P2P Energy Trading of EVs Using Blockchain Technology in Centralized and Decentralized Networks: A Review

: Peer-to-peer (P2P) energy trading has attracted a lot of attention and the number of electric vehicles (EVs) has increased in the past couple of years. Toward sustainable mobility, EVs meet the standard development goals (SDGs) for attaining a sustainable future in the transport sector. This development and increasing number of EVs creates an opportunity for prosumers to trade electricity. Considering this opportunity, this review article aims to provide an in-depth analysis of P2P energy trading of EVs using blockchain in centralized and decentralized networks, which enables prosumers to exchange energy directly with one another. The paper is aimed to provide the reader with a state-of-the-art review on the P2P energy trading for EVs, considering different blockchain algorithms that are practically implemented or still in the research phase. Moreover, the paper presents blockchain applications, current trends, and future challenges of EVs’ energy trading. P2P energy trading for EVs using blockchain algorithms can be successfully implemented considering real-time scenarios and economically beneﬁts smart sustainable societies.


Introduction
The proliferation of P2P energy trading has changed the whole concept of how energy was distributed a decade ago.This proliferation has increased the number of prosumers in electric distribution networks [1,2].Additionally, today's energy trading system is undergoing a paradigm shift from centralized to decentralized networks due to its reliability, security, and transparency [3].The existing energy networks are limited for P2P trading and still comprise some technical barriers.Generally, an electric network has a graded structure that permits electricity to flow in a single direction from the power grid to the primary distribution.With that, electric vehicles are involved as a primary addition to the energy network [4].EVs are an emerging technology, and the increasing number of EVs directly plays a pivotal role in P2P energy trading.P2P energy trading involves the direct exchange of electricity between energy producers and consumers, facilitated by digital platforms.EVs are equipped with energy storage systems that may enable excess energy to be injected back to the grid or shared directly with other EVs [5].As such, EVs serve as mobile energy storage units that can help balance the supply and demand in P2P energy trading networks.The energy storage system within the EVs store surplus energy during peak production periods while discharging it in P2P trade or when needed to enhance the grid's stability and resilience [6].This dynamic interaction provides a more efficient and decentralized energy trading ecosystem, which empowers EV owners to actively participate in sustainable energy management [7].Hence, EVs are prominent players in P2P energy trading by serving prosumers, leveraging blockchain technology for transparent, secure, and decentralized transactions [8].Blockchain is a decentralized digital ledger, which ensures the integrity and traceability of energy trade among EVs with no intermediaries [9,10].Some projects and real-time studies on the use of blockchain for P2P EV energy trading have been presented in Energies 2024, 17, 2135 2 of 17 the literature.In Chongqing, China, a blockchain-based vehicle-to-vehicle (V2V) electricity trading framework was proposed to address a range of anxieties in EVs, establish a new business model, and implement a coalition joining strategy by using consortium blockchain technology to reduce the cost of EV charging and increase the revenue for EV discharging, compared to grid trading [11].Another study was conducted in India to investigate India's energy sector's transition toward sustainability.The study focused on blockchain-enabled P2P energy trading to promote open-source electricity and decentralized systems [12].A real-time study conducted on a blockchain-driven energy trading framework, to facilitate direct transactions between EV prosumers and critical load consumers, was presented in [13].The study aimed to provide trusted transactions, privacy protection, and efficient optimization through comparison with the traditional wholesale markets in Paisley, UK.A project supported by the Ministry of Education and National Research Foundation of Korea was implemented on blockchain-based P2P energy trading for EV charging payment systems to address the issues of overcharging, smart contracts, and electronic wallets.With that, a brief analysis on resource utilization and transaction performance, offering potential benefits, was conducted for smart-city policymakers [14].Australia has recently initiated a startup project named "Power Ledger", aiming to establish an energy trading platform that ensures transparency, security, and interoperability using blockchain technology.This platform enables the real-time transfer of energy tokens to deal with energy buyers and sellers [15].
In the literature, there are two main methods for P2P trading with EVs: centralized and decentralized networks [4,5,16].Centralized P2P trading networks operate with a central entity, typically a utility or a third-party intermediary, managing and overseeing the exchange of electricity.Transactions in this model are regulated and verified by a central authority, ensuring a controlled and regulated business environment [4].Centralized networks often adhere to established regulatory frameworks, providing participants security and compliance.They can optimize resource allocation and manage grid stability effectively to ensure the system's reliability [17].Centralized systems enhance security measures and accountability through reducing the risk of fraudulent activities while ensuring a transparent transaction process [18].However, the control system creates a vulnerability, as any failure in the central system could disrupt the entire network.Moreover, participants may have limited control in managing their energy transactions, which rely heavily on the decisions of the central authority [19].This may lead to a concentration of power in the hands of a few entities, potentially creating monopolistic situations [20].Conversely, decentralized P2P trading networks operate based on a distributed ledger technology, such as blockchain, where transactions are validated by a network of participants, without the need for a central authority.This model promotes P2P energy trading, and reduces dependency on intermediate authorities [4,16,20].With this model, participants gain greater control over their energy transactions, with the ability to make direct agreements without central oversight [21].This system is resilient to failures, as the absence of a central point of control reduces the impact of system-wide disruptions and offers enhanced privacy and security because the participants will have more control over their data [22].However, decentralized systems face scalability issues, which limits their ability to handle a large number of transactions simultaneously [23].It is still evolving; therefore, implementing and maintaining decentralized networks still face technical complexities, and require a solid framework using blockchain and associated technologies [24].
In the literature, researchers have explored the integration of both centralized and decentralized distribution networks for P2P energy trading of EVs using various approaches, including game theory, double auction, and blockchain, to facilitate efficient and secured transactions [5,25,26].Many researchers have provided a review of other technologies, such as game theory [25,27,28] and double auction [26,29], for P2P energy trading of EVs [30].However, less attention has been paid to reviewing the blockchain technology for both centralized and decentralized networks for EV P2P energy trading.Therefore, considering this gap, this paper aims to review blockchain technology for EV trading on both centralized and decentralized networks.
The main contributions of this paper are as follows: • The paper provides an overview of P2P energy trading of EVs using blockchain technology.
• It comprehensively discusses P2P energy trading of EVs using blockchain in the contexts of both centralized and decentralized networks.

