Logo: to the web site of Uppsala University

This study explores how the utilization of electric vehicles (EVs) and a stationary battery energy storage system (BESS) can help manage capacity constraints and enhance resilience in a local distribution grid. The Swedish power system is expected to undergo substantial changes due to shifts in electricity consumption and an increasing share of variable renewable electricity generation. Grid capacity limitations are one of the primary barriers to electrification. Electrification is progressing faster than both grid reinforcement and the expansion of renewable electricity generation. Integrating energy storage systems and flexibility into the grid may offer an alternative to conventional grid reinforcements.

The study is divided into two main parts. Firstly, the availability of an EV fleet was conducted for two scenarios – for 10 and 90 % EV penetration – and based on regional demographics, user behavior, and a mean-value theoretical model of vehicle type. Second, based on the concept of a Virtual Power Line (VPL), a theoretical model was developed and simulated using real grid data and load data for three one-week periods representing high (winter), medium (spring/autumn) and low (summer) load scenarios. The simulated system includes a hybrid photovoltaic (PV) park with a stationary BESS and the two EV scenarios. The VPL scenario was compared to two reference cases, one as the system is today and one with unmanaged EV charging and PV park included in the system.

The benefits of the VPL concept are dependent on the load conditions and power level of installed PV generation in the system. During the high load conditions, normally during winter, the VPL reduces peak loads and manages all instances of capacity limitation, while also increasing the local transfer capacity and enabling EV charging within system constraints. During low and medium load conditions the VPL enables less curtailment of PV generation. The results indicate that up to 5 % more PV generation could be utilized in the system with an integrated BESS. By optimizing the operational strategy of BESS, there is a potential that even more, if not all, PV generation can be utilized in the system. In terms of impact on EV charging the average charging power was reduced by 5 % compared to uncontrolled charging for all but two cases with high load and high EV penetration (90 %). During these exceptions these reductions reached 40 %. Furthermore, it was seen that the VPL concept could be utilized to a greater extent for a lower charging power compared to a higher. The maximum discharging power required per EV peaks at of 25 % of the allowed discharge capacity.