It would not be that hard to create solar or other kinds of renewable energy. Not enough to start manufacturing, but certainly enough for some lights and telephone systems. There are still books and hardware most places.
Although, aside from them driving diesel there would be very little usable gasoline left. Unless you wanted to try your hand at distilling it again.
And why no molotov cocktails? A little fire would take care of most of their problems.
Daryl should be able to make moonshine.
IIRC, Alexandria was set up with solar and other stuff to be a self sustainable environment.