E-carsharing: would shared e-cars foster or impede the integration of variable renewables?

Adeline Guéret^1,2, Wolf-Peter Schill¹ and Carlos Gaete-Morales¹

¹Deutsches Institut für Wirtschaftsforschung (DIW Berlin), Germany, ²Technische Universität Berlin (TU Berlin), Germany

Over the last decade, carsharing benefited from a growing popular support. Besides, carsharing could help transport decarbonization and limit negative externalities (noise, congestion, local air pollution) on human and environmental systems, especially if it entails an overall reduction of the passenger vehicle fleet.

E-carsharing refers here to carsharing relying on battery electric vehicles (BEVs). BEVs are at the crossroads of the decarbonization of both the transport and the power systems since electrifying passenger cars emerged not only as one key aspect of transport decarbonization but also as a source of increased flexibility for future power systems relying on variable renewable energy. This is particularly the case if BEVs are charging flexibly and even more so when they are equipped with bidirectional charging (V2G).

While sharing electric cars can entail various benefits compared to privately-owned BEVs, their impacts on the power system flexibility are not clear. Usage patterns of shared vehicles differ from those of privately-owned cars. Hence, the total number of hours during which shared BEVs can be connected to the grid decreases and so does their flexibility potential compared to privately-owned BEVs. Carsharing could also substitute private vehicle ownership and entail a smaller overall BEV fleet. This would amount to a smaller overall storage capacity provided by the transport system. From a power system perspective, for a given renewable energy share (RES) in power demand, this may in turn increase the need for stationary electricity storage, which could translate into higher power system costs.

In this paper, we investigate potential impacts of e-carsharing on the power sector in Germany in 2030 and their implications for the resource use related to BEVs under variable renewables integration constraints.

We consider car travel diaries collected in the Mobility in Germany survey as sequences. For each 5-minutes time step, sequences encapsulate the travel status of individuals, i.e., whether they are using a car or not. We then derive driving profiles for various geographical settings (from metropolises to rural areas) using HAC. This allows to account for usage patterns of different car user groups and their potential temporal complementarity. Based on these profiles, we retrieve yearly BEV load time series at an hourly resolution from the open-source tool emobpy (Gaete-Morales et al., 2021), both for a baseline scenario and e-carsharing scenarios, the latter clearly identifying user groups most likely to switch to e-carsharing.

In a second step, we feed BEV load time series into an open-source linear optimization power system model (DIETERpy). Under given assumptions for the renewable energy share in the energy mix and the size of the BEV fleet in 2030, we compare system costs and the optimal power technology dispatch for alternative scenarios with privately-owned or shared BEVs. Scenarios account for different levels of diffusion of e-carsharing across car user groups and geographical settings as well as of flexible charging strategies. We pay peculiar attention to the need for stationary battery storage and put it in perspective with the change in the BEV fleet size and the overall battery capacity provided by BEVs.

Our results quantify the trade-off between the flexibility brought by BEVs to the power system on the one hand and the co-benefits brought by e-carsharing on the other, assuming no change in individual car mobility needs. We expect that system costs in the e-carsharing scenarios increase due to the greater need of stationary storage. This increase should depend on the share of mobility needs fulfilled by e-carsharing. Hence, results provide quantitative insights on the extent to which e-carsharing could enable the integration of variable renewables while providing many positive externalities, particularly in cities.