A Comprehensive Evaluation of Renewable Energy Systems with a Backup to Provide a Part of Electrical Needs of a Hospital: A Case Study in Grid-connected Mode

With sensitive and important systems in hospitals requiring an uninterrupted power supply, finding solutions for power outages is becoming increasingly crucial. Iran's favorable potential for renewable energy makes wind and solar energy viable options to support hospital electricity needs and contribute to sustainable development goals. The present work investigates, for the first time


A B S T R A C T
With sensitive and important systems in hospitals requiring an uninterrupted power supply, finding solutions for power outages is becoming increasingly crucial. Iran's favorable potential for renewable energy makes wind and solar energy viable options to support hospital electricity needs and contribute to sustainable development goals. The present work investigates, for the first time, the electricity supply of a part of the Parsian Hospital in Shahrekord using HOMER software. The use of real electricity exchange data with the national grid and the new generation of tree-shaped wind turbines are unique advantages. Results show that an optimal renewable energy-based system consisting of two 1-kW solar cells and a 1-kW electric converter costs $0.111 per kWh and solar cells generate 3% or 2999 kWh/year. The optimal scenario produces 55193 kg of CO2 annually due to national grid electricity use, highlighting the importance of renewable energy adoption in hospitals. doi: 10

INTRODUCTION
Access to constant and stable electricity is crucial for the effective and efficient performance of medical equipment [1,2]. Due to technical and operational issues in Iran's national electricity grid, it is not always feasible to rely on urban electricity for hospital equipment [3]. Therefore, hospitals should have electrical backup equipment available for each electronic device used, given their significance. Iran has excellent potential for wind and solar energy [4][5][6][7], which are also environmentally friendly [8]. Thus, it is logical and necessary to utilize these sources to provide a portion of hospital electricity. Researchers believe that renewable energies can become the primary choice for energy production due to the limited resources of fossil fuels and environmental pollution [9]. Iran, with its geographical location, has significant potential in renewable energy production, making it necessary to prioritize renewable energy development [10]. Table 1 summarized some recent works in the field of hospital electricity supply using renewable energy.
Based on the information presented in Table 1, it is evident that incorporating renewable energy sources into hospital electricity supply is a highly strategic move. Additionally, none of the previous studies have examined the impact of annual interest rates and diesel prices on the technical, economic, and environmental aspects of the system under investigation. Therefore, this study aims to assess the feasibility of utilizing renewable energy sources to provide a portion of Shahrekord Parsian Hospital's electricity needs. The primary objective is to identify the most cost-effective wind and solar-based system that can be connected to the national electricity grid using HOMER software. This study investigates various factors such as renewable energy usage, cost per kWh of electricity produced, annual electricity grid purchases, sensitivity analysis on interest rates and fossil fuel prices, among others.
The scientific novelty of the present work lies in its comprehensive analysis and assessment of the feasibility and effectiveness of integrating renewable energy systems with backup to meet a portion of a hospital's electricity demand. This study presents a unique approach to address the challenges associated with ensuring a reliable and sustainable power supply for critical healthcare facilities, which has significant implications for energy policy, healthcare management, and environmental sustainability. The research findings provide valuable insights into the technical, economic, and environmental aspects of renewable energy integration in grid-connected hospital settings, contributing to the advancement of knowledge in this field.

Investigated area and its potential
Shahrekord, located 85 km southwest of Isfahan, is a central city in Iran and serves as the capital of Chaharmahal and Bakhtiari province. The city has a population of 190,441 people and sits at an altitude of 2060 m above the sea level, making it the highest provincial capital in Iran. Shahrekord boasts good wind and solar potential, placing it among the top 50% of high-potential areas in the country according to Iran's Chaharmahal and Bakhtiari province offers a clean climate, cold mineral water springs, pristine nature, medicinal plant species, and relaxing natural attractions that make it a promising destination for health tourism. The authors of this work aim to develop the necessary infrastructure to promote health tourism in the region. Parsian Hospital in Shahrekord is the only private sector hospital in Chaharmahal and Bakhtiari province with 7 floors and 18 thousand m 2 of infrastructure and is under investigation by the authors.

