Most cars are idly parked 90-95% of the time. With an accelerated shift to using electric vehicles (EVs), batteries of EVs offer enormous potential in terms of using their vast collective storage capacity as a flexible solution to support the grid, which can be taxed with an intermittent renewable energy supply. Bi-directional electric vehicle charging (V2X) refers to EV chargers that allow not only for charging the battery of the EV but also for taking energy from the car battery and pushing it back to the grid when needed.
There are two primary receivers of power from an EV: the grid (V2G) and the electricity from a home or building (V2H). Bi-directional charging creates greater synergy between the clean transport sector and renewable energy sources, as the car batteries can store excess energy created by variable renewable sources, such as wind and solar, and then provide power to the grid or home when demand is high or energy production is low. This reduces curtailment, lowers the need for grid infrastructure investments and allows for higher renewable energy integration. In addition, V2H charging can act as an emergency power source during power outages, and V2G can provide vehicle owners with extra income through arbitrage of time-variable energy prices.
Problems to be solved
|Grid congestion ||Growing energy consumption ||Fluctuating generation of renewables ||Uneven peaks in energy usage |
The costs of a bi-directional electric vehicle charging system occur due to the interface costs, which are 3-5 times higher than that of unidirectional smart charging. Additionally new hardware is neccessary and the batteries might be degredated more quickly.
As cities generate more and more renewable energy to reach their carbon neutrality targets, bidirectional charging offers a cheaper energy strorage system to balance and optimize the grid. However, for bi-directional charging to be successful in a city, there must be regulations and policy supporting such a solution:
- For V2G technology to be enticing enough to be deployed at a high scale, EV owners must be able to ‘stack’ revenue streams from the flexibility services their car battery provides. A Danish pilot project found revenue streams of an average 1860 EUR per year (Andersen, 2021).
- There also needs to be a high level of EV deployment in the city with the same V2X capabilities to enable aggregation of the EV batteries to create a sort of virtual power plant.
- The EV charging stations and distribution networks need to be interoperable to prevent vendor lock-in and allow for cost-effective connectivity between EVs and diverse charging infrastructure.
- Studies have additionally shown that solar-based electricity systems see the most incremental benefits from bidirectional charging.
As the technology is new, cities can promote sustainable behavior by building the infrastructure on a small scale (e.g. the municipal fleet) with the intention to build on the solution long-term. In addition, to support wide scale deployment of bi-directional charging, newly planned charging stations should be ‘smart’ chargers that are capable of facilitating the grid service described with the V2X solution.
Stakeholder Map of a Bidirectional Electric Vehicle Charging System (BABLE, 2021)
According to Germany’s Centre for Solar Energy and Hydrogen Research (ZSW), 5.6 million EVs were on the world’s roads as of the beginning of 2019. If most of the passenger vehicles sold from 2040 onwards were electric, more than 1 billion EVs could be on the road by 2050. This would mean that by mid-century around 14 terawatt-hours (TWh) of EV batteries would be available to provide grid services, compared to a projected 9 TWh of stationary battery capacity. EVs typically only need to charge for 10% of the time they stand idle and are parked 95% of the time, leaving 85% of their lifetime to, in theory, provide grid flexibility services (Mohammadi, 2019).
Bi-directional charging points are still a nascent technology and very few are on the market. Thus, the cost structure varies widely and is expected to change as the technology matures.