No. Just as with other equivents, you can take part in as many or as few DFS events as you like.
If you do not wish to participate, simply opt out in the app when you receive a notification of an upcoming DFS equivent.
However, if you want to earn the additional points available for reducing your energy usage during DFS equivents then you will need to confirm your participation in the app before each event, so we know that you want to take part.