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With the rise in the demand for electric vehicles, the need for a reliable charging infrastructure increases to accommodate the rapid public adoption of this type of transportation. Simultaneously, local electricity grids are being under pressure and require support from naturally abundant and inexpensive alternative energy sources such as wind and solar. This is why the world has recently witnessed the emergence of renewable energy-based charging stations that have received great acclaim.
- renewable energy
- wind
- solar
- electric vehicle
- charging station
1. Introduction
The remarkable increase in the use of electric vehicles (EVs) has resulted in a massive rise in demand for electric energy across the globe. The global electric vehicle market has grown significantly. The number of EVs on the road in 2010 was a few hundred; this number rose to approximately three million in 2017 and approximately six million in early 2019 [1]. Electric vehicles are exciting alternatives to conventional vehicles (CVs). With zero carbon emissions during operation, the EV has the ability to reduce total climate effect and pollutant emissions significantly. As fossil fuels are phased out to a greater degree, the need for biofuels would also be reduced. Electric motors have an efficiency of 80–95% [2], making them a more appealing choice than CVs, which have an efficiency of less than 20% [3]. EVs are also a critical element of modern transportation, because they incorporate a variety of new industrial technologies (e.g., an electric motor, a battery, and a charging facility). However, the adoption of electric vehicles is not going as well as predicted. The limited range and slow charging time of EVs are widely regarded as the most serious barriers to promotion [4][5]. Although electric vehicles have a high purchase price, they have low maintenance costs and use substantially less energy than conventional vehicles.
The remarkable increase in the use of electric vehicles (EVs) has resulted in a massive rise in demand for electric energy across the globe. The global electric vehicle market has grown significantly. The number of EVs on the road in 2010 was a few hundred; this number rose to approximately three million in 2017 and approximately six million in early 2019 [1]. Electric vehicles are exciting alternatives to conventional vehicles (CVs). With zero carbon emissions during operation, the EV has the ability to reduce total climate effect and pollutant emissions significantly. As fossil fuels are phased out to a greater degree, the need for biofuels would also be reduced. Electric motors have an efficiency of 80–95% [2], making them a more appealing choice than CVs, which have an efficiency of less than 20% [3]. EVs are also a critical element of modern transportation, because they incorporate a variety of new industrial technologies (e.g., an electric motor, a battery, and a charging facility). However, the adoption of electric vehicles is not going as well as predicted. The limited range and slow charging time of EVs are widely regarded as the most serious barriers to promotion [4,5]. Although electric vehicles have a high purchase price, they have low maintenance costs and use substantially less energy than conventional vehicles.
According to the rapid increase of EV demand and EV charging, many research centers, and energy supplying companies began thinking seriously about reducing the pressure on local electricity networks because of the increasing number of electric vehicle charging points. Renewable energy sources such as wind and solar are some of the most effective solutions to bridge this deficit faced by local electricity networks, potentially supporting the EV charging infrastructure [6].
After the announcement of the rapid development of the EV at the turn of the millennium, renewable energy-based charging infrastructure (RCI) research began with the effort of wind and solar charging infrastructure [7][8][9][10][11][12]. It envisioned a charging facility that could match EV demand with renewables and direct current (DC) to improve shortcomings of conventional charging infrastructure. The traditional charging stations affect the grid’s stability with issues such as harmonics, fluctuations, and voltage outages [8][9][12]. By contrast, the RCI has several advantages, such as high efficiency [13], low system cost [14], and simple arrangement [15][16]. Besides, it requires less power conversion levels than those in alternating current (AC)-based facilities [17][18]. The RCI can contribute significantly to reducing carbon emissions and expanding the energy domain’s penetration of renewable energy sources. Moreover, RCI has the potential to lower the cost of EV charging [19]. However, uncertainties of the renewable sources (e.g., seasonal variations in wind speed and sun irradiance and daily randomness in cloud coverage for solar panels) and load characteristics of EVs (e.g., battery capacity, number and types of EVs, stop time, charging start time, and the initial state of charge) are serious challenges in implementing the RCI [20].
