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Scientific Reports volume 14, Article number: 29833 (2024 ) Cite this article gi pole
To enhance efficient and sustainable energy usage in street lighting systems, a nano-grid infrastructure comprising an energy harvesting, storage, and management system is integrated. This paper investigated the feasibility in terms of energy production and economic evaluation of using various energy harvesting for photovoltaic, piezoelectric, and wind energy in a nano-grid street lighting system. The photovoltaic system was evaluated based on the factors of annual actual solar radiation, power losses, and system performance using the PVsyst software. The piezoelectric energy production was studied and designed. Optimal piezoelectric installation for maximum power generation was analyzed in terms of deformation and stress using ANSYS software. For wind power generation, the wind turbine characteristics, along with its location, were designed to optimize power output using computational fluid dynamic simulations in ANSYS software. After that, economic evaluation for the proposed energy harvesting systems for nano-grid street lighting system are analyzed and compared in terms of DPP, NPV, IRR, and LCOE. In addition, the optimization of using PV, a wind system, a hybrid PV—wind system for nano-grid street lighting systems was conducted using HOMER Pro software. The results indicated that generating power through PV, piezoelectric, and wind energy was feasible. However, economic evaluation unveiled the infeasibility of employing piezoelectric and wind energy systems due to their elevated investment costs relative to their power generation capabilities. The dynamics of power generation from PV and wind systems, along with street lighting consumption, significantly impacted the dimensions of energy harvesting and storage systems, as well as their economic feasibility. The hybrid PV-wind system exhibited strong economic feasibility.
Street lighting is very important for drivers to detect vehicles and objects at night. However, many street lighting systems suffer from energy inefficiency, such as using light source that energy inefficiency1,2,3. To address this issue, the light source of street lighting systems has been upgraded to light-emitting diode (LED) luminaires. LEDs offer notable advantages including energy savings, high lighting quality, and long service life1,2,3,4,5.
In addition, a growing interest in integrating energy harvesting systems from renewable energy such as photovoltaic (PV)6,7,8, piezoelectric energy9,10,11,12, and wind energy13,14,15,16 to use with street lighting systems. It is a matter that is gaining attention. Because it can Increase energy efficiency Reduce energy costs and reduce greenhouse gas emissions This trend is gaining attention due to its potential to enhance energy efficiency, decrease energy expenses, and mitigate greenhouse gas emissions. Paper6 outlined the design of a PV center aimed at providing basic lighting, thus fostering income-generating opportunities within the community. Paper7 was to examine and contrast the environmental aspects of two street lighting technologies: the conventional grid-connected system and the standalone PV system. Paper8 conducted a feasibility analysis of PV and battery components to power local street lighting. However, PV presents several limitations, including variability in energy production, disparities between energy generation and usage, issues with overvoltage, and challenges with reverse power flow7. Furthermore, the expenses associated with a PV system, encompassing both PV panels and batteries, can negatively impact the sensitivity analysis concerning investments6.
Besides PV, piezoelectric and wind energy can also be harnessed to power street lighting systems. A piezoelectric energy harvesting system generates electrical energy by harnessing the mechanical force generated by moving vehicles upon piezoelectric materials embedded within the street surface9,10,11,12. In the paper10, the design of the street piezoelectric devices material and parameters, which were determined based on the mechanical characteristics of the pavement, was introduced. To establish a quantifiable relationship between vehicle loads and the electrical energy generated by a piezoelectric energy harvesting system, Paper11 conducted an analysis of the vehicle’s rolling process over the piezoelectric device. In Paper12, piezoelectric signals were collected from piezoelectric devices embedded within asphalt mixture specimens using a data collector, with the aim of enhancing energy efficiency. While this system does not require energy expenses, it generates a relatively small quantity of electrical energy. Therefore, the utilization of small-scale electrical devices or sensors is unavoidable9,10,11,12.
For wind energy, the wind energy harvesting system generates electrical energy by utilizing the wind velocity generated by moving vehicles to rotate the turbine13,14,15,16. Numerous research endeavors have explored the viability and effectiveness of harnessing wind energy generated by vehicular motion14,15,16. Several investigations have scrutinized the efficacy, form, and placement of wind turbines through the development of experimental configurations tested in controlled wind tunnel environments13,15. However, accurately assessing wind turbine efficiency based on real-world wind velocities from vehicle movement poses challenges. Consequently, certain studies have employed computational fluid dynamics (CFD) to evaluate the impact of designed wind turbines, wind velocities, wind flow patterns, and energy efficiency14,16.
