Photovoltaic Solar Energy for Street Lighting: A Case Study at Kuwaiti Roundabout, Gaza Strip, Palestine

Increased population and economic growth resulted in the extension of cities and the consequent expansion of streets to assist in the transportation of people and commodities to and from these cities, leading to a rise in energy consumption for street lighting. Street lighting makes cities more appealing, offers a civilized outlook for communities, and emphasizes interesting landmarks at night. However, the most significant reason for street lighting is to increase traffic safety and save lives. Proper and well-designed lighting is crucial for safe roads, fewer automobile accidents, and better comfort for drivers and pedestrians. Studies have shown that good roadway illumination reduces pedestrian accidents by around 50% [1].

The Gaza Strip's energy sources are allocated as follows: 120 MW from the Israeli Electricity Company, 65 megawatts from the Strip's lone producing station, and roughly 2 megawatts from solar energy, even though the Gaza Strip requires approximately 450 megawatts, with a 55% shortage. As a result of this shortage, the Gaza Electricity Distribution Company operates on a contingency schedule that includes eight hours (or more) of on-and-off electricity [2]. In Palestine, the household sector consumes the most energy (60%), followed by the service and commercial sectors (26% for each), and the industrial sector (13%). While the agriculture sector utilizes less than 1% [3].

Using solar energy for street lighting is an effective and sustainable technique for reducing energy consumption and greenhouse gas emissions. LED streetlights may run efficiently by harnessing sunlight and converting it into electrical power via solar panels. These lights use light-dependent resistors (LDRs) that automatically adapt based on ambient light levels [4], [5]. Furthermore, sophisticated technologies are used for these lights. For example, piezoelectric sensors enable the creation of extra electrical energy from the pressure applied by cars on the road, increasing the system's energy efficiency [6].

Adoption of solar-energy-based street lighting systems improves the performance and durability of existing infrastructure while also lowering costs [7]. Economic analysis has shown that deploying PV systems for street lighting results in a quick return on investment as well as significant environmental benefits from reduced carbon dioxide (CO₂) emissions [8]. As a result, solar-powered street lighting systems are not only environmentally beneficial but also financially profitable when compared to traditional lighting techniques.

The development of smart cities and a reduction in the prices of solar street lighting solutions will increase the value of the solar street lighting market from \$5.7 billion in 2019 to \$14.6 billion by 2030, at a 9.4% compound annual growth rate (CAGR) during 2020-2030 (forecast period) [9]. The global deployment of solar-powered street lighting has increased in recent years, indicating a substantial move toward sustainable energy options. One innovative option is the installation of off-grid solar energy systems, in which solar panels gather sunlight during the day. This captured solar energy is then stored in batteries and released to power street lighting at night [10]. Another novel approach connects PV systems to the grid, allowing excess energy generated during daylight hours to be sent to the grid and used to illuminate streets after dark [11]. In Libya, Khalil et al. [12] studied the effects of switching Libya's street lighting from fossil fuels to solar energy, concentrating on a 4-kilometer stretch of road equipped with four different kinds of lamps: stand-alone solar-powered LED lamps, conventional high pressure sodium (HPS) lamps, conventional LED lamps, and grid-connected solar-powered LED lamps. According to their research, switching from HPS lamps to LED lighting can cut CO₂ emissions and electricity use by 75%. Ibrahim et al. [13] suggested using solar energy in Egypt to power an intelligent smart street light system in Giza. Using a 15 W LED Philips lamp, a 45 W monocrystalline panel, a 12 V 37.5 AH lithium-ion battery, and a 10 A 12 V charge controller, they assessed the viability of solar street lighting and found considerable promise. Several nations in the Middle East and North Africa (MENA) have conducted solar cell experiments, with notable results in terms of industry, development, and utilization [12], [13], [14], [15], [16], [17].

Advanced solar street lighting systems use LEDs with automated intensity adjustments and are powered by solar energy. This guarantees ideal brightness levels during peak usage periods and allows for smooth switching on and off during the night [4]. Despite these advances, standalone solar streetlights (SASSL) suffer issues such as early battery failure owing to undercharging and low energy output from PV modules [11]. To address these challenges, a highly innovative and cost-effective smart solar streetlight was created. This next-generation design includes defect detection technologies as well as continuous monitoring of solar and battery voltage to handle possible difficulties ahead of time [18]. By effectively tackling technical concerns and leveraging advancements in monitoring and fault detection, the smart solar streetlight offers enhanced reliability and performance. This not only reinforces the viability of solar energy as a sustainable and efficient solution for street lighting but also contributes to the global transition towards cleaner and greener urban infrastructure.

