Techno-Econo-Enviro Assessment of Photovoltaic-Thermal (PV-T) System for Residential Use in Iran Based on Köppen Climate Classification

,


Introduction
Energy supply technology is currently facing a range of challenges, including price fluctuations, concerns about energy security, and environmental issues [1].Environmental degradation, depletion of natural resources, global warming, air pollution, climate change, widespread droughts, and other similar threats have compelled many countries to reduce their reliance on fossil fuels and transition to cleaner energy sources [2,3].Given these problems, it appears that developing renewable energy in accordance with the potential of each region while also making rational use of fossil fuels is a suitable solution [4,5].These issues serve as the primary drivers for the creation of new and more efficient electricity production systems [6].Therefore, it is undeniable that investigating the potential and feasibility of various technologies related to renewable energy is of utmost importance [7].
In Iran in 2020, fossil fuel-based electricity accounted for over 86% of the country's electricity supply portfolio.Iran holds the top position globally in terms of underutilizing its capacity [4].Moreover, Iran ranks among the top ten carbon producers worldwide and stands as the largest producer of CO 2 in the Middle East.Solar energy emerges as a promising technology that can contribute to transforming Iran into a sustainable society [8].
Renewable energies currently provide approximately 15% of the final energy demand in buildings.However, there continues to be an increase in energy demand within buildings.From 2009 to 2019, there was a yearly increase of 5.3%

Source Year
Purposes Method and tools Results [14] 2014 Design and investigation of a heat pump system with PV-T to supply domestic heating and electrical needs Field studies, experimental In this particular experiment, the hybrid system achieved an electrical output of approximately 15%.This system effectively fulfills the hot water requirements for domestic use during the summer.However, in seasons with less sunlight, the hot water tank needs to be charged by the brine heat pump.
[15] 2018 Checking the efficiency of a direct water heating PV-T apparatus Empirical, theoretical, field studies, and library The PV-T water collector system is capable of providing hot water at around 80 °C for a family of four while also generating additional electricity for household use in Cyprus.Specifically, with a radiation level of 4.5 kWh/m 2 , it exhibits a thermal efficiency of 53.4% and an electrical efficiency of 13.4%.[16] 2018 Analogy of efficiency and expense of several PV-T apparatus with diverse parameters such as fluids, thermal absorbers, PV materials, and glazing structures Using the analytical network process to obtain the optimal option for Asia According to the hypothesis that thermal and electrical energies hold equal value to decision-makers, the optimal design for PV-T is a decentralized and unglazed system that utilizes water as the working fluid.
[17] 2018 Investigation of air and water-based PV-T from the perspective of exergy and energy Field studies and mathematical equations (using the first law and the second law of thermodynamics) Exergy yields range from 5% to 25%, while energy yields range from 40% to 70%.The electrical output ranges from 10% to 25%, and thermal gain ranges from 40% to 75%.Previous research suggests that modifying the collector design can enhance PV-T performance.
[18] 2018 Finding the optimal angle of inclination, investigating the relationship between the PV-T orientation and the generated thermal and electric power, comparing the laboratory result with software simulation Field studies in central Poland, tests under authentic conditions, and Polysun software The maximum efficiency values for PV, solar thermal collector, and PV-T have been determined and found to be satisfactory under both field and laboratory conditions.
Additionally, simulation results obtained using Polysun software align reasonably well with experimental data obtained in the laboratory.
[19] 2019 Investigation of a hybrid PV-T system for an application in a sports center in Italy Thermodynamic assessment and simulation with TRNSYS Approximately 40% of the electricity requirement was provided.Also, the system provides about 25% of the required space heating and around 60% of the hot water heating and pool requirement.
[20] 2019 Comparison of the solar system based on PV-T collector and evacuated tube collectors for providing heating and cooling with PV system for providing electricity for the energy demand of Bari University.

Field studies, experimental
A solar combined cooling, heating, and power system with a capacity of 1.68 MWp meets approximately 30% of the university's space heating needs, 50% of its cooling needs, and 16.5% of its electrical needs.This system can remove around 900 tons of CO 2 per year, which is about 1.5% more than a PV system and 15% more than an evacuated tube collector-based system.