After the announcement of the rapid development of the EV at the turn of the millennium, renewable energy-based charging infrastructure (RCI) research began with the effort of wind and solar charging infrastructure [7,8,9,10,11,12]. It envisioned a charging facility that could match EV demand with renewables and direct current (DC) to improve shortcomings of conventional charging infrastructure. The traditional charging stations affect the grid’s stability with issues such as harmonics, fluctuations, and voltage outages [8,9,12]. By contrast, the RCI has several advantages, such as high efficiency [13], low system cost [14], and simple arrangement [15,16]. Besides, it requires less power conversion levels than those in alternating current (AC)-based facilities [17,18]. The RCI can contribute significantly to reducing carbon emissions and expanding the energy domain’s penetration of renewable energy sources. Moreover, RCI has the potential to lower the cost of EV charging [19]. However, uncertainties of the renewable sources (e.g., seasonal variations in wind speed and sun irradiance and daily randomness in cloud coverage for solar panels) and load characteristics of EVs (e.g., battery capacity, number and types of EVs, stop time, charging start time, and the initial state of charge) are serious challenges in implementing the RCI [20].
Currently, there is an ongoing considerable research work on the aforementioned topics. At the same time, other researchers are working on various aspects of implementation and operation of RCI, such as optimal planning, controlling and sizing, pricing approaches, and examination of the key factors influencing the linking of EV load directly with the RCI. For instance, few studies reviewed EV charging infrastructure research; however, they considered general technical aspects and did not concentrate on renewable energy sources (e.g., [1][21]). Another study reviewed the RCI studies but with the focus on the consumer preferences and interactions with EVs [22]. To our knowledge, no study has reviewed RCI studies extensively by discussing all related research areas.
Currently, there is an ongoing considerable research work on the aforementioned topics. At the same time, other researchers are working on various aspects of implementation and operation of RCI, such as optimal planning, controlling and sizing, pricing approaches, and examination of the key factors influencing the linking of EV load directly with the RCI. For instance, few studies reviewed EV charging infrastructure research; however, they considered general technical aspects and did not concentrate on renewable energy sources (e.g., [1,21]). Another study reviewed the RCI studies but with the focus on the consumer preferences and interactions with EVs [22]. To our knowledge, no study has reviewed RCI studies extensively by discussing all related research areas.
2. Technological Infrastructure
In many countries of the world, electric vehicles are becoming progressively more popular. However, the absence of charging stations limits the widespread acceptance of EVs by users worldwide. As EV usage grows, EV charging stations are installed in more public spaces [23][24]. By contrast, if the EVs are charged through an existing fossil-fuel-powered system, they will negatively affect the distribution system and the environment [25]. With solar energy from photovoltaic (PV) panels and wind sources having great potential to produce electricity, charging would be an immense solution. It would also represent a sustainable advancement towards a clean environment [23]. Depending on the sources of energy available (e.g., solar radiation and wind speed), the electricity output of the charging facility can be either inferior (less than the needed power) or very high (over the power consumption). Most of the literature indicated that the installation of PV solar systems and wind energy conversion systems with the power grid is advanced and technically viable [26].
In many countries of the world, electric vehicles are becoming progressively more popular. However, the absence of charging stations limits the widespread acceptance of EVs by users worldwide. As EV usage grows, EV charging stations are installed in more public spaces [23,24]. By contrast, if the EVs are charged through an existing fossil-fuel-powered system, they will negatively affect the distribution system and the environment [25]. With solar energy from photovoltaic (PV) panels and wind sources having great potential to produce electricity, charging would be an immense solution. It would also represent a sustainable advancement towards a clean environment [23]. Depending on the sources of energy available (e.g., solar radiation and wind speed), the electricity output of the charging facility can be either inferior (less than the needed power) or very high (over the power consumption). Most of the literature indicated that the installation of PV solar systems and wind energy conversion systems with the power grid is advanced and technically viable [26].
However, the promising approach for balancing the generation of electricity from renewable energy sources can be achieved using configurable dispatch loads or energy storage systems, as it can provide electricity in low power generation [27]. The energy storage system’s utilization to stabilize the power grid is no longer a new technology. Other energy sources, such as concentrated solar energy, flywheel, dedicated battery, and hydro-pumped storage systems, are some of the technologies that have been utilized. Smart meters, wireless sensors, advanced communication, and power converters are some of emerging technologies in the industry [28][29][30][31][32].