The use of solar powered LED street lights has arisen as an intriguing topic for both research and practical applications in the commercial sphere. Currently, there is a significant transition away from conventional high intensity discharge (HID) lamps, notably HPS lamps, and toward more energy-efficient LED lights [19]. In modern installations, the essential components of a solar-powered LED street light system include a solar panel, an LED light fixture, a rechargeable battery, a controller, and a pole.

During daylight hours, the solar panel converts sunlight into power, charging the battery for later usage. A charge controller regulates the charging process to guarantee that the battery is healthy and long-lasting. A control circuit monitors the performance of the LED bulb and, in many cases, incorporates sensors such as LDRs to alter brightness based on ambient light conditions. These components are usually attached to a pole for easy installation. The solar panel is strategically positioned atop the pole to reduce shadowing, optimizing solar energy absorption and system efficiency [19]. This arrangement allows for continuous charging cycles and excellent performance from the LED street light system.

The purpose of this study is to solve the issue of inadequate illumination at the Kuwaiti roundabout in the Gaza Strip, Palestine. Persistent power outages have left the roundabout inadequately lighted, resulting in several automobile accidents. This roundabout is significant since it is located on the main route that connects Gaza's eastern and western districts. This study aims to present realistic alternatives for lighting the roundabout using solar energy via the placement of solar cells. In addition, this study discusses numerous possibilities for adopting solar-powered lighting systems and provides recommendations based on a thorough investigation.

This section presents the concerns of system design and the selection of the optimal design. The study methodology can be divided into two parts:

a) Use of mathematical modeling to design solar PV systems step by step.

b) Validation of the simulation result using PVsyst v7.3.

The Kuwaiti roundabout (Figure 1) is located on Salah El-Deen Street in the middle of the Gaza Strip. Salah El-Deen Street connects Gaza's east and west. At the Kuwaiti roundabout, four streets converge, each with two directions and a width of 12 meters. A Kuwaiti roundabout is surrounded by four 12-meter-tall electrical poles spaced 30 meters apart. Each pole is equipped with three 150-watt illumination lights.

Research on the solar radiation was conducted at the study site of the Kuwaiti roundabout (31.4799 N, 34.4423 E). Using Meteonorm 8.1 (https://meteonorm.com/en/meteonorm-version-8), the average irradiation is $5.4 \mathrm{kWh}/\mathrm{m}^2/$day.

The goal of each scenario is to illuminate the roundabout in times of power outages with solar energy, while the lighting lamps work with electricity in times of availability.

In this study, six scenarios were proposed to light a Kuwaiti roundabout, which are the most proposed ones in the literature. In addition, the chosen components were taken from local markets.

Scenario 1: Centralized systems with a 400 W sodium lamp and a 220 volt alternating current (VAC) input voltage.

Scenario 2: Centralized systems using a 150 W LED lamp with a 220 VAC input voltage.

Scenario 3: Decentralized independent systems (each lighting pole contains all the components of the complete system), using a 150 W LED lamp with a 220 VAC input voltage.

Scenario 4: Decentralized independent systems equipped with a 150 W LED lamp and a 24 direct current voltage (VDC) input voltage.

Scenario 5: Decentralized independent systems, using a 150 W LED lamp and an input voltage of 24 VDC or 220 VAC.

Scenario 6: All-in-one LED solar street lighting solution.

To make the analysis easier, the following assumptions were considered:

a) There is no shading or partial shading on the panel.

b) Neglect of the degradation in energy production with time.

c) There are no faults occurring in controllers.

This study has several limitations. Harsh weather factors were not taken into consideration, such as storms during the operation and/or the safety of the panels. The impact of dust accumulation and cleaning work was also not taken into account in energy and economic calculations [20]. The study did not consider other schemes of street lighting, such as the scheme proposed by Nader [1]. In addition, as for the impact of the technical characteristics on the performance of the entire system, a sensitivity analysis was not made.