Although power generation from the mentioned energy harvesting systems is clean energy and abundant energy resources without energy costs, the generated power is fluctuated and uncertain, making it difficult to respond promptly to changing energy demand. To deal with these issues, the combination of energy harvesting, and energy storage systems formulates a nano-grid system17,18,19,20,21,22,23,24. Local generation and storage enable the nano-grid to operate independently, offering numerous practical advantages over traditional power systems when the grid is unavailable20. In Paper21, conducted emission characteristics of nano-grid systems based on using grid-connected and stand-alone micro-inverters were presented. Various hybrid energy harvesting systems, along with their control, optimization, and supervision strategies, were discussed in22. To overcome uncertainty and achieve power balance through power management algorithms in nano-grid systems, Paper23,24 studied the energy optimization of PV, batteries, fuel cells, and hydrogen storage using HOMER Pro.
However, enhancing the energy efficiency of street lighting systems with nano-grid technology can significantly affect investment costs. This is primarily attributed to the higher expense associated with implementing a sophisticated energy management system. Earlier research articles presented economic evaluations to confirm that the investment was acceptable25,26,27,28. Paper25 conducts a techno-economic analysis of PV street lighting systems. The author suggests that the systems could become feasible if the decreasing trend in PV system costs persists and electricity prices rise. Paper26 introduced a comprehensive framework for the efficient utilization of hybrid renewable energy sources. Through the application of the multi-objective Artificial Electric Field Algorithm (AEFA), it achieved the optimal allocation and sizing of Soft Open Points (SOPs) and the integration of hybrid renewable energy resources. This proposed system showcased an economically viable solution while maintaining acceptable levels of emissions and fuel consumption. The paper27 claims that a comprehensive perspective must combine technology-focused approaches to hybrid renewable energy sources with economic considerations. This study emphasizes techno-economic analysis with optimized sizing of hybrid components of renewable energy systems. Furthermore, a feasibility and sensitivity analysis of off-grid and grid-connected microgrids powered by renewable energy, exploring the potential of wind and PV energy in various locations was investigated in28. This complexity arises from hybrid systems and nano-grids, which incorporate diverse renewable energy sources. Economic analyses are conducted using HOMER Pro software26,27,28.
The aforementioned research articles indicate widespread adoption of PV harvesting systems integrated into street lighting infrastructure6,7,8. However, the implementation of piezoelectric and wind energy harvesting systems for street lighting has largely remained confined to prototypes and simulations9,10,11,12,13,14,15,16. Due to the inherent power fluctuations in energy harvesting systems, Paper17,18,19,20,21,22,23,24 implemented a nano-grid system that incorporates energy management among various components, including energy harvesting systems, energy storage systems, energy consumption, and interactions with the electrical grid. Furthermore, economic feasibility is an important factor for developing the conventional system to a nano-grid system25,26,27,28.
In this field of study, we investigated the feasibility of employing various types of energy storage systems from both a power quality and economic standpoint, particularly in the context of street lighting systems powered by PV29. We explored the advancement of street lighting systems incorporating nano-grid technology, in both standalone and grid-connected configurations30. A study was undertaken to decrease the energy consumption of nano-grid street lighting systems through adaptive lighting control, aiming to enhance the feasibility of installing an energy storage system for managing energy in these systems31.
This paper focuses on increasing energy efficiency in nano-grid street lighting systems. The study of feasibility on the utilization of various energy harvesting systems, such as PV, piezoelectric, and wind energy, for nano-grid street lighting systems is presented. PV harvesting systems involve the installation of PV panels on street light poles to generate electrical energy during the daytime. Piezoelectric energy harvesting systems accomplish power generation by capturing energy from the vehicle’s movement. A street surface composed of piezoelectric materials for energy harvesting is employed. Wind energy harvesting systems are established by vertical wind turbines on islands or alongside roadways, which utilize both natural wind force and the wind generated by vehicle movement to generate electrical energy. The potential for generating electric power from the wind speed generated by vehicle movement is analyzed. Additionally, the economic evaluation of integrating PV, piezoelectric, and wind energy harvesting systems into nano-grid street lighting systems was also presented.
The main contributions of this study can be summarized as follows:
Energy harvesting of PV for the nano-grid street lighting system was evaluated based on the factors of annual actual solar radiation, power losses in the PV system, and system performance using the PhotoVoltaic System (PVsyst) software version 7.4.832.
Energy harvesting of a piezoelectric power-generating street surface was studied and designed. Optimal piezoelectric installation for maximum power generation was analyzed in terms of deformation and stress using the Analysis System (ANSYS) software version 2019 R133.
Energy harvesting of wind power for the nano-grid street lighting system was investigated. The wind turbine characteristics, along with its placement, were designed to optimize power generation. The feasibility of the power generation was analyzed by the CFD method based on the finite volume method.
