Meeting the Hospital Oxygen Demand with a Decentralized Autonomous PV System: Effect of PV Tracking Systems
When it comes to supplying oxygen, current standard hospitals in Iran have proven inadequate in the face of the COVID-19 pandemic, particularly during infection peaks. Power disruptions drastically reduce the oxygen pressure in hospitals, putting patients’ health at risk. The present study is the first to attempt to power an oxygen concentrator with a solar-energy-based system. The HOMER 2.81 package was used for technical–economic–environmental–energy analysis. The most notable aspects of this work include evaluating different available solar trackers, using up-to-date equipment price data and up-to-date inflation rate, considering the temperature effects on solar cell performance, sensitivity analysis for the best scenario, considering pollution penalties, and using a three-time tariff system with price incentives for renewable power. The study has been carried out at Hajar Hospital, Shahrekord, Chaharmahal and Bakhtiari Province, Iran. The study showed that, by supplying 60% of the power demand, the dual-axis solar tracking system offered the highest annual power output (47,478 kWh). Furthermore, generating power at—
Introduction
Access to electric power is essential for societies to thrive and improve living standards (Jahangiri et al. 2019a). The well-being and health quality of the people are telling indicators of the level of standards in a country and require well-equipped, reliable healthcare facilities to uphold. To be able to provide their services, healthcare facilities of any size, namely large, e.g., hospitals, medium, e.g., health centers, and small, e.g., clinics, must have access to modern equipment and technologies, all of which operate on electricity (Franco et al. 2017).
Given the high-reliability requirements of the equipment used in healthcare facilities, as the slightest disruption could inflict irrecoverable damage, the power input must be supplied to ensure the highest availability (Ghaderian et al. 2020). Patients are most at risk during power cuts when vital equipment ceases to operate, making secondary power supplies essential. For this purpose, hospitals often rely on diesel generators, which are challenged by environmental pollution, high power production costs, loud noise, high maintenance costs, and long supply delays (Olatomiwa 2016).
The solution can be found in renewable sources of energy, such as solar, that are environmentally friendly, highly reliable and durable, and abundant (Jahangiri et al. 2018a; Zaniani et al. 2015; Pahlavan et al. 2018). Figure 1 shows global solar power production over the past decade (Renewables 2021 Global Status Report 2021). As evident, with an additional 139 GWh compared to the preceding year, solar power production reached 760 GWh in 2020.
The high cost of Photovoltaic (PV) systems necessitates maximizing their efficiency (Jahangiri et al. 2020a). To increase efficiency, the orientation of the solar panels to the variable position of the sun in the sky and normal to its rays must be maintained. Accordingly, solar trackers are used to follow the sun’s movements and maximize energy collection (Bouzakri et al. 2021). Two types of trackers are used in solar systems, namely single- and dual-axis trackers. Figure 2 illustrates the different types of solar trackers.
Oxygen supply is an essential part of treatment for infectious disease, asthma, bronchitis, chronic lung disease, and COVID-19 patients (a COVID-19 patient needs 30 times as much oxygen as a typical patient), and its interruption can be fatal. Figure 3 shows the significance of oxygen concentrators as essential equipment in healthcare facilities, particularly larger ones, including hospitals. The hospital oxygen concentrator’s failure or its power cut will claim lives (Stoller et al. 2000). A schematic of the oxygen concentrator is depicted in Fig. 4, outlining its internal components and function.
In the following, the literature on the power supply of equipment in a hospital, a hospital unit, or a clinic using renewable energy, particularly solar energy, is reviewed (Table 1).
.008/kWh due to selling power to the grid, the vertical-axis tracker was found to be the most economical design. Comparing the configuration with a vertical-axis tracker with the conventional scenario (relying on the power distribution grid), the investment is estimated to be recovered in three years with 234,300 in savings by the end of the 25th year. In the best economic scenario, 6137 kg CO2 is produced, and the analysis revealed the negative impact of a temperature rise on the performance and solar power output.