The availability of climatic and load data, the choice of system modeling, and parameter estimations are the main sources of uncertainty. The cost of renewable energy facilities also results in uncertainty. According to Fathi et al. [21], the prices of solar instrumentation varied by 360%. However, the uncertainty of PV systems is considered the lowest among all renewable energy systems, not exceeding 4% [22].

The following steps were taken for each situation:

a) Determining the demand for power consumption.

b) Determining the suitable size for PV modules.

c) Choosing appropriate inverters and charge controllers.

d) Calculating the battery capacity.

e) Choosing proper cables and wiring.

f) Selecting circuit breaker and fuse safety.

g) Determining the angle of inclination for the panels using computation.

h) Determining the cost of energy (COE) and payback period.

Table 1 shows the number of streetlights and their capacities, as well as the expected monthly and yearly total consumption. It is worth noting that streetlight usage changes throughout the year, with an increase in the winter and a decrease in the summer. As a result, streetlights were designed to operate for an average of twelve hours every day [10].

Off-grid systems (Figure 2) rely only on solar power. They may consist merely of PV modules and a load, or include batteries for energy storage. When batteries are used, charge regulators are incorporated. These regulators deactivate the PV modules upon full battery charge and may also disable the load to prevent battery drain below a certain threshold, as shown in the figure below.

As an illustration, Scenario 2 was employed to elucidate detailed calculations and simulations for the proposed system, as outlined in Sections 2.8 and 2.9, respectively. Then Scenario 6 was explained.

When designing the PV system using mathematical equations, Scenario 2 was chosen as an example to demonstrate the calculations.

The governing equation of the electrical characteristics ($\zeta_{PV}$) of the PV panel under real operation and climatic conditions is given by the following equation [23]:

where, $\zeta_{P V}$ and $\zeta_{S T C}$ denote the real and standard test conditions (STC) of any electrical characteristic, such as current, voltage, power, and efficiency; $H_t$ and $H_{S T C}$ are the states for global solar radiation incident on the PV panel and the STC solar radiation; $T_{S T C}$ and $T_{c e l l}$ are the cell's surface temperatures at STC and under real conditions; $\beta_\zeta$ is the temperature coefficient of the characteristic. It is challenging to estimate $T_{c e l l}$. The following empirical equation has been used to determine the cell surface temperature $T_{c e l l}$ as a function of ambient air temperature $T_{\infty}$ and the global solar radiation $H_t$ by many researchers [24], [25], [26], [27]:

The following equations were used to determine the PV size:

Therefore, eight panels were needed to cover the load. RSM132-8-650BMDG PV panel type was chosen according to the recommendation of Nassar et al. [28], which is consistent with the specifications in Table 2.

It is critical to realize that the tilt angle of the PV module is the angle between the module and the ground. As a result, it is critical to select the appropriate tilt angle for maximum solar energy absorption. The PV module keeps a steady tilt throughout the year, aiming to find the tilt angle that allows for the most solar radiation intake. The solar panels were fixed south-facing at an angle of 30° based on the recommendation of local researchers [30], [31]. At this position, the maximum yearly insolation value is 5.4 kWh/m²/day.

The inverter is required to operate at 1.25 times the peak power. Therefore, the rated power of the inverter equals:

Selected according to the research by Nassar et al. [32], the inverter (MPS-3500H) can satisfy this condition and is available in the local market. Table 3 presents its specifications.

Two arrays of panels, each with four panels connected in series, were used to provide the necessary voltage and current [34]. The following are the VOC and ISC that result from this configuration:

The current from the PV array is 36.36A, which is lower than the maximum solar charge current of 110A.

The capacity of the required batteries can be estimated as follows [35], [36]:

The depth of discharge (DoD) was taken at 50%.

The 200AH type FUSION model was chosen for the batteries, as it is available on the market.

As for the connection of batteries, 11 branches were used to fulfill the above condition, with each branch having a two-battery connection in series.

Table 4 displays the total cost of the system. However, the cost depends on the DoD for the batteries. Table 5 displays the number of batteries which change as the DoD changes, which in turn affects the total cost of the system.