•
It emphasizes the key concerns, current trends, and future directions in the field of P2P energy trading of EVs using blockchain.

Methodology
The methodology employed to conduct the literature review on P2P energy trading for both centralized and decentralized networks involved a systematic and comprehensive approach.To identify relevant papers, a thorough search of academic databases was conducted, focusing on relevant published papers in the literature from 2010 to 2024.The search strings included terms such as "P2P energy trading", "electric vehicles", and "blockchain technology."To enhance reliability, the three co-authors performed the searches independently multiple times, cross-referencing and compiling their findings.Initially identifying over 160 papers, the team then evaluated each paper's relevance based on abstracts, introductions, and conclusions.Papers that did not specifically address P2P energy trading for EVs using blockchain for both centralized and decentralized networks were excluded from further consideration.The iterative process also involved refining keywords based on highly cited/classical articles and adding new terms as necessary during the search process.Multiple databases were explored to diversify the data sources, and keyword abstraction was carried out by the co-authors in the fields of blockchain technology, energy trading, and electric vehicles.This rigorous methodology ensured the inclusion of over 95 relevant papers for detailed analysis in this review.Out of the 95 papers reviewed, 29 were focused on centralized networks, 41 on decentralized networks, and the remaining papers were generally related to P2P energy trading of EVS and blockchain.Table 1 presents the answers to some questions that may be raised about this review paper.To encourage EV owners to participate in energy trading, especially during the peak demand hours, to provide economic benefit to power grids.

Why is a decentralized mechanism preferred over a centralized network?
A decentralized mechanism is preferred for its energy trading, data security, network reliability, and trustworthy platform among peer-to-peer customers, as well as the elimination of sharing their personal information with a third party.
3. Why is blockchain technology used as a trading mechanism for energy?
For secure information and energy trading, the detailed reason for using blockchain technology is discussed in the following sections.
4. Has the previous work related to this topic not been sufficient?
Most of the previous work was lacking because of aspects such as P2P energy trading of EVs, blockchain technology, centralized networks, and decentralized networks.

Overview of Energy Trading of EVs Using Blockchain Technology
This section provides an overview of P2P energy trading of EVs specifically, reviewing the structure and implications of this innovative approach.Additionally, this section presents a review on the blockchain technology, decentralized ledger system, smart contracts, and automated self-executing contracts, which facilitate secure transactions.

