@ryanc most simply it's a literary and social movement about defeating apathy and despair by imagining achievable but radically good futures so that we can have something to aim towards and motivate us. Part of having them achievable is that it always involves stuff that we can do now ourselves, so there's not a clear boundary between what we imagine and what we're tangibly building. The 'solar' part is the practical yet abundant and decentralised energy we can work with right now and on a much bigger scale, and the 'punk' part is acknowledging that achieving these futures won't be simple or easy but refusing to give up hope
I hope that helps, happy to answer any more questions on the topic!