1 Introduction
Power generation is the largest source of CO
2 emissions, while transportation accounts for more than a third of CO
2 emissions from energy end-use sectors. In 2022, global CO
2 emissions from the transportation and power sectors reached 8 and 14.8 Gt, respectively. To achieve Net Zero Emissions (NZE), the proportion of unabated fossil fuels in global electricity generation must be reduced from over 60% to below 30% by 2030, and the CO
2 emissions in the transportation sector must decrease by more than 3% annually (
IEA, 2024). Luckily, the rapid adoption of electric vehicles (EVs) and renewable generation presents significant opportunities for reducing transportation emissions and enhancing the sustainability of energy systems. However, the existing charging infrastructure is inadequate to meet rapidly increasing charging demand. Additionally, the significant rise of EVs will exacerbate peak grid demand. The incoordination between power and transportation systems could hinder sustainable power generation development, and impede the decarbonization of both sectors. Over the past decades, the coordination between power and transportation systems has been extensively explored and made significant progress, particularly in smart charging and discharging of EVs. The development of Vehicle-to-Grid (V2G) technology not only enables EVs to draw power from the grid and optimize the charging demand for smart charging, but also sends electricity back to the grid by aggregating EVs and charging infrastructures. Nevertheless, the integration of EVs, charging infrastructure, and the grid under unified cloud-based control remains challenging.
The integration of power systems and transportation systems occurs across three hierarchical levels: individual, regional, and trans-regional. Prior research has primarily concentrated on addressing this integration at the individual (
Baumgartner et al., 2023) and regional (
Zabihi and Parhamfar, 2025) scales, with less attention devoted to large-scale coordination and scheduling operating across regions. This research gap stems primarily from the fact that V2G initiatives are currently restricted to small-scale pilot projects, lacking broad, large-scale applications. However, the sharp increase in EVs and the corresponding rise in charging needs create a growing urgency for research focused on trans-regional scheduling strategies. While initial studies by some researchers have begun to address this challenge (
Zhang et al., 2024), they frequently neglect the crucial point that coordination between power and transport systems is not an inherently self-generating phenomenon. Instead, achieving such coordination depends critically upon several prerequisites: unified resource aggregation through aggregators, comprehensive large-scale cloud control systems deployment, and proactive policy implementation and strong impetus from government authorities. Consequently, this commentary proposes 5S objectives (smart charging, synergistic infrastructure, and storable grid for stable and sustainable power and transportation systems) covering individual, regional, and trans-regional levels. We propose an innovative framework incorporating charging and discharging strategies, advanced charging infrastructure technologies, and cloud-based aggregation to enhance grid sustainability, resilience, and efficiency. This framework is crucial in advancing decarbonization goals for power and transportation systems. We emphasize the broad applicability of this framework, demonstrating its relevance to carbon reduction targets for developed and developing countries (Fig.1).
2 Smart charging
The global EV sales exceeded 10 million, accounting for 14% of total vehicle sales in 2022 (
IEA, 2024). The rapid growth of EVs has positioned them as a key factor in the interaction between transportation and power systems at the individual level. EV users charge at similar times, such as after commuting to the workplace and returning home. These time periods coincide with grid peak hours, which implies that additional power generation facilities must be deployed to meet the increased demand. The additional power generation is often provided by thermal power plants rather than renewable energy sources, hindering grid stability and renewable energy promotion. Since most EV parking time is longer than the time required for battery charging, this provides opportunities for smart charging implementations.