Peer-to-Peer Energy Trading
In recent years, the rapid expansion of distributed energy resources and EVs has altered the paradigm of energy production and consumption.This transformation has led to the emergence of prosumers who can actively participate in electricity generation [31].When prosumers have excess electrical energy, they will have a spectrum of choices, such as storing this surplus energy for later use, injecting it into the electricity grid, or even offering it for sale to other energy consumers [32].This direct exchange of energy between prosumers and consumers is generally referred to as P2P energy trading.Figure 1 illustrates the P2P energy trading of EVs.The figure highlights four key players: electric companies, prosumers, consumers, and energy-sharing coordinators.Prosumers not only generate electricity but also consume it, while consumers solely consume electricity [33].P2P energy trading of EVs using a blockchain technology framework is a driver for both prosumers and consumers.When prosumers have a high storage capacity, they can participate in energy trade and sell it to consumers.This business model facilitates both an economic benefit for prosumers and fulfillment of energy demand for consumers.Blockchain technology, as will be explained in Section 3.2, pertains to transactions in the dynamic environment to facilitate the exchange of both energy and financial resources.EVs have the flexibility to sell electricity to either consumers or fellow prosumers, with the entire process seamlessly orchestrated through a blockchain in centralized and decentralized networks, which serves as an energy exchange coordinator.This coordination in both networks is further emphasized by the unidirectional trading arrows, which signify that consumers can exclusively receive energy from the energy-sharing coordinator.The bidirectional trading arrows in the figure describe the prosumers' ability to both procure and supply electricity to the energy-sharing coordinator [34].
When prosumers have excess electrical energy, they will have a spectrum of choices, such as storing this surplus energy for later use, injecting it into the electricity grid, or even offering it for sale to other energy consumers [32].This direct exchange of energy between prosumers and consumers is generally referred to as P2P energy trading.Figure 1 illustrates the P2P energy trading of EVs.The figure highlights four key players: electric companies, prosumers, consumers, and energy-sharing coordinators.Prosumers not only generate electricity but also consume it, while consumers solely consume electricity [33].P2P energy trading of EVs using a blockchain technology framework is a driver for both prosumers and consumers.When prosumers have a high storage capacity, they can participate in energy trade and sell it to consumers.This business model facilitates both an economic benefit for prosumers and fulfillment of energy demand for consumers.Blockchain technology, as will be explained in Section 3.2, pertains to transactions in the dynamic environment to facilitate the exchange of both energy and financial resources.EVs have the flexibility to sell electricity to either consumers or fellow prosumers, with the entire process seamlessly orchestrated through a blockchain in centralized and decentralized networks, which serves as an energy exchange coordinator.This coordination in both networks is further emphasized by the unidirectional trading arrows, which signify that consumers can exclusively receive energy from the energy-sharing coordinator.The bidirectional trading arrows in the figure describe the prosumers' ability to both procure and supply electricity to the energy-sharing coordinator [34].
Recent advancements in the literature on P2P energy trading of EVs via blockchain have emphasized several controversies, such as scalability propaganda and security issues, as well as some viewpoints on regulatory compliance and market access [9].This paper provides an in-depth analysis of these concerns within both centralized and decentralized network frameworks.To tackle any further controversies and viewpoints, research scholars are working on the technical aspects of security, big data, simultaneous transactions, energy flow with an energy loss record, etc., and implementing this technology as a prototype on a small scale for reliable and sustainable P2P energy trading using blockchain technology [11,12].Recent advancements in the literature on P2P energy trading of EVs via blockchain have emphasized several controversies, such as scalability propaganda and security issues, as well as some viewpoints on regulatory compliance and market access [9].This paper provides an in-depth analysis of these concerns within both centralized and decentralized network frameworks.To tackle any further controversies and viewpoints, research scholars are working on the technical aspects of security, big data, simultaneous transactions, energy flow with an energy loss record, etc., and implementing this technology as a Energies 2024, 17, 2135 5 of 17 prototype on a small scale for reliable and sustainable P2P energy trading using blockchain technology [11,12].

