3. August 2023 By Ellen Szczepaniak and Felix Magdeburg
Vehicle-to-grid – the Holy Grail of storage solutions?
At the end of the film Indiana Jones and the Last Crusade, Harrison Ford is forced to make a nearly impossible choice: pick out the Holy Grail from the plethora of cups and goblets in front of him. How could he know which one was the right one?
Turning our attention back to the real world, we must not forget the all-too-present challenges we face in the energy transition. These include the influence of fluctuating weather patterns on supply stability, grid expansion and the storage of electricity.
Storing electricity is still one of the main challenges in the energy transition. This is down to the fact that electricity also needs to be consumed again when it is generated so as not to impair the quality of the electricity grid. If a disproportionately larger quantity of electricity is consumed than is generated, or vice versa, this might cause a blackout. The transformation from centralised energy generation to decentralised energy generation will lead to increasingly strong load peaks in the grid due to the use of wind and PV systems. These load peaks must therefore be absorbed by storage technologies. There are already some options available for storing surplus electricity, for example, via pumped storage power plants, power-to-heat and power-to-gas plants, large-scale batteries or coupled swarm storage (many virtually interconnected and controllable small batteries). The market has high hopes for the new vehicle-to-X technologies.
Vehicle-to-home, vehicle-to-load or vehicle-to-grid
Vehicle-to-home (V2H) describes the approach in which electricity from the battery of an electric car is fed back into the home grid or a grid in other buildings. This allows home optimisation, tariff-optimised charging/discharging to be controlled or power outages to be bridged.
Put simply, vehicle-to-load (V2L) describes the charging of household appliances directly via the car’s battery. For example, mobile phones, hairdryers or laptops can be charged and operated directly from the car’s battery via an integrated Schuko plug socket (the type of plug used throughout most of Europe).
Vehicle-to-grid solutions (V2G), on the other hand, are a concept for supplying electrical power from the batteries of electric and hybrid cars back into the public grid. Unlike purely electric cars, vehicles that are capable of bidirectional charging are not only able draw electrical energy from the grid, but also feed it back into the grid or home via special charging stations as part of an intelligent energy system during increased grid load periods (bidirectional charging). The advantage here is that security of supply is ensured. Whereas up to now the market has provided the supply based on demand, in the future, the supply will show a much higher fluctuation, as there will not always be the same amount of sunshine and wind. In the event of increased supply, V2G-capable vehicles can be used to absorb surplus electricity or to provide balancing power in the event of increased demand.
Vehicle-to-grid approaches are based on the fact that most vehicles are parked for most of the day. For example, most private vehicles in Germany are on the move for less than two hours a day and are thus available for V2G applications for most of the day. Since the charging time is usually much shorter than the actual standing time, the charging time of the batteries can be adapted to the respective requirements in the power grid and the electric cars can thus be used for load management. Assuming that 70 per cent of vehicles have a battery size of 20 kilowatt hours (kWh) and the battery is 50 per cent charged, one million electric cars could provide seven gigawatt hours (GWh) of additional storage capacity. Even if all the vehicles were only connected to the grid in single phase via normal, three-kilowatt household sockets, there would still be a control power of 2.1 gigawatts available. However, if 90 per cent of all cars in Germany were converted to electric cars as described above, they could store 277 GWh of electrical energy and provide 83 GW of balancing energy.
In addition, all vehicle-to-x applications enable sector coupling. This would require all electric cars to enable bidirectional charging, which is far from being the case for all e-vehicles or is only possible to a limited extent. The energy flow is controlled by a bidirectional charging option such as a wallbox or a home energy management system (HEMS).
Which solutions are the best ones right now?
We have said that V2G is not the same as V2H or V2L. But the technological requirements for the respective electric cars to support a bidirectional charging flow are the same.
If electric cars are to be used as decentralised storage locations in the future, then they will need to be supported by the right infrastructure. The bidirectional charging process for electric car sees the alternating current (AC) from the power grid converted into direct current (DC). This is necessary because the battery of the electric car only works and is operated with direct current. The conversion takes place either in the electric car or in the charging infrastructure via a built-in inverter in each case. Vehicles manufactured in Asia that are equipped with a CHAdeMO plug are able to feed electricity back into the grid in particular.
There are only a few models that support bidirectional charging right now. These include the Nissan LEAF, the Nissan e-NV200, the Mitsubishi Outlander, the Mitsubishi i-MiEV, the Hyundai Ioniq 5, the Kia EV6 and the Volvo EX90 (from 2023). In addition, the latest Volkswagen ID.3 and ID.4 models can be retrofitted with the technology.
Unlike the choice Indiana Jones had to make, there is actually more than one correct answer here – in fact, all of the solutions are valid ones and can be used for their individual scenarios. Let us now trade theory for real life application so we can compare the three solutions in greater detail.
In order to use V2X technologies in principle, the electric vehicle (BEV) must have a bidirectional charging function and be connected to a charging point to be able to use this functionality. This in turn means that the charging infrastructure must be expanded on a massive scale, not only to charge the car, but also to be able to use it as battery storage in the grid. This would mean expansion not only on motorways, but also in urban centres, workplaces and places where people park for long periods of time.
In terms of the technical implementation, this solution must be able to communicate with the charging infrastructure in addition to the necessary battery and the battery management system (BMS), and an inverter must be installed to convert the electricity.
Furthermore, although both AC and DC charging are both suitable charging options, it makes more sense from an economic point of view to use AC charging points for the integration into V2X, as they are much cheaper. In addition, the ability to rapidly charge and discharge is probably not needed if a suitable target size of vehicles is provided. At the moment, however, only the Asian CHAdeMo fast-charging system supports bidirectional charging. The European/North American CCS variant should also support bidirectional loading in conjunction with ISO 151118.
The first use cases:
In October 2018, charging solution provider The Mobility House, energy supplier ENERVIE, transmission system operator Amprion and car manufacturer Nissan unveiled the first bidirectionally chargeable electric car (Nissan Leaf) that qualifies for primary control power according to all the regulatory requirements of a transmission system operator (TSO). This means that this electric car can be integrated into the German power grid as a control power plant and compensate for fluctuations (such as impending power outages) in the power grid within seconds by feeding in primary control power.
In addition, a study carried out in Switzerland has shown that using electric battery storage systems as buffer storage can reduce electricity system costs by up to 14 per cent. The vehicle also created additional advantages thanks to its more efficient utilisation of renewable energies – provided they can be stored temporarily during peak production periods – and in fact, it lessens the severity of market price fluctuations between hours and days.
In addition to these opportunities, there are still also questions that need answering, such as: How might this be scaled economically? How will the participants in this market be remunerated? How will the control system be implemented? One possible solution to these questions could be to use virtual power plants to control swarm batteries.
And how does the story end?
We cannot say with any certainty that we have found the Holy Grail like Indiana Jones did. It is likely that a combination of technologies will end up being implemented. What is certain, however, is that there will be more storage options on the market to meet the high demand or supply of electricity.
You can find more exciting topics from the adesso world in our previously published blog posts.