Economic evaluation for the proposed energy harvesting systems for nano-grid street lighting system are analyzed and compared in terms of DPP, NPV, IRR, and LCOE.
The optimization of employing energy harvesting versus energy storage to enhance the economic viability of the nano-grid street lighting system was examined using Hybrid Optimization Model for Multiple Energy Resources (HOMER Pro) software version 3.16.234.
The remainder of this paper is organized as follows. Section “Nano-grid street lighting systems” introduces the concept of nano-grid street lighting systems. Section “Feasibility of using different energy harvesting systems in terms of economic analysis and energy generation performance” presents feasibility evaluation of using various energy harvesting systems for the nano-grid street lighting system in terms of power generation and economic evaluation, and section “PV and wind energy-harvesting optimization for nano-grid street lighting” demonstrates the optimization of energy harvesting and energy storage for nano-grid street lighting system. Finally, section “Conclusion” outlines the conclusions of this study.
For efficient and sustainable energy usage in street lighting systems, it is recommended to implement an energy harvesting, storage, and management system known as “a nano-grid system.” Figure 1 depicts the layout of the integration of nano-grid concept into street lighting systems, comprising energy-harvesting systems, energy-storage systems, light sources, and energy-management systems.
Energy harvesting systems from PV, piezoelectric, and wind energy sources serve as electric power sources for street lighting systems. PV is generated during daylight hours from solar irradiation energy using PV panels. For using piezoelectric systems and wind turbines, electrical energy is generated through the movement of vehicles along street. Piezoelectric systems involve installing street surfaces made of piezoelectric materials, which function as power generators. When vehicles pass over these surfaces, they exert pressure, generating electrical energy. Wind turbines placed vertically on street -traffic islands harness wind power generated by the movement of vehicles to produce electrical energy.
The power sources for nano-grid street lighting systems consist of energy-harvesting systems that vary in output depending on environmental conditions. Thus, energy storage systems are employed to address these challenges.
LED technology presents energy efficiency, lighting performance, and lifespan. Hence, LED luminaires are the preferred light sources utilized in nano-grid street lighting systems.
(1) The feasibility of energy production: Electrical energy from a PV system is generated by converting solar radiation into electrical energy using a PV panel. For a nano-grid street lighting system, a PV panel is installed on a pole to generate electrical energy for the street lighting system at night.
PV for the nano-grid street lighting system was evaluated using the PVsyst software based on the annual actual solar radiation, power losses in the PV system, and system performance. The nano-grid street light lighting system using a 120 W LED luminaire was designed to cover 12 h a day from 6:00 pm to 6:00 am. Therefore, the energy required to supply the nano-grid street lighting system was 1440 Wh/day. According to the Department of Alternative Energy Development and Efficiency of the Ministry of Energy, Thailand has an average daily solar irradiation of approximately 5 kWh/m235. The geographic parameters used to estimate the electric power produced by a PV system installed in Bangkok, Thailand (latitude: 13.74 °N, longitude: 100.67 °E, 13 m above sea level) based on the NASA–SSE satellite data in the PVsyst program are listed in Table 2.
For the PV generation simulation, the installation of a PV system for a nano-grid single street lighting system was considered. In this case study, a monocrystalline silicon PV panel of 350 W was installed with a tilt angle of 15°. The PV panel had a width of 992 mm and a length of 1956 mm, with an efficiency of 20%.
Figure 2a shows the performance ratio (PR) of the PV system, which describes the power generated by the PV system compared with the installed power. The installed PV system had an average annual PR ratio of 82.2%. Figure 2b shows the average daily power produced by the PV system per month. It was found that the highest power was produced during February, March, and April, owing to the high solar irradiation. Considering the power produced by the system per unit size of installed PV system, it was found that there is an annual average value of 4.42 kWh/kW/day. Thus, the electrical energy produced from the PV system is 1547 kWh, which is sufficient for a 120-W LED luminaire nano-grid street lighting system.
(2) The feasibility of economic evaluation: Table 3 shows the results of the economic evaluation of installing a PV harvesting system combined with a street lighting system. The installation of the additional PV harvesting system incurred extra costs totaling 34,320 USD. The PV harvesting system can generate 35,770 kWh per year, translating to an income of 5960 USD per year from electrical energy savings. An economic evaluation revealed the feasibility of installing a PV harvesting system with a street lighting system. However, installing the additional PV harvesting system yields income solely from electricity savings, which may not be highly attractive for investment. This is attributed to the long discounted payback period (DPP) owing to the high cost and limited lifespan of the energy storage system. However, the internal rate of return (IRR) and net present value (NPV) provide satisfactory results for the investment over a 20-year period.