2
International Journal of Energy Research in renewable electricity used for heat generation in buildings.
In contrast, the portion of electricity used for building heating only increased by 1.3% during this period [9].Energy consumption in buildings has also experienced a gradual increase from 2009 to 2019, with an average annual growth rate of 1%.However, the COVID-19 pandemic had a tempo-rary impact on this trend, leading to a slight decrease in energy requirements as many public and commercial buildings transitioned to low-energy operations.Preliminary estimates suggest that as economic activities resume in 2021, building energy consumption will return to its previous high levels.It is worth noting that approximately one-third of the The overall performance of PV-T systems is influenced by design parameters.To develop new PV-T systems, efforts are needed in accurate modeling, discovering new materials, improving system stability, and designing energy storage systems.
[24] 2019 Investigating the efficiency of conventional solar thermal power plants and comparing the outcomes with hybrid systems Experimental, library, and mathematical equations Hybrid PV-T systems have a relative increase in exergy efficiency between 10 and 15% compared to PV-only systems in three cities.Additionally, based on the first and second laws of thermodynamics, a PV-T power plant generates more energy than a conventional solar system.Economic studies show that PV power plants are more cost-effective due to the low price of the technology.
[25] 2020 Review of various thermal and electrical aspects of PV-T apparatuses and previous research Library Specific design aspects such as adding vanes, thin metal sheets, roll band absorbers, and porous media to the flow duct directly impact the efficiency of hybrid systems.The use of new technologies like thermoelectric generators, phase change materials, and nanofluids further increases the overall efficiency of this system.
[26] 2021 Investigating the efficiency of a hybrid solar system in Romania Library, experimental The study found that the overall efficiency was approximately 73%.When exposed to solar radiation of 840 W/m 2 , the electrical power generated by the system increased by around 10.3%.Additionally, the temperature of the water produced rose by 10 °C in proportion to the flow rate.
[27] 2021 PV-T modeling with a spiral heat collector with a copper tube ANSYS 18.0 software By increasing the flow rate of water, the PV-T system's final performance improved to about 54% when exposed to radiation of 800 W/m 2 .
[28] 2022 Review and compare the performance of PV-T in reliable sources Library The solar thermal and photovoltaic thermal system without glazing and serpentine collector demonstrated the best thermal and electrical performance.The use of CuO/ water nanofluid further enhanced performance but required more pumping power.
3 International Journal of Energy Research  Table 2: Equations governing the PV-T system.

Formula Definition
No. of equation Total energy efficiency of PV-T systems [25] (1) Thermal efficiency [25] (2) Electrical efficiency [25] (3) Calculation of electrical efficiency according to module temperature [17] (4)   world's total energy consumption is directly used in buildings, with thermal energy accounting for about 77% and electrical energy for the remaining 23% [9].Therefore, focusing on this sector can significantly contribute to reducing nonrenewable energy consumption.One effective method for harnessing solar energy is through the use of PV-T collectors [10,11].These devices have the advantage of producing a higher energy output per unit area compared to solar thermal collectors or photovoltaic panels [12].Due to the growing interest in electrified heating systems, there is expected to be an increased demand for PV-T collectors in 2021.In fact, thirty manufacturers reported sales of at least 88 MWh of PV-T systems within the year, representing a significant growth of 45% compared to the 61 MWh sold in 2020.The largest emerging markets in this industry include France, the Netherlands, Israel, Germany, and Spain [9].Researchers believe that the PV-T market is still in its early stages.As of the end of 2020, there were approximately 1,275,431 m 2 of PV-T systems operating worldwide.Moreover, an average annual market growth rate of around 9% has been observed from 2017 to 2020 [13].
Up until now, there have been numerous extensive studies conducted on the different types, components, working fluids, and optimization methods of the PV-T system.Overall, scholars have commonly utilized manual and field-laboratory methods, as well as various software tools (as shown in Table 1).
Based on the research literature, there have been few studies that have focused on the potential efficiency of PV-T in different climates.Some researchers, like Farahani and Alibeigi [29], have examined PV-T in Iran.They investigated the performance of photovoltaic-thermal-thermoelectric generators in several Iranian cities.Their findings showed that the performance is influenced by temperature and radiation intensity.Additionally, the amount of electricity generated increases with more thermoelectric generator modules.Kerman City had the highest thermoelectric generator efficiency, while Bojnord City had the highest PV-T efficiency.In another article, Farahani et al. studied a combined-cycle PV-T heat exchanger to provide air conditioning for a 200 m 2 building in nine Ira-nian cities using Carrier software.They found that the power utility of the PV-T system increased by 5% in winter and 8% in summer, with Tabriz City having the highest power efficiency.Kerman had the highest electrical energy usage [30].However, specific emission reduction statistics and climate data for all cities were not provided in their research.Given the issues associated with nonrenewable energy consumption and Iran's position in fuel consumption and pollution production, as well as its abundant solar radiation potential and significant use of housing for thermal and electrical purposes, this study is aimed at evaluating the technical, economic, and environmental aspects of implementing residential PV-T systems in Iran.The results will be compared to previous research findings.
This study provides a comprehensive analysis of the feasibility, modeling, and comparison of PV-T systems to supply electricity and heat to residential units in 28 cities with 9 different climates in Iran based on the Köppen climate classification.The importance of the study lies in the assessment of the feasibility and performance of PV-T systems for residential use in Iran, considering the country's diverse climates and the urgent need to shift towards renewable energy sources to reduce environmental pollution and dependence on fossil fuels.The findings of this study provide valuable insights into the environmental and economic benefits of using PV-T systems in residential units, which can guide policymakers, researchers, and engineers in the implementation of renewable energy solutions in Iran and other regions with similar climate conditions.

