WP2.4-6 EV Portfolio Management and Grid Impact Study

31. October 2011

The report from WP 2.4-6 is about EV control systems, wind power and car portfolio management analysis and grid impact on distribution and transmission levels.

The EV portfolio management has been studied in order to develope an EV charging management algorithm to utilize renewalbe energy production for EV charging as much as possible. The EV grid impact study is to evaluate the impact of different charging scenarios on power system operation on both system level and local distribution netowrks.

According to the spot prices in the Nordic power market, the spot prices are normally low when there is a lot of wind power production. Therefore, a spot price based EV charging scenario has been developed to have the EV charging at the expected time periods when the spot prices are low. The concept can utilize the wind power for EV charging as much as possible and minimize the EV charging cost at the same time. In order to investigate the benefits of the spot price based EV charging scenario, two more charging scenarios have been studied as well, i.e. plug and charging scenario and timer based charging

The intention of the grid impact study of EV integration is to investigate and quantify the impact of different EV charging scenarios on the grid operation from the power component loading and voltage profile perspectives. the Bornholm island has been selected to implement the EV charging case studies. The Bornholm power system is considered a generic Danish distribution system since it represents 1% land, 1% population and 1% electricity consumption. Moreover, the Bornholm power system has 30% wind power penetration which represents the future power systems quite well.

The study of EV portfolio management and grid impact has been successfully finished by Dong Energy and CET, DTU. Dong Energy has used the driving data from the Danish transport survey and the historical spot price data from the Nordic power market to develop the spot price based charging scenarios. The EV charging schedules have been delivered from DONG Energy to CET, DTU to implement the EV grid impact study with the developed Bornholm power system model which consists of the grid model and the existing demand model. The overloading results have been delivered from CET, DTU to DONG Energy to improve the EV charging scenarios. It has been observed that all the charging strategies can cause load peaks. This will sooner or later cause problems in the DSO grid. The fleet operator has the ability to limit its consumption, but with the current market setup, there are no incentives to do so. Anyways, information about such limitations will have to be conveyed by the DSO – one possibility could be a future DSO congestion market.

The congestion market is supported by the economic interests from the DSO and the consumers. Introducing a congestion market, the DSO may postpone or omit new grid reinforcements. Using the grid to the limit may also increase the risks of getting black outs and expenses for getting the grid line up working again (changing fuses). The costs of these expenses are difficult to estimate as they depend on the local circumstances. It should however be noted that particularly the expenses for grid reinforcements are significant. The above expenses are associated with the DSO and may be decreased introducing a
congestion market. For the consumers, a congestion market introduces limits on the overall maximum power. Thus the high peaks resulting from charging EVs in the hour with the lowest spot price must be spread out over some hours (but still with low spot price). This cost should be counterbalanced by the reduced costs for the DSO.

The major findings of the EV grid impact study results are:

  • The transformers are the bottlenecks to handle the EV charging demands. 
  • From the loading perspective, the low power charging option is more favorable, i.e. the existing grids can accommodate 20% EV penetration in most cases and the fleet charging scenario benefits are more obvious.
  • There is no under‐voltage issue with up to 20% EV penetration with +/‐ 5% voltage limit.
  • The dumbcharging EV demands are quite distributed due to the quite flat distribution of EV reaching home time.
  • In the case of 3 phase 16 A charging, it is very important to design an efficient scheme to alleviate the congestion caused by EV charging demands, e.g. efficient DSO market to stimulate the EV charging demand shifting, direct control, etc.


Arne Hejde Nielsen