Thermoeconomic Analysis of a Solar-Assisted Industrial Process Heating System

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Introduction
Global energy demand is increasing day by day due to economic evolution and modernization, and the probable future gap between energy demand and supply is projected as huge [1,2].Not only the industrial sector but also modern agriculture is growingly adopting various modern technologies that are transforming this sector into energy intensive [3].To attain a global security between energy demands and supply and ensure environmental safety as well, scientists are currently emphasizing on realizing a balance between conventional fossil fuels and renewables [1].Most of the forecasts predict that global energy consumption will increase by 33% between 2010 and 2030, the lion's share of which will be fed in the industrial sector [4].Currently, global average industrial energy consumption is approximately 35%, which is swelling rapidly due to rapid economic growth of China, India, and other Southeast Asian countries [5].But, the major concern with widespread and substantial burning of fossil fuels consists in the environmentally harmful CO 2 emission that alone contributes to 76% of the global warming [6].
Major industries including food processing, dyeing, drying, pulp and paper processing, and petroleum refining utilize fossil fuels to produce process heat in the form of either steam or boiling water [7,8].Globally, industrial sector generates about a cumulative 47% of the emissions through burning fossil fuels [9].Hence, increasing the span of renewable energy application in process industries and reducing fossil fuel consumption must be traded off in order to alleviate industrial emissions [10].Environmental issues with the fossil fuels together with their fast depletion are putting an urgency to adopt renewables as an alternative, in which solar energy comes in the first place since it is practically inexhaustible and accessible in direct and indirect forms [11,12].World leaders have agreed to encounter approximately 45% of the global energy demand with solar energy by 2050 [13].
Energy from the sun can be harvested in the form of heat and electricity, wherein conversion efficiency of solar to thermal is essentially superior [14,15].Furthermore, conversion efficiency of solar thermal collectors (STC) is better than the conventional electric heaters [16][17][18].In this regard, photovoltaic thermal (PVT) systems can be envisaged as another option since they deliver dual output-heat and electricity.However, a downside of PVT technology is that it can produce only low-temperature thermal energy in the range of 35 to 40 °C [12,19].A vast potential implementation of solar thermal in industrial process heat (IPH) is still in its budding phase since commercial application needs heat generation at the medium-to high-temperature range [20].To upraise the application of solar thermal in IPH, a novel concept of an integrated solar-assisted process heating system composed of PVT with STC can serve to overcome the drawbacks of the isolated systems.
In the literature, research related to energetic and exergetic analysis of the individual PVT and FPC has been reported by numerous researchers.The energy and exergy analysis of glazed and unglazed PVT system has been investigated by Kazemian et al. [21][22][23], reporting that thermal energy and exergy efficiency of glazed PVT (74.14 and 0.76%) is greater than unglazed PVT (71.29 and 0.65%); however, it is opposite for electrical energy and exergy efficiency, i.e., it is greater for unglazed PVT (14.17 and 13.47%) than glazed PVT (13.40 and 12.99%), respectively.Similar works by various researchers [24][25][26][27] have reported that thermal efficiency of glazed PVT is more than unglazed PVT, while the trend is reversed for electrical efficiency.In addition, the effect of various designs of thermal absorbers in PVT has demonstrated a remarkable effect of increase in thermal and electrical performance as investigated by [28][29][30][31][32][33].However, the major drawback of the PVT system is that it cannot give high thermal output, and if arrangements are made to achieve higher thermal output, it will greatly increase the cell temperature, and ultimately, it decreases the electrical efficiency.
Compared to the PVT system, the FPC system can output high-grade thermal energy and higher outlet temperature having drawback as zero electricity generation.The energy and exergy analysis of FPC has been investigated by Tong et al. [34] reporting the energy and exergy efficiency (63.6 and 1.25%) for water as a working fluid; however, adding the nanoparticles in the water in the flat plate solar collector could improve the energy and exergy efficiency.In addition, similar results from the previous studies of FPC [35][36][37][38][39][40][41][42] reported that the energy and exergy efficiency of solar collector ranged from 40 to 71% and 2 to 8.78%, respectively, and varies depending upon the design of FPC, operating parameters, and type of working fluid.Also, [43,44] carried out the energy and exergy analysis for FPC with phase change material (PCM) and reported the average energy and exergy efficiencies in the range of 40 to 45% and 2 to 3.5%, respectively.Recently, for the first time, a steady two-dimensional mathematical model has been modeled for the integrated system for both PVT and STC, and this model is validated from other articles and previous work [19,45].Although a good number of simulation and experimental studies on isolated systems have been reported in literature, but detailed workable simulation model for integrated system and its realtime experimental validation is yet to be carried out.Also, no transient system simulation is available to perform parametric analysis of various parameters of an integrated system including water inlet temperature, mass flow rate, outlet temperature, ambient temperature, solar thermal collector heat gain, and rate of heat supplied from auxiliary system.Moreover, the long-term performance of such SAPH systems is yet to be analyzed extensively.In the present research, dynamic simulation models of two novel solar-assisted cascaded systems (PVT-FPC and PVT-HPETC) have been designed and developed together with three isolated systems (PVT, FPC, and HPETC).The well-engineered cascaded system can supply uninterrupted industrial process heat as per required industrial temperature ranges.All the systems have been modeled and simulated in TRNSYS, and outdoor experimental analysis has been carried out under typical Malaysian conditions to validate the models.This research is aimed at presenting a comparative analysis of the cascaded system over against three isolated systems, viz., PVT, FPC, and HPETC based on energy, exergy, and economic analysis to examine the aptness of the novel cascaded systems.