METHODOLOGY
The HOMER software is responsible for assessing and designing micropower systems that are optimal for small power generation in two states: connected and disconnected from the power grid, in order to achieve desired application goals [22]. Once the possible configurations have been simulated, the HOMER system presents a list of configurations sorted by total net present cost, allowing for comparison of different system design options [23]. To gain a better understanding of the software's functionality, as well as its inputs and outputs, Figure 1 displays a flowchart of how the software operates [24].

Input data and governing equations
The most crucial data required by the software is the hourly electricity consumption over a year, which is obtained by reading the hospital's electricity meter. Based on the hospital's electricity consumption data, January has the highest demand for electricity, with a maximum amount of 60 kW. Other important data include solar radiation intensity and wind speed, which are based on a 20-year average for the region in question. The price of diesel used is $0.06 per liter 1 , while the project has a useful life of 25 years and an annual interest rate of 18% [25]. Table 2 provides information on device prices and specifications used in the simulated system.
In relation to the pricing of renewable electricity sold to and purchased from the national electricity grid, the prices are based on literature [26] and were provided in response to a query from technical experts at the electricity organization. The pricing structure includes a three-time tariff and an incentive price for purchasing renewable electricity. It should be noted that these prices apply to systems with a capacity of less than 20 kW. The cost of purchasing electricity from the grid during lowload, mid-load, and peak times is $0.005, $0.007, and $0.012 per kWh, respectively. The corresponding prices for selling electricity to the grid are $0.0318, $0.0445, and $0.0763 per kWh, respectively. HOMER software uses equations 1 and 2 to calculate the output power of solar panels and wind turbines, respectively [27,28].
The efficiency of the diesel generator in HOMER software is obtained by the following equation [29].
(3) η gen = 3.6 P gen ṁf uel × LHV fuel In the HOMER software, electricity exchange with the national grid is obtained by the following equation [30]. Economic calculations in the software, which include determining the parameters of the total net present cost and the adjusted cost of electricity, are performed by the following equations [31][32][33][34].

