Series Electromobility: Use Cases for bidirectional charging

Electromobility is a central research area of the FFE and is part of numerous research projects. In the following series of articles, different topics are presented. One focus is on scenarios for electric vehicles and charging stations in Germany. Furthermore, the different charging plugs are explained and different possibilities of grid integration by controlled and bidirectional charging are described. Finally, the climate footprint of electric vehicles is discussed.

This article is the sixth of a series of 7 articles which will now be published successively on our website.

Overview of the topics of the article series on electromobility
1.   Development of electromobility
2.   Charging points
3.   Plugtypes
4.   Private and public charging
5.   Smart Charging
6.   Use Cases for bidirectional charging
7.   Climate assessment of electric vehicles

 

Bidirectional charging creates a number of opportunities in its connection to the grid, homes or commercial buildings that can generate a source of revenue. These opportunities have been identified as Use Cases and will be developed in the project “Bidirectional Charging Management” (BCM).

The bidirectional charging Use Cases can be separated into three groups: Vehicle-to-Grid (V2G), Vehicle-to-Home (V2H) und Vehicle-to-Business (V2H). V2G means active marketing or the provision of system/network services by bidirectional electric vehicles (EVs) so that costs are reduced or income is generated (front-the-meter). In contrast, the other two groups aim at local optimization behind the meter.

Table 1 gives an overview of selected bidirectional charging Use Cases and their implementation in BCM.

 Use cases for bidirectional charging

Table 1: Overview of selected bidirectional charging Use Cases

Short description of the Use Cases:

 

Peak shaving: Reduction of the peak load at a (company) location with recording performance measurement (RLM) by controlled charging/discharging of bidirectional vehicles. This results in a price reduction due to the lower maximum contracted power.

Increase of self-consumption: Increase of self-consumption of generated electricity (e.g. by a PV system) or reduction of grid usage by temporarily storing the excess electricity in the vehicle battery and supplying the household from this less expensive energy stored in the bidirectional EV.

Time arbitrage (Intraday): Aggregation and marketing of the dis-/charging flexibility of bidirectional vehicles on the intraday market. The EV is charged at times when prices are low and discharged when prices are high.

Time arbitrage (Day-Ahead): Aggregation and marketing of the dis-/charging flexibility of bidirectional vehicles on the day-ahead market. The EV is charged at times when prices are low and discharged when prices are high.

Real green electricity (with PPA): Optimization of the load profile at a commercial site with bidirectional vehicles to achieve the highest possible proportion of green electricity in order to maximize energy volumes contracted under power-purchase agreements (PPA), save money and (demonstrably) build a green image.

Primary balancing power: Provision of primary balancing power with an aggregated bidirectional EV pool. The Electric Vehicle Supply Equipment (EVSE) measures the grid frequency decentral (or perspective regional measurement by TSO) and discharges if the grid frequency is too low or charges if the frequency it too high.

Local network service: Provision of local flexibility for the DSO (possibly TSO) to remedy network bottlenecks. The bidirectional vehicles dis-/charge based on a signal from the network operator or an aggregator.

Redispatch: Provision of regional flexibility for TSO/DSO to deal with bottlenecks in the transmission/distribution grid. For this purpose, bidirectional EVs charge in front of the bottleneck and discharge behind the bottleneck.

Provision of reactive power: Supply of reactive power specified by the grid operator in a defined network region by the EVSE. The required reactive power is specified by the network operator. The reactive power can be provided continuously by the EVSE, even without a connected EV.

Tariff-optimized dis-/charge: Utilization of time-variable electricity tariffs by charging at times when electricity prices are low and discharging the EV battery to supply the household at times when electricity prices are high.

Fleet management: Optimize the fleet charge, so the maximum grid usage is reduced. If necessary, EVs feed energy back to enable the charging of higher-priority EVs without exceeding the maximum supply power. This Use Case is very similar to peak shaving.

Real green electricity (CO2 based): The bidirectional EVs are charged in times of low specific CO2 emissions in the grid area and discharged in times of high specific CO2 emissions.

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