Methodology
The research methodology used in this study is a quantitative approach.The study uses modeling and comparison of the PV-T system to supply electricity and heat to residential units in 28 cities with 9 climates of Iran.Based on the weather database in the Meteonorm 7.3.3software, an effort has been made to choose several stations in different regions of Iran.This approach ensures that the findings of this study are   Performance analysis has been done using Polysun 9.0 and PVsyst software.The study also includes an environmental assessment by examining the reduction in CO 2 emissions.In this study, the initial step involved determining the optimal angle for each city using PVsyst 6.6.8 software.Subsequently, the system and demand information were inputted into Polysun 9.0 for simulation purposes.The advantages and disadvantages of electricity production, heat, total power output, cost of power production, losses, and emissions were evaluated for different cities in Iran based on specific goals.The simulation plan for the system and its components in Polysun 9.0 was taken into account to achieve these objectives.Figure 1 illustrates the structure of a PV-T system.The overall efficiency (η PVT ) of the PV-T system is influenced by factors such as air mass flow rate, solar collector type, absorber variations (e.g., baffles and thin metallic sheets in the cooling duct), sheet and tube absorber, roll band absorber, and temperature [25] (Table 2).Table 2 also presents calculations for system performance, CO 2 reduction, and fuel savings.

Case Study Location
Iran is situated in the southwestern part of Asia, specifically in the Middle East region, which is known for its vast deserts and clear skies.With a total area of 1,648,195 km 2 , Iran has ample space for renewable energy sources.Each region within the country possesses different potential for solar energy [8].Iran benefits from a diverse climate, which increases the feasibility of utilizing renewable energy sources [4].The Köppen classification system, widely used by researchers, has undergone modifications over time due to criticisms [32].The updated Köppen-Geiger classification system is now commonly used [33].Recent surveys con-ducted between 1990 and 2014 reveal that out of the 31 climate groups identified by Köppen-Geiger, Iran encompasses nine of them (see Figure 2) [34].
Electricity usage in residential, industrial, agricultural, and commercial sectors is increasing [36].Gas and oil account for 99% of energy production in Iran, while renewable energies only make up 1%.It is worth noting that Iran is situated in a region with high solar radiation, with an annual average of about 20 to 30 MJ/m 2 .In central regions, this value is even higher [37] (Figure 3).
Iran has abundant sources of renewable energy, particularly solar energy, due to its high solar radiation and vast available land.This suggests that the use of solar systems in Iran would be cost-effective.However, despite this potential, Iran's solar market remains undeveloped [8].Currently, there are 103 MW of renewable power plants already installed in the country, with an additional 42 MW under construction.In terms of the country's renewable power plants, 44% are solar, 40% are wind, 13% are small hydropower, 2% are heat recovery, and 1% are biomass [4].