However, the promising approach for balancing the generation of electricity from renewable energy sources can be achieved using configurable dispatch loads or energy storage systems, as it can provide electricity in low power generation [27]. The energy storage system’s utilization to stabilize the power grid is no longer a new technology. Other energy sources, such as concentrated solar energy, flywheel, dedicated battery, and hydro-pumped storage systems, are some of the technologies that have been utilized. Smart meters, wireless sensors, advanced communication, and power converters are some of emerging technologies in the industry [28,29,30,31,32].
2.1. Energy Storage and Fast Charging Systems
It was reported in [33] that unregulated charging would contribute to the overloading allocation of transformers and feeders and, eventually, the power supply. Hence, most of the literature has suggested stationary energy storage and fast charging systems to overcome this challenging problem [33]. Energy storage limits the charging infrastructure and runs costs by serving electric vehicles during the system’s uttermost load intervals [34][35]. Energy storage can also improve electric vehicles’ stability by supplying necessary and sufficient energy to reach charging stations in the case of emergencies. Many studies were carried out on the benefits of stationary energy storage with fast charging systems [34][36][37]. However, to obtain such benefits, an optimum size of the energy storage system is required, taking into account the energy tariffs, expected degree of penetration, and load profiles of EVs [33].
It was reported in [33] that unregulated charging would contribute to the overloading allocation of transformers and feeders and, eventually, the power supply. Hence, most of the literature has suggested stationary energy storage and fast charging systems to overcome this challenging problem [33]. Energy storage limits the charging infrastructure and runs costs by serving electric vehicles during the system’s uttermost load intervals [34,35]. Energy storage can also improve electric vehicles’ stability by supplying necessary and sufficient energy to reach charging stations in the case of emergencies. Many studies were carried out on the benefits of stationary energy storage with fast charging systems [34,36,37]. However, to obtain such benefits, an optimum size of the energy storage system is required, taking into account the energy tariffs, expected degree of penetration, and load profiles of EVs [33].2.2. Storage Battery and Controller
Solar-powered batteries can fulfill unreliable grid electricity demands, which are strong charge, discharge, and intermittent full-charging periods. A range of battery types fulfills these specific criteria. The major battery storage subgroups reviewed for solar energy include a lead-acid battery, lithium-ion battery, and flow battery [38][39].
Solar-powered batteries can fulfill unreliable grid electricity demands, which are strong charge, discharge, and intermittent full-charging periods. A range of battery types fulfills these specific criteria. The major battery storage subgroups reviewed for solar energy include a lead-acid battery, lithium-ion battery, and flow battery [38,39]. To save the additional energy produced by photovoltaics, a central controller is required to redirect the generated power to the battery, as illustrated in . Many scholars have investigated the sequence of controllers that are used in photovoltaics. They highlighted that it is essential to improve the productivity of solar energy generation through a maximum power point tracker (MPPT) and pulse width modulated (PWM) technologies [40].
Figure 1.
2.3. Converters
When it comes to a solar converter, the PV arrays are connected to a DC/DC converter that allows for full power point tracking control. The AC/DC converter is in charge of converting DC/AC power in a bidirectional fashion. The power used from the grid is primarily AC. It must be converted into DC to charge the electric vehicles. The conversion of power occurs before the charging begins or relays the power from the grid to electricity networks.
Therefore, the converters have unique roles in photovoltaic systems based on balanced energy conversion [41]. Different forms and requirements have been examined in detail, for example, string inverters, in which panels are installed in combination with a micro-inverter, and central inverters, where panels are installed with separate inverters and micro-inverter power optimizers that require further monitoring. These power optimizers are used to track photovoltaic panel arrays’ overall performance to constantly alter and change the attached load that keeps the system at maximum operational capability [42].
3. Appropriate Renewable Energy Sources
Wind and solar energies are considered to be reliable substitution sources of conventional energy sources because of their economic and environmental benefits [11][43][44][45]. However, one of the disadvantages of these renewable sources is their inconsistency in offering energy. They do not generate power all the time, and they are intermittent. However, a few suggestions for solar-based charging facilities are discussed in [35][36][46]. The researchers proposed charging infrastructure dedicated to the range of low to medium EVs. In [47], the researchers suggested charging EVs from solar energy using the DC link voltage sensing. The aim is to lower the burden on the distribution transformer. However, solar energy limitation to charge wide-range EVs will lower the chances of implementing more solar-based charging stations.