Methodology
The methodical phases in resolving the research problem have been discoursed in detail in this research.A combination of simulation and on-site experimental investigation has been adopted in this research work.To limit experimental uncertainties, apposite assumptions made during simulation are examined meticulously.A solar-assisted process heating (SAPH) system is an isolated solar thermal collector (be it an FPC or HPETC) or multiple collectors cascaded in series or solar thermal collector integrated with photovoltaic thermal (PVT) collector producing an outlet temperature to serve industrial process heating (IPH) purpose.The concept of a SAPH system comprised of PVT and STC.The PVT collector converts a portion of the incident solar radiation into electricity, the remaining energy being dissipated as heat is utilized to preheat the heat transfer fluid (HTF: water).Afterwards, the preheated water passes through the STC, which further heats up the water and raises the outlet temperature to a desired level.The water outlet temperature can be regulated by adding more collectors in series and also by controlling the HTF flow rate to some extent.This high-temperature water can be directly employed for IPH applications or stored as sensible or latent heat storage and supplied to application ends.In the meantime, the electricity produced from PVT is used to run a DC electric water heater to supply auxiliary heat that can ensure an uninterrupted supply of heat.[46].The integrated solar-assisted process heating (SAPH) system comprises of a PVT module and an FPC and HPETC connected in series.The schematic and experimental setup of SAPH as shown in Figures 2(a) and 2(b) has an FPC and HPETC integrated with a PVT collector and an auxiliary DC electric water heater with forced circulation by means of a pump and closed distribution to storage tanks.The measurement ranges and accuracy of the instruments used are given in Table 1.
After the modeling and simulation have been completed, all systems were mounted on metallic structures held at an angle of optimum magnitude (calculated using equations (1) and ( 2)) facing to the south in order to intercept the maximum radiations throughout the day.Cooper's equation as employed for slope calculation is given by [33,47] δ = 23 45 sin 284 + n 1 365 × 2π , 1 where δ is the solar declination, n 1 is the day of the year, and β is the angle of inclination.In equation (1), the term 23.45 is in degrees, and the term within the parenthesis is in radian.
Heat gain: Thermal (energy) efficiency: Exergy is the amount of energy that would transform to productive use.The basic principle of exergy analysis is defined on the basis of the second law of thermodynamics, which states that the thermal energy cannot be transformed without the change of temperature.Equations for thermal and electrical exergy equations are given as [49][50][51][52] where T s is sun temperature which is considered as 5,777 K.
Overall exergy efficiency: 2.3.2.Uncertainty Analysis.An uncertainty analysis is performed on both thermal and electrical parameters for both energy and exergy analysis.Suppose that parameters u 1, u 2, u 3, u m , u m+1 ⋯ u n are measured with uncertainties δu 1, δ u 2, δu 3, , δu m, δu m+1, , ⋯δu n , then the fractional uncertainty of U is written as [53] δU Using the above equation ( 10) and equations of energy and exergy efficiency, fractional uncertainties can be calculated.The uncertainties of the measuring instruments are given in Table 1.Employing the above analysis, the maximum uncertainty is calculated and found to be less than 5.0% for all parameters.Therefore, uncertainty values within this limit indicate the reliability of the measured data [53].

