Design of a hybrid wind-solar street lighting system to power LED lights on highway poles

: This is an experimental study that investigates the performance of a hybrid wind-solar street lighting system and its cost of energy. The site local design conditions of solar irradiation and wind velocity were employed in the design of the system components. HOMER software was also used to determine the Levelized Cost of Energy (LCOE) and energy performance indices, which provides an assessment of the system’s economic feasibility. The hybrid power supply system comprised of an integrated two photovoltaic (PV) solar modules and a combined Banki-Darrieus wind turbines. The second PV module was used to extend the battery storage for longer runtime, and the Banki-Darrieus wind turbines were used also to boost the battery charge for times when there is wind but no sunshine, especially in winter and at night. The results indicated that the hybrid system proved to be operating successfully to supply power for a street LED light of 30 watts. A wind power of 113 W was reached for a maximum wind speed that was recorded in the year 2021 of 12.10 m/s. The efficiency of the combined Banki-Darrieus wind turbine is 56.64%. In addition, based on the HOMER optimization analysis of three scenarios, of which, using either a solar PV system or the combined wind turbines each alone, or using the hybrid wind-solar system. The software results showed that the hybrid wind-solar system is the most economically feasible case. Diode; SCC: Short Circuit Current; PV: Photovoltaic; AD: Autonomy Days; A_ω: Rotor Wind Blades Swept Area (m^2); B_Loss: Battery Loss Factor; C_P: Wind Turbine Power Coefficient; P_Peak: Peak Power of PV Module; BAC: Battery Amperage Capacity; LCOE: Levelized Cost of Energy; O&M: Operation and Maintenance; PBP: Pay-Back Period; LF: Losses Factor; PR: Performance Ratio; CCC: The Charge Controller Current; DHL: Daily Hourly Load; DL: Daily Load; DOD: Depth of Discharge; NS: Number of Strings; NV: Nominal Voltage of the Battery; P: Wind Electrical Power (kW); PR: Performance Ratio; PVW: Solar PV Wattage; SCC: The Short Circuit Current; SDH: Sun Daily Hours; WTC: Wind Turbine Capacity; R: Radius of Banki Turbine


Introduction
Energy storage systems are used to help save an excess generation of clean electrical power from different renewable energy resources to be used later at periods when no adequate renewable energy resources are available. In the last three decades, hybrid energy systems were developed and innovated as a response to solar and wind energy resources utilization. For instance, hybrid energy systems can be used in places, where the electricity tariff of the electrical grid is highly expensive, and in locations, where the electrical grid is weak and intermittent, or at times when solar radiation is weak, as well as wind energy is not sufficient to generate clean electrical power.
Many papers have been published in recent years with increasing attention to hybrid systems of renewable energy.
Khare, V. et.al [1] used hybrid energy systems that are featured with their high capability to increase the rate of reliability of several renewable energy systems. They investigated experimentally the economic feasibility of a hybrid wind-solar energy system to offer clean electrical power for street lighting in low-traffic roads, in which, they sized the wind turbine, solar PV modules, batteries, charge controller, and converter. They selected metal halide lamps as they are the most appropriate light bulbs for low-traffic roads. Their results revealed that solar and wind energy resources can be utilized to operate low-consuming streetlights. In addition, findings confirmed that the annual energy generation equaled 371.7 kWh, whereas the annual energy consumption amounted to 222.8 kWh. Consequently, the remaining amount (148.9 kWh) could be exported to the electrical network making a profit from the hybrid wind-solar energy system. Al-Tarawneh [2] focused on experimental research to calculate the annual cost savings and payback period of using LED streetlights powered via solar PV modules, Al-Tarawneh's experimental work revealed that using LED lights operated by PV power can achieve energy savings of 65% and annual energy savings of 484,261 JD, ($1 = 0.71 JD), for five major streets in Jordan. In addition, the payback period of the renewable energy system for streetlights equaled 1.47 years.
Mazzeo, H. et al., [3] examined the dynamic and energy reliability analysis of renewable hybrid system consisting of a photovoltaic solar generator, a wind micro generator and an electric generator with a storage battery to supply power for a heat pump. The heat pump is employed for heating and cooling air-conditioning of an office building environment. The dynamic simulation results identified the most contemporary load compared with the availability of the renewable source and determined the system energy reliability.
Elmorshedy, et al., [4] proposed in their study a joint and conceptual approach for technoeconomic and dynamic rule-based power control of an off-grid solar-wind renewable energy system. Their design results indicated that the hybrid renewable energy system, which integrated solar, wind, lead-acid batteries, and converter with optimal capacities of 55 kW, 18 kW, 325 kW and 42 kW, respectively, is the most cost-effective alternative with the minimum net present and energy costs of $232,423.3 and $0.3458/kWh, respectively.
Mazzeo, D. et al., [5] reviewed and made statistical analysis starting from data extracted from recent articles concerning hybrid systems. The goal of the review was to create an upgradable matrix literature database that categorizes the content of all articles into categories like geographical distribution, component configurations, operating mode and auxiliary components used to support it, intended uses, study methodologies (simulation, experimental, economic, energy, environmental, and social analysis, and so on) and software used. Furthermore, all optimization algorithms, energy, economic, environmental, and social indicators available in the literature were extracted and elaborated in order to identify the most commonly used.
Wadi, M. [6] investigated a case study of a hybrid wind-solar energy system to offer electrical power for street lighting in Turkey. He utilized a hybrid energy system and fuzzy control to control the operation and production of streetlights. The aim was to control the LED light intensity according to the battery voltage and wind speed.
Ricci, R. [7] used a hybrid renewable energy system, which integrated solar, wind, lead-acid batteries and inverter, and created optimal capacities of 55 kW, 18 kW, 325 kW and 42 kW, respectively. The most cost-effective alternative with the minimum net current energy costs were $232, $423.3 and $0.3458/kWh, respectively.
Georges, S. & Slaoui, F. [8] made a comparative study between LED and high-pressure sodium light bulbs. They made an analysis to size and design each component of a hybrid wind-solar energy system, which included wind turbines, solar PV panels, Gel batteries and charge controllers. The results indicated that using 40 kW solar PV system and 40 kW wind system for 80 Watt-1,000 LED street costs $80,000. Moreover, replacing high-pressure sodium bulbs with 80 Watt LED can achieve $2.66 savings in the initial installed cost of streetlights.
Al-Sarraj, et, al. [9] conducted a study aiming to assess the economic viability related to the use of a hybrid solar and wind energy system to provide clean electrical power for a facility in Iraq. They used HOMER software to estimate the hybrid system's economic feasibility. Their analysis results revealed that power produced from the solar PV system is 61.6 kW/annum, while the power from wind is 2.7 kW/annum. This experimental study will highlight the beneficial effects and primary responsibilities of hybrid energy systems in achieving energy security, sustainability and reliability of wind PV solar systems for street lighting. The work will attempt to provide enough electric power to eliminate the need for electric power from the national electric grid, which can help save money and manpower for operation and maintenance (O&M) and reduce carbon emissions with reliable LED lighting. Moreover, HOMER software was used to analyze a similar system that uses solar and wind energy to provide electrical power for LED street lights. The LCOE, which is defined as an investment index that described the total price of energy provided by the renewable energy system by dividing the total initial cost by the annual savings, was calculated to determine the economic viability of the entire system.

