As I've mentioned in other comments, my main criticism is not with how narrow it is. Socialist realism has has a range that encompasses what solar-punk is aiming at, but extends far beyond that. It offers a holistic and plausible vision of a socialist world.

Another issue with solar-punk is that it's very superficial in nature and doesn't really offer a realistic representation of what a society powered by renewables might look like. For example, this is what real life solar farms look like today in China:

Solar-punk vastly understates the role of technology in its vision, it doesn't discuss how this technology would be produced. It's just an utopian vision that, in my opinion, creates skewed expectations. Since solar-punk is meant to be political art it