Methodology
The commercial software package HOMER was employed for a technical and economic evaluation of the renewable system. The package relies on two optimization algorithms (Baruah et al. 2021), namely HOMER Search Space and HOMER Optimizer. HOMER Search Space uses the grid search algorithm, and Optimizer relies on a proprietary derivative-free algorithm for simulation.
These algorithms aim to go through all possible configurations to find the system with the minimum cost (Jahangiri et al. 2017). Figure 6 depicts HOMER’s function using a flowchart. The inputs, parameters, and optimization at different stages are all shown on the flowchart.
The inputs of HOMER analyses are introduced in the following:
3.1 Load Data
An AirSep NewLife oxygen concentrator with continuous flow and a maximum output capacity of 10 LPM oxygen with \(92\; \pm \;3\) purity was used. The device has a 590 W power rating (Stationary Oxygen Concentrator Comparison Chart 2021), and in this study, it was attempted to supply 10 oxygen concentrators with grid-connected solar cells.
In the calculations, 15% and 20% of random day-to-day and hour-to-hour variability were taken into account, respectively (Mostafaeipour et al. 2020a). Figure 7 depicts the power demand profile with an 11.5 kW peak in March. over, the load factor is 0.514.
3.2 Resource Assessment
Renewable power production relied on solar energy, for which the selected area has the great potential (Ghaderian et al. 2020). Figure 8 presents the average monthly radiation, average monthly clearness index, and average monthly temperature. The annual averages of these parameters are 5.06 kWh/m 2.day, 0.591 and 14 °C, respectively.
3.3 System Component
Figure 9 shows a schematic of the simulated system. Solar cells have been used to produce power, batteries to store the surplus output, and a converter to transform DC to AC and vice versa. The studied system is connected to the grid. The implementation of the system is readily discussed.
3.3.1 Solar PV
Solar panels convert solar radiation to electric power. The output power of PV cells is a function of radiation, cell temperature, and the derating factor (Moein et al. 2018). The power output of the solar cells is calculated based on the following relationship using HOMER (Moein et al. 2018):
where \(T_\) is calculated from the following relationship:
3.3.2 Grid
Since the studied system was grid-connected, HOMER calculated power exchange with the grid from Eq. 3 (Ebrahimi et al. 2019).
In this relation, \(E_\) represents power purchase from the grid minus power sale in the jth month at the rate i in \(\). \(C_,\;i\) is the grid’s power price at the rate i in \(\frac\mathrm\\mathrm\). and \(C_\;i\) is the price at which power is sold to the grid at the rate i in \(\frac\mathrm\\mathrm\).
3.3.3 Battery
Batteries were used to store the surplus power output to compensate for the unreliability of renewable energy sources. The maximum storage capacity of the battery can be calculated from the following relation using HOMER (Jahangiri et al. 2018b):
where \(P_ \cdot \max \cdot \) is the maximum power output of the battery for a given period in kW, \(P_ \cdot \max \cdot \) is the charging power corresponding to the maximum charging rate in kW, \(P_ \cdot \max \cdot \) denotes the charging power corresponding to the maximum charging current in kW, and \(\eta_ \cdot C\) shows the charging efficiency of the battery in a percent.
3.3.4 Converter
A power converter is needed to maintain the stability of renewable energy systems and convert between AC and DC power. Converters comprise inverters and rectifiers, the output powers of which ( \(P_ \cdot \). and \(P_ \cdot \) ) can be calculated from the following equations using HOMER (Baruah et al. 2021).
where \(\eta_\) denotes the inverter efficiency in percents, \(\eta_\) is the rectifier efficiency in percents, \(P_\) shows the AC input power in kW, and \(P_\) is the DC input power in kW.
