This is a fine story about a solar flare (CME) caused EMP. My biggest gripe is that at least half the people in this story are so clueless, so slow to pick up on the long-term implications of what they see. “We’ve had power outages before, and they always get the power on after a few days, so don’t worry, oh, and give us all the food and water you managed to gather or we’ll come and take it …” (paraphrasing). I’m sure there will be people like that, but not everyone.
I also think an impotent government walling people into chaotic cities is a little over the top, but it is a common theme in this genre that I enjoy.