Economic Analysis.
In the present research, the discounted cash flow (DCF) method has been adopted that employs three criteria, viz., NPV, IRR, and PBP in selecting the most economical and profitable project [11,54].The economic analysis is conducted based on the thermal performance of isolated and cascaded systems.Table 2 presents the main assumptions and parameters which have been used in the present economic analysis.
(1) Net Present Value (NPV).NPV is expressed by [11] where NPV is the net present value index, C 0 is the initial investment cost, C i is the expected cash flow in the i-th period (i-th month or year), r is the discount rate, and i is the number of project plant life periods (months or years).The expected cash flow consists of all incomes and expenditures of the project during the plant life.In this method of evaluation, if the NPV of a project is positive, the project is considered acceptable, economical, and profitable.While if the NPV is negative, it will be evaluated as unacceptable and nonprofitable.(2) Internal Rate of Return (IRR).IRR is obtained from the NPV formula considering a zero net present value [11].
Based on this method of assessment, if the project rate of return is more than the interest rate of investment, then the project is considered economical; if it is less, then the plan will be evaluated nonprofitable.The net income of successive years is discounted to year zero at the rate that comply with the minimum attractive rate of return (MARR).Once the

International Journal of Energy Research
IRR is calculated, it should be compared with the MARR.If the IRR is greater than MARR, the investment is economically viable.If the IRR is lower than MARR, the investment is not economically interesting.When IRR and MARR are equal, the investor is economically indifferent between the project and the opportunity cost.Similar to the NPV, the project with the highest IRR is also financially more interesting [55].
(3) Payback Period (PBP).Equations ( 13) and ( 14) are used to calculate the PBP.The value of n, which is obtained from the equations, shows the period that the total initial investment of the project returns to the investors.So, a project which has less n index is more economical and more attractive to investors [11].
where C o is the cash flow of i-th period and CF is the equivalent annual cash flow.
(4) Levelized Cost of Heat (LCOH).In order to compare differing system designs, a standard metric named levelized cost of energy is employed that combines two disparate energy flows into one bottom-line metric.The levelized cost of heat (LCOH), adopted in the present analysis, allows a side-byside comparison of differing solar thermal technologies and technical specifications which examines the technical and financial factors affecting the cost of heat production of a SAPH system.Levelized cost of heat (LCOH) is calculated by dividing the lifetime cost of the system by the lifetime energy generation.The cost of the system is calculated by summing the annual net cash flow attributed to the installation and operation of the system, including expenses and revenue, over the lifetime of the system.In order to improve (reduce) the LCOH, either the cash flow needs to be reduced by mitigating costs or the energy generation must be increased through technical advances, such as improved efficiency.
Conventional solar thermal systems collect the entire spectrum of light, and the high energy ultraviolet and visible regions of the spectrum are arguably more valuable when harvested as electricity considering the relative cost of electricity (2-3× higher than natural gas).Because of this, there have been several projects dedicated to developing hybrid systems for combined heat and power applications.Such hybrid systems can attain improved energy or exergy efficiency relative to standalone systems.The electricity produced from the PV can be used to offset the electricity usage in a facility, effectively saving on power costs.This cost savings can be added into the cash flow calculations, reducing the overall annual operation costs.In this manner, the overall LCOH can be reduced compared to conventional 6 International Journal of Energy Research solar thermal systems.Herein, a LCOH model has been presented which examines the technical and economic factors which affect the cost of heat production for a hybrid system using the electricity produced to subsidize the cost of heat.The LCOH is calculated using equation (15).The annual cash flow (equation ( 16)) is comprised of the savings from electricity generation (+) based on the cost of electricity and operation and maintenance (O&M) costs (−) including both photovoltaic and thermal components.The annual present value was calculated based off a nominal discount rate (dr) of 8% using equation (17) where n is the year of operation.The net present value (NPV) for a lifetime of 20 years was calculated by summing the annual present values and subtracting the initial up-front capital cost.Yearly thermal and electrical energy generation was taken from the previous analysis.The electricity generation was used in combination with the price of electricity to calculate the electricity savings for annual cash flow.Like the cash flow, the present value of thermal energy generation was discounted at 8% annually.The NPV for thermal generation was the summation of annual present values as represented in equation ( 18) [56].Only the thermal energy was included in the NPV for energy generation, as heat is what is being priced.
PV th = E th 1 + dr n 18

Results and Discussion
The outcomes of the present research along with corresponding physical explanations are described in this section.Data were collected for the incessant flow of hot water at required ranges of temperature and flow rates ranging from 0.5 to 4.0 LPM and variation of solar radiation from 0 to 1000 W/m 2 .