Wind and solar energies are considered to be reliable substitution sources of conventional energy sources because of their economic and environmental benefits [11,43,44,45]. However, one of the disadvantages of these renewable sources is their inconsistency in offering energy. They do not generate power all the time, and they are intermittent. However, a few suggestions for solar-based charging facilities are discussed in [35,36,46]. The researchers proposed charging infrastructure dedicated to the range of low to medium EVs. In [47], the researchers suggested charging EVs from solar energy using the DC link voltage sensing. The aim is to lower the burden on the distribution transformer. However, solar energy limitation to charge wide-range EVs will lower the chances of implementing more solar-based charging stations.
Research work on the control and optimization of wind turbines (WT) has demonstrated that wind energy is an appropriate choice for EV charging infrastructure. In [44], the researchers discussed the advantages of implementing charging stations based on large-scale turbines and found that EVs could be a critical factor for enabling the high penetration of wind energy. Considering the challenges of traditional scheduling and dispatching mechanisms, researchers in [48] developed a model of utilizing the flexibility of charging EVs to optimally compensate for wind energy fluctuations. They found that shifting EVs’ charging to times with high wind availability achieved cost savings. In another study [49], the possibility of using wind energy as a direct source for power EV charging stations were investigated. The researchers implemented an interval-based method corresponding to the time slot taken for EV charging for wind energy conversion and evaluated using various constraints and parameters, including the averaging time interval for wind speed, different turbine manufacturers, and regular high-resolution wind speed datasets. The analysis indicated that the use of direct wind to EV provides enough constant power for large-scale charging stations.
The researchers in [50] developed optimal charging infrastructure using wind turbines for different charging modes concerning the optimal charging power. The infrastructure is connected to the grid and has an energy storage system. The rated power was optimized on 52, 84, and 116 kW for slow, intermediate, and quick-speed charging, respectively. On the other hand, the study [50] developed a power management model to enhance wind energy reliability.
However, we can conclude that solar and wind energies are appropriate sources for EV charging infrastructure. A charging facility can be either hybrid (solar and wind) or non-hybrid with the use of suitable storage capacity to support the charging process during the fluctuation of sources. The power generator’s sizing depends mainly on the type of charging (fast, medium, or slow). Nonetheless, the use of battery storage has a negative impact on the environment. The study results of [51] indicate that global electronic mobility demand will boost the production of batteries by 2030 to around 1725 GWh, and nickel will be the dominant raw material in the lithium-ion battery. Currently, batteries’ demand represents 4% of the annual global nickel production, and the gradual scenario is that nickel demand would rise to 34% of present mining production in 2030. Even if nickel is an important component for plants, like every metal and chemical, the quality of the environment for flora and fauna may be negatively affected by its excessive amounts. As a result, nickel is strictly controlled and subjected to rigorous evaluations under a variety of legislative frameworks [52].
4. Control and Energy Management
Connecting the renewable energy-based stations to the grid leads to several challenges. Besides the grid integration and fluctuation issues, the charging operation presents a critical shortage due to the inharmonious charging process concerning power quality and demand [53], specifically for fast-charging stations [54]. Hence, it is crucial to control the charging behavior to reduce these issues’ impacts. For example, an analysis of electricity production conducted by [55] to calculate relevant performance indicators of the electricity supplied by the grid indicated significant variability of the CO
Connecting the renewable energy-based stations to the grid leads to several challenges. Besides the grid integration and fluctuation issues, the charging operation presents a critical shortage due to the inharmonious charging process concerning power quality and demand [86], specifically for fast-charging stations [87]. Hence, it is crucial to control the charging behavior to reduce these issues’ impacts. For example, an analysis of electricity production conducted by [88] to calculate relevant performance indicators of the electricity supplied by the grid indicated significant variability of the CO
2
emissions. It highlights the need for accurate knowledge of operational parameters to support future
smart grid management. Therefore, the management of the EV charging behavior would moderate the fluctuation of renewable energy, optimize the grid’s peak demand, and make efficient load characteristics of the grid [56]. The literature comprises several studies on impacts of charging loads on the grid. For example, Green et al. [57] studied impacts of EVs on the distribution network, and Amini et al. [58] discussed effects of large-scale charging infrastructure on the system’s total loss. In [59], a probabilistic model is used to investigate incremental impacts of EV charging on the distribution network.
management. Therefore, the management of the EV charging behavior would moderate the fluctuation of renewable energy, optimize the grid’s peak demand, and make efficient load characteristics of the grid [89]. The literature comprises several studies on impacts of charging loads on the grid. For example, Green et al. [90] studied impacts of EVs on the distribution network, and Amini et al. [91] discussed effects of large-scale charging infrastructure on the system’s total loss. In [92], a probabilistic model is used to investigate incremental impacts of EV charging on the distribution network.
