Re: The solar panels roll out using stored kinetic energy
From ESA about DART:
The deployment happens in two stages: the first part takes place about five minutes after separation and is spring-driven, unfolding the solar arrays to about 40% within four minutes. The second part is motorised, and will fully extend the solar arrays.
Having proved the concept with DART and this being smaller it is probably completely spring driven.
Elastic bands might have problems with the range of temperatures they'd be exposed to in space.