Characterising the flexibility of electric vehicle charging strategies: a systematic review and assessment

ABSTRACT

The increasing uptake of electric vehicles (EVs) has raised concerns about the impact a large fleet could have on electricity markets and distribution grids alike. Charging strategies have emerged as a means to provide flexibility, especially to electricity distribution grids, by controlling the EV charging process. This paper presents a typification of charging strategies and introduces a conceptual framework for appraising their flexibility in distribution grids. This is underpinned by data collected through an aggregative systematic literature review. The framework is derived from an exploratory qualitative content analysis of the sampled data and encompasses four flexibility dimensions: time, duration, quantity, and location of charging. Structural elements of a charging strategy are also explored, complementing the framework. Finally, the paper also presents a quantitative data analysis assessing the level of flexibility provided by each charging strategy. Results show that flexibility dimensions are not equally exploited, direct control strategies do not strictly outperform other control alternatives and innovative charging structures are yet to thrive for flexibility supply to increase. These findings contribute to better-informed, evidence-based policy interventions.

KEYWORDS:

• Electric vehicles
• charging strategy
• flexibility
• distribution grid
• controlled charging

Acknowledgements

The authors thank Prof. Olaf Zawacki-Richter for the feedback provided to the methodological section of this paper and to Mr Karl Reimer for the data screening and collection. We also thank Mr Richard Hartl for the valuable discussions and feedback and Mrs Beatriz Lopez for editing and proofreading the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Table A1 in the Appendix shows the accessibility share of publications sought for retrieval.

2 In this study, penetration rates are calculated as the ratio of the number of EVs per household. Self reported penetration was also accepted.

3 Plotted data correspond to two-thirds of the charging strategies analysed. One-third of the data which corresponds to uncontrolled strategies was not plotted to improve the visualisation of smaller intersections

4 For the descriptive statistical analysis presented in Section 5, observations with missing values were selectively discarded when required by the technique of analysis used.

5 Although outside the scope of this research, several studies in other fields (e.g. urban planning) have primarily explored the location of EV charging stations. This could contribute to exploring locational flexibility if combined with the study of charging strategies and their interplay with the other three dimensions of flexibility.

6 There might be other criteria and frameworks the authors are unaware of, which could diverge from this assessment of direct control strategies.

Additional information

Funding

This work was supported by the Boysen-TU Dresden-Research Training Group.