Results
In Table 4, the results of the four evaluated scenarios are shown. It was found that the highest solar power production, supplying 60% of the demand, corresponded to the case of using a dual-axis tracker. Configurations with vertical- and horizontal-axis trackers follow with 58 and 54% fulfillment. Without trackers, solar cells would provide 51% of the power demand. According to these results, coupling solar cells with power from the grid is the most cost-effective option in the first, third, and fourth scenarios. However, relying solely on the grid, the cheapest choice is the second scenario (with a horizontal-axis tracker). Cycle Charging was also found to be the superior dispatch strategy compared to Load Following in all scenarios.
In Fig. 12, the cash flow over the project’s 25-year lifetime for scenario 3.1 is plotted. The costs at the beginning (0th year) included the purchase of solar cells and converters. The cost of replacing the power converters in the 15th year was also considered, in addition to the annual maintenance expenses of the converters and solar cells. The revenue includes power sales to the grid during the 25-year service life. The power converter is salvaged in the 25th year, also contributing to the revenues.
In Fig. 13, the average monthly power output is plotted, showing that 58% of the required electricity is supplied by solar cells and the rest by the national grid. Power production was the highest in June, whereas December corresponded with the lowest power output.
In Fig. 14, the output power contour of the solar cells is depicted. Between 11 AM and 3 PM, power output peaked at 22.2 kW. The average daily output was 122 kWh, and the solar cells had a capacity factor of 25.4%. Every year, solar cells produce 44,453 kWh in 4385 working hours.
In Fig. 15, the output power contour of the inverter is depicted. The average inverter output reached 4.8 kW, with a maximum output of 18 kW and a 26.7% capacity factor. The inverters showed an annual loss of 2217 kWh, which is the discrepancy between their 44,337 kWh input and 42,120 kWh output.
Table 5 shows power exchange with the grid. According to the results in Table 5, more power is sold to the grid than bought from it in May, June, and July. December corresponds to the biggest purchase from the grid, namely 3148 kWh. Also, Table 5 shows that 20,542 kWh is sold to the grid every year, whereas 30,252 kWh is received from it. Based on the three-time tariff and Fig. 14, most of the power was sold to the grid during average demand hours for 0.445 \(\frac\).
How to Design and Install a Solar PV System?
Today our modern world needs energy for various day to day applications such as industrial manufacturing, heating, transport, agricultural, lightning applications, etc. Most of our energy need is usually satisfied by non-renewable sources of energy such as coal, crude oil, natural gas, etc. But the utilization of such resources has caused a heavy impact on our environment.
Also, this form of energy resource is not uniformly distributed on the earth. There is an uncertainty of market such as in the case of crude oil as it depends on production and extraction from its reserves. Due to the limited availability of non-renewable sources, the demand for renewable sources has grown in recent years.
Solar energy has been at the center of attention when it comes to renewable energy sources. It is readily available in an abundant form and has the potential to meet our entire planet’s energy requirement. The solar standalone PV system as shown in fig 1 is one of the approaches when it comes to fulfilling our energy demand independent of the utility. Hence in the following, we will see briefly the planning, designing, and installation of a standalone PV system for electricity generation.
- : A Complete Guide About Solar Panel Installation. Step by Step Procedure with Calculation Diagrams
Planning of a Standalone PV system
Site assessment, surveying solar energy resource assessment:
Since the output generated by the PV system varies significantly depending on the time and geographical location it becomes of utmost importance to have an appropriate selection of the site for the standalone PV installation. Thus, the following points must be considered for the assessment and selection of locations for installation.
- Minimum Shade: It must be made sure that the selected site either at rooftop or ground should not have shades or should not have any structure that intercepts the solar radiation falling on the panels to be installed. Also, make sure that there won’t be any structural construction soon surrounding the installation that might cause the problem of shading.
- Surface Area: The surface area of the site at which the PV installation is intended should be known, to have an estimation of the size and number of panels required to generate the required power output for the load. This also helps to plan the installation of inverter, converts, and battery banks.