Input Data
Based on Figure 4, the standards state that an average family of four consumes approximately 10 kWh of electricity per day, with an annual consumption of around 3500 kWh.Additionally, the daily hot water demand is 200 L. The proposed model consists of a residential unit spanning 148 m 2 across two floors, equipped with a 7.5 kW gas boiler, an 800 L tank, a 2.5 kW PV-T panel, and a pump.The specifications for each component are inputted into the software.The feasibility and economic-environmental aspects of implementing the PV-T system in various cities and regions in Iran (28 cities and 9 regions) have been assessed using Polysun 9.0 simulation software.

Results
Table 3 provides the average annual outdoor temperature in °C and the amount of radiation on the surface of the collectors in kWh for the stations being studied.This includes the effective energy, taking into account losses from the incidence angle modifier (IAM) and shadows, also measured in kWh.The station with the highest annual radiation on the collectors' surface is Shiraz, with 38,388 kWh, while Rasht has the lowest at 23,594 kWh.Similarly, Shiraz and Rasht have the highest and lowest annual effective energy values, respectively, considering IAM losses and shadows.
The optimal angle values for installation were determined using PVsyst 6.6.8 software.The calculations were based on comparing the drop percentage to zero to achieve an optimal state.The software provided an angle limit, and the maximum angle listed in the table for each station was considered the installation angle.According to simulation results, Bojnoord has the highest annual optimal angle at 39 degrees, while Bandar Abbas has the lowest at 27 degrees.Table 3 also presents data on annual electricity generation from photovoltaic panels integrated with thermal collectors (PV-T collectors) in terms of direct current (DC) and alternating current (AC) electricity production measured in kWh.Shiraz has the highest electricity production at 4,315 kWh, while Rasht has the lowest at 2,741 kWh (Figure 5).Analyzing the annual energy provided by the collectors in terms of heat transfer to working fluid (excluding losses from pipes and tanks), Birjand has the highest value at 3,661.3 kWh, whereas Rasht has the lowest value at 1,875.7 kWh (Table 3 and Figure 5).
The system performance parameter allows for an objective comparison between different systems.A higher value indicates better results, which is obtained from Equation 5 [39].In this case, the system designed in Bandar Abbas and Zahedan has the best performance with values of 4.67 and 1.9, respectively, while the worst performance is seen in the system in Rasht and Sari with values of 0.88 and 0.96, respectively.
These results demonstrate the ability of the designed system to meet the energy needs of different stations.However, it is evident that the designed system is unable to supply the required energy for Arak and Hamadan stations.Therefore, an upgrade is necessary for these stations.The heating energy demand for the designed building is equivalent to the annual amount of energy provided by the radiators in the heated space.Additionally, simulations and analyses reveal that Bandar Abbas has supplied the highest percentage of energy needs through solar energy at 91.6%, while Ardabil has supplied the lowest amount at 22.6%.Similarly, when considering hot water supply through solar energy, Bandar Abbas has provided the highest percentage at 91.6%, while Rasht has provided the lowest amount at 39.8%.Furthermore, simulations show that Bandar Abbas has supplied the highest percentage of average energy required for heating a house through solar energy at 91.6%, whereas Ardabil has supplied only 8.8%.To calculate CO 2 emission prevention, we multiply the amount of solar energy in the tank (S sol ) by the CO 2 emission from fuel and divide it by the annual efficiency of the boiler (Equation 6).
The column regarding the decrease in CO 2 emissions indicates that Birjand station will have the greatest reduction in CO 2 emissions, with a value of 942.1 kg, while Rasht station will have the lowest reduction, with a value of 482.7 kg (Table 4 and Figure 6).
The software has calculated the solar energy received from the windows in kWh and the total annual energy loss through the building and air exchange.Urmia station has the highest amount of total annual energy losses through building and air exchange, at a rate of 38745.8kWh, while Ahvaz station has the lowest amount at a rate of 22530.6 kWh.The following table displays the annual heat loss through the tank wall and connections (Table 5).The highest and lowest costs of producing AC electricity and electrical-thermal energy are associated   11 International Journal of Energy Research with Rasht stations, at amounts of 0.511 and 0.530 $/kWh, respectively, while Shiraz has amounts of 0.324 and 0.308 $/ kWh, respectively.Table 5 shows the maximum savings in annual fuel consumption achieved through the use of solar energy technology, measured in m 3 of natural gas equivalent and kWh equivalent.The highest savings are seen in Birjand station at 387.4 m 3 , while Rasht station has the lowest savings at 198.5 m 3 (Table 5 and Figure 7).According to Equation 7, which calculates energy savings, the solar energy in the tank (S sol ) is divided by the calorific value of the fuel and the total annual efficiency of the boiler.