Blockchain Technology
Blockchain technology is a distributed ledger technology (DLT) that records P2P energy trading information across a network in an immutable and secure manner.It consists of a chain of blocks that contain transaction information, and these blocks are linked with digital currencies [3].The DLT makes sure there is no external party participation in the transaction process, and this makes blockchain technology more secure and reliable for P2P energy trading.For example, if electricity units are purchased from the EV using a bank card, the transaction will only be approved by the authority if that amount is available in that account.Therefore, the intercessor indicated here is a financial institution or a corporation that links the consumer and supplier.On the other hand, P2P energy trading DLT features blockchain technology with no external involvement, and it provides smart contracts, cryptocurrency, and digital methods of payment [35].Figure 2 shows how blockchain technology is used for P2P energy trading in which a financial institution is involved in the conversion of cryptocurrency into real currency.Figure 3 shows P2P energy trading using blockchain technology without the involvement of a financial institution.While blockchain technology offers autonomy and security in P2P energy trading, its reliance on cryptocurrencies proposes regulatory challenges due to massive adoption.As adoption increases, the need for sophisticated infrastructure and consensus mechanisms may pose scalability issues, particularly in decentralized networks.Moreover, ensuring compatibility and interoperability among a high number of participants remains a significant difficulty for seamless integration into existing energy systems [5,15].ergy trading information across a network in an immutable and secure manner.It consists of a chain of blocks that contain transaction information, and these blocks are linked with digital currencies [3].The DLT makes sure there is no external party participation in the transaction process, and this makes blockchain technology more secure and reliable for P2P energy trading.For example, if electricity units are purchased from the EV using a bank card, the transaction will only be approved by the authority if that amount is available in that account.Therefore, the intercessor indicated here is a financial institution or a corporation that links the consumer and supplier.On the other hand, P2P energy trading DLT features blockchain technology with no external involvement, and it provides smart contracts, cryptocurrency, and digital methods of payment [35].Figure 2 shows how blockchain technology is used for P2P energy trading in which a financial institution is involved in the conversion of cryptocurrency into real currency.Figure 3 shows P2P energy trading using blockchain technology without the involvement of a financial institution.While blockchain technology offers autonomy and security in P2P energy trading, its reliance on cryptocurrencies proposes regulatory challenges due to massive adoption.As adoption increases, the need for sophisticated infrastructure and consensus mechanisms may pose scalability issues, particularly in decentralized networks.Moreover, ensuring compatibility and interoperability among a high number of participants remains a significant difficulty for seamless integration into existing energy systems [5,15].
Blockchain technology offers several benefits, specifically in terms of transparency, security, and efficiency.Decentralized operations using blockchain provide some benefits, including time savings and cost reduction, by eliminating intermediaries and streamlining verification processes, online transactions, costs related to paperwork, manual processing, and third-party fees [19].It has enhanced security features to reduce fraud risks and cyberattacks to save businesses from costly security breaches.Furthermore, blockchain technology has the potential to significantly increase the trading frequency by enabling real-time settlement and reducing transactional problems.It enhances market activity and liquidity, as transactions are carried out more quickly and securely [23].Using blockchain trade can save 50-60% of the time, save costs by 30-80%, and increase the trading frequency by 40-90% [36,37], depending on the number of prosumers and consumers participating in this behavior.Blockchain technology offers several benefits, specifically in terms of transparency, security, and efficiency.Decentralized operations using blockchain provide some benefits, including time savings and cost reduction, by eliminating intermediaries and streamlining verification processes, online transactions, costs related to paperwork, manual processing, and third-party fees [19].It has enhanced security features to reduce fraud risks and cyberattacks to save businesses from costly security breaches.Furthermore, blockchain technology has the potential to significantly increase the trading frequency by enabling real-time settlement and reducing transactional problems.It enhances market activity and liquidity, as transactions are carried out more quickly and securely [23].Using blockchain trade can save 50-60% of the time, save costs by 30-80%, and increase the trading frequency by 40-90% [36,37], depending on the number of prosumers and consumers participating in this behavior.

Smart Contract
A smart contract is a self-executing code that resides on the blockchain and operates autonomously without the need for any intermediary or third party.In P2P energy trading, this introduces trust among peers, as the execution of the contract is transparent and cannot be tampered with [38].Smart contracts can be modified to meet specific requirements, allowing for the insertion of code, rules, objects, and data models.Once deployed on the blockchain, a smart contract becomes an immutable part of the network [39].In real-time scenarios, Ethereum's basic smart contracts are often preferred over Bitcoin's smart contracts [35].While Bitcoin smart contracts are primarily designed for validating currency transactions, the Ethereum network offers a broader range of use cases [40].

Smart Contract
A smart contract is a self-executing code that resides on the blockchain and operates autonomously without the need for any intermediary or third party.In P2P energy trading, this introduces trust among peers, as the execution of the contract is transparent and cannot be tampered with [38].Smart contracts can be modified to meet specific requirements, allowing for the insertion of code, rules, objects, and data models.Once deployed on the blockchain, a smart contract becomes an immutable part of the network [39].In realtime scenarios, Ethereum's basic smart contracts are often preferred over Bitcoin's smart contracts [35].While Bitcoin smart contracts are primarily designed for validating currency transactions, the Ethereum network offers a broader range of use cases [40].Figure 4 illustrates the structure and functioning of a smart contract.

Smart Contract
A smart contract is a self-executing code that resides on the blockchain and operates autonomously without the need for any intermediary or third party.In P2P energy trading, this introduces trust among peers, as the execution of the contract is transparent and cannot be tampered with [38].Smart contracts can be modified to meet specific requirements, allowing for the insertion of code, rules, objects, and data models.Once deployed on the blockchain, a smart contract becomes an immutable part of the network [39].In real-time scenarios, Ethereum's basic smart contracts are often preferred over Bitcoin's smart contracts [35].While Bitcoin smart contracts are primarily designed for validating currency transactions, the Ethereum network offers a broader range of use cases [40].Blockchain provides a transparent and secure platform for P2P energy trading and enables smart contracts by generating a tokenization system.Smart contracts can automate various kinds of transactions and payments among the parties based on predefined rules and conditions [41].The blockchain-oriented charging system allows EV owners to look at P2P electricity trading as a business model that serves as an online market.In a similar context, an account generation mechanism is introduced to deal with the trading trends.The account charting technique safeguards the data confidentiality of prosumers and consumers, as payments are controlled by the smart contract and stated properly by assigning the tokens corresponding to the overall sold volume of the energy.The blockchain also focuses on the arrangement of the energy exchange and charging behavior of electric vehicles to preserve their privacy by upholding the traceability of the transactions [42].This also leads to determining various kinds of transactions among them.Electric vehicles also need to submit a request for the proper amount of energy units, and the contract acts as the marketplace because it forwards the request to the proper providers for fulfilling the energy requirement of the EV.

