Bidirectional charging allows an EV not only to draw power from the grid to charge its batteries but also to discharge and supply power back to the grid or a home. The technology could redefine the role of EVs in our energy systems, presenting both opportunities and challenges for the future of electric mobility and grid management.

The dual functionality of bidirectional charging is facilitated by power electronics and communication systems integrated into both the vehicle and the charging infrastructure. The concept relies on two primary modes: vehicle-to-grid (V2G) and vehicle-to-home (V2H) or vehicle-to-building (V2B).

V2G technology enables EVs to provide power back to the electrical grid through a bidirectional charger that includes a DC to AC converter. This system allows EVs to support local, regional or national energy needs by intelligently managing charging cycles. During periods of low energy demand, EVs can charge, and during peak demand they can return electricity to the grid.

This approach takes advantage of the fact that cars are typically parked 95% of the time, meaning that with the proper infrastructure and strategic planning, parked EVs could serve as large-scale energy storage units. Consequently, EVs can act as mobile batteries, contributing to the stability and reliability of future power grids, ensuring a consistent energy supply for all users. Notably, a UK Power Networks study highlighted that airport car parks could potentially power 1.3 million homes, demonstrating the large-scale applicability of V2G technology.

V2H (and V2B) technology enables EVs to supply electricity to a house or other buildings through a bidirectional charger with a built-in DC to AC converter. V2H, similar to V2G, helps balance local and national energy grids. By charging an EV at night when electricity demand is low and using that stored power to run a home during the day, V2H can reduce electricity consumption during peak periods. This ensures homes have sufficient power when needed and reduces the overall strain on the grid. In the UK, the Park & Flex project aims to optimise this potential by integrating EVs into local energy systems to enhance flexibility and efficiency.

Bidirectional charging versus smart charging
Smart charging optimises the EV charging process by controlling the timing and rate through a smart device rather than a manual on/off switch. This system utilises data connections between the EV and the charger. For example, smart EV charging apps manage the charging to schedule for the most efficient times based on demand and cost, which varies by country and energy operator. This can lead to economic benefits for customers, such as preferential night-charging rates. In addition, smart charging helps prevent grid overload by avoiding simultaneous charging by many EV owners.

While bidirectional charging focuses on the vehicle's interaction with the grid to supply and receive energy, smart charging emphasises optimising ‘when and how’ the EV charges to enhance efficiency and cost-effectiveness.

A bidirectional charger leverages the vehicle as a distributed energy resource (DER). This approach provides substantial financial benefits and contributes to grid stability, especially as more renewable energy sources are integrated.

With a bidirectional charger, an EV can return excess energy to the grid, providing a source of income potentially. This is particularly advantageous in countries with varying energy prices throughout the day, such as Spain or the UK. Charging the EV during off-peak hours and discharging during peak hours enables capitalisation of dynamic pricing models. Initial studies estimate that an EV could bring its owner around €400 a year, potentially totalling €3,700 over the vehicle’s lifetime. Participation in frequency regulation markets can increase these earnings significantly, with estimates of up to €9,000 over the car’s lifetime.

Bidirectional charging also facilitates energy resilience at both household and community levels. In the event of power outages, EVs equipped with bidirectional chargers can act as backup power sources, ensuring electricity is available for essential needs such as powering heaters, refrigerators and other essential devices.

Similarly, after the 2011 earthquake and tsunami in Japan, which caused widespread power outages, Nissan Leaf owners used their vehicles to power their homes. Elsewhere, a pilot project in the Netherlands showed that neighbourhoods with multiple bidirectional EVs could maintain essential services during grid failures, significantly improving community resilience.

According to the National Oceanic and Atmospheric Administration (NOAA), the frequency of extreme weather events in the US has increased by 67% since the 1980s. As these events become more common, the ability to use EVs as backup power sources will become increasingly valuable.

Bidirectional charging not only supports individual households but also contributes to broader energy security. For example, a study by the University of Warwick found that if 10% of vehicles in a city were equipped with bidirectional charging, they could supply up to 4.5% of the city’s electricity demand during an outage, significantly enhancing overall grid resilience.

In the event of power outages, EVs equipped with bidirectional chargers can act as backup power sources, ensuring electricity is available for essential needs such as powering heaters, refrigerators and other essential devices.

Challenges and considerations
While the potential benefits of bidirectional charging are significant, several challenges must be addressed to fully realise its potential.

A key priority for EV owners is battery degradation. There are fears that frequent cycling of the EV battery for grid services can accelerate battery degradation. However, one study found that continuous use of V2G technology could actually reduce battery degradation by 10%. Meanwhile, research conducted by the National Renewable Energy Laboratory (NREL) found that while V2G services could lead to quicker battery wear, advanced battery management systems (BMS) are being developed to mitigate this issue. Companies like Tesla and Nissan are investing in BMS technology to ensure that the economic benefits of V2G outweigh the costs associated with reduced battery lifespan. Another study by the University of Warwick showed that smart charging algorithms could reduce battery degradation by as much as 50%, making V2G more economically viable for EV owners.

Also, the implementation of bidirectional charging requires supportive regulatory frameworks. This includes market structures, incentives and policies that encourage EV owners to participate in grid services. In California, the California Public Utilities Commission (CPUC) has introduced regulations that support V2G technology, offering financial incentives for EV owners who provide grid services. Similarly, Japan’s Ministry of Economy, Trade, and Industry (METI) has established guidelines to integrate V2G into the national grid, promoting energy resilience and efficiency.

A far greater challenge is that widespread adoption of bidirectional charging necessitates significant upgrades to the existing electrical infrastructure. This includes the development of compatible charging stations and grid integration technologies.

A report by the International Energy Agency (IEA) highlights that by 2030, over $600bn/y will be needed globally to upgrade electrical grids to support V2G technology. The good news is that it is possible. In Denmark, the Parker project has integrated V2G technology into the national grid, demonstrating the feasibility of such infrastructure upgrades.

Thirdly, for bidirectional charging to be successful, EV owners need to be educated about its benefits and operational complexities. User-friendly interfaces and integration with existing energy systems are vital for driving consumer adoption. A survey by the Smart Electric Power Alliance (SEPA) found that 70% of EV owners were unaware of V2G technology, indicating a significant gap in consumer knowledge. Educational programmes and intuitive software solutions are essential for increasing awareness and adoption rates. Companies like Enel X are developing platforms that simplify the V2G process, making it more accessible for everyday consumers.

The path forward
Bidirectional charging could revolutionise the role of EVs within our energy systems. By enabling EVs to both draw power from and supply power to the grid, this technology offers significant benefits for grid stability, renewable energy integration and individual financial savings. The capacity of EVs to act as mobile energy storage units can enhance energy resilience, particularly during power outages and extreme weather events.

While challenges such as battery degradation, regulatory hurdles and the need for infrastructure upgrades must be addressed, ongoing advancements in battery management systems, supportive policies and pilot projects demonstrate the feasibility and potential of bidirectional charging.

• Further reading: ‘End of the ICE Age looms as EV sales accelerate’. Electric vehicle (EV) sales are steadily lapping those of traditional internal combustion engines (ICE) across the globe. But sales are not linear in all markets. And the effect of removal of subsidies cannot be dismissed, along with concerns about having sufficient batteries.
• Cleaner and greener transport is a crucial part of the UK’s journey to net zero, and EVs have a vital role to play in this urgent transition. Melanie Shufflebotham, Chief Operating Officer, Zapmap, looks at the current state of play in the UK EV charging infrastructure and the challenges ahead.