By Daniel Thøgersen Balle, AAU Communication and Public Affairs
Photo: Private

As Denmark advances its green transition and electrifies the transport sector, a new challenge emerges: What should be done with the growing number of electric vehicle batteries once they can no longer be used in cars?

Cecilie Skov Johansen explored this question in her master’s thesis at Aalborg University, where she studied Sustainable Cities. Instead of letting these batteries become waste, Cecilie investigates how they can be given a second life as energy storage units in the power grid - so-called second-life batteries.

Cecilie Skov Johansen has worked extensively on analyzing the technical potential of using electric vehicle batteries as energy storage units, while also addressing the systemic barriers that currently limit their widespread adoption. To better understand the complexity of the issue, she initiated a collaboration with Green Power Denmark, the organization representing the Danish energy sector.

This partnership provided Cecilie with hands-on insights and ensured that her thesis was not only theoretical but also practically applicable.

Her research revealed that second-life batteries are ideally suited for rapid storage tasks, such as grid stabilization. Using a quantitative model, she estimates that by 2050, Denmark could achieve up to 15 GWh of storage capacity simply by repurposing retired EV batteries - equivalent to more than an hour of electricity supply for the entire country.

Through her collaboration, Cecilie gained a deeper understanding of the practical and political barriers hindering the deployment of second-life batteries. With the right policy measures and infrastructure investments, these batteries could become a key component in Denmark’s future flexible energy system.

Her thesis work left a strong impression on Green Power Denmark, where she has since been offered a position.