Modeling and Experimental
Validation.The simulation models of the two SAPH systems modeled and simulated in TRNSYS have been validated using real-time experimental assessment.It can be seen from Figure 3 that the simulated and experimental results of water outlet temperature based on variation in solar irradiance agree quantitatively and qualitatively for both PVT-FPC and PVT-HPETC configurations.For the validation, the data is extracted from the comprehensive dataset of experimental values collected over several months.The thoroughgoing compliance of the simulation and experimental outcomes confirms the validity of the TRNSYS model in predicting the thermal and electrical behavior of the cascaded systems.
3.2.Thermal Performance Analysis 3.2.1.Energetic Analysis.In this section, energy interactions of the cascaded SAPH and the isolated systems have been presented.Cascading PVT with FPC and HPETC not only augments thermal performance, but it aids to maintain the thermal efficiency at various flow rates.The thermal efficiency for isolated PVT, FPC, and HPETC decreases rapidly with an increase in flow rate, but as for cascaded units, the thermal efficiency is steady and stable, particularly after 1.5 L/min.This is a necessary characteristic of the cascading FPC and HPETC with PVT.The advantages of hybridization will be further shown in Figure 4, which indicates that the thermal performance of the cascaded PVT-HPETC and PVT-FPC systems is still considerably higher, well below the minimum degree of solar irradiance.From Figure 4, it  7 International Journal of Energy Research would have been seen that the minimum thermal efficiency of cascaded PVT-HPETC and PVT-FPC systems is approximately 58.56 and 53.57%, respectively, which is obtained at very low solar irradiance of 100 W/m 2 , whereas the thermal efficiency of individual HPETC and FPC system with the same degree of solar irradiance is near 37.28 and 17.86% only.From Figure 4, it can also be seen that the maximum thermal efficiency of cascaded PVT-HPETC and PVT-FPC systems is approximately 81 and 77%, respectively, which is obtained at very low solar irradiance of 1000 W/m 2 .The literature work on the cascaded PVT and STC system is not available; however, in many experimental research on the PVT system, the energy efficiency ranges between 35 and 74% have been reported [14,21,22,25,30,32,33,[57][58][59][60][61].Similarly, results for energy efficiency of FPC and HPETC systems are reported in the range of 25-71% [34-36, 38, 41, 62, 63] and 30-85% [64,65], respectively.Ayompe et al. [66] also compared the thermal performance of FPC and HPETC and reported that the HPETC system proves its better performance compared to the FPC which is also proved in this study.Overall, among all the systems, the cascaded system has better advantages over other individual systems as it can obtain a high output temperature with high thermal heat gain and efficiency.

Exergetic Analysis.
In this section, the actual available efficiency for isolated as well as cascaded systems has been investigated.The effects of solar irradiance on the thermal, electrical, and overall exergy efficiency have been presented in Figure 5.It can be seen that the electrical exergy parameter of PVT and PVT cascaded with FPC and HPETC units is similar and varies insignificantly under varying solar irradiance; thus, thermal exergy parameter determines the overall efficiency trend.The effect of solar irradiance on thermal exergy efficiency defines a bell-shaped curve where the thermal exergy efficiency increases to a solar irradiance of 600 W/m 2 and then ultimately decreases.The highest thermal exergy efficiency achieved by the PVT-HPETC and 9 International Journal of Energy Research PVT-FPC systems is significantly low at just 0.83% and 0.69% as shown in Figure 5.However, the exergy efficiency of the cascaded device is comparatively higher due to the electrical exergy addition.Figure 5 also indicates that the overall exergy efficiency of the PVT-HPETC and PVT-FPC systems is more than 11.12 and 12.72% under varying solar irradiance, respectively.Related patterns for the exergetic analysis have been found in the literature on PVT, FPC, and HPETC.It has been shown that the exergy efficiency of the PVT system varies from 11 to 14% [21, 24-26, 33, 50, 67].However, for STC, it is very low and reported to vary between 2 and 9% [34-36, 38, 39].