Due to the flexibility of EVs’ charging profiles, EVs can reduce their impacts on the grid by delaying and pausing charging times during peak grid periods or under high electricity price scenarios (
Brinkel et al., 2024). In delayed charging, EVs begin charging after a certain period of time upon arriving at the charging station, while in paused charging, EVs will cease charging and enter a dormant state. In addition, the flexibility of EV users in choosing charging locations can optimize charging behaviors. The EV charging session can be shifted to a new charging time by directing vehicles to charge in specific areas (
Wu et al., 2024). For example, if an EV arrives home at 8 PM on Sunday and is expected to arrive in a public area by 8 AM on Monday, its charging session at home can be shifted to the public area to avoid grid peak. Smart charging (power and location scheduling) can benefit grid operators and EV users. For the grid, these strategies help reduce peak load. EV users can charge more during the lower price hours and less during the higher price hours, thereby reducing costs. Governments and utilities often implement specific rate designs to incentivize EV drivers to adopt flexible charging patterns. As an example, the Sacramento Municipal Utility District (SMUD) provides a
0.015/kWh credit for charging during off-peak hours (midnight to 6 AM) (
SMUD, 2025). Similarly, Austin Energy offers tiered flat rates for off-peak residential charging:
30 per month for demand below 10 kW and a fixed rate of
50 per month for customers exceeding 10 kW demand. Charging during peak periods, however, is billed based on actual energy usage (
Austin Energy, 2022).
To achieve flexible EV smart charging, it is essential to develop accurate EV energy consumption and management models to precisely analyze and regulate EV charging demand and charging behavior. Delaying and paused charging time may result in insufficient charging. To avoid this issue, it is essential to carefully consider drivers’ potential travel patterns, energy consumption needs, and dwell time. Moreover, policymakers or grid operators need to provide appropriate dynamic pricing costs and/or subsidies to smart charging users for charging cost reduction.
3 Synergistic infrastructure
At the regional level, the rapid growth of EVs necessitates the deployment of charging infrastructure. In 2023, China built 3.386 million new charging infrastructures, bringing the total to 8.596 million facilities. The deployment of charging stations is aligned with charging demand. After estimating the charging demand based on the drivers’ travel and charging behavior statistics, planners can utilize its flexibility to regulate EV demand and achieve peak load control for the grid (
Wu et al., 2024). However, increasing the flexibility of EV demand requires the construction of more public charging stations, which entails higher construction and operational costs. Therefore, charging infrastructure planning should comprehensively consider factors such as charging demand, investment costs, and optimal charging scheduling to balance economic efficiency and convenience.
Furthermore, integrating renewable energy generation and energy storage systems into charging facilities to transform them into energy hubs is an effective strategy to address grid peek issues (
Zhong et al., 2024). In this case, charging facilities are equipped with rooftop photovoltaic (PV) panels and energy storage systems. Renewable energy is first stored in the energy storage system and used to charge EVs when needed. This approach can reduce up to 5.7% emissions and ease grid congestion (
Liu et al., 2024). A case study in Bangladesh examined charging stations integrated with PV systems, biogas generators, and battery storage. The results demonstrated a 34.68% decrease in carbon emissions relative to traditional charging infrastructure (
Karmaker et al., 2018). Furthermore, in addition to promoting renewable energy development, deploying PV installations at charging points can effectively address the challenge of securing stable electricity access in underdeveloped regions. For example, Electrify America, a US company, established 30 off-grid solar EV charging stations in rural California equipped with sun-tracking solar arrays and battery storage, providing up to 3.5 kW charging capacity for two vehicles (
Electrify America, 2023). Similarly, Kenya launched its first solar-powered battery charging and swapping hub for rural transportation in 2023, aiming to address the significant challenges of constructing and maintaining fueling infrastructure in remote regions (
Kuhudzai, 2023). However, this approach only applies to facilities where large-scale PV power generation can be deployed, such as large public charging stations, bus stations, and train stations. For private charging stations, it is recommended to integrate with local microgrids, utilizing the renewable energy within microgrid to facilitate the decarbonization of both power grid and transportation systems. A study based on the Car as Power Plant project at The Green Village in the Netherlands demonstrated that integrating 10 all-electric households and 5 EVs could reduce annual grid electricity consumption by about 71%. This approach was also shown to facilitate attaining net-zero energy building objectives for buildings within the microgrid (
Robledo et al., 2018).
