1. Introduction
Global industrialization and world population growth have raised the demand for electricity, and the world’s power consumption is estimated to increase by 50% until 2050 [
1]. Fossil fuels are the primary source for supplying the world’s energy demand, which contributes to global warming. By consuming fossil fuels, greenhouse gas emissions are emitted into the earth’s atmosphere. Adverse effects on public health and climate change issues are inevitable due to the increased level of greenhouse gas emissions. Considering all the mentioned issues, it is essential to supply the world’s power demand using renewable energy resources (RESs), such as photovoltaics (PV) and wind turbine (WT) systems [
2]. The heat and radiant light from the Sun are the primary resource of all the RESs, excluding geothermal energy. Therefore, the energy from the Sun is the most promising energy, as it is capable of capturing energy to the world’s yearly demand in less than an hour. By hybridizing PV systems, as the technology for capturing solar energy, with various energy storage systems (ESSs) and fuel cells (FCs), it is possible to generate unlimited energy, which eliminates the disadvantageous of the periodic nature of RESs [
3,
4,
5].
Most of the papers in the scope of the enviro-techno-economic assessments have utilized RESs to merely supply electrical loads. Nevertheless, providing electric loads by RESs is not simply a way for sustainable development since about 29% of the gas emissions are produced by vehicles [
6]. Hence, electric vehicles (EV) should be supplied with RESs besides the electric load. Furthermore, in real-world residential hybrid systems, thermal loads also exist in the system’s configuration. An accurate design consists of the thermal requirements of the system, including thermal demand and supplying equipment. Therefore, we divided the literature review into three categories, as indicated in
Figure 1. In the first category, electric loads are supplied by RESs, ESSs, and sometimes conventional generators. Due to the high intermittence of RESs, they are equipped with ESSs, diesel generators, and FCs. Utilizing these backup resources improves the stability and reliability of the hybrid systems significantly. In the second category, AC electric loads and EV electricity consumption are provided using RESs, ESSs, and conventional generators. In the last category, thermal and electric demands are provided by the mentioned sources. The reviewed papers generally utilized HOMER software for simulation and optimization of the hybrid energy systems. This is because of the reasonable accuracy and speed of the software in planning problems and techno-economic analysis [
7]. The authors of [
8] compared the optimization results of HOMER software with heuristic algorithms, such as particle swarm optimization (PSO) and artificial bee colony (ABC). According to their comparisons, HOMER software achieved identical results and accuracy.
Considering the first category, the authors of [
9] analyzed the techno-economic feasibility of hybrid conventional fuel-based and RESs, as well as RESs and main grid, for a standalone system in a local place in Iran. HOMER software was used for performing optimization in this study. Simulation results indicated that a hybrid renewable energy system leads to an emission-free climate for both grid-connected and off-grid energy systems. Another study [
10] investigated the optimal sizing of the hybrid energy systems for meeting power demands of a small hotel on Kish Island, Iran. It was revealed that the combination of WT/ESS/Diesel is the most economical configuration. In [
11], the optimal system design of on and off-grid hybrid energy system is conducted for nonresidential users in the southern region of Iran. Additionally, the effect of government energy policies and yearly load growth rate on the system’s viability was discussed. In [
12], a hybrid energy system is optimized for supplying a household in Tehran, Iran by accounting for financial and reliability terms. In [
13], optimal planning of PV/ESSs/Diesel was studied using HOMER. Furthermore, they studied the effect of the diesel fuel cost variations to guarantee whether the suggested system is proper for the cases. In another study [
14], the scholars utilized HOMER software to assess techno-economic viability of the off-grid hybrid energy system. In a similar study [
15], the planning of a hybrid PV/ESSs/Diesel system was conducted for a village Algerian Saharan community. Furthermore, the authors utilized HOMER software to perform the study. The PSO with the ε-constraint method is implemented for optimum design of hybrid PV/ESSs/Diesel system for a local place in Algeria [
16]. The authors of [
17] performed an economical-technical viability study for a standalone hybrid system with a variable climatic environment using HOMER software. In the second category, however, researchers incorporated EVs loads or charging station sizing in their studies. It should be mentioned that, even in charging stations, sizing EVs’ consumption loads should be considered, according to the historical/estimated data. In [
18], hybrid WT/PV/energy charging stations are designed and optimized by HOMER tools. The authors claim that the proposed sizing methodology applies to other places in the world. The optimal configuration for the hybrid system includes 44.4% of WT power and 55.6% of PV power. The electricity generation is 843,150 kWh/year with the 0.064
$/kWh generation cost. In another study conducted in Vietnam [
19], the techno-economic analysis and optimum sizing of PV/EV charging stations are under various conditions of solar irradiation. The results indicated that the optimum system and investment efficiency of EV/PV charging stations in municipal areas are considerably dependent on the solar irradiation values and feed-in tariff (FIT) prices of rooftop PV systems. The economic and environmental benefits of stand-alone and grid integration are thoroughly analyzed in [
20] for several climatic regions using hybrid optimization model for electric renewables (HOMER). The design and optimization of off-grid hybrid microgrid systems for different load dispatch strategies is presented in [
21] by evaluating the component sizes, system responses, and various cost analyses of the system presented. In [
22], a techno-economic assessment of the hybrid RESs system was conducted using HOMER software. The system is optimized to supply the loads including electric and hydrogen loads. It is assumed that the FC-based EV consumes hydrogen energy for transportation. The system is designed for a family house with 100% RESs. The studies from the third category consider both thermal and electric loads and their power supply sources. The researchers in [
23] suggested a standalone hybrid system to provide electric and thermal demands in different climates of Australia. According to their findings, the WT/PV/ESS/conventional gas turbine system leads to the minimum COE for all the locations. They have used HOMER software for their investigations. In another study [
24], an identical energy system is suggested to meet thermal and electric loads demands. The researchers analyzed two energy management methods utilized in HOMER software. The strategies are cycle charging and load following. Furthermore, based on their analysis, both cycle charging and load following methods effectively improve the system performance. The suggested system was also investigated in both on-grid and standalone modes.