- Rooftop: In the case of the rooftop installation the type of roof and its structure must be known. In the case of tilt roofs, the angle of tilt must be known and necessary mounting must be used to make the panels have more incidents of solar radiation i.e. ideally the radiation angle must be perpendicular to the PV panel and practically as close as to 90 degrees.
- Routes: Possible routes for the cables from an inverter, battery bank, charge controller, and PV array must be planned in a way that would have minimum utilization of cables and lower voltage drop in cables. The designer should choose between the efficiency and the cost of the system.
To estimate the output power the solar energy assessment of the selected site is of foremost significance. Insolation is defined as the measure of the sun’s energy received in a specified area over a period of time. You can find this data using a pyranometer, however, it is not necessary as you can find the insolation data at your nearest meteorological station. While assessing the solar energy the data can be measured in two ways as follows:
- Kilowatt-hours per square meter per day (KWh/m 2 /day): It is a quantity of energy measured in kilowatt-hours, falling on square meter per day.
- Daily Peak Sun Hours (PSH): Number of hours in a day during which irradiance averages to 1000 W/m 2.
Peak sun hours are most commonly used as they simplify the calculations. Do not get confused with the “Mean Sunshine Hours” and “Peak Sun Hours” which you would collect from the meteorological station. The “Mean sunshine hours” indicates the number of hours the sunshine’s were as the “Peak sun hours” is the actual amount of energy received in KWh/m 2 /day. Amongst all months over a period of year use the lowest mean daily insolation value as it will make sure that the system will operate in a more reliable way when the sun is least due to unsuitable weather conditions.
Calculation of Energy Demand
The size of the standalone PV system depends on the load demand. The load and its operating time vary for different appliances, therefore special care must be taken during energy demand calculations. The energy consumption of the load can be determined by multiplying the power rating (W) of the load by its number of hours of operation. Thus, the unit can be written as watt × hour or simply Wh.
Energy demand Watt-hour = Power rating in Watt × Duration of operation in hours.
Thus, the daily total energy demand in Wh is calculated by adding the individual load demand of each appliance per day.
Total energy demand Watt-hour = ∑ (Power rating in Watt × Duration of operation in hours).
A system should be designed for the worst-case scenario i.e. for the day when the energy demand is highest. A system designed for the highest demand will ensure that the system is reliable. If the system meets the peak load demand it will meet the lowest demand. But designing the system for the highest demand will increase the overall cost of the system. On the other hand, the system will be fully utilized only during the peak load demand. So, we have to choose between cost and reliability of the system.
Inverter Converter (Charge Controller) Ratings
For choosing the proper inverter both the input and output voltage and current rating should be specified. The inverter’s output voltage is specified by the system load, it should be able to handle the load current and the current taken from the battery bank. Based on the total connected load to the system the inverter power rating can be specified.
Let’s consider 2.5 kVA in our case, hence an inverter with power handling capacity having a size of 20-30% higher than the power running the load should be chosen from the market. In the case of motor load, it should be 3-5 times higher than the power demand of such an appliance. In the case of the converter, the charge controller is rated in current and voltage. Its current rating is calculated by using the short-circuit current rating of the PV module. The value of voltage is the same as the nominal voltage of batteries.
Converter and Charge Controller Sizing
The charge controller rating should be 125% of the photovoltaic panel short circuit current. In other words, It should be 25% greater than the short circuit current of solar panel.
Size of solar charge controller in amperes = Short-circuit current of PV × 1.25 (Safety factor).
For example, we need a 6 numbers each of 160W solar panels for our system. Following are the related date of PV panel.
Suppose the PV module specification are as follow.
The required rating of solar charge controller is = (4 panels x 10 A) x 1.25 = 50 A
Now, a 50A charge controller is needed for the 12V DC system configuration.
Note: This formula is not applicable on MPPT Solar chargers. Please refer to the user manual or check the nameplate data rating for proper sizing.
Inverter Sizing
The size of Inverter should be 25% bigger than the total load due to losses and efficiency problem in the inverter. In other words, It should be rated 125% than the total load required in watts. For example, if the required wattage is 2400W, than the size of inverter should be:
So we need a 3kW of inverter in case of 2400W load.
