Why AC-Bidirectionality is the key to a widescale V2G deployment

Why AC-Bidirectionality is the key to a widescale V2G deployment

Dennis Schulmeyer

Vehicle-to-Grid (V2G) is a powerful vision, with the potential to transform energy systems on a large scale and highly efficient. The basic idea is that BEV are used to temporarily store power when renewable energy sources supply more power than is needed, and to feed it back to the grid when demand is higher than supply.

More and more OEMs have started offering vehicles that can charge bidirectionally, a technical prerequisite for V2G. Generally, this can be done in two ways, with AC or DC. Which one is chosen determines where the bidirectional charger is located: Bidirectional AC charging requires a corresponding onboard charger (OBC), while bidirectional DC charging needs a charger in the charging point.

Some manufacturers already opted for DC. I think, however, that we would give away an enormous opportunity. In my view, a widescale implementation of V2G in the service of a fast, effective tackling of climate change, is only possible with bidirectional AC charging.

Why V2G is important

To keep power grids stable, supply and demand must always be balanced. Wind and sun, however, don’t care about human energy needs. If we want to use renewable energy sources on an industrial scale, we need massive and highly agile storage capacities.

Here, BEV have several advantages over other storage options. First, they will be there anyways: millions of mobile, high-capacity battery packs. At the same time, they’re mostly idle. In Germany, cars are parked around 23 hours per day on average. It would be a tremendous waste of resources to not use that storage capacity.

Given a smart connection to the grid, BEV can store and deliver the power with the necessary speed to provide operating reserve: Short-term frequency deviations in the electricity grid must be adjusted in a matter of seconds. With V2G, connected electric vehicles can easily provide such adjustments by charging or discharging their batteries.

Third, where there are a lot of cars, i.e., areas with dense population and / or industry, usually the overall energy consumption is also higher. In other words, the storage created by the vehicles’ batteries would be distributed according to the power demand. This would help ease grid congestions and reduce the need to upgrade power grids tremendously, speeding up the energy transition even further while at the same time reducing costs.

Image of World Map of Mains Voltages
World Map of Mains Voltages

Challenges of scaling

During the day, cars are being parked in various places. To harness as much of that time as possible for V2G, the cars need to be able to connect to the grid everywhere people regularly park: at home, of course, but also at work, at the supermarket, the sports park, the gym etc. In short: The number of charging points must be greater than the number of cars.

This creates several challenges, like the need to orchestrate millions of charging processes, considering individual user needs and preferences as well as real-time adaptions to physical conditions of the electricity grid. These issues need to be addressed with both hardware and software. With our company LADE we are working on a comprehensive, scalable solution that solves these problems.

But it also has an important economic implication: When talking about such big numbers, charging points should be as cost-efficient as possible.

AC will always be cheaper than DC

DC charging has some great benefits, especially when it comes to speed. From long distance trips to emergency rescue, there’s a number of very plausible use cases. When time is not of the essence, however, the advantages of AC charging increase tremendously, especially in terms of economic efficiency.

A key factor in this is the location of the bidirectional charger. As mentioned before, it’s inside the vehicle when charging bidirectionally on AC, and in the charging point when charging bidirectionally on DC. This reason alone makes AC charging infrastructure much less complicated to build and maintain, and there are more. AC charging infrastructure is and always will be cheaper.

Put differently, we have to decide whether to install the bidirectional chargers inside the car or the charging infrastructure and we should choose the option requiring less resources. Considering a nationwide V2G-grid, the difference between AC and DC charging infrastructure would add up to dozens of billions of Euros in Germany alone. For the vast majority of use cases, the AC option is better both in terms of economic efficiency and sustainability.

Nonetheless, there are reservations and misconceptions revolving around bidirectional AC charging, which I want to address.

Objection 1: It’s too complicated and expensive to equip BEV with an OBC.