Optimization of the Collector Configuration.
The amount of solar energy harvest from a solar thermal system directly depends on the area of collector.On the other hand, there is a certain limit for solar energy availability even in the daytime; hence, in industrial process heating (IPH) applications, it is not practicable to assume solar energy penetration ("solar energy penetration" refers to contribution in the total heat requirement) more than 40-50%.Moreover, there exists an inverse relationship (though not linear) between collector efficiency and span of the collector.Hence, collector area optimization becomes an important issue in large-scale solar thermal applications.This section presents the optimization practice of solar collector area for industrial process heat requirements.
It may be noted from Figures 6(a)-6(e) that with an increase in area of the collector, the solar energy penetration for all systems increases for every process heat temperatures (60, 70, and 80 °C), the rate of increment being steep up to a certain area and rather bland after that.In contrast, the collector of efficiency decreases.Therefore, it is necessary to have a trade-off between the collector efficiency and solar energy penetration for an optimum area of collector which can fulfil the minimum industrial process heat (IPH) requirements.Therefore, in this research, solar energy penetration share is obtained in the range of 50-80% due to intermittency of the renewable energy sources, and according to this range, the optimized area of solar thermal collector required is estimated.This is a significant and attractive consideration in applying these technologies to utilize solar energy.Also, summarized results for the optimized area are given in Table 3.

Economic Feasibility Analysis.
From the energetic and exergetic analysis, it has been confirmed that the thermal performance of isolated HPETC and cascaded PVT-HPETC is better than other systems, while the total investment needed for FPC and PVT is lower than that of HPETC or PVT-HPETC.So, economic aspects become significant for final selection between these collectors for solar-assisted process heating in IPH to be justified for commercial installation.
Economic feasibility analyses of different SAPH systems have been presented for Malaysian weather conditions.The analysis has been carried out for three different processes temperatures such as 60, 70, and 80 °C.It has already been revealed from thermal performance of the systems that these systems perform better at 1.0 LPM, so the economic analysis is primarily done for the optimized flow rate of 1.0 LPM.
As a part of economic analysis, NPV, IRR, and PBP of five different SAPH systems have been evaluated for diverse criteria like with and without CERs.CERs are additional source of revenue that are basically awarded by the United Nations (UN) to member nations for preventing one ton of carbon dioxide emissions [68].These are usually issued to member states for projects achieving greenhouse gas reductions using Clean Development Mechanisms (CDM).CDMs make it possible for these projects to occur and set In evaluating NPV, IRR, and PBP for the isolated and cascaded SAPH systems, several prolepsis and parameters have been assumed (Table 2).Carbon emissions price per ton in the case of GHS and GLS are taken as US$ 80 and US$ 40 per ton, respectively.NPV, IRR, and PBP are calculated from equations ( 11)-( 14) for all five systems in accordance with energetic and exergetic viewpoints.In NPV, the total future revenues are converted into the equivalent earnings at the beginning time of the project, and then, the required initial capital of project is deducted from it.For the IRR, a discount rate is calculated from the discounted income of project to the amount of investment.IRR is the rate of return which equals the present value of project income to the present value of its costs that makes the NPV of all cash flows from a particular project equal to zero.PBP is an investment appraisal technique which implies the amount of time taken by the investment to recover the initial investment, and it is calculated as a ratio of cash flow of i-th period and equivalent annual cash flow.In estimating the present value, a discount rate of 8% has been considered since the inflation rate in Malaysia is very low (3-4%) [71].
(3) Isolated HPETC System.In the case of isolated HPETC system (Figures 9(a     Thus, it can be concluded that the involvement of CERs in both scenarios plays an important role in attracting the use of these technologies in a broader perspective.Internal rate return (IRR) is a measure of the project profitability.If the IRR of the project is higher and more than the minimum attractive rate of return (MARR) (usually >10%), then it is defined as a profitable project [55].It may be also concluded from the above discussion that for the same area of collector required, the solar energy penetration increased significantly in the case of isolated HPETC and cascaded PVT-HPETC systems as compared to other isolated and cascaded systems.

