitransparent and 133 kWh for opaque PV module.CIGS modules have shown the minimum annual electricity which is 125.9 and 120 kWh for semitransparent and opaque, respectively.Table 2 shows the net present capital value of each type of PV modules.c-Si has shown higher net present value (542.67$)than the other PV modules.It is because of high capital cost (212.96$)due to shortage of availability of the material and expensive manufacturing process.For all the PV modules, kWh/kWp values are also calculated to show the energy generated divided by the STC rating.Table 3 compares the energy rating values of all the semitransparent and opaque PV modules in kWh/kWp, electricity per installed power.Semitransparent PV modules have higher kWh/kWp (∼4%) than that of the opaque ones while among all the PV modules a-Si exhibited highest kWh/kWp and CIGS has lowest kWh/kWp.The reason behind this is the higher annual electricity of a-Si PV module and lowest annual electricity of CIGS.Table 4 shows the  en and  ex for each PV module.Irrespective of solar cell type, the semitransparent PV module exhibited less  en and less  ex .The reason behind this is that the semitransparent PV modules have shown the higher efficiencies throughout the year compared to the opaque ones as in case of c-Si PV modules; the packing factor is considered to be 0.89.
In that case the solar radiation falling on the nonpacking area is transmitted through the semitransparent module, whereas in case of opaque modules it is absorbed by the tedlar sheet.The absorption of solar radiation by tedlar sheet results into the increment in cell temperature, due to which the module efficiency decreases.But in case of thin film PV modules, the packing factor is considered to be 1 and there will be no nonpacking area.However, the higher efficiencies in semitransparent thin film PV modules compared to the opaque ones can be understood from their thin film property.Due to very low film thicknesses some of the heat of the incident radiation is transmitted through the back glass sheet but in case of opaque modules it was absorbed by the tedlar sheet.The absorption of solar heat by the tedlar sheet results in increments in the module temperature, due to which the module efficiency decreases.Therefore, semitransparent PV modules exhibited higher energy flux rate products and higher exergy flux rates as compared to the opaque ones that causes lower  en and  ex .Among all the PV technologies in both cases (semitransparent and opaque) a-Si has shown higher  en and  ex because it exhibited higher energy flux rate products and higher exergy flux rate products because of higher efficiency.
The ratios of thermodynamic loss rate to net present value ( en ) for all the PV modules are shown in Figure 5.It was observed that semitransparent PV module exhibited lower  en than the opaque ones for all the PV technologies.Similarly Figure 6 shows  ex for all the PV modules and it was found to be lower for the semitransparent PV module.It is because of the lower energy and exergy flux rate products in semitransparent PV module.Table 5 shows the CO 2 emission reduction per annum (tCO 2 e) and environmental cost reduction per annum ($) for all the PV modules.From Table 5 it is clear that, for all the PV technologies, the semitransparent modules have shown higher CO 2 emission reduction per annum (tCO 2 e) giving higher environmental cost reduction per annum ($).The reason behind this is that the semitransparent PV module exhibited higher annual electricity.Among all the technologies it was found that a-Si PV module earns highest carbon credit and therefore higher maximum environmental cost reduction per annum compared to other PV modules.The reason behind this is the same as a-Si PV module having higher annual electricity.

Conclusions
On the basis of the present studies the following conclusions have been drawn.(i) Semitransparent PV modules exhibited higher annual electricity and higher kWh/kWp compared to the opaque ones, whereas among all the PV modules a-Si has shown the maximum annual electricity generation and maximum kWh/kWp.
(ii) Semitransparent PV modules exhibited lower  en and  ex giving lower  en and  ex , whereas among all the PV technologies, c-Si exhibited lowest energy rate and exergy rate.
(iii) Net CO 2 mitigation (tCO 2 e) per annum was found to be maximum in semitransparent PV module giving higher environmental cost reduction per annum ($).Among all the technologies, a-Si PV module earns highest carbon credit and higher maximum environmental cost reduction per annum compared to other PV modules.
Therefore, as a whole for energy saving and impact on environment point of view, the semitransparent PV module is more beneficial than opaque ones.

Figure 2 :Figure 3 :
Figure 2: Hourly variation of solar intensity I(t) for each month.

Figure 4 :
Figure 4: Annual electricity for different material semitransparent and opaque PV modules.

Figure 5 :
Figure 5: Ratio of thermodynamic energy loss rate to the net present value ( en ) for different material semitransparent and opaque PV modules.

Figure 6 :
Figure 6: Ratios of thermodynamic exergy loss rate to the net present value ( ex ) for different material semitransparent and opaque PV modules.

Table 1 :
Design parameters of opaque and semitransparent PV modules.

Table 2 :
Net present value (NPV) for different material PV modules.

Table 3 :
Energy rating values in kWh/kWp for different material semitransparent and opaque PV modules.

Table 4 :
Net energy loss rate and net exergy loss rate for different material semitransparent and opaque PV modules.

Table 5 :
The values of CO 2 emission reduction per annum (tCO 2 e) and environmental cost reduction per annum ($) for different material semitransparent and opaque PV modules.