P2P Energy Trading of EVs for Centralized and Decentralized Networks
This section provides a comprehensive literature review on the evolving landscape of P2P energy trading of EVs within centralized and decentralized energy trading networks.This review reports 18 papers focusing on centralized and 27 on decentralized energy trading networks for P2P energy trading of EVs.

Centralized Network
Centralized P2P energy trading refers to a network that performs energy exchange and transactions between prosumers and consumers facilitated by a centralized entity or platform [43].The main challenges of a centralized P2P energy trading system is it significantly depends on local regulations, the large number of prosumers and consumers, market conditions, extended contentions, and the specific goals of the participating entities [5,34].Some technical aspects of a centralized energy trading network are presented in Table 2. Figure 5 illustrates the P2P energy trading in a centralized network using blockchain technology [44,45].Blockchain provides a transparent and secure platform for P2P energy trading and enables smart contracts by generating a tokenization system.Smart contracts can automate various kinds of transactions and payments among the parties based on predefined rules and conditions [41].The blockchain-oriented charging system allows EV owners to look at P2P electricity trading as a business model that serves as an online market.In a similar context, an account generation mechanism is introduced to deal with the trading trends.The account charting technique safeguards the data confidentiality of prosumers and consumers, as payments are controlled by the smart contract and stated properly by assigning the tokens corresponding to the overall sold volume of the energy.The blockchain also focuses on the arrangement of the energy exchange and charging behavior of electric vehicles to preserve their privacy by upholding the traceability of the transactions [42].This also leads to determining various kinds of transactions among them.Electric vehicles also need to submit a request for the proper amount of energy units, and the contract acts as the marketplace because it forwards the request to the proper providers for fulfilling the energy requirement of the EV.

P2P Energy Trading of EVs for Centralized and Decentralized Networks
This section provides a comprehensive literature review on the evolving landscape of P2P energy trading of EVs within centralized and decentralized energy trading networks.This review reports 18 papers focusing on centralized and 27 on decentralized energy trading networks for P2P energy trading of EVs.

Centralized Network
Centralized P2P energy trading refers to a network that performs energy exchange and transactions between prosumers and consumers facilitated by a centralized entity or platform [43].The main challenges of a centralized P2P energy trading system is it significantly depends on local regulations, the large number of prosumers and consumers, market conditions, extended contentions, and the specific goals of the participating entities [5,34].Some technical aspects of a centralized energy trading network are presented in Table 2. Figure 5 illustrates the P2P energy trading in a centralized network using blockchain technology [44,45].
Table 3 presents some of the relevant work in this area, along with the advantages and disadvantages of each proposed technique.In this table, it is to be noted that a comparative analysis of distributed energy trading was carried out; however, it did not cover all the techniques presented in the literature, but most of them.Table 3 presents some of the relevant work in this area, along with the advantages and disadvantages of each proposed technique.In this table, it is to be noted that a comparative analysis of distributed energy trading was carried out; however, it did not cover all the techniques presented in the literature, but most of them.Table 3. Proposed techniques in a centralized network and their comparative analysis.

Ref.
Technique Limitations/Difficulties Advantages Disadvantages [21,46] Robust energy trading (RET) algorithm Limited scalability when dealing with large-scale EV energy markets due to computational burden.
The proposed scheme balances supply and demand responses in the V2G mode of operation.
The proposed algorithm focuses on a distributed network with less transparency. [19] Activity-based model is used for a particular population in Belgium Difficulty in accurately representing diverse energy consumption behaviors within the population.
Economically beneficial for users and reduces the burden on the grid during peak hours.
Charging and discharging pattern is only focused for a limited interval of time.[47,48] Nash equilibrium game theory approach Assumption of rational behavior may not always hold in real-world energy markets.
The proposed algorithm minimizes energy transition costs.
Privacy concerns, as it includes serving as a medium of trading. [49,50]

Stackelberg game and energy pricing equilibrium
Complexity in modeling dynamic interactions between energy producers and consumers.
Facilitates energy pricing equilibrium.
Focuses on V2G trading only. [51] Real-time energy management for EVs equipped with RES Dependency on accurate and up-to-date data for effective decision-making, susceptible to errors and delays.
Different pricing schemes are suggested.
The study shows simulations only for real-time data.
[52,53] Distributed energy resources (DERs) Integration challenges due to diverse technologies and varying levels of control and management.
A thorough study of the energy market with the distributed energy sector.
RES is the main source of electricity generation. [