Charging infrastructure equipped with high-quality communication devices is crucial for implementing V2G systems. The charging infrastructure’s operational system needs to monitor the grid status, renewable energy generation, EV charging in real time, while maintaining communication with both EVs and grid through cloud. The charging time of EVs, especially fast charging (from a few minutes to several hours), requires charging facilities to have highly automated control and high communication frequencies. Thus, adopting expensive communication equipment and a high-performance operator system is necessary, which results in additional power load. It may raise privacy and regulatory concerns, as communication data includes EV drivers’ personal and travel information. Therefore, designing low-cost, energy-efficient, secure, and effective communication systems for charging infrastructure is essential.
4 Storable grid
At the trans-regional level, the grid is integrated with EVs and charging infrastructure with charging and discharging capabilities to achieve stability and sustainability. It can even provide temporary power to community microgrids during power outages caused by disasters such as hurricanes, tsunamis, and fires. EVs and charging facilities with energy storage devices can help the grid achieve supply-demand equilibrium. They can participate in the electricity market by leveraging their flexibility in charging and discharging to generate profits (
Liu et al., 2024). To encourage engagement in V2G initiatives, electricity markets often provide subsidies to participants. A notable example is the 2007 V2G pilot program undertaken by PJM and the University of Delaware, where an electric BMW Mini earned around $100 monthly for providing grid services – specifically, charging and discharging according to PJM frequency regulation signals (
PJM, 2007).
However, the charging and discharging power of an EV or charging facility is insufficient to meet the minimum requirements of the grid. Therefore, it is necessary to aggregate hundreds to thousands of EVs or charging facilities to reach the threshold required by the grid. Thus, they need to be coordinated under a unified cloud-based control system to participate in the electricity market. Since the cloud system must manage tens of thousands of agents, the immense complexity makes centralized algorithms infeasible, necessitating the development of large-scale aggregation models (Muessel et al., 2023). By adopting a distributed model, model complexity can be reduced, and computational efficiency can be improved. However, this may lead to suboptimal solutions or control errors. Artificial Intelligence (AI) driven models can effectively balance efficiency and accuracy. Trained on historical data and optimized in real time, these models achieve EV charging scheduling, load forecasting, grid management, and renewable energy integration. AI enhances grid efficiency, stability, and sustainability by predicting demand, automating fault detection, improving energy consumption behavior, supporting carbon reduction goals, and promoting more efficient energy systems. Additionally, active discharging could lead to battery degradation, resulting in economic losses for EVs and charging facility owners. Therefore, assessing the comprehensive benefits of V2G systems and developing corresponding policies are necessary.
5 Cloud aggregation for stable and sustainable power and transportation systems
Scheduling EVs, charging infrastructure, and the power grid require cloud-based aggregation. The nature of cloud aggregation differs based on scale, each characterized by distinct participants and spatial scopes. At the individual level, participants are typically confined to EV drivers. They participate in smart charging programs via mobile apps, aiming to shift their charging activities away from periods of peak grid demand. Correspondingly, the cloud platform’s role at this level is predominantly informational, supplying data on grid peak times. The regional level involves cooperative interaction between EV drivers and charging infrastructure. These regions (e.g., charging stations, communities, supermarkets, hospitals) usually constitute relatively independent geographical zones. Collaboration within these areas is frequently structured around an internal microgrid, operating with limited or absent ties to the broader grid. Fundamental communication with vehicles and charging stations within the controlled area is mandatory for these regional operations. This necessitates upgrading the charging infrastructure and developing advanced mobile applications tailored for EV driver interaction. At the trans-regional level, EVs, charging infrastructure, and the grid all function as participants in coordination, demanding strong cloud-based aggregation. The geographical extent can span a city, several cities, or an entire country. Achieving this integration requires comprehensive upgrades to vehicles, charging facilities, and the grid itself, all of which must be unified under the management of an aggregator. Participation in electricity markets is then typically facilitated through pricing and bidding. Consequently, the associated cloud platform must be capable of collecting and processing data at a city-wide or national scale, thereby demanding highly advanced systems for data collection, communication, and computation. The cloud center may require hundreds of staff for operations and thousands of CPUs and GPUs for computation. Policymakers need to establish dedicated scheduling departments to enable nationwide V2G implementation. At the trans-regional level, the flexibility of aggregation can smooth the fluctuating output of renewable energy generation. This will enhance grid stability, making it more acceptable for renewable energy plants to grid operators and improving the profitability of renewable energy plants, thereby promoting renewable energy development. At the same time, when new energy power generation suddenly increases, it can lower electricity prices, allowing EVs and charging facilities to benefit from lower electricity prices and reducing the operational costs of cloud-based aggregation.