(1) The feasibility of energy production: Piezoelectric materials are used to generate electrical energy by converting the mechanical energy exerted on them into electrical energy. In nano-grid street lighting systems, piezoelectric materials are used to generate power from vehicle movements on street surfaces. To achieve energy efficiency, power-generating street surfaces need to be designed to an optimal size, which can transfer stress to piezoelectric materials as well as provide durability for use in real environments.
This section presents the design of a piezoelectric power-generating street surface for powering a nano-grid street lighting system. In addition, the feasibility of installing piezoelectric materials on a power-generating street surface was investigated using the ANSYS software.
A PPA-2011 piezoelectric sheet with a length of 71 mm, width of 25.4 mm, and thickness of 0.76 mm, as shown in Fig. 3, was used to assemble the power-generating street surface37. The PPA-2011 piezoelectric sheet consists of two sheets of piezoelectric materials, with length of 46 mm and width of 20.8 mm, sandwiched by a copper sheet and FR4 epoxy, as presented in Table 4. According to the specifications, the piezoelectric sheet could produce a maximum power of 34 mW when the piezoelectric sheet is bent with a peak-to-peak distance of 18.5 mm.
The simulation results from the ANSYS software for studying the feasibility of piezoelectric installation on a power-generating street surface are divided into two case studies: optimal piezoelectric sheet installation and optimal position for fixing the piezoelectric sheet.
(a) Optimal piezoelectric sheet installation results: The voltage produced by a piezoelectric sheet depends on the natural frequency of the piezoelectric sheet. If a piezoelectric sheet can be designed to have a natural frequency close to the vehicle’s movement frequency, which is a low natural frequency, the power produced from the piezoelectric power-generating street surface can be increased. The displacement and natural frequency of the free oscillations of the piezoelectric sheet under a mechanical load applied to the piezoelectric material depend on the type of installation, which can be as follows (Fig. 4): (1) base mounting, (2) base edge mounting, (3) both ends mounting, and (4) cantilever mounting types.
As shown in Fig. 4, the installation of the piezoelectric sheet with different mountings resulted in different natural frequency oscillations of the piezoelectric sheet. The mounting types of base mounting, both ends mounting, and cantilever mounting provided natural frequencies of 140,000, 1126.4, 152.55, and 23.68 Hz, respectively. The simulation results showed that cantilever mounting yielded the lowest natural frequency. Therefore, a cantilever-mounting type was considered in the design of the piezoelectric power-generating street surface.
(b) Optimal position for fixing the piezoelectric sheet results: The simulation results of the deformation and stress values at various positions for fixing the piezoelectric sheet were divided into the end (position 1), middle (position 2), and outer (position 3) positions, are presented in Figs. 5 and 6, and 7. Generally, the piezoelectric sheet can easily break. If the force generated by vehicle movement directly sent to the piezoelectric sheet, it will cause damage. In actual use, the piezoelectric sheet must be structurally engineered to prevent damage from vehicle movement. To study the effect of fixing the piezoelectric sheet, a mechanical force of 300 N was assumed and applied to the cantilever-mounted piezoelectric sheet.
Displacement and the natural frequency from different types of piezoelectric sheet installation.
Mechanical simulation of piezoelectric sheet in fixing position 1.
Mechanical simulation of piezoelectric sheet in fixing position 2.
Mechanical simulation of piezoelectric sheet in fixing position 3.
The simulation results indicated that the piezoelectric sheet fixed at position 1 exhibited the highest deformation and stress. As a result, this position produces the highest electrical power compared with those resulting from fixing the piezoelectric sheets in positions 2 and 3 under the same operating conditions. The piezoelectric sheet for a power-generating street surface should be designed to have an appropriate deformation distance by considering the energy efficiency factor and limitations of the piezoelectric sheet.
The results of this study indicate that the cantilever-mounting type is suitable for piezoelectric-power-generating street surfaces. The mounting point on the outer edge of the piezoelectric sheet yields the maximum stress and deformation values. Thus, the design of the piezoelectric power-generating street surface is based on a cantilever-mounting type with prototype dimensions of 100 mm in width and 100 mm in length, which is the optimal size, as shown in Fig. 8.
The designed piezoelectric power-generating street surface.