54,55] Internet of Energy (IoE) technique
Vulnerability to cybersecurity threats and data privacy concerns in interconnected energy systems.
The proposed scheme effectively reduces energy waste.
Mainly focuses on renewable energy sources.
The reviewed work in Table 3 is related to distributed networks, which lack accuracy, transparency, and security.For this purpose, a secure system of trading and transaction is required.The blockchain comes to mind because it was identified after Bitcoin was extensively employed [56].The centralized approach to blockchain technology provides empirical results and economic benefits.On the other hand, the number of EVs is predicted to elevate the situation by developing coordinated bids.For this, the internet will help to provide data storage and smart security management [24].
The blockchain introduces blocks for transactions in a proper way, and each block is genuinely authenticated by the peer nodes based on a predefined consensus algorithm [49].Meanwhile, for P2P energy trading, different charging stations have smart meters and controllers, along with unique node information that leads to storing the data that must be authenticated by using blockchain technology [57][58][59].The electrical vehicle owner has a numerical folder for payment and utilizes digital currency with the help of a smart phone application.In that application, centralized energy trading of EVs by using blockchain technology initializes transactions with the help of a node in the chain holding a smart contract [60,61].For this, DLT was employed for monetary operations; however, numerous Energies 2024, 17, 2135 9 of 17 studies found that this knowledge could be utilized to create structures beyond monetary ones and exchange multiple secure transactions [39].This is because of the immiscible clarity in DLT.That is why P2P energy trading in a centralized network would be highly adaptable and efficient for existing energy network infrastructure.

Decentralized Network
The decentralized P2P energy trading network describes an energy exchange and transactions between prosumers and consumers facilitated by the individuals anywhere they want, without the interference of utility companies [5].Some technical aspects of the decentralized P2P energy trading network are outlined in Table 4. Figure 6 illustrates the P2P energy trading in a decentralized network using blockchain technology [45].
In [19], the authors introduced an anonymous compensation scheme for EV battery discharging to encourage a larger number of EVs to participate in energy trading.EVs trade a certain amount of electricity to the grid and motivate other EV owners to participate.Another study [40] discussed a blockchain-based approach incorporating game theory to establish a consensus between EVs and grids for energy transfers.While this platform supported small transactions, the energy price remained fixed by the grid, ensuring consistent energy supply costs without compromise.After analyzing blockchain technology and fixed contracts, Xia et al. [62] employed smart contracts and edge computing to enhance the efficiency and durability of energy trades.The authors solved the computational problem using the stack Elberg game and backward induction method.Similar to the previous blockchain-based approach, this method lacked a solution for altering the fixed price set by the discharging vehicle.In [63], the authors discussed local energy trading, where energy transfers occurred in a localized way to avoid complex transportation over long distances.They implemented local P2P energy trading, with fixed inducements provided to discharging EVs.In [64], the authors suggested a power management technique grounded on artificial intelligence to predict energy levels in EVs.The study in [65] aimed to reduce segregated network load variation based on energy flow restrictions.The paper discussed mixed-integer matters and suggested an approach to solve the problems.The proposed decentralized trade architecture was built on grouping blockchain to enhance competence by using a smart contract implementation algorithm.However, the cost of energy trading was not discussed in this work.In [66], a method for implementing blockchain with smart contracts was proposed to reduce the segregated network load variation.The consensus algorithm used was grounded on the Byzantine fault tolerance problem.Energy was allocated to charging EVs based on a fixed number of discharging EVs at the charging spot at the best price.However, this method lacked an EV trading mechanism and its validation.
P2P energy trading based on a consensus protocol was adapted to optimally satisfy power demand using renewable energy resources [34].In another study presented in [67], a method was proposed to address privacy concerns throughout energy trading using data mining algorithms.The proposed method obtains user confidentiality details, particularly when users are geographically close during energy trading.The authors proposed a consortium blockchain-based solution to mitigate privacy leaks while maintaining trading functions.They shed light on EV trading users' privacy in the smart grid and visualized the distribution of energy sales from prosumers [67,68].A distributed process for EV charging, aimed at minimizing power variations and reducing total charging costs for customers, was presented in [64].The proposed method initially calculates the electricity capacity based on the capabilities of EVs, charging prices, and methods of charging.Then, it employs the iceberg instruction administration algorithm to improve EV charging as well as discharging processes.While this approach is cost-effective, it significantly reflects stability between complexity of functioning and non-functioning of chains and the scalability of EV energy trading [69].Table 5 presents some classical and recently published proposed techniques and limitations of decentralized networks.
well as discharging processes.While this approach is cost-effective, it significantly reflects stability between complexity of functioning and non-functioning of chains and the scalability of EV energy trading [69].Table 5 presents some classical and recently published proposed techniques and limitations of decentralized networks.