Each component in the above computation was carefully chosen based on its accessibility in the regional market. This guarantees that the parts utilized for the project not only fit the standards and specifications needed but are also easily accessible. The goal of sourcing components locally is to make procurement simpler, shorten lead times, and assist regional vendors. The close proximity of suppliers enables quicker maintenance and replacements, guaranteeing the project's seamless completion. The Levelized cost of energy (LCOE) is an economic measure to estimate the project profit and a reference for comparison with other production choices. The cost of environmental damage produced by CO₂ may be used to compute LCOE using the following equation [37]:

where, $C_{O \& M}$ denotes the cost of operation and maintenance (\$/year), $C$ is the capital cost $(\$), E_t$ is the power $(\mathrm{kW})$ of the proposed system, $n$ denotes the device lifetime (30 years), $r$ is the annual inflation rate (8%), and the subscripts $H$ and $B$ denote the two power generation systems of hydropower turbine and biogas-based generator. In addition, the number 8760 refers to the number of working hours in a year.

When designing the PV system using PVsyst, Scenario 2 was chosen as an example to demonstrate the simulation using PVsyst system v7.3. Several steps were taken for the simulation.

The planning and simulation of a 5.2 kWp solar PV system were conducted using PVsyst software version 7.3. As a powerful software for PV systems, PVsyst is designed for architects, engineers, and researchers. It is also a very useful educational tool, including a detailed contextual “Help” menu that explains the procedures and models used and offers a user-friendly approach with a guide to developing a project. PVsyst is able to import meteo and personal data from many different sources and allows for both preliminary and post-analysis assessments of potential power generation [38]. The system is designed according to the specifications outlined in the methodology, which includes the selection and rating of PV modules, inverters, and array configurations tailored for a 5.2 kWp solar PV system, as shown in Figure 3. This comprehensive approach ensures accurate planning and optimization of the system's performance. The PVsys software has been validated and extensively used by local commercials, engineers and scientists in order to evaluate the feasibility of PV solar systems in the Gaza Strip [39], [40], [41].

a) Performance ratio

Figure 4 displays the performance ratio of this system, which is 67.6%, meaning that only 32.4% of the energy generated through the PV panels is lost in the system.

As depicted in Figure 5, the normalized production per installed kWp demonstrates a nominal power of 5.2 kWp for each month in the year. The maximum occurs in June which is the hottest month of the year.

b) Daily input/output diagram

Figure 6 shows the connection between the worldwide incidents of solar irradiation on the collector plane (measured in kWh/m²/day) and the effective energy production (measured in kWh/day) at the array's output. The amount of solar irradiation a PV module obtains directly affects its production. The technology produces more electricity when the PV panel's sun irradiation rises. Put another way, a PV system produces more energy when there is more sunshine.

Table 6 shows a comparison between the calculated and simulated PV systems.

As shown in Table 6, there is a high level of agreement between the calculated and simulated values for both systems. This alignment underscores the accuracy and reliability of the calculations and simulations performed. Therefore, individuals may confidently choose any method without hesitation.

This section explains Scenario 6, which is the all-in-one LED solar street light, as shown in Figure 7.

In this case, the PV panel, the light, and the sensors are in one piece. The model used is BW-SSL-05B, which is also available in Gaza. Table 7 presents all the specifications of the all-in-one system.

The calculations detailed in the preceding sections were meticulously replicated for each scenario, encompassing all options except for Scenario 6, which was thoroughly elaborated upon in Section 2.11. The results of this study were summarized as follows:

a) Case study 1

The design was made using the central system in the presence of sodium flashlights. It was found that sodium flashlights consumed a high capacity using manual calculations in addition to simulation, leading to the need for 56 batteries and 20 solar cell panels, in addition to the number of two inverters, as shown in the table. The main problem with this design is that an area of no less than 60 $\mathrm{m}^2$ is needed to place the system components, which is not available for every roundabout on the road, in addition to the high cost.

b) Case study 2

Sodium lamps were replaced with lamps equivalent to the intensity of lighting, which are LED lamps with a capacity of 150 watts. This design shows the advantages of LED lamps, with the number of batteries decreasing from 56 to 22, that of solar cell panels from 20 to 8, and inverters from 2 to 1. The area ranges from 60 $\mathrm{m}^2$ to 30 $\mathrm{m}^2$. It was also found in this design that it is not possible to provide an area of 30 $\mathrm{m}^2$ for each roundabout on the road.

c) Case study 3

The design was made using an independent system to solve the space problem that appeared in the first and second case studies. The independent system means that each lighting pole carries all the components of the system. The Kuwaiti roundabout consists of four columns, with each column consisting of three LED lights with a capacity of 150 watts. It was found that each lighting pole requires two solar panels, six batteries, and one inverter. The cost increased slightly, as indicated in the table, due to the use of an inverter for each lighting pole.