Management of the charging process in a controlled mode increases the capacity of charging a large number of EVs. Using the maximum renewable energy generated and smart coordination with the grid can decrease the power load of the charging equipment on the grid and ensure cleaner energy. By contrast, integrating the energy storage with the charging station enables disengaging EV load from the grid, moving the charging time to off-peak, and controlling renewable energy’s uncertainty and fluctuation [54].
Management of the charging process in a controlled mode increases the capacity of charging a large number of EVs. Using the maximum renewable energy generated and smart coordination with the grid can decrease the power load of the charging equipment on the grid and ensure cleaner energy. By contrast, integrating the energy storage with the charging station enables disengaging EV load from the grid, moving the charging time to off-peak, and controlling renewable energy’s uncertainty and fluctuation [87].
Moreover, most EVs’ parking time is up to 95% per day in the charging area; thus, the V2G concept was raised [60]. EVs can be charged at low pricing hours and discharge at high pricing hours, making EVs a distributed energy facility. This mechanism offers EV drivers the chance to lower the charging cost through the price difference [61]. The excellent interaction among the grid and large-scale or high-distance range EVs leads to the smart charging and discharging strategy [62].
Moreover, most EVs’ parking time is up to 95% per day in the charging area; thus, the V2G concept was raised [93]. EVs can be charged at low pricing hours and discharge at high pricing hours, making EVs a distributed energy facility. This mechanism offers EV drivers the chance to lower the charging cost through the price difference [94]. The excellent interaction among the grid and large-scale or high-distance range EVs leads to the smart charging and discharging strategy [95].
The literature has many studies concerning energy management for EVs associated with renewable energy sources. For example, Wi et al. [63] proposed a charging control algorithm to schedule EV charging associated with PV in smart buildings. The proposed strategy is based on predicted PV energy generation and baseload power demand. However, uncertainties of EV charging demand were not considered. Similarly, another scheduling algorithm was proposed by [64] for smart buildings that can efficiently reduce CO
The literature has many studies concerning energy management for EVs associated with renewable energy sources. For example, Wi et al. [96] proposed a charging control algorithm to schedule EV charging associated with PV in smart buildings. The proposed strategy is based on predicted PV energy generation and baseload power demand. However, uncertainties of EV charging demand were not considered. Similarly, another scheduling algorithm was proposed by [97] for smart buildings that can efficiently reduce CO
2
emissions. However, the study did not consider the flexibility of EV charging demand.
Several studies consider appropriate strategies for controlling EV charging. For instance, Razo et al. [65] proposed a vehicle-originating-signals strategy for controlling EV charging by reducing communication overhead with minor effects on performance. Liao et al. [66] proposed a scheme for EV charging control that considers the energy storage system and renewable energy power. In [67], an optimal scheduling method was introduced for charging infrastructure associated with a microgrid. Kumar et al. [68] evaluated various combinations of different priority control criteria on EVs’ ability to charge and charging fairness.
Several studies consider appropriate strategies for controlling EV charging. For instance, Razo et al. [98] proposed a vehicle-originating-signals strategy for controlling EV charging by reducing communication overhead with minor effects on performance. Liao et al. [99] proposed a scheme for EV charging control that considers the energy storage system and renewable energy power. In [100], an optimal scheduling method was introduced for charging infrastructure associated with a microgrid. Kumar et al. [101] evaluated various combinations of different priority control criteria on EVs’ ability to charge and charging fairness.
Table 1 summarizes the other recent studies concerning energy management of renewable energy-based charging infrastructure. It is noticeable that the dominant criterion is focused mainly on the energy management associated with a PV system that is connected to the grid; consequently, the wind energy and the energy storage system are not sufficiently considered.
