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Bidirectional charging: The (still) missing piece of the modern energy system puzzle

Electric vehicles are increasingly becoming a key component of a sustainable energy system. Thanks to bidirectional charging, they can not only absorb and store energy, but also feed it back into the grid when required. This capability opens up a wide range of possibilities – from stabilising the electricity grid to optimising energy costs and making more efficient use of renewable energies.

However, bidirectional charging not only brings with it practical applications, but also expands the function of electric vehicles into flexible energy storage systems with added value for the entire energy system. But what technical, regulatory and economic framework conditions need to be created in order to establish bidirectional charging on a large scale – and how can users and providers alike be integrated into such a system? In the current issue of eMove360° magazine in german language, Kien Khang Le, charging infrastructure expert at Stuttgart-based charging infrastructure specialist eliso, explains the opportunities and challenges now facing the industry.

Bidirectional charging: From vehicle to energy centre

Bidirectional charging opens up far more possibilities for electric vehicles than just mobility. They are becoming essential components of a future-orientated energy system and are making an important contribution to the energy transition. There are various possible applications, in particular vehicle-to-grid (V2G). This concept makes it possible to feed the electricity from the electric vehicle battery into the public power grid via a suitable charging infrastructure. This allows energy to be fed back into the grid when demand is high, while electricity is stored in the vehicle when there is a surplus. In this way, electric vehicles are integrated into the energy system in a grid-friendly manner, helping to smooth load peaks and increase security of supply. There is also economic potential, for example through electricity trading or the provision of balancing power.

Furthermore, with vehicle-to-home (V2H) or vehicle-to-building (V2B), the vehicle battery is used as a stationary storage unit that provides electricity for homes or buildings in order to optimise self-consumption, reduce costs when electricity prices are high or provide emergency power. In addition, Vehicle-to-Load (V2L) allows the battery to be used as a mobile power source. This enables the flexible use of electrical energy, for example when camping to power appliances such as fridges or lighting, on construction sites for power tools or in emergencies to supply medical equipment or other critical infrastructure with electricity.

Balancing load peaks and utilising excess capacity

Vehicle-to-grid (V2G) is a key component in the expansion of a public charging network. ‘Vehicle-to-grid turns electric vehicles and charging stations into active elements of grid stabilisation that can effectively balance out fluctuations in the energy system,’ says Kien Khang Le.

‘V2G makes it possible to store surplus electricity in vehicle batteries and feed it back into the grid when required, thereby increasing security of supply and achieving more efficient utilisation of existing energy resources. At the same time, vehicle owners can benefit from financial savings.’

But how exactly does it work? When using V2G, electric vehicles are intelligently connected to the power grid via a charging infrastructure. The charging points communicate with the grid in real time and control the flow of energy as required. ‘If electricity consumption in the grid suddenly increases, electric vehicles can feed energy from their batteries into the grid to compensate for peak loads. Conversely, the vehicles charge their batteries when there is overcapacity in the power grid, for example on sunny days or in strong winds when a particularly large amount of renewable electricity is being generated. In this way, they stabilise the power grid and promote the efficient use and integration of electric vehicles and renewable energies into the energy system.’

Technical requirements

One of the key requirements for V2G is bidirectional inverters and smart metering systems to measure and bill energy flows. Smart load management solutions ensure that the available energy is distributed efficiently. Standardised communication interfaces, such as the ISO 15118 standard, play a central role here. They enable standardised and efficient data transmission between the vehicle, charging point and grid operator. Without these standards, smooth interaction and coordination between the players involved would not be guaranteed. In particular, the ISO 15118 standard ensures secure authentication, the optimisation of charging and discharging processes and the integration of intelligent functions such as plug-and-charge.

For the use of bidirectional charging, the grid connection capacity on site must also be taken into account. This must be designed in such a way that both charging and feeding back energy is possible without jeopardising grid stability. Another technical challenge is the precise measurement of energy flows, which must be individually assigned to each vehicle. ‘The allocation of energy flows is not only a technical challenge, but also a challenge in terms of data protection and tax law, which must first be regulated by the legislator.’

Regulatory challenges

In addition to the technical infrastructure, a clear regulatory framework is required. These include standards for the grid connection, minimum and maximum capacities for feeding energy back into the grid and regulations for vehicle access to the V2G market. ‘We need clear guidelines on how electric vehicles can and may operate as mobile storage units,’ says the expert.

In addition, ambiguities regarding grid charges and potential levies on energy fed back into the grid still need to be resolved. In order to make V2G attractive for all parties involved, business models that make sense for the market must be developed in addition to the technical and regulatory framework conditions.

eliso specialises in charging infrastructure and has been operating charging stations for the electric car drivers of today and tomorrow since 2016. Headquartered in Stuttgart and based in Berlin, the company builds and operates a constantly growing network of public ultra-fast charging stations for all electric vehicles throughout Germany. In doing so, eliso is focussing on future-proof locations in convenient locations where charging is possible with up to 400 kW charging power. From the very beginning, eliso has made it its mission to work on the electromobile future every day and create the structures for sustainable mobility. Since 2022, eliso has been part of VINCI Concessions, one of the leading European operators of mobility infrastructure. In September 2023, eliso was selected by the federal government as the operator for the German network.