10.2023 - 11.2023

Flexumer – Model-based evaluation of annual electricity costs of various private flexumers

The Flexumer project was commissioned by DEW21 – Dortmunder Energie- und Wasserversorgung GmbH. The background of this project is section §14a of the EnWG, which came into effect on the first of January in 2024, regarding the integration of controllable electricity-consuming assets. Controllable energy-consuming assets, such as private heat pumps and charging stations for electric vehicles, have higher power levels than most common household appliances. Additionally, these controllable assets often involve simultaneous electricity consumption. As a significant portion of the existing low-voltage grids are not adequately designed for a rapid increase in electrification, the network operator is allowed to temporarily reduce the electricity consumption of controllable energy-consuming assets to ensure the security of supply. During times of high grid load network operators may reduce the consumption to as low as 4.2 kW. Within the project, an investigation was conducted to assess how this power limitation affects electricity costs in private households with different types of controllable electricity-consuming assets (Flexumers). The project’s objective is to determine the annual electricity costs for various groups of Flexumers in the DEW21 grid area. DEW21 aims to integrate these results into an analysis in collaboration with envelio GmbH to determine in which scenario lower costs for the overall system arise:

  • Scenario 1: Network-optimized (Network) – Flexumers are curtailed as needed (§14a) ⟷ Network expansion costs are kept as low as possible
  • Scenario 2: Market-optimized (Market) – No power limitation, Flexumers can operate market-oriented ⟷ Larger network expansion is expected


The first step is the joint definition of different Flexumer groups in the DEW21 grid area. The respective flexumer groups can consist of electric vehicles, heat pumps, stationary battery storage systems and photovoltaic systems. In addition to defining representative properties for the components under consideration, synthetic driving profiles of the electric vehicles and representative electrical and thermal load profiles of the households from the household generator are generated for the subsequent simulations. The linear optimization model eFlame then calculates the minimum annual electricity costs of the respective flexumer groups. The year 2021 was used as the observation period for the simulations. In order to create a comparison according to the two scenarios, the different groups are each optimized once with a curtailment to 4.2 kW or without power limitation. The final step is to evaluate the simulation results.

Figure 1: Methodology in three steps


Figure 2 shows the flexumer groups defined for the study. A representative single-family household with an average annual electricity consumption of 3000 kWh/a and a specific space heating requirement of 100 kWh/(a m²) was analyzed. With regard to the charging strategy, the electric vehicle in group G can be charged bidirectionally.

Figure 2: Definition of the different flexumer groups

In addition to the grid– and market-optimized scenarios, direct charging was also considered as a reference in the results. In this case, the electric vehicles are charged uncontrolled as soon as they are plugged in at the wallbox. Figure 3 illustrates the annual electricity costs and the annual peak power for the various flexumer groups. In the grid-optimized scenario, the annual electricity costs increase only minimally, although the annual power peak for all groups is drastically reduced to 4.2 kW. Therefore, under the assumptions made for Flexumer, only minor annual additional costs for electricity (< €100) are to be expected due to grid restrictions. A comparison of the different flexumer groups shows only minor effects on flexumer with only one flexible component (A, H). Flexumers whose optimization tends to take place behind-the-meter (B, F) are also less affected by the power limitation. Groups with high front-of-the-meter flexibility (C, D, E, G), on the other hand, are more affected by the grid limitation. Households are thus motivated to optimize their own consumption as a result of the grid restriction.

Figure 3: Annual electricity costs and annual power peaks from the different scenarios per flexumer group

However, it must be taken into account in the results that the simulations were carried out with perfect foresight and must therefore be interpreted as an optimum. In addition, the day-ahead prices used from 2021 only have moderate price spreads. Furthermore, the simulations with grid restriction for Flexumer with heat pump could only be implemented with a thermal storage system.


[1] Integration steuerbarer Verbrauchseinrichtungen  (abgerufen am 01.02.2024)