“It’s a long way to the top if you wanna rock ’n’ roll.”

—AC/DC

Expectations are high for vehicle-to-grid (V2G) technology to unlock the massive storage potential of electric vehicles and support the clean energy transition. But a crucial and often underappreciated debate may be stalling its progress: should V2G operate primarily through AC (on-board) or DC (off-board) systems?

At the heart of this distinction is the inverter—the component that converts the direct current (DC) stored in an EV battery into alternating current (AC) used by the electric grid. In V2G-DC systems, this power conversion occurs in the external DC charging station, which houses a bidirectional inverter. In V2G-AC systems, the inverter is built into the vehicle itself, allowing energy to flow through a bidirectional AC charging port to buildings or the grid.

The AC/DC Debate

The AC vs. DC architectural choice has far-reaching implications for cost, efficiency, noise, and grid interconnection, as well as for how V2G functionality is coordinated. In both AC and DC systems, ISO 15118 generally specifies that commands originate from the vehicle side during standard charging. However, in dynamic operating modes—when real-time adjustments to charging or discharging are needed—the electric vehicle supply equipment (EVSE) typically controls the power flow, regardless of whether it’s an AC or DC system. This interplay between vehicle and EVSE control is central to how grid interaction and power export are managed in practice.

After numerous conversations with experts in the field, there is no clear consensus among industry stakeholders on which architecture—AC or DC—should dominate, and this unresolved debate is a barrier to scaling V2G. Some view V2G-DC as the clear winner for its efficiency and technical simplicity. Others argue V2G-AC is more scalable and consumer-friendly.

V2G: AC vs. DC

Feature	V2G-AC (On-board)	V2G-DC (Off-board)
Power Conversion	Inside the vehicle (onboard inverter)	External to the car (in the charger)
Efficiency	Typically 5-10% less efficient	Higher round-trip efficiency
Hardware Cost	Expected lower external cost, but higher car component cost	High (potentially expensive chargers and cables)
Noise	Can be noisy (onboard liquid-cooled systems)	Quiet (cooling systems in charger)
Grid Interconnection	Complicated (mobile inverter lacks clear rules)	Well-understood (fixed inverter)
Standards Status	Standards (UL 1741 Supplement SC + SAE J3072) nearing completion; alternative paired EV/EVSE certifications under development	Supported by UL 1741 Supplement SB; certification pathway in place and used in pilots
Use Case Fit	Residential, workplace, car-share networks	Fleets, commercial depots, high-power sites
Deployment Today	Lab/pilot testing in the U.S., commercial offerings announced in some EU markets (e.g., France, UK)	Dominant in U.S. (school buses, DC pilots)

DC in the U.S.: Practical, Proven, and Predominant

In the United States, V2G activity is overwhelmingly concentrated in DC-based systems, particularly in the school bus and commercial fleet sectors. This is not coincidental—utilities and regulators already understand how to interconnect these systems because they mirror familiar technologies like stationary batteries and rooftop solar. V2G-DC chargers behave like grid-tied inverters, making use of the well-established UL 1741 Supplement SB, which provides a means for testing and certifying that the IEEE 1547 standards are implemented correctly. This regulatory familiarity has allowed V2G-DC projects to move beyond the pilot phase and into early commercial deployment in multiple states.

By contrast, V2G-AC remains in the testbed phase, with only a handful of pilot projects under development—most notably at the University of Delaware,^[1]  which has been a pioneer in this space. These projects explore the use of onboard inverters to export power back to the grid via bidirectional AC charging, but widespread adoption is held back by gaps in standards and certification.

The dominant standard supporting V2G functionality worldwide today remains CHAdeMO and its variants (e.g., Chaoji, GB/T), but its relevance is declining in the U.S. and Europe as it is limited in these markets to models like the Nissan LEAF. The Europe/North American-focused Combined Charging System (CCS)—specifically CCS Combo 1 in North America—is still being adapted for full bidirectional operation. Progress is being made through the ISO 15118-20 standard, which adds support for V2G functionality.