As shown in Fig. 8, the piezoelectric power-generating street surface consists of three PAA-2011 piezoelectric sheets, top cover, side covers, protection sheet, air gap, and rubber sheet. The piezoelectric sheet can generate the maximum power when the peak-to-peak bending distance (deformation) equals 18.5 mm. Therefore, a safe distance for deformation in the cantilever-mounting installation was set as 9 mm. To avoid damage to the piezoelectric sheet, the front and side covers were made of aluminum with an elastic modulus of 71 GPa, tensile strength of 460 MPa, and density of 2.78 g/cm3. The bottom cover was made of steel with an elastic modulus of 203 GPa, tensile strength of 415 MPa, and density of 7.85 g/cm3. The cover responded to the transfer of directional force from the vehicle to the top of the piezoelectric sheets to prevent damage. The protective sheet used in the proposed method has a circular shape with sufficient flexibility, strength, and electrical and thermal resistance. Hence, polypropylene was selected as material. It has an elastic modulus equal to 1.6 GPa, tensile strength equal to 90 MPa, heat resistance up to 120 °C, and 1015 Ω/cm electrical resistance. The air gap was also used as a space for electrical wiring. The rubber sheets can reduce the mechanical force, vibration, and deformation caused by vehicle movement.
2) The feasibility of economic evaluation: An economic evaluation of utilizing piezoelectric street surfaces to generate electrical energy for street lighting systems is presented. The energy-generating street surface measures 0.1 m in width and length, with a spacing of 0.348 m between each energy-generating street surface38. The designed piezoelectric power-generating street surface comprises three PAA-2011 piezoelectric sheets, each capable of generating a maximum power of 34 mW. Consequently, the designed surface can generate a total maximum power of 0.102 W. Cost analysis of implementing energy-generating street surfaces, including energy and economic evaluation results, for their utilization as a source of electrical energy in street lighting systems is presented in Table 5.
As shown in Table 5, the results indicate that installing an energy-generating street surface spanning a street length of 1 km can generate 9.24 kWh of electrical energy annually, translating to an income of 1.53 USD per year from electrical energy costs. Investment analysis revealed that the installation cost of an energy-generating street surface system amounted to 305,596 USD, exceedingly twice the cost of installing a PV harvesting system. However, upon comparing the efficiency of electrical energy production, it was observed that the PV system outperforms the piezoelectric energy harvesting systems. The economic evaluation revealed that installing an energy harvesting system utilizing piezoelectric materials on the street surface is impractical, due to an extended payback period, negative net present value, and lack of internal rate of returns.
(1) The feasibility of energy production: The objective of installing a wind turbine is to harvest electrical energy generated by the motion of vehicles traveling on the street. Due to area constraints, vertical-axis wind turbines are considered. Savonius vertical wind turbines are employed as generators to harvest wind energy produced by the movement of vehicles. Although these wind turbines may have relatively low aerodynamic efficiency, they provide outstanding generating electrical energy at low wind speeds and demonstrate good energy efficiency.
Savonius wind turbine with two blades utilized in the study.
To evaluate the economic viability of installing an electric wind turbine, a two-blade Savonius wind turbine was chosen. This decision was based on its capacity to offer a higher wind power coefficient compared to turbines featuring one or three blades41. Figure 9 depicts the dimensions of a two-blade Savonius wind turbine used for harvesting wind energy with a street lighting system42. The turbine blades are intricately designed with multiple curves to enhance the efficiency of electrical power generation. A minimum width of 1.2 m for the traffic island was taken into account, aligning with the street median and widening design recommendations provided by the Department of Highways in Thailand43. A wind turbine is characterized by a height (H) of 1 m and a turbine diameter (D) of 1 m. The detailed components of an electric wind turbine are outlined in Table 6.
To assess the feasibility of generating electrical energy through wind turbines used to harvest wind energy from vehicle movement, two types of vehicles were considered: cars and buses. Their simplified dimensions are depicted in Fig. 10. The car’s dimensions are 4.5 m in length, 1.8 m in width, and 2.0 m in height, whereas the bus measures 8.0 m in length, 2.4 m in width, and 3.0 m in height. To streamline the aerodynamic investigations, the vehicle geometry used in the simulation was simplified to reduce complexity and computation time. Furthermore, the vehicles were considered stationary, as indicated by a study44 which demonstrated that there were no significant differences in wind speeds and characteristics between dynamic and static scenarios. A computational fluid dynamics (CFD) technique employing numerical calculations with the finite volume method is utilized to solve the fluid mechanics equations based on the Navier–Stokes equation. To simulate vehicle movement scenarios, the vehicle is configured to travel at a speed of 90 km/h (25 m/s).
Impact of wind velocity resulting from vehicle motion on the wind turbine at different locations.
