Cool post-apocalyptic world inhabited by a badass heroine

The opening scene shows our heroine as a total badass, especially when she thinks "she did not have TIME for this" in a seemingly threatening scene. But she quickly proves the thought correct when she takes down her attackers. This book has interesting post-apocalyptic premise: world ruin caused by solar flares, a simultaneously crazy and completely realistic concept. I'm intrigued by Knox and his role -- is he going to end up being a good guy or a bad guy?? I'm interested to learn more about this world and see how the plot pans out!