3 summarizes the other recent studies concerning energy management of renewable energy-based charging infrastructure. It is noticeable that the dominant criterion is focused mainly on the energy management associated with a PV system that is connected to the grid; consequently, the wind energy and the energy storage system are not sufficiently considered.
Table 13.
Energy management studies related to renewable energy-based charging stations.
|
Study |
Configuration |
Aim |
Method |
Remarks |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Standalone hybrid renewable systems | |||||||||||
Minimizing the use of battery storage and maximizing the use of renewable sources with zero charging rejection | |||||||||||
The simulation was developed to find the minimum of a constrained non-linear multi-variable function | |||||||||||
Different scenarios are introduced and analyzed | |||||||||||
Standalone hybrid renewable systems | |||||||||||
Optimal scheduling for power supply | |||||||||||
The energy resources and realistic EV charging data were simulated | |||||||||||
The power scheduling was optimized | |||||||||||
PV–WT-Grid | |||||||||||
Maximizing use of renewable sources | |||||||||||
Experimenting with the maximum power point tracking technique | |||||||||||
The infrastructure is capable of providing sufficient energy in response to the load demand | |||||||||||
PV–BESS–Grid | |||||||||||
Support of high charging rates and penetration of the energy system into the grid | |||||||||||
Simulation and prototype experimental | |||||||||||
They demonstrated the effectiveness and benefits of a hybrid grid-connected energy system | |||||||||||
PV–Grid | |||||||||||
Discussing critical aspects of renewable resources-based fast charging | |||||||||||
Review | |||||||||||
Recommendations and useful information related to renewable energy-based DC fast charging | |||||||||||
WT–Diesel Generator–BESS | |||||||||||
Minimizing use of the dump load normally associated with diesel operation | |||||||||||
Simulation | |||||||||||
Optimizes charging/discharging cycles of the storage system and system operation cost | |||||||||||
PV–Grid | |||||||||||
Improving self-consumption of PV energy and lower its impacts on the grid | |||||||||||
Simulation-based on real-time data acquisition of the demand and generation without forecasting | |||||||||||
Proves the proposed strategy’s efficiency that can be used in embedded systems for real-time allocation of the EV charging rate | |||||||||||
|
[19] | |||||||||||
PV–Grid | |||||||||||
Comparing an optimal charge-scheduling strategy with an uncontrolled charging case | |||||||||||
An hourly simulation was used by considering statistical data for driving distances, different types of vehicles, parking time, installation cost, tax rebates and incentives | |||||||||||
Confirms feasibility of PV-based infrastructure, benefits to EVs’ drivers and the garage owner and the need for an optimal charging controller | |||||||||||
PV–Grid | |||||||||||
Determining optimal schedules of EV according to the predicted PV power and demand | |||||||||||
Simulation and prototype | |||||||||||
Demonstrates the effectiveness of the proposed smart EV charging method | |||||||||||
PV–Grid | |||||||||||
Minimizing operation costs | |||||||||||
Simulation and economic analysis | |||||||||||
Confirms applicability of the strategy to DC distribution buildings, for energy cost reduction | |||||||||||
PV–Grid | |||||||||||
Providing a day-ahead upper limit profile of the charging infrastructure’s power consumption | |||||||||||
Simulations and sensitivity analysis | |||||||||||
Demonstrates feasibility and relevance of the proposed strategy | |||||||||||
PV–WT–Fuel Cells–Grid | |||||||||||
Minimizing the total cost | |||||||||||
Simulations based on the genetic algorithm method | |||||||||||
Presents the optimal number of parking lots under optimal scheduling of PHEVs | |||||||||||
PV–WT– Thermal Storage –BESS–Grid | |||||||||||
Minimizing operating costs and CO | 2 emissions | ||||||||||
Case study | |||||||||||
Demonstrates reduction in costs and CO | 2 | emissions | |||||||||
PV–WT– Fuel Cells –Grid | |||||||||||
Integrating scheduling and management of intermittent renewable generation and EVs in a microgrid | |||||||||||
Case study | |||||||||||
Satisfies technical and financial objectives of infrastructure and economic and security issues of the microgrid | |||||||||||
|
[81] |
[114] |
PV–BESS–Grid | Reducing operation cost | Simulation based on two algorithms and a case study |
The case study confirms effectiveness of the proposed algorithms in reducing the cost |