Daily Energy Supplied to Inverter
Let us consider in our case the daily energy consumption by the load is 2700 Wh. Note that the inverter has its efficiency, thus the energy supplied to the inverter should be more than the energy used by the load, so the losses in the inverter can be compensated. Assuming 90% efficiency in our case, the total energy supplied by the battery to the inverter would be given as;
Energy supplied by the battery to the inverter input = 2700 / 0.90 = 3000 Wh/per day.
System Voltage
The inverter input voltage is referred to as the system voltage. It is also the overall battery pack voltage. This system voltage is decided by the selected individual battery voltage, line current, maximum allowable voltage drop, and power loss in the cable. Usually, the voltage of the batteries is 12 V so will be the system voltage. But if we need higher voltage it should be multiples of 12 V. i.e. 12 V, 24 V, 36 V, and so on.
By decreasing the current, power loss and voltage drop in the cable can be reduced, this can be done by increasing the system voltage. This will increase the number of batteries in the series. Therefore, one must choose between power loss and system voltage. Now for our case let us consider the system voltage of 24 V.
Sizing of the Batteries
While sizing the battery some parameters are needed to be considered as follows:
Example:
Suppose we have the following electrical load in watts where we need a 12V, 120W solar panel system design and installation.
- An LED lamp of 40W for 12 Hours per day.
- A refrigerator of 80W for 8 Hours per day.
- A DC Fan of 60W for 6 Hours per day.
Now let’s find the number of solar panels, rating and sizing of charge controller, inverter and batteries etc.
Finding the Total Load
Total Load in Wh / day
= (40W x 12 hours) (80W x 8 hours) (60W x 6 hours)
= 1480 Wh / per day
The required wattage by Solar Panels System
= 1480 Wh x 1.3 … (1.3 is the factor used for energy lost in the system)
= 1924 Wh/day
Finding the Size and No. of Solar Panels
WPeak Capacity of Solar Panel
= 1924 Wh /3.2
Required No of Solar Panels
No of Solar Panels = 5 Solar Panel Modules
This way, the 5 solar panels each of 120W will capable to power up our load requirements.
Find the Rating and Size of Inverter
As there is only AC loads in our system for specific time (i.e. no additional direct DC load connected to the batteries) and our total required wattage is:
Now, the rating of inverter should be 25% greater than the total load due to losses in the inverter.
Inverter Rating Size = 225 W
Find the Size, Rating No of Batteries
Our load wattage and operational time in hours
= (40W x 12 hours) (80W x 8 hours) (60W x 6 hours)
Nominal Voltage of Deep Cycle Battery = 12V
Required Days of Autonomy (Power by batteries without solar panel power) = 2 days.
[(40W x 12 hours) (80W x 8 hours) (60W x 6 hours) / (0.85 x 0.6 x 12V)] x 2 days
The required capacity of batteries in Ampere-hour = 483.6 Ah
This way, we need a 12V 500Ah battery capacity for 2 days of autonomy.
In this case, we may use 4 number of batteries each of 12 V, 125Ah connected in parallel.
If the available battery capacity is 175Ah, 12 V, we may use 3 number of batteries. You can get the exact number of batteries by dividing the required capacity of batteries in Ampere-hour by the available battery Ah rating.
Required Number of batteries = Required capacity of batteries in Ampere-hour / Available battery Ah rating
Find The Rating and Size of Solar Charge Controller
The charge controller should be 125% (or 25% greater) than the solar panel short circuit current.
Size of solar charge controller in Amp = Short circuit current of PV × 1.25
The required rating of solar charge controller is = (5 panels x 8.8 A) x 1.25 = 44 A
So you can use the next nearest rated charge controller which is 45A.
Note that this method can’t be used to find the exact size of MPPT solar chargers. Please refer to the user manual provided by the manufacturer or see the nameplate rating printed on it.