To achieve trans-regional cloud aggregation, EVs, charging infrastructure, and grid all require the installation of communication facilities. Currently, the grid has established comprehensive communication and automatic control systems. Public charging infrastructures are typically equipped with communication devices with remote control capabilities. However, the lack of communication capabilities in EVs and the inability to regulate charging power are the main factors hindering smart charging development. To address this issue, vehicle drivers can communicate with the cloud through AI-driven applications to enable V2G scheduling. The applications guide EV drivers in implementing charging delays or scheduling charging locations based on factors such as the EV location, surrounding environment, and grid status. However, most EVs are unable to pause or delay charging. To address this issue, vehicles can continue charging at a minimal power level to reduce their impact on the power grid (
Brinkel et al., 2024).
Several pilot projects employing cloud-based aggregation for V2G functionalities have been implemented at the regional level. A notable example occurred from January 30, 2016, to September 30, 2017, where 29 US Los Angeles Air Force Base EVs contributed 373 MWh in aggregate for grid balancing services within the California electricity market (
Black et al., 2018). In addition, pilots have been conducted in Germany (FfE, 2023), Denmark (
Arias et al., 2018), and the UK (
UKRI, 2025), among other locations. Nevertheless, scaling V2G operations to a trans-regional scope remains a formidable difficulty. With the development of autonomous driving technology and Vehicle-to-Everything (V2X), vehicle charging demands and locations will be transmitted to the cloud through V2X (
Chang et al., 2024). The cloud calculates the optimal charging destination and smart charging strategy for EVs based on the real-time grid status and surrounding environment, and then transmits to EVs via V2X (
Li et al., 2024). Therefore, higher-level connected and autonomous vehicles will contribute to advancements in V2G technology.
6 Opportunities and challenges
In the future, integrating EVs, charging infrastructure, and the grid under cloud-based aggregation will represent a disruptive technology. In such a system, smart connected EVs and charging infrastructure can autonomously charge and discharge to the grid, enhancing grid stability, supporting renewable energy development, and accelerating the decarbonization of transportation and power systems. As communication costs, energy storage costs, and operational expenses continue to decline, V2G technology holds significant potential to strengthen the resilience of power systems.
However, some critical challenges remain in constructing a low-cost, efficient, and secure V2G system. First, the widespread adoption of V2G necessitates large-scale upgrades to existing infrastructure, encompassing charging stations and the associated power grid infrastructure supporting charging. This represents a significant financial expenditure, particularly for deployment in remote regions. Secondly, a significant impediment arises from the lack of standardization concerning both the batteries and charging ports used in EVs. Driven by market competition, many EV manufacturers have developed their proprietary standards, which are often incompatible with alternative systems. Consequently, regulatory authorities need to implement a unified standard framework for EVs to facilitate the large-scale V2G application. Thirdly, the existing legal framework in many countries currently lacks provisions for establishing contracts governing flexible charging loads between aggregators and grid operators. Consequently, governments need to develop appropriate policies that establish minimum market entry requirements for aggregators and enhance coordination between grid operators and these aggregators. Simultaneously, measures should be implemented to encourage the participation of individual customers in flexible charging services provided by aggregators and grid operators. Fourthly, the substantial volume of data communication inherent in V2G operations raises public concerns regarding the cybersecurity of smart charging networks. To safeguard privacy, it is incumbent upon governments to establish a legal framework specifically governing the collection and transmission of smart charging information. This framework must ensure informational security.
Despite the numerous challenges, the coordination between power and transportation systems plays an essential role in mitigating pollution and achieving sustainable development. In the future, the development of autonomous vehicles, communication technology, and AI-driven modeling will offer solutions to address these challenges.
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