Meanwhile, the North American Charging Standard (NACS), originally developed by Tesla but now adopted by most major automakers, is built on the same ISO 15118 and DIN 70121 protocols as CCS and is technically capable of supporting bidirectional charging. While Tesla has been slow to enable V2X across its lineup, it plans to add the capability starting in 2025, and early NACS adopters like Ford, Rivian, and Hyundai are already offering or preparing two-way charging features.

On the certification front, UL 1741 Supplement SB is finalized and widely applied to V2G-DC systems, which are treated as stationary DERs. For V2G-AC systems, the complementary UL 1741 Supplement SC standard for bidirectional electric EVSE remains under development and is due for the first release by the end of 2025. Once complete, it will provide a formal certification pathway for bidirectional AC EVSE that can interoperate with SAE J3072-certified onboard bidirectional inverters using defined communications standards and EV connectors. SAE J3072 defines multiple standards-based methods for EVs and EVSE to communicate and interoperate in compliance with IEEE 1547-2018 requirements for grid support inverters.

In the meantime, there are efforts underway to develop an alternative pathway for V2G-AC system certification using the existing UL 9741 + UL 1741 Supplement SB standards, where the vehicle and bidirectional AC EVSE are tested and certified as a paired system. However, this approach comes with a critical limitation: the certified EV is only authorized to export power when connected to the specific charger with which it was certified. It cannot roam and discharge from any other charger, effectively binding the vehicle to a single V2G-certified configuration—an approach that limits flexibility and complicates broader deployment.

But make no mistake—DC remains the dominant architecture for V2G in the U.S. The supporting ecosystem of vehicles, chargers, utility interconnection procedures, and regulatory understanding is already established. While V2G-AC is technically promising, it remains limited by a lack of certification tools, interoperability standards, and interconnection clarity. Until these pieces are fully aligned, V2G-DC will continue to lead U.S. deployment—especially in fleet applications where scale and reliability are paramount.

AC V2G Advancing in Europe

Across Europe, V2G-AC technology is beginning to transition from pilot projects to real commercial offerings. In countries like France, the UK, and the Netherlands, the combination of supportive policy, bundled offerings, and smart tariffs is proving that V2G-AC may be ready to scale. Like the alternative V2G-AC certification pathway described above, these countries use a paired certification process, where the EV and AC charger are tested together as a V2G system—following EU standards instead of UL protocols. Under this framework, the EV is permitted to export power only when connected to the specific charger it was certified with, which limits roaming and interoperability but provides a clear regulatory path forward.

In France, Renault Group, Mobilize, and The Mobility House have launched what may be the first fully commercial AC V2G offering.^[2] Customers leasing a Renault 5 or Alpine A290 can now receive free charging through the Mobilize PowerBox bidirectional AC charger, enabled by a special energy contract. The system aggregates EVs to provide grid services, turning vehicles into mobile power plants—without compromising driving needs. While this launch is currently exclusive to France, a rollout in Germany is planned once regulatory conditions catch up, including reforms to avoid double grid fees and enable smart metering.

In the UK, energy supplier Octopus Energy has partnered with BYD to offer the Power Pack Bundle, the country’s first commercial AC V2G package.^[3] The bundle includes a V2G-enabled BYD Dolphin, a Zaptec Pro AC charger, and access to a dynamic smart tariff. Customers plug in at night and let Octopus’s Kraken platform manage charging and discharging automatically—earning free home charging in return.

In the Netherlands, Utrecht is leading one of the world’s first citywide public V2G deployments, combining car sharing, solar energy, and bidirectional charging.^[4] The Utrecht Energised project—developed by Renault Group, Mobilize, MyWheels, and We Drive Solar in partnership with the Municipality of Utrecht—aims to deploy 500 bidirectional Renault EVs, including the Renault 5 E-Tech, through the MyWheels car-sharing platform. These EVs are paired with public AC bidirectional chargers and aggregation technology to provide flexible capacity to the local grid. With 35% of rooftops in Utrecht already covered in solar panels, the V2G fleet is designed to help balance energy supply and demand during periods of solar overgeneration. Once fully deployed, the vehicles will supply up to 10% of the region’s flexibility needs.”