Authors of [
25] compared genetic algorithm and HOMER software for optimum configuration of a hybrid energy system, consisting of WT/PV/ESS/boiler. The genetic algorithm results showed that the suggested configuration is reliable (99.92%) and is suitable to meet thermal and electric loads. In [
26], optimal sizing of hybrid energy systems is performed to provide thermal and electric demands of a small village in Iran. Simulation results indicated that the configuration of PV/WT/biogas is the optimal system configuration with the lowest NPC. Besides, utilization of the ESSs and FCs were not economically feasible, but their capability to raise the system flexibility was not negligible. In [
27], a renewable-based energy system is suggested to provide thermal and electric loads. The optimization is performed by HOMER software. HOMER utilizes a non-derivative optimization for recognizing the best system with the lowest NPC among hundreds of structures. It was found that RESs play a key part in providing both electric and thermal loads. The cost of the system is also reduced by selling surplus power to the main grid.
Reviewing previous research works in the literature, it can be observed that there is a lack in the knowledge for proposing a hybrid energy system that meets the demands of EV, electric, and thermal loads. While these demands were separately investigated in previous papers, no comprehensive study is available that considers the combination of these loads in their research. However, it is essential to mention that residential households consume both electric and thermal loads in real-world applications. In addition, technological advances and global efforts to alleviate greenhouse emissions have increased EVs utilization in residential houses. It is estimated to grow in large cities such as Tehran. Considering all the mentioned terms, accurate planning and sizing are achieved by considering the mentioned demands in techno-economic analysis. The aim of this paper is to investigate an optimal design of the hybrid energy system for a residential household with EV, thermal, and electric loads. The proposed hybrid system is relatively novel and consists of the PV system, ESS, converter, gas-based FC, boiler, and thermal load controller (TLC).
The contributions of the paper are summarized as below:
EV load demand, thermal, and electric loads in the optimization of the hybrid energy system is considered.
Utilizing a TLC, in addition to the gas-based FC, which is also utilized for converting excess RESs power generation to thermal energy, to reduce the amounts of greenhouse gas emissions.
A sensitivity analysis on the influential parameters of the systems, such as inflation rate and interest rate, as well as analyzing the possible consequences on the optimization results are performed.
The remainder of the paper is as follows. In
Section 2, methodology of the study including system structure, formulation, and modeling of the components, as well as system input data, are provided. In
Section 3, simulation results of the paper, based on the introduced scenarios, are discussed. In
Section 4, a sensitivity analysis on the economical parameters of the system is performed. In the last section, a conclusion including the important results of the study is provided.
4. Conclusions
In this paper, a hybrid energy system, consisting of PV/ESS/FC/TLC/Boiler/Converter, is proposed to supply three types of loads. The loads consist of the consumer’s AC electric demand, the EV’s DC electricity consumption, and thermal load demand. The optimal system configuration included 14 kW of the PV system, 15 kW of FC, 2.86 kW of Converter, 100 kW of ESS, and 20 kW of TLC. The COE and NPC of the hybrid energy system achieved 0.0409 $/kWh and $230,223, respectively. The PV system provides most of the AC and DC loads of the system. The ESS plays a key role in supplying the EV’s electricity consumption at night hours. The TLC converted the surplus generation of the PV system to thermal power. This has led to a decrease in emissions of the system. The FC also produced sufficient electrical and thermal power, especially during peak thermal loads. The proposed hybrid energy system emitted 2144 kg/yr of CO2 and 0.0813 kg/yr of CO.
Neglecting TLC from the hybrid system configuration significantly affected the result. For instance, NPC and COE values increased considerably, and more NG is consumed to meet the thermal demand of the system, which led to the production of more emissions. Moreover, RF of the system decreased from 66.2% to 24.7%. The impact of PV/ESS ignorance was even more severe, such that the NPC and COE values had notable rises, and the operation of NG-based sources, such as FC and boiler, were significant. Therefore, notable emission production was observed, which indicates the importance of PV system utilization in hybrid energy systems. A sensitivity analysis is conducted on two influential parameters of the system, such as inflation rate and discount rate. The results indicate that the NPC and COE of the suggested hybrid system increase in higher ratios of the discount rate. In contrast, the NPC and COE of the hybrid system reduce when the inflation rate increases. In addition, an increase or decrease in inflation and discount rate of the system does not impact the optimal configuration of the hybrid energy system. The RF of the system, however, increases by raising the inflation rate of the system.