Levelized Cost of Heat (LCOH) Analysis.
In order to adequately compare isolated and cascaded systems, a standard metric, LCOH, has been employed that combines two disparate energy flows (i.e., heat and electricity) into one bottom-line metric.The proposed LCOH model is applied to both isolated and cascaded systems, and results are illustrated in Figures 12(a) and 12(b).It can be seen from the figure that the cascaded systems offer a reduced LCOH in comparison to isolated installations at the same solar energy penetration, as much of the cost in the hybrid system is shared between the electric and thermal subsystems.Due to the higher collector efficiency of the cascaded system, the total collector area can be reduced, and solar energy penetration share can be increased.In the case of isolated systems (Figure 12(a)), the LCOH of the PVT system is lower than both FPC and PVT due to simultaneous heat and electricity production; however, the solar energy penetration is higher for isolated HPETC than the other two systems.For the PVT system, LCOH at process heat temperature (60, 70, and 80 °C) and solar energy penetration (67.50%, 64.54%, and 61.67%) is MYR 0.193, MYR 0.184, and MYR 0.176 per kWh, respectively.In the case of the FPC system, LCOH at process heat temperature (60, 70, and 80 °C) and solar energy penetration (61.79%, 59.29%, and 56.59%) is MYR 0.207, MYR 0.199, and MYR 0.192 per kWh, respectively.And for the HPETC system, LCOH at process heat temperature (60, 70, and 80 °C) and solar energy penetration (69.14%, 66.68%, and 64.95%) is MYR 0.211, MYR 0.208, and MYR 0.204 per kWh, respectively.
In the case of cascaded systems (Figure 12(b)), the LCOH of the PVT-FPC system is lower than PVT-HPETC due to the low capital cost; however, the solar energy penetration is higher in the case of PVT-HPETC than PVT-FPC system for the same collector area.For the PVT-FPC system, LCOH at process heat temperature (60, 70, and 80 °C) and solar energy penetration (65.01%, 61.58%, and 58.26%) is MYR 0.203, MYR 0.193, and MYR 0.181 per kWh, respectively.In comparison, LCOH for PVT-HPETC at process heat temperature (60, 70, and 80 °C) and solar energy penetration (78.50%, 75.71%, and 73.10%) is MYR 0.214, MYR 0.208, and MYR 0.201 per kWh, respectively.
However, it is worth to note that LCOH for all the cases is less than the existing cost of heat generation which proves that these systems are economically feasible.Overall, the PVT-HPETC system performs better and gives the higher solar energy penetration at low collector areas.
From the discussions in the preceding sections, it is quite apparent that none of the systems are economically feasible without CER for every process temperature (60, 70, or 80 °C), which is evident from the negative values of NPV, very low IRR, and high PBP.On the other hand, the introduction of CERs (be it with GLS or GHS) brings about significant changes in NPV, IRR, and PBP values.

Conclusions
A novel solar-assisted process heating (SAPH) system has been designed to realize low to medium industrial process heat demand at minimum fossil fuel usage.A dynamic simulation model has been built in TRNSYS to predict the optimum configuration and performance of this system at different flow rates of the heat transfer fluid.The model has been authenticated through prototype implementation and outdoor experimentation.Outlet water temperature, solar energy penetration, and annual energy generated increase with an increase in collector area.Therefore, collector area optimization is important to select an optimum collector area that can fulfil our selected process heat temperatures (60, 70, and 80 °C).
The major inferences from the thermoeconomic analysis are summarized as follows: (i) Maximum outlet temperatures of water achieved with PVT-HPETC and PVT-FPC systems are 71.5 and 66 °C, while that with isolated HPETC and FPC system are 60.5 and 56

°C
(ii) Maximum energy (thermal) efficiency of PVT-HPETC and PVT-FPC system are 81% and 77%, respectively (iii) PVT-HPETC and PVT-FPC systems achieved the maximum exergy efficiency of 13.22% and 12.72%, respectively (iv) Performance mapping ascertains that SAPH performs better at an optimum mass flow rate of 1.0 LPM  Exergy.

Figure 2 :
Figure 2: (a) Schematic and (b) experimental setup of the SAPH system.