Finding the Cable, CB, Switches Plug Ampacity
Use the following tools and explanatory posts with charts to find the exact amperage rating of wire and cables, switches plugs and circuit breakers.
The standalone PV system is an excellent way to utilize the readily available eco-friendly energy of the sun. Its design and installation are convenient and reliable for small, medium, and large-scale energy requirements. Such a system makes the availability of electricity almost anywhere in the world, especially in remote areas. It makes the energy consumer independent of the utility and other sources of energy such as coal, natural gas, etc.
Such a system can have no negative impact on our environment and can provide energy for long periods after its installation. The above systematic design and installation provide useful guidelines for our need for clean and sustainable energy in the modern world.
Solar Piling The Heart of Utility-Scale Solar
As more gigawatts of solar capacity are added to the grid, contractors need innovative ways of driving pile that can handle the tight tolerances, uneven terrain, and varying pile dimensions required for today’s solar arrays. Automation is a field-proven solution that can restore schedule certainty on even the most challenging projects.
Piling is demanding, and traditional means and methods are being pushed to their limits. Built engineers have spent thousands of hours developing an advanced autonomous solution that can rise to meet the challenges of utility-scale solar.
The Bold Standard
Don’t compromise with your tools. The RPD 35 is a fully autonomous robotic pile driver that combines four steps — surveying, pile distribution, pile driving, and as-builts — into a single robot. Take advantage of the superior production and efficiency gains that only a robot can deliver, and outshine the competition.
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Maximum Power Point Tracking (MPPT)
Two MPPT techniques are implemented using the variant subsystem. Set the variant variable MPPT to 0 to choose the perturbation and observation MPPT. Set the variable MPPT to 1 to choose incremental conductance.
Boost DC-DC converter is used to control the solar PV power. When battery is not fully charged solar PV plant operated in maximum power point. When battery is fully charged and load is smaller than the PV power, solar PV is operated in constant output DC bus voltage control mode.
Battery Management System (BMS)
The battery management system uses a bi-directional DC-DC converter. The battery is charged by the buck converter configuration and it is discharged using the boost converter configuration. To improve battery performance and life cycle, systems with battery backup have limited maximum battery charging and discharging current. This example sets a limit on the maximum amount of power that a battery can supply to the load and absorb from the solar PV source. Here, the maximum charging power is equal to the solar plant capacity at the standard test condition. The chosen maximum charging power should be able to recharge the battery sooner than the battery recharge time specified by the user.
Here, separate controller is used for charging and discharging operation. BMS controller have two loops, an outer voltage loop and inner current loop.
Single-Phase Constant Voltage AC Power Supply
The single-phase constant voltage AC power supply provides a constant AC voltage to the connected complex loads. A single-phase inverter converts the output DC voltage from the boost converter to a constant single AC voltage supply. Choose a suitable PI controller to control the output voltage of the single-pahse inverter. To provide a smooth AC supply to the load, this model uses a LC filter.
Supervisory Control(Mode Control) Parameters
Stand-alone PV system in this example comprises seven operating modes. These modes are selected based on DC bus voltage, solar irradiance and state of charge of the battery. The DC bus voltage level is used as a measure to detect a load imbalance. If the DC bus voltage is greater than /. the system is generating more power than what the load is requiring. If the DC bus voltage is less than /. then the load is requiring more power than what the system is generating.
DC bus voltage level ) /. solar irradiance and the battery state of charge are used to decide the suitable operating mode.
Operating modes of the stand-alone PV AC System are:
- Mode-0. Start mode (Default simulation starting mode)
- Mode-1. PV in output voltage control, battery fully charged and isolated
- Mode-2. PV in maximum power point, battery is charging
- Mode-3. PV in maximum power point, battery is discharging
- Mode-4. Night mode, PV shutdown, battery is discharging
- Mode-5. Total system shutdown
- Mode-6. PV in maximum power point, battery is charging, load is disconnected
Stateflow mode control diagram