Fronius on Bidirectional charging in Australia: Navigating Standards, Interoperability, and Industry Collaboration

By storing excess solar energy for later use, batteries ensure that more of the generated power is utilized on-site rather than exported at low tariff rates. Through bidirectional EV charging, known as Vehicle-to-Everything (V2X) technology, EVs can take on many of the roles of a stationary BESS by not only absorbing excess PV power, but powering loads (V2L), homes (V2H), and even return power to the grid (V2G). The mobility of EV's, combined with exceptional storage capacity, enhances the overall adaptability and value of the home energy ecosystem, enabling new opportunities for grid services, energy trading, and resilience during outages. Electric vehicles (EVs) are rapidly evolving beyond their traditional role as just transportation tools, emerging as essential components of the modern energy ecosystem. 

However, unlocking the full potential of bidirectional charging involves overcoming hurdles related to standardized communication protocols, regulatory frameworks, and cross-industry collaboration. These challenges are being actively addressed around the world, including here in Australia, where progress continues to pave the way for a smarter, more sustainable energy future.

Firstly, lets understand what bidirectional charging is:

Bidirectional charging allows EVs to charge and discharge power, effectively turning EVs into mobile energy assets. There are two primary approaches: DC bidirectional charging and AC bidirectional charging. In both, the EV's stored battery energy must be transformed from (D)irect (C)urrent, to (A)lternating (C)urrent, to discharge into the energy grid. When using AC bidirectional charging, the needed DC-AC inverter is built into the car, whilst when DC bidirectional charging the DC-AC inverter is located within the charging station.

DC bidirectional charging is the more widely adopted method for V2G applications, as it enables a charging station to interface directly with an EV’s battery for both charging and discharging. This is primarily done through one of two DC charging standards: CHAdeMO or CCS2.

CHAdeMO has historically been the leading standard for bidirectional DC charging worldwide, driven by Japanese automakers in collaboration with equipment manufacturers to enable V2G functionality. However, CCS2 is with its advantages as the dominant global charging standard, with most new EVs adopting it, now including those from Japanese manufacturers. Despite this shift, CCS2 still trails CHAdeMO in terms of proven V2G capability and interoperability. Unlike CHAdeMO, which was designed with bidirectional capability early on, CCS2 requires software updates to facilitate interoperable bidirectional power flow. Significant industry efforts are underway to close this gap, and ongoing advancements in standardization and interoperability continue to drive progress.

A key advantage of DC bidirectional charging is its standardized approach to grid connection which is similar to solar inverters and therefore already welcomed (like Fronius PV inverters) by grid operators. Also, DC chargers relocate the power conversion hardware to the charging station. For a bidirectional DC charger, this shift reduces the size, weight, and complexity of the vehicle's onboard charger. Furthermore, this allows the electric vehicle to not only remain cheaper, lighter and more efficient when commuting but also independent from the changing grid requirements and interchangeable within the homeowners eco system. Consequently, the DC charging station can accommodate larger, more powerful and efficient (e.g. no coolant flow from HVAC needed) converters that are not constrained by the physical limitations of being installed inside a vehicle. Using rugged offboard electronics (like a Fronius PV inverter is), also reduces wear and tear on the onboard electronics, plus opens possibilities for further future improvements (power saving) within the car.

AC bidirectional charging leverages an EV's onboard charger to manage both the charging and discharging processes. While AC Vehicle-to-Grid (V2G) is still in its early stages with related standards (grid, communication, safety) still in draft form, its considered a crucial feature that will likely gain momentum following the development of DC bidirectional charging. This method is also seen as a potentially more cost-effective solution, benefiting from vehicle-scale production economies and simpler installation processes. However, the additional costs of this feature would ultimately be embedded in the cost of every equipped/sold EV. At the same time, from a regulatory and standards perspective, the requirements are still evolving, and clear frameworks are yet to be established which may lead to further complexities and unforeseen hardware changes in AC bidirectional charging.

A key challenge is that if energy from the EV is fed back into the house or even into the grid, the respective requirements from the grid operator must be fulfilled. In the case of an AC charger an EV must distinguish between different grid requirements, depending on where the vehicle is currently plugged in.

Key Challenges in Bidirectional Charging

Achieving widespread adoption of bidirectional charging technologies requires addressing several factors, with technological readiness being central to Fronius as a technology provider. The preparedness of EVs and EV chargers to work seamlessly and interoperability is key piece of the puzzle. A core element in interoperability is the communication standard utilized by CCS, specifically the ISO 15118 series. ISO 15118 is the standard for communication between EVs and chargers within the CCS framework. The series comprises two key versions: ISO 15118-2 and the more recent ISO 15118-20.

ISO 15118-2: Foundation for Communication of CCS Charging

ISO 15118-2 introduced features such as Plug & Charge, enabling automated authentication and billing processes which EV manufacturers are already implementing. However, while ISO 15118-2 makes this possible, the framework lacks the specifications required for seamless and interoperable bidirectional charging applications. Despite ISO 15118-2 not addressing bidirectional charging, technicians found tricks to make it possible which are outside of this specification. Besides this, manufacturers can leverage proprietary communication via the included VAS (value added services) in ISO15118-2. Therefore, implementations of ISO 15118-2 vary among manufacturers, leading to the development of OEM specific bidirectional charging solutions. Some EV OEMs are also pursuing proprietary bidirectional charging solutions, further limiting interoperability across brands; however, this is likely to be an intermediary solution.

ISO 15118-20: The Advancements and Challenges

ISO 15118-20 enhances its predecessor by fully supporting V2G functionalities, providing a more robust framework for bidirectional energy integration. This standard is well defined for DC bidirectional charging, however AC bidirectional charging was left out. This is intended to be fixed with additional amendments to the standard, which are in draft form at the moment. ISO 15118-20 introduces advanced security measures, including enforced data security protocols such as TLS 1.3, to protect communication between EVs and chargers, which is especially important in the public charging domain. However, the adoption of ISO 15118-20 is not yet widespread on cars, and its implementation is still evolving. Moreover, ISO 15118-20 is not backward compatible with ISO 15118-2, meaning that EVs and chargers will support both versions for seamless functionality.