Conclusion
This research has demonstrated the feasibility and potential benefits of utilizing PV-T systems in residential units in Iran.The ability of these systems to generate both electricity and heat simultaneously enhances energy efficiency and reduces the reliance on multiple energy sources.By investigating 28 cities with 9 different climates in Iran, this study has provided a comprehensive evaluation of the performance of PV-T systems.The use of analytical software such as Polysun 9.0 and PVsyst 6.6.8 has allowed for accurate modeling and comparison of the system's capabilities over a one-year duration.The scientific novelty of this research lies in the simultaneous utilization of two analytical software, which enhances the reliability and accuracy of the findings.Additionally, the thoroughness of the study in considering the impact of climate on the performance of PV-T systems adds further value to its conclusions.The results obtained from this research highlight the potential for widespread adoption of PV-T systems in Iran, given its abundant solar energy resources and diverse climates.Implementing these systems can contribute to reducing greenhouse gas emissions, improving energy efficiency, and decreasing dependence on traditional energy sources.Overall, this study provides valuable insights into the feasibility and benefits of utilizing PV-T systems for residential units in Iran.It serves as a foundation for further research and encourages policymakers to consider implementing these systems as part of their sustainable energy strategies.The investigation found that: The solar energy in the tank (kW) η PVT : Total energy efficiency of PV-T systems (-) η th : Thermal efficiency (-) η e : Electrical efficiency (-) Ac: Collector area (m 2 ) C: Coolant specific heat capacity (J/(kg• °C)) I m : Electric current (A) S: Collision of solar irradiation (W/m 2 ) T in , T out : Temperatures of coolant (air/water) in inlet and outlet, respectively ( °C) T pv : Module temperature ( °C) T ref : Reference temperature ( °C) V m : Maximum power point operation voltage (V) m: Working fluid mass flow rate (kg) β ref : Temperature coefficient (-) η ref : Reference yield of PV module (-) PV-T: Photovoltaic-thermal (-) IAM: Incidence angle modifier (-) DC: Direct current (-) AC: Alternating current (-).

Data Availability
All data used to support the findings of this study are included within the article.

Figure 5 :
Figure 5: AC power generation, energy supplied by collectors (Q sol ), and their sum.

Figure 7 :
Figure 7: AC electricity generation cost and electrical and thermal energy in Iranian cities.

Table 1 :
Previous studies on PV-T.

Table 3 :
Average temperature, amount of radiation, annual optimal angle, electricity production, and the annual amount of energy supplied by collectors for the climates and cities of Iran with PVsyst 6.6.8 and Polysun 9.0 software.

Table 4 :
System performance, system ability to supply energy, heating energy demand, percentage of energy supplied from the solar, and CO comprehensive and the results obtained are more trustworthy.

Table 5 :
Energy loss in the studied residential unit.
Bandar Abbas and Bojnoord have the lowest and highest annual optimum angles, respectively (ii) Shiraz has the highest radiation on the surface of collectors, while Rasht has the lowest (iii) Bandar Abbas and Zahedan have the best system performance, while Rasht and Sari have the worst (iv) Shiraz has the highest AC electricity generation, while Rasht has the lowest (v) Ardabil has the highest heating energy demand, while Bandar Abbas has the lowest (vi) Bandar Abbas has the highest percentage of energy supplied through solar energy, while Ardabil has the lowest (vii) Birjand has the highest reduction in CO 2 emissions, while Rasht has the least (viii) Urmia has the highest total energy loss, while Ahvaz has the lowest (ix) Rasht has the highest cost of electricity production, while Shiraz has the lowest (x) Birjand has the highest savings in fuel consumption, while Rasht has the lowest7.Suggestions for Further WorkFor future research, it is suggested that these scenarios be investigated for other applications such as administrative, commercial, educational, industrial, and medical spaces.Also, the method used in this research can be applied to other countries with different potentials.Another topic that can be of interest to researchers is calculating the amount of exergy in the investigated systems.Also, by installing solar systems on different sites, the experimental results can be compared with the results of the present work.