Figure 11 displays the wind speed profiles generated by the movement of vehicles impacting wind turbines at various positions. The simulation results indicate that both cars and buses exhibit similar wind load patterns. When the vehicle approaches the wind turbine, it induces wind to spin the turbine. Subsequently, when the vehicle aligns with the wind turbine, the wind velocity decreases, resulting in lower electrical power generation during this period. However, as the vehicle passes by the wind turbine, the region affected by the two counter-rotating vortices creates the strongest wind area, resulting in high wind velocity. Consequently, electrical power was predominantly generated within this high-wind area. In the case of a car, as shown in Fig. 11a, the wind speed reaches 7 m/s as the car approaches the wind turbine, while moving away from the wind turbine, it reaches a maximum wind speed of 10 m/s. In the case of a bus, when it approaches the wind turbine, it can generate a wind speed of 9 m/s, but as it moves away from the wind turbine, the maximum air speed that can be achieved is 14 m/s.
(2) The feasibility of economic evaluation: To evaluate the economic feasibility of integrating a wind energy harvesting system with a street lighting system, a vertical wind turbine rated at 100 watts, measuring 1 m in width and 1 m in height, was employed in the analysis. The wind turbines were mounted on a street island with a height of 0.5 m, spaced at 1.8 m apart from each other (1.2 times the height of the turbines). The expenses associated with installing the wind turbines, encompassing energy and economic evaluation, are presented in Table 7.
As shown in Table 7, The results indicate that implementing a wind energy harvesting system with turbines for a 1-km street lighting system generates 83,021 kwh of electrical energy annually, translating to 13,837 USD in revenue from electrical energy. The cost of wind turbine installation is 156,690 USD. While wind energy harvesting systems give higher initial investments compared to PV harvesting systems, they have the capacity to generate more electricity along the same street length. However, the economic evaluation results indicate that investing in the wind energy harvesting system may not be worthwhile due to its long payback period, negative net present value, and low internal rate of return. Nevertheless, compared to piezoelectric energy harvesting systems, it proves to be more economically viable as it has a lower levelized cost of energy (LCOE).
Using energy harvesting sources such as PV, piezoelectric energy, and wind energy for producing electrical energy for street lighting systems reveals that the generated electrical energy fluctuates based on natural factors. PV power varies with solar radiation, which changes throughout the day and across seasons, resulting in unequal daily energy production. Piezoelectric energy fluctuates based on vehicle movement behaviors such as size, weight, speed, and traffic density. Wind energy fluctuates based on two factors: (1) natural wind speed, which varies throughout the year, and (2) wind speed generated by vehicle movement, which depends on vehicle speed, vehicle size, and traffic density. Therefore, using electrical energy produced from energy harvesting sources to power street lighting systems always requires an energy storage system for effective energy management.
In commercial, PV is widely used, leading to market competition, which in turn drives the development of increased efficiency and reduced costs. Piezoelectric energy is not yet widely popular due to the low energy efficiency and high cost of piezo plate materials. It may be suitable for applications requiring small amounts of electricity, such as light signs and sensors. Wind energy is a popular energy harvesting source. However, vertical wind turbines have not received much attention because they are less efficient than horizontal wind turbines, leading to higher costs and difficulty in procurement. Thus, the results of the study show that the PV and the wind system can produce sufficient electrical energy for street lighting systems. However, the wind system has high costs and is not economically feasibility. For piezoelectric energy, it produces insufficient electrical energy for street lighting systems and contributes to high investment costs. Hence, it is not suitable as a source of electrical energy production. In addition, the advantages and disadvantages of using various energy resources for nano-grid street lighting systems are summarized and depicted in Table 8.
To comprehensively expand the economic evaluation, the energy harvesting sources and storage systems employed for the nano-grid street lighting system were efficiently optimized utilizing HOMER Pro software as presented in Fig. 12. PV and wind energy harvesting sources have been investigated since they have been deemed economically viable, as presented in the preceding section. Lead-acid and lithium-ion batteries, known for their high performance in energy harvesting applications29, have been employed for energy storage purposes. The power generated by PV and wind energy and the power stored in energy storages are in the form of direct current (DC), while the power of electrical grid and street lighting systems use alternating current (AC). To make use of the power between DC and AC systems, a converter is employed. NASA prediction of worldwide energy resource database in HOMER Pro software providing the monthly average for solar radiation and monthly average wind speed located in Thailand was utilized as resources for PV and wind power generation, as illustrated id Fig. 13a,b, respectively. In the case of wind speed, the monthly average wind speed included the average wind speed caused by vehicle movement and was measured using an anemometer installed at 0.5 m height. The average wind speed generated by vehicle movement was calculated using an assumed wind speed of 7 m/s impacting the turbines. The duration of this wind speed affecting a wind turbine, at a vehicle speed of 90 km/h, is 1 s. The number of vehicles per day is 20,000 cars per lane. The 1 km nano-grid street lighting system consisted of 56 luminaires with 120 W LED, which consumed 80.64 kWh/day or 28,096 kWh/y.