Techniques Limitations/Difficulties Advantages Disadvantages
eberg order exemethod is used.
Equity share is not different in peak timings and base-load timings.
Helps conceal the true order size, reducing market impact.
May result in partial execution of the order at suboptimal prices.nsortium blockconvex-concave que is used.Edge ting is used for g blocks.
The history of previous data is stored in a private database, which could be a threat to EV owners' privacy.
Offers enhanced privacy and scalability compared to public blockchains.
Requires trust among consortium members, potentially leading to centralization.
tine fault toleronsensus algo-No compensation or original currency has been offered for discharging EVs.
Reduces latency and bandwidth usage by processing data closer to the source.
Relies on stable and reliable network connectivity to the edge devices.
The private data of customers were used before going into the system.
Ensures network reliability and security even in the presence of malicious Higher computational overhead compared to other consensus algo-

Ref. Techniques Limitations/Difficulties
Advantages Disadvantages [18,71] The iceberg order execution method is used.
Equity share is not different in peak timings and base-load timings.
Helps conceal the true order size, reducing market impact.
May result in partial execution of the order at suboptimal prices.
[ 72,73] The consortium blockchain convex-concave technique is used.Edge computing is used for creating blocks.
The history of previous data is stored in a private database, which could be a threat to EV owners' privacy.
Offers enhanced privacy and scalability compared to public blockchains.
Requires trust among consortium members, potentially leading to centralization.
No compensation or original currency has been offered for discharging EVs.
Reduces latency and bandwidth usage by processing data closer to the source.
Relies on stable and reliable network connectivity to the edge devices.
The private data of customers were used before going into the system.
Ensures network reliability and security even in the presence of malicious nodes.
Higher computational overhead compared to other consensus algorithms.
Completely focuses on the pricing strategy and economic welfare of the users.Does not focus on how to do trading in remote areas.
Enables efficient coordination and optimization of distributed energy resources.
Complexity in managing diverse energy sources and their interactions.
[ Helps in modeling strategic interactions and decision-making.
Assumptions about rationality and perfect information may not always hold. [79] Ring signature, aggregator signature, and public key infrastructure.
There is no concept of bidding, which will lose the interest of users.Misuse of contact-based authentication is a problem.
Offers enhanced privacy and security in transactions.
Implementation complexity and potential scalability issues. [80,81] Aggregator-based microgrid structure blockchain is used as a tool.
High prices are required for the execution of blockchain.
Enables efficient management and trading of energy within microgrids.
Requires trust in the aggregator and potential centralization risks.[82,83] Iteration double-auction mechanism is used.
The pricing method for electricity is fixed.
Allows for iterative bidding and price adjustments, improving market efficiency.
Increased complexity in auction design and implementation.
A server is involved in the smart contract, due to which the privacy of users can be compromised.
Enables decentralized applications on resource-constrained devices.
Limited processing power and storage capacity on Raspberry Pi devices.
Mainly discusses EV trading in smart grids and how to reduce electricity bills by trading.Does not focus on a trading algorithm.
Models strategic interactions between leaders and followers in a hierarchy approach.
Assumes perfect information and rational decision-making, which may not always hold.

Major Concerns to Implement P2P Energy Trading
Several parameters need to be encountered at the customer level to make P2P energy trading successful in developed countries' markets.The P2P energy trading of EVs using blockchain technology is kind of a complex structure, but by understanding some major concerns, the trading platform can be made accessible and successful for the sellers and buyers [42,87].Some of the major concerns are discussed below.

Trustworthy Platform
A reliable platform is much needed for the application of effective P2P energy trading of EVs, and all layers involved should be managed by that platform [83].For instance, the supplier of electricity should provide data to their peers about how much excess energy they have, and the customer who wants to buy the energy can send a requirement to the platform.Therefore, to perform this process efficiently, a platform is required to manage the demand and needs of both the seller and buyer according to real-time data.The platform should also keep a record of all the transactions happening [84].

Supervisory Framework
The monitoring system has a big task to make P2P energy trading of EVs successful at the client level.In the framework that defines all the regulations in favor of stakeholders at either close neighborhood or regional levels [88], without being biased, the rights and obligations of all the participants involved in trading should be equally divided.

Attaining Technical Requirements
For the successful outcomes of P2P energy trading of EVs, owners act collectively to meet practical constraints at the physical, software, and communications levels [20].Prosumers trade surplus energy, algorithms work in software, and power grids manage charging stations using electric meters to empower energy trading in centralized or decentralized networks [89].

Roles and Responsibilities
The roles and responsibilities to implement P2P energy trading of EVs are: EV owners involved in the P2P energy trading network should be very well identified, trusted, and registered [89].Operators should monitor and manage energy providers/distribution companies, consumers, prosumers, and platform providers for optimized energy demand and supply.One of the main responsibilities is to ensure data privacy and secure transactions [90].