Research methodology
The following main methodological steps were conducted in carrying out this study: • A review, field survey, and analysis of energy demand for street lighting of past relevant applications were carried out.
• Analysis and assessment of the wind and solar radiation energy potential at the geographical location of the experimental setup were conducted.
• An estimation of the PV system size and design of the combined wind turbine system were made.
• The experiments and measurements were performed to check the success of the operation of the hybrid system in street lighting.

•
The HOMER software was used in order to check the economic feasibility of the hybrid windsolar system.

Design and performance analysis
To calculate the clean electrical power value produced from the wind turbine, the following equation is used [10]: where is the wind electrical power, is the air density, is the wind turbine power coefficient, is the wind turbine blades swept area, and is the wind speed. To calculate the wind turbine power required to feed the load of the streetlight, Eq 2 is used [11]: where is the wind turbine capacity, is the Banki turbine's radius, and η is the efficiency. The needed solar PV panels power is calculated via the equation [12]: where is the solar PV power, is the daily load, is the sun daily hours, is the losses factor, and is the performance ratio. The PV module power capacity is computed using the formula: The overall watt peak needed for the PV module, is computed using the formula: = To calculate the battery amperage, the following equation is used [13]: where is the battery amperage capacity, is the daily hourly load, is the autonomy days, is the depth of discharge, is the battery loss factor, and is the battery's nominal voltage. The charge controller current, , is calculated using the equation: where is the number of strings, is the short circuit current, and is the average losses.

Wind turbine design
Based on the measured wind data at the site, the Banki-Darius wind turbine was designed. The Banki wind turbine comprised of two layers, one on top of the other. Each layer had 8 blades. The diameter of the Banki wind turbine is 39 cm, with a total height of 68.5 cm. This yielded a wing area of 0.2672 m². The response speed of the Banki wind turbines is between 5 and 25 m/s [14]. Noting that the density of air is 1.22 kg/m 3 at an atmospheric pressure of 101.325 kPa [15], the maximum efficiency of the combined wind turbine is estimated to be 56.64%, according to the Betz limit [16]. Substituting all values of these parameters into Eq 1 resulted in a wind power of 12.22 W and 1,528.10 W for wind speeds of 5 and 25 m/s, respectively. However, the maximum wind speed recorded in the year 2021 at the site was 12.10 m/s, which provided a maximum power of the wind turbine of about 113 W. Figure 1 shows the fabrication and design processes for the combined Banki-Darrieus wind turbine. To generate more efficient electrical power from wind power, three Darieus wind blades positioned between the hub height were incorporated into the Banki wind turbine to form the combined wind system, as shown in Figure 2. The capacity of the combined wind turbine can reach 300 Watt.   To generate clean electricity from solar radiation, an 80 Watts solar PV polycrystalline CENTSYS module was therefore selected. However, a second 80W PV module was added in order to enhance charging of the battery for longer runtime at times of low solar irradiation.
The datasheet of the 80-Watt PV module is represented in Table 2.