Figure 3 :Figure 4 :
Figure 3: Comparison between simulated and experimental results of water outlet temperature.

Figure 7 :
Figure 7: Variation in (a) NPV, (b) IRR, and (c) PBP as a function of collector area for isolated PVT system.

Figure 8 :
Figure 8: Variation in (a) NPV, (b) IRR, and (c) PBP as a function of collector area for isolated FPC system.

Figure 9 :
Figure 9: Variation in (a) NPV, (b) IRR, and (c) PBP as a function of collector area for isolated HPETC system.

Figure 10 :
Figure 10: Variation in (a) NPV, (b) IRR, and (c) PBP as a function of collector area for cascaded PVT-FPC system.

Figure 11 :
Figure 11: Variation in (a) NPV, (b) IRR, and (c) PBP as a function of collector area for cascaded PVT-HPETC system.

Figure 12 :
Figure 12: LCOH as a function of collector area for (a) isolated systems and (b) cascaded systems.
International Journal of Energy Research series with a PVT collector.The setting is such that the outlet water of PVT flows into the FPC or HPETC, which further gets heated by the solar irradiance.Based on this idea, a detailed cascaded SAPH model is built in TRNSYS for performance evaluation in this section.Figure1displays the block diagram of a TRNSYS model.
2.1.Model Development.Cascaded SAPH consists of a solar thermal collector (either FPC or HPETC) connected in 2 FPC = ταA FPC I or E s HPETC = τ gco τ gco α c A HPETC N hp I,

Table 1 :
Measurement ranges and accuracy of the instruments and sensors.

Table 2 :
Parameters and assumptions for economic analysis.
Note: 1 USD is taken as 4.27 MYR during the conduct of this research study.

Table 3 :
Summary table for area optimization.
ten years of plant operations, the first ten years for a renewable energy project being exempted from tax [69].3.3.1.NPV, IRR, and PBP Analysis.Net present value (NPV), internal rate of return (IRR), and payback period (PBP) have been evaluated based on different criteria, namely, with and without certified emission reductions (CERs).Two subsce-narios, viz., global high scenario (GHS) and global low scenario (GLS) in the case of CER have been considered in accordance with World Bank Report 2019 [70].
16 International Journal of Energy Research (v) The optimized collector area for different systems are (a) In the case of the PVT system, 5.43, 7.26, and 9.25 m 2 for 60, 70, and 80 °C process temperatures, respectively (b) In the case of the FPC system, 5.26, 6.74, and 8.26 m 2 for 60, 70, and 80 °C process temperatures, respectively (c) In the case of the HPETC system, 4.93, 6.21, and 7.55 m 2 for 60, 70, and 80 °C process temperatures, respectively (d) In the case of the PVT-FPC system, 3.08, 4.17, and 5.32 m 2 for 60, 70, and 80 °C process temperatures, respectively (e) In the case of the PVT-HPETC system, 3.85, 4.98, and 6.10 m 2 for 60, 70, and 80 °C process temperatures, respectively (vi) In the case of the HPETC system and GLS, the IRR and PBP obtained are 21.64, 20.29, and 18.92% and 4.09, 4.29, and 4.51 years for 60, 70, and 80 °C, respectively (vii) In the case of the HPETC system and GHS, the IRR and PBP obtained are 37.81%, 35.97%, and 34.13% and 2.54, 2.66, and 2.78 years for 60, 70, and 80 °C, respectively (viii) In the case of the PVT-HPETC system and GLS, the IRR and PBP obtained are 22.28%, 21.33%, and 20.38% and 4.00, 4.13, and 4.28 years for 60, 70, and 80 °C, respectively (ix) In the case of the PVT-HPETC system and GHS, the IRR and PBP obtained are 39.24%, 37.95%, and 36.66% and 2.46, 2.54, and 2.62 years for 60, 70, and 80 °C, respectively (x) LCOH for HPETC and PVT-HPETC at process heat temperatures of 60, 70, and 80 °C are 0.224, 0.219, and 0.215 MYR/kWh, and 0.216, 0.210, and 0.204 MYR/kWh, respectively.It is worth to note that LCOH is less than the existing cost of heat generation which proves that these systems are economically feasible Orientation angle towards the equator n 1 : Specific day number of the year τ: Coefficient of transmittance η: Efficiency.