Our objective in the optimization is to design the most economically viable nano-grid street lighting system. This involves considering the costs of PV, wind energy, hybrid PV and wind energy, lead-acid batteries, lithium-ion batteries, the lifespan of the equipment, and the fluctuations in renewable energy production that affect battery lifespan. Table 9 presents parameters for optimal nano-grid street lighting system design, including capital cost, replacement cost, operation and maintenance cost, and lifetime of PV, wind energy, energy storage, and converter. Additionally, economic factors of discount rate, project lifetime, and electricity rate used for economic evaluation based on PDD, IRR, NPV are taken into consideration. The constraints are: (i) the energy harvesting system with an energy storage system must supply energy to the street lighting system throughout the year; (ii) solar radiation and wind speed data are based on conditions in Thailand, so the optimal results are specific to Thailand; (iii) the average wind speed generated by vehicle movement is assumed to be constant, based on vehicle movement at 90 km/h.
Schematic diagram of nano-grid street lighting system from HOMER Pro software.
Average monthly solar and wind energy resources used for optimization.
Monthly electricity consumption and generation.
Figure 14 illustrates the electrical energy production from various energy harvesting systems in comparison to the year-round energy consumption of street lighting systems, comprising the PV harvesting system depicted in Fig. 14a, the wind energy harvesting system in Fig. 14b, and the hybrid PV—wind energy harvesting system in Fig. 14c. The results reveal that on average, the electrical power generated by energy harvesting systems each month surpasses the energy supplied to street lighting systems. This surplus accounts for the fluctuations in energy production from energy harvesting systems, which rely on natural factors. The surplus energy is stored in an energy storage system, which is then utilized to power street lighting systems during periods when electrical energy production is insufficient. In PV harvesting systems, the majority of energy production takes place during the daytime. However, during the rainy season from June to September, there is a decrease in the monthly average solar radiation intensity, leading to reduced energy generation. To ensure sufficient energy supply for street lighting systems throughout the year, it is essential to design the PV system and energy storage systems with a larger rated size. This will enable the system to cope with fluctuations in energy production and effectively cover energy requirements, including during periods of lower solar radiation. For wind energy harvesting systems, both naturally occurring wind energy and wind energy generated by vehicle movement are considered as energy sources. Analysis of the average wind force each month indicates that it remains relatively stable and is not significantly influenced by seasonal variations. Consequently, the installation of an electric wind turbine with a lower power rating is sufficient for producing electrical energy for street lighting systems over the same distance throughout the year. In a hybrid system combining PV and wind energy harvesting systems, the wind system takes precedence as the primary energy source due to its superior performance, while the PV system serves to offset periods of inadequate wind power generation. Consequently, this approach reduces the required size of both the energy harvesting and storage systems.
Table 10 illustrates the optimization of combined PV and wind energy harvesting systems with lead–acid and lithium–ion battery energy storage. For the nano–grid street lighting systems, combining a PV harvesting system with a lead–acid battery energy storage system incurs high costs of 139,550 USD. This is primarily due to the fluctuation and mismatch between the electrical energy produced by the PV system and energy consumed by the street lighting systems, along with the efficiency limitations of lead–acid batteries. It necessitates a larger PV system and substantial lead-acid batteries for providing backup to the street lighting systems. Due to the larger PV system and substantial lead-acid batteries, a high energy production of 62,090 kWh per year is achieved. However, the lifespan of lead–acid batteries diminishes, leading to escalated replacement expenses, rendering them economically impractical. Although the utilization of lithium–ion batteries in PV systems provided a high initial investment cost of 87,350 USD, it obviates the need for frequent battery replacements and provides high energy density. Thus, the economic evaluation outcomes were feasible based on DPP of 19.7 years, IRR of 0.8%, and NPV of 10,950 USD. Wind systems employing both lead-acid and lithium–ion batteries exhibit enhanced economic viability higher than PVs. Due to low energy density of lead-acid batteries, the wind system with lead-acid batteries gives larger capacity than using lithium–ion batteries, which provides electrical energy production of 62,460 kWh per year and 48,050 kWh per year for the cases of lead-acid and lithium–ion batteries, respectively. For economic evaluation, the utilization of lithium–ion batteries yields superior outcomes due to their inherent high rate of depth of discharge and extended lifespan. Consequently, the requisite size of the wind and energy storage systems diminishes, reducing investment costs. The wind system with lithium–ion batteries has DPP of 13.7 years, IRR of 4.9% and NPV of 42,820 USD.