It can be noted that the use of inverters in the first, second, and third study cases provides the possibility for the lamps to operate if electricity and charging are available through the electricity network. However, this leads to an increase in the load on the network due to the charging process of the system.

d) Case study 4

The inverter was replaced with a charge controller to get rid of the loading problem on the network and disconnect from the network completely. In this case, LED lights operating at a continuous voltage of 24 volts were used, but the lights did not work if electricity was available.

e) Case study 5

The LED lamps were replaced with lamps operating at a constant voltage of 24 volts and an alternating voltage of 220 volts. A switch was used for two sources of electricity, i.e., cells or the electricity network, as shown in the figure. In this case study, the independent system was adopted to get rid of the space problem that appeared in the first and second case studies. A charging controller was used in addition to the switch instead of the inverter, eliminating the loading problem on the network. Floodlights operating with two voltage sources were used to provide the possibility of lighting if electricity was available from the network or through the solar energy system, thereby making it possible to charge the system for an additional day without loading the network. After comparing the designs, it was found that this case study is the best design for the Kuwaiti roundabout in relation to the cases mentioned above.

f) Case study 6

This case study discusses a searchlight that runs entirely on solar energy at a low price, in addition to a set of features, as shown in the above table. This case is considered a proposal for use in the future. No experiment was conducted previously to prove the efficiency of the system.

Table 8 shows an exhaustive comparison of the six scenarios, offering a comprehensive insight into the various factors considered and outcomes observed across the different setups.

Various case studies were explored in this study, aiming to optimize solar-powered lighting systems for the Kuwaiti roundabout. A central system utilizing sodium flashlights was initially investigated, which highlighted challenges such as high power consumption, space requirements, and cost implications. The transition to LED lamps in the second case study demonstrated significant improvements in efficiency and cost-effectiveness, albeit with continued spatial constraints. The third case study introduced an independent system design, distributing components across lighting poles to address space limitations. However, this approach slightly increases costs due to the use of individual inverters.

Further improvements were made in the fourth case study, which replaced inverters with charge controllers, alleviating network loading concerns but presenting limitations with LED light operation in the presence of available electricity. The fifth case study showcased an innovative solution with dual-voltage lamps and a switch mechanism, offering versatility in power sources and addressing space constraints effectively. In comparison, this design emerged as the most suitable solution for the Kuwaiti roundabout.

Finally, the proposal of a solar-powered searchlight in the sixth case study presents a promising avenue for future consideration, albeit requiring experimental validation to confirm its efficiency. Overall, this study underscores the importance of considering factors such as power consumption, space utilization, and cost-effectiveness when designing solar lighting systems for urban environments. By exploring various design options and innovative solutions, this study paves the way for sustainable and efficient lighting solutions in the communities in the Gaza Strip.

The following recommendations were proposed for further research:

a) Integration of car detection sensors: Future research should include improved sensors capable of detecting approaching automobiles. These sensors may be strategically positioned throughout the roundabout to detect the presence of vehicles. When the sensors detect something, they may activate the lights automatically, providing cars with better visibility and safety while negotiating the roundabout. Furthermore, the incorporation of a sophisticated control system allows the lights to be switched off when no cars are detected, thereby saving energy and minimizing wasteful lighting during low-traffic periods.

b) Development of an early problem detection control system: Another recommendation is to create a complete control system equipped with sensors and monitoring devices to detect and solve possible difficulties early on. By continually monitoring the lighting system's performance, this control system may detect abnormalities, such as faulty components or inconsistencies in energy usage. Early identification of faults enables early intervention and preventative maintenance, reducing the danger of further damage and preserving the lighting infrastructure's dependability and lifetime.

The implementation of these ideas in future studies can considerably enhance the functioning and efficiency of the roundabout's lighting system, resulting in safer travel conditions and optimized energy use.