Scalability and Budget
Another crucial aspect to consider is the scalability of P2P energy trading to multienergy generation/trading and the network-associated costs.Currently, there are multiple scenarios envisioned for energy trading networks, and some researchers have introduced optimized energy sources for distribution co-generations [91], encompassing a range of prosumers and consumers [70], from small-scale setups to local and city-wide electricity trading with grids [92].The scalability directly impacts the overall costs and pricing of energy units within the P2P energy trading of EVs [93].

Policies and Protocols
This review included disciplinary policies that are required to implement P2P energy trading of EVs [94].Firstly, policies should focus on the existing grids to encourage P2P energy trading without any addition of standalone systems.Secondly, the designed P2P energy trading network should be compatible for extension of EVs/prosumers, addition of RES, and decentralization of connections [95].Thirdly, protocols are required to manage P2P energy trading at private, government, and local levels, without the involvement of any third party to facilitate the prosumers and consumers [96].Lastly, participants can easily trade and perform transactions using a platform of blockchain-based smart contract technology.

Current Trends and Future Directions
The current research demonstrates how P2P energy trading is in demand and will be used globally in the coming years of this decade.The current research trends are as follows:

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Electric vehicles have emerged as a promising technology for achieving sustainability in the transportation sector.The increasing number of EVs has attracted researchers to work on EV energy trading.

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Nowadays, blockchain technology performs an important role in P2P energy trading frameworks because it provides trust, transparency, secure transactions, and information privacy to all prosumers and consumers.

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Smart contracts allow real-time settlements in P2P energy trading.Currently, researchers are interested in and working on blockchain-based smart contract platforms utilizing different algorithms for P2P trading.

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To combat environmental pollution caused by conventional fossil fuel vehicles, widespread adoption of EVs by the public is essential.In that scenario, the rise of EVs drives complex infrastructure of P2P trading.Some researchers are exploring how EV owners selling and storing energy would impact the network infrastructure.
The consumers usually use the traditional method of trading.The concept of P2P energy trading using blockchain is very new to them.Due to its profitability, it may take less time to accept this trend, and some of the future directions are listed below:

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In the future, "prosumers", as EV owners, will not only consume but also produce and sell energy to the grid.

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Developing a blockchain-backed P2P electricity trading framework with an energyefficient consensus algorithm will provide high economic benefits.It can also facilitate the cross-border renewable energy trading network involving prosumers and smallscale microgrids.

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In renewable energy, such as solar, wind, and hydro, sometimes, the generated energy exceeds the need and ends up wasted.This would be avoided by using smart meters and contracts using blockchain technology.When the network has extra energy, these smart contracts will send it to EVs' storage.

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Establishing new smart contracts for P2P energy trading will enable optimized energy utilization, which incorporates a novel strategic way to deal with environmental compliance measures.

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For dynamic load forecasting and energy management, demand-side management will be revolutionized to optimize energy consumption.By leveraging blockchain technology, it will create an efficient and responsive system that adapts in real-time to shifting energy demands.This innovative approach will not only enhance energy efficiency but also promote sustainability by enabling the seamless integration of renewable energy sources into electricity grids.

Conclusions
In conclusion, P2P energy trading is gaining popularity as a unique field of study in the current landscape.Researchers are increasingly turning to blockchain technology for P2P tradeoff.When combined through smart contracts, blockchain technology can provide secure transactions.Various algorithms have been reviewed: some of them have been practically implemented, some are still in trial phases, and others are currently under investigation.However, there is still a lack of comprehensive information regarding the progress made in this field, so the use of centralized or decentralized networks, current trends, and future directions were reviewed here.This paper discussed several papers that highlight the practicality of blockchain technology in the context of EV energy trading.It also identified and discussed the open challenges in terms of major concerns that need to be addressed to meet the necessities of EV energy trading networks.
The proliferation of P2P energy trading has revolutionized the existing energy network, and blockchain technology has gained traction in the energy market.It depicts prodigious potential in facilitating P2P energy trading for EVs.In terms of security, researchers have emphasized the importance of blockchain technology, which enhances the security and reliability of trading.

Figure 2 .
Figure 2. P2P energy trading using blockchain technology with the involvement of a financial institution.

Figure 2 .
Figure 2. P2P energy trading using blockchain technology with the involvement of a financial institution.

18 Figure 3 .
Figure 3. P2P energy trading using blockchain technology without the involvement of financial institutions.
Figure 4 illustrates the structure and functioning of a smart contract.

Energies 2024 , 18 Figure 3 .
Figure 3. P2P energy trading using blockchain technology without the involvement of financial institutions.
Figure 4 illustrates the structure and functioning of a smart contract.

Figure 5 .
Figure 5. P2P energy trading in a centralized network using blockchain technology.

Figure 5 .
Figure 5. P2P energy trading in a centralized network using blockchain technology.

Table 1 .
Answers to some questions relevant to this review paper.

Table 5 .
Proposed techniques in decentralized networks and their comparative analysis.

Table 5 .
Proposed techniques in decentralized networks and their comparative analysis.