The hybrid system utilizing both lead–acid and lithium–ion batteries demonstrates economic viability. However, employing lead-acid batteries as energy storage systems for the nano–grid street lighting system leads to a larger size requirement for both energy harvesting and storage systems; the PV of 5.98 kW and the wind system of 10 kW are selected along with 113 kWh lead-acid batteries. Consequently, this results in high investment costs of 82,030 USD, leading to DPP of 15.8 years, IRR of 3.4%, and NPV of 16,280 USD. In the case of using lithium-ion batteries, the sizes for both energy harvesting and storage systems are decreased owing to high energy density of the lithium-ion batteries. For this reason, the use of hybrid energy harvesting systems in combination with PV and wind energy harvesting systems with lithium-ion battery energy storage systems provides the most suitable economic feasible choice for nano–grid street lighting systems, which is DPP of 13 years, IRR of 5.5%, and NPV of 45,820 USD.
This paper presents a study of the feasibility of developing a street lighting system using nano-grid technology using energy harvesting of PV, piezoelectric energy, and wind energy in terms of energy production and economic evaluation. Furthermore, the optimization of using PV, a wind system, a hybrid PV—wind system lead-acid batteries, and lithium-ion batteries was implemented.
By considering the power produced from the installed PV system, the installed PV system for the nano-grid street lighting system has an average annual PR ratio of 82.2%, which is an annual average value sufficient for the nano-grid street lighting system. For piezoelectric energy, piezoelectric sheet installation and position for fixing the piezoelectric sheet were optimized. The installation of the piezoelectric sheet in different mounting resulted in different natural frequency oscillations. It has been proved that the cantilever mounting type is suitable for piezoelectric power-generating street surfaces, and the mounting point on the outer edge of the piezoelectric sheet yields maximum stress and deformation value. Although a piezoelectric power-generating street surface can feasibly generate electrical energy, the generated energy is relatively low, which is insufficient for the street lighting system. In the case of wind energy, the simulation results indicate that the wind speed generated by vehicle movement has potential to produce the electrical energy for the nano-grid street lighting system.
The economic evaluation based on DPP, IRR, NPV, and LCOE indicators was employed. Although the PV and the wind system can produce sufficient electrical energy for street lighting systems, the wind system has high costs and is not economically feasibility. In addition, the costs of energy storage play a dominant role in determining economic feasibility. If the system requires high reliability, the costs of energy harvesting systems and storage increase, reducing economic feasibility, i.e. long DPP, low IRR, and less NPV. For piezoelectric energy, it produces insufficient electrical energy for street lighting systems and contributes to high investment costs, resulting in failed economic feasibility. Hence, it is not suitable as the energy harvesting source for the nano-grid street lighting system.
The optimization of PV and wind systems into a nano-grid street lighting system proves economic feasibility. The lifetime of an energy storage system is influenced by its efficiency and operational behavior. For the PV harvesting system, the generated electrical energy and the energy consumption of street lighting systems are mismatched, causing battery lifespan degradation. To address this issue, the battery sizing is increased, resulting in higher installation costs. Consequently, PV systems are less economically feasible. In contrast, wind power systems generate energy consistently throughout the day. For this reason, the size of the batteries is optimally decreased, enhancing the economic feasibility of the nano-grid street lighting systems. However, hybrid PV -wind energy harvesting systems offer the most economic feasible option for nano-grid street lighting systems. The wind system is prioritized as the primary energy source due to its superior performance, with the PV system used to supplement periods of insufficient wind power generation. As a result, this strategy reduces the necessary size of both the energy harvesting and storage systems.
In future work, the nano-grid street lighting systems utilizing various energy harvesting sources is designed to interact with the electrical grid; electrical energy can be exchanged between the nano-grid street lighting systems and the electrical grid. The functionality, power quality, economic feasibility, and environmental sustainability are investigated and discussed.
The datasets used and analysed during the current study available from the corresponding author on reasonable request.
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The work presented in this paper is part of a research project sponsored (No. 2564-02-01-005) by King Mongkut’s Institute of Technology Ladkrabang Research Fund. The authors would like to thank them for their financial support.
School of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand
Atthapol Ngaopitakkul & Suntiti Yoomak
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Ngaopitakkul, A., Yoomak, S. Investigating the feasibility of nano-grid infrastructure integration into street lighting systems based on energy production and economic evaluation. Sci Rep 14, 29833 (2024). https://doi.org/10.1038/s41598-024-80689-4
DOI: https://doi.org/10.1038/s41598-024-80689-4
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