Yes, installing bidirectional AC chargers inside the vehicle causes costs and complexity. However, the additional expenditures are smaller than one might think. At least in Europe, onboard chargers for regular (unidirectional) AC charging are already mandatory to ensure power supply in emergencies. The costs to make AC chargers bidirectional would add up to a few dozen Euros per vehicle. The additional weight also doesn’t make that much of a difference.

More importantly, I think this is not a burden, but an opportunity! For OEMs, bidirectional onboard chargers are a gateway to create even more value for their customers. The use cases for Vehicle-to-Load are endless, from charging a laptop to powering a cooling unit on a camping trip or a market stand. Going even further, Vehicle-to-Grid transforms the vehicle into a source of revenue. AC infrastructure, enabling comprehensive coverage, would help to maximize that income. I am sure customers are willing to pay for such benefits.

Objection 2: AC charging capacity is too low.

AC charging sometimes has the image of being slow. Setting aside the fact that this is better for the battery: If the number of cars connected to the grid is large enough, AC charging is more than enough. Assuming an average battery capacity of only 50 kWh per car and a maximum charging power of 11 kW, all BEV that are already driving on German roads today would provide a capacity of 31 GWh and a possible power rating of 6.82 GW. This practically resembles the power of all hydro pumped storage facilities in Germany and 80 % of their capacity.  By 2030, some 15 million BEV in Germany seem reasonable: If only half of them is connected to the grid with an onboard bidirectional charger capable to deliver 11 kW, this sums up to 82.5 GW, which could power all of Germany! 11 kW surely is more than enough!

To make the potential of V2G more tangible, we created a tool that simulates and visualises the potential of V2G (free to use at v2g.lade.de). Based on real world data, the tool simulates scenarios for the expansion of e-mobility and renewable energies. Of course, the reality is complex, but the tool illustrates quite nicely that wind, solar and V2G alone can serve a huge portion of energy demand.

Objection 3: Different OBC would be needed for different regions of the world.

The third objection draws on the fact that globally, different grids operate on different technologies. Onboard chargers would need to reflect this. More specifically, they need to feed power with a certain frequency into the grid. OEMs would be required to fit their products with different hardware depending on the region.

Again, I think this is much less of a problem than many think. Firstly, it’s actually not that many different regions. If you look at a world map of grid frequencies, you can see that all of Europe, most of Asia, Australia and Oceania, most of Africa and parts of South America are running their grids on around 230 V and 50 Hz. North and Central America can be covered with a second type of charger. With only two different hardware parts, the vast majority of the world could be served.

Secondly, its nothing new for car manufacturers to adhere to different regulations. There can be several hundred different parts in the “same” car in the European Union and the US, ranging from control units to the bending of the rear mirror. I don’t say that’s always easy or convenient, but one should assume that OEMs have a lot of experience and expertise in this regard. In any case, if this effort helps to substantially cut CO2 emissions with cars, of all things, it should be worth it.

A graph showing a V2G-Simulator
V2G-Simulator:
  • Blue line: Grid load
    • Red shaded: Residual load
    • Light green: Batteries charge
    • Dark green: Batteries discharge
    • Yellow: Photovoltaics
    • Dark blue: Wind onsore
    • Light blue: Wind offshore
    • Grey: Hydropower

Joint efforts

As a developer and producer of AC charging infrastructure, I don’t want to escape responsibility. I don’t argue for bidirectional AC charging because we produce AC charging points. Rather, we produce AC charging points because we consider it the more efficient, more sustainable technology.

V2G for climate’s sake can’t be realised by one company or one country alone. It needs teamwork, cooperation, and open standards. To do our part, we develop hardware that is not only scalable and cost-efficient, but also assures the quality of the power fed into the grid to ensure network stability. In this regard, we see ourselves as partners or trustee for both grid operators and OEMs, helping to ensure grid quality and reliability of supply.

To help implement V2G successfully, we are already working with OEMs, suppliers and research institutes. Developing smart, innovative, and beneficial technical solutions, we hope to help speed up the world’s transformation to renewable energies.

Dennis Schulmeyer, founder and CEO of LADE GMBH

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