While these examples show that V2G-AC is technically feasible and gaining commercial interest, questions remain about whether it can scale across Europe. The continent’s fragmented grid codes, inconsistent smart meter deployment, and misaligned grid fee structures—particularly in large markets like Germany—pose significant hurdles. Even in countries pushing ahead, such as France and the UK, progress relies heavily on bundled offers and niche programs rather than systemic market readiness. Without a concerted effort to harmonize regulations, reform tariffs, and streamline certification, V2G-AC risks remaining a patchwork of isolated initiatives rather than a scalable solution.

The Great V2G Fork: AC, DC, and the Road to Scale

The lack of clarity on the future of V2G-AC vs. V2G-DC has created a dilemma for automakers and charger manufacturers alike. Should they invest in integrating bidirectional inverters directly into vehicles (AC) or continue relying on external bidirectional chargers (DC)? The market is split, and that split is slowing progress. Without standardization and without OEMs endorsing and implementing standards-based V2G interoperability, EVSE manufacturers are understandably hesitant to commit to mass production of V2G-capable equipment, uncertain which technical path will ultimately dominate.

“We’ll likely see V2G-DC dominate in the commercial market, where DC systems are already well-supported. But in the light vehicle segment, I expect a mix, with V2G-DC to dominate in the short-term with V2G-AC offerings coming to market in the 2 – 4 year timeframe—driven by application needs, product design, and local policies.”

Breaking through the AC/DC divide will require action on several fronts:

• Finalize Standards: UL 1741 Supplement SC and SAE J3072 must be completed and adopted to give V2G-AC a viable certification path—and to realize its full interoperability and roaming potential, where any certified EV can export power through any compliant charger.
• Neutral Infrastructure Investment: Public funding should be agnostic on inverter location, instead focusing on use cases—depots, homes, workplaces—that best fit each architecture.
• Automaker and Charger Coordination: Industry groups must converge on a baseline set of V2G capabilities to avoid a fractured and confusing market.
• Regulate to Enable: Policymakers should prioritize interoperability and interconnection reform, not pick technology winners.

The road to V2G scale won’t be paved by any single standard or technology. Harmonizing efforts across technical, regulatory, and commercial domains will help us get there faster—and unlock the full value of electric vehicles as flexible assets for a cleaner, more resilient grid. It doesn’t have to be either/or—we could see the technology advance through a mix of architectures working together to meet diverse market needs.

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Note: The author would like to thank Glenn Skutt, PhD, for his review and helpful comments. Any remaining errors or omissions are the sole responsibility of the author.

^[1] See University of Delaware, Multi-sector partnership leads to first practical pilot of vehicle-to-grid power, available at https://www.udel.edu/faculty-staff/media-experts/spotlight/?postid=10175 and PG&E,

^[2] See Mobility House, Charge for Free – Renault Group, Mobilize and The Mobility House launch Vehicle-to-Grid in France, while Germany is establishing the regulatory framework, available at https://www.mobilityhouse.com/int_en/our-company/newsroom/article/charge-for-free-renault-group-mobilize-and-the-mobility-house-launch-vehicle-to-grid-in-france-while-germany-is-establishing-the-regulatory-framework.

^[3] See Automotive World, Octopus & BYD turbocharge EV revolution with all inclusive car and charging bundle, available at https://www.automotiveworld.com/news-releases/octopus-byd-turbocharge-ev-revolution-with-all-inclusive-car-and-charging-bundle/.

^[4] See Smart Energy International, V2G car-sharing project Utrecht Energised goes live, available at https://www.smart-energy.com/industry-sectors/electric-vehicles/v2g-car-sharing-project-utrecht-energised-goes-live/.