Battery
To select the battery, Eq 6 was used to determine the amperage of the battery. Substituting the values of Eq 6 is based on of 300 Wh, is 3 days, is 0.85 according to the high temperature losses at the site weather conditions, was assumed 60%, and of 12 V leads to of 147 Ah. Thus, 150 Ah Gel battery was chosen, the specifications and datasheet of the Gel battery used in the hybrid energy system are presented in Table 3. In this study, three charge controllers were used, one for each of the two solar PV modules and the third for the combined wind turbine. For solar PV module, the following equations present the calculations of voltage and current of the PV charge controller, which included the maximum power of PV module that is 80 Watt, the maximum voltage of PV module that is 18 Watt, and the maximum current for the PV module that is 4.44 Ampere. The open circuit voltage of the PV module is 22 Volts, and the short current circuit for the PV module is 4.85 Ampere. Substituting the previous values in Eq 7, yields: Therefore, the charge controller should be rated at 6.5 Ampere at the 12 Volts. For the wind turbine, based on data on a 300 W catalogue of vertical axis wind turbine, the charge controller voltage is 12 volts, whilst the open circuit current is less than 20 Ampere.
A charge controller is used in this system to provide protection for the lithium-ion battery used to store electrical energy. Charge controller can prevent battery from high level of depth of discharge (DOD), and high level of state of charge (SOC), which can help maintain high lifespan of the battery [17]. The charge controllers used in this study for both solar PV modules and the combined Banki-Darrieus wind turbine are shown in Figure 3.

The overall system configuration
The overall system's components are presented in Figure 3 above. Whereas, the electrical connection of the hybrid solar-wind system is shown in Figure 4, in which the PV module one and the combined wind turbine system work for providing extra electrical charge for the battery, while the PV module two is the one in charge of lighting the LED light at night by the battery and through its charge controller.

Results and discussions
This section presents the experimental and numerical results obtained in this work. Figure 5 indicates that the average power that could be obtained from the wind speed, which ranges between 30 and 120 Watt.   It is indicated from the Figure 6 that the current ranged between around 0.9 (minimum value) and 4.6 Amp (maximum value), while the voltage values ranged between around 0.7 Volts and 15.34 Volts. Correspondingly, the power values ranged between a minimum value of approximately 0.6 Watt and a maximum of 70 Watt. Figure 7 indicates that the current of the battery load was approximately constant over the day ranging between 2.2 and 2.4 Ampere. The value of voltage varied between roughly 12.2 and 12.8 Volts, providing a power that ranged between 27 and 30 Watts.   meters. The figure indicates that the light intensity ranges between around 3,450 and 3,600 L/m 2 , which occurs between 8:00 pm and 5:00 am. Outside this range of time, the LED streetlight provides no light intensity as it is programmed not to operate.

Experimental results
These results have indicated that the combined Banki-Darrieus wind turbine that included three Darrieus wind blades and two layers of the Banki wind turbine, each with eight blades, and the two PV modules, each of 80 W capacity, were appropriate to light a street LED lamp of 30 Watts.

Numerical results
After conducting optimization, sensitivity analysis, and simulation through the HOMER software package for the system presented in Figure 9, it was found that there were 3 possible scenarios of the hybrid solar PV-wind system in terms of economic feasibility. The three cases are presented in Table 4.   (3) (PV panels and battery). The system's net present cost equals $1,243.50, while the system's operating price in this scenario equals $22.22. Surely, the software results showed that the hybrid windsolar system is the most economically feasible case.

Conclusions
This experimental and numerical study investigated the suitability of a wind-solar hybrid system in lighting street LED lights on highway poles. The hybrid system includes a combined Banki-Darrieus wind turbine integrated with a PV solar system to provide energy to light a 30 W street lamp. The numerical part of this study included the use of HOMER software to check the levelized cost of energy of the hybrid system, which provided an assessment of the system's economic feasibility.
The main results of this experimental and theoretical study revealed the following findings: 1. The experimental results revealed that the design of the Banki-Darrieus wind turbine that included three Darrieus wind blades and two layers of the Banki wind turbine, each with eight blades and of a diameter of 39 cm and a total height of 68.5 cm, and the two PV modules, each of 80 W capacity, were adequate to light the 30 W LED street lamp. 2. The maximum wind speed recorded in 2021 at the experimental site was 12.10 m/s, which provided the wind turbine power of 113 Watts. 3. The HOMER software numerical results revealed that the hybrid wind-solar system is the most economically feasible case among using either wind or solar system alone.