Results
The wind speed data of the Lutak station was used to validate the present work. A comparison was made between the Weibull function drawn by Teimourian  [35] et al. [39] and the present work, as shown in Figure 2. The data used by Teimourian et al. [36] were obtained through fitting wind energy data for parameters c and k equal to 7.22 and 1.6, respectively, using an analytical method. In contrast, the present work was done using HOMER software, resulting in c and k values of 7.36 and 1.97, respectively. The Weibull function was chosen for validation as it measures wind occurrence potential and actual probability fit. Figure 2 demonstrates good agreement between the results of the Weibull function of the present work and Teimourian et al.'s [36] findings.
In the present study, sensitivity analysis was utilized to evaluate the annual interest rate and fuel price in order to determine the most optimal outcome. After simulating all modes using software, it was determined that an interest rate of 18% and a fuel price of $0.06 were the most suitable parameters for the investigated system. All Figure 2. Validation of the results of the HOMER software compared to the work of others [36] using the Weibull function results presented in this work are based on these two data points, with the system being connected to the power grid and capable of exchanging up to 1000 kW of electricity. Table 3 displays the results of 12 examined scenarios, with scenario 1 being determined as the most economic option with a total net present cost of $54,303 and a cost of $0.111 per kWh of electricity produced. This scenario utilizes two 1 kW solar panels and a 1 kW electrical converter, with solar panels producing approximately 3% (2999 kWh/year) of the total electricity produced throughout the year.
The software output for the first three days of January is shown in Figure 3, indicating that due to limitations in electrical conversion capacity, there is approximately 267 kWh/year of excess electricity produced by solar cells that cannot be converted to AC power and sold to the power grid. Adding an electrical converter would not be economical and would increase costs; instead, it is recommended to use a battery for storage which would result in further cost increases. Figure 4 illustrates the power output generated by solar panels, with electricity production occurring for 4384 hours due to solar exposure. The capacity factor of the solar panels is 17.1%, resulting in an average output power of 0.34 kW. The uniform cost of electricity is $0.399/kWh. Table 4 displays the amount of electricity exchanged with the national electricity grid, indicating that most of the produced solar electricity is consumed and only a small amount is sold to the national electricity grid. The annual amount of electricity purchased from the grid is 87337 kWh, while only 5 kWh of electricity is sold to the national grid. In scenario one, where the electric converter functions solely as an inverter due to nonoperational diesel generators and wind turbines, the performance factor of the inverter is calculated as 1.28%. The inverter experiences an annual loss of 273 kWh with In scenario six, where only one wind turbine with a capacity of 1 kW is used to supply required electricity, each kWh produced costs $0.171 -approximately a 54% increase from scenario one. This scenario has a total NPC of $83,838 with only 4% supplied by wind turbinegenerated electricity and 96% supplied by grid-generated electricity. Pollutants caused by grid-generated electricity include 54554 kg CO2, 237 kg SO2, and 116 kg NOx annually according to Table 3 results. Table 3 presents the results for scenario 12, which utilizes two 1 kW solar panels, a wind turbine, a generator, 4 batteries, and a 1 kW electric converter. The cost per kWh of electricity is $0.184, with a total NPC of $91,059. The generator requires 128 liters of fuel and operates for 624 hours annually. The wind turbine produces 4% of the electricity, while the solar panel produces 3%, the diesel generator produces 1%, and the grid produces 92%. The diesel generator is started 152 times per year and has a useful life of 24 years. The batteries have their highest charge in March and never reach zero charge throughout the year. They have a loss of 257 kWh/year and a useful life of 10 years. Table 5 shows that scenario 12 purchases 83,821 kWh from the grid while selling only 573 kWh to the national grid. In July, it sells the highest amount of renewable electricity to the grid at 106 kWh while the lowest amount of renewable electricity to the grid only 19 kWh in February. During hot months when national electricity consumption is high, renewable energy production also increases. Scenario 12 emits pollutants including 52949 kg of CO2, 0.831 kg of CO, 0.0921 kg of unburned carbon, 0.0627 kg of fine matter, 229 kg of SO2,and119 kg of NOx per year due to power grid and diesel generator fuel use.
The results of the sensitivity analysis are shown in Figure 5. Based on the results, since the optimal system includes the national electricity grid, the price of diesel has no effect on the results, but with an increase in the Battery, 1 Diesel generator annual real interest rate, the total NPC drastically decreases. In other words, an increase in inflation will make the use of the national electricity grid more justified.
The results of the superior scenario were compared with the traditional scenario (only the national power grid) in Figure 6. Based on the results, it can be seen that during the useful life of the project, there is a very slight difference between the results of the superior scenario and the traditional scenario from the economic point of view. But it should be mentioned that based on environmental analysis, the best scenario leads to a reduction of more than 1.6 tons of produced pollutants during the year, which is due to the production of solar electricity.

CONCLUSION
Continuous availability of electricity is very important and critical for healthcare organizations because every second without electricity can become a matter of life or death. Therefore, the aim of the present work is the feasibility of supplying a part of the electricity of Parsian Hospital located in Shahrekord using wind and solar energy, which uses national grid electricity and diesel generator as backup systems. In order to find the optimal hybrid system, HOMER software was used, which performs technical-economical-energy-environmental analyses on all 299376 available configurations. The use of a three-time electricity tariff, taking into account the incentive purchase price of renewable electricity, the use of updated equipment price data and the inflation rate, as well as the use of the new generation of wind turbines, are among the advantages of the present work compared to previous similar works. These advantages make the results of the present work more consistent with the existing reality. The important results of the present work are: • The solar panel-based scenario is the most economical with a price of $0.111 per kWh and a total NPC of $54,303.

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In the best scenario, 3% of the total energy required is provided by solar energy and the amount of pollution caused by the use of the national electricity grid is about 55 tons/year.

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The lowest cost per kWh of electricity produced is $0.109, which corresponds to the solar panel-diesel generator scenario.

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The highest percentage of electricity production by renewable energies is 7%, which is seen in the solar panel-wind turbine scenarios.

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The use of solar panels in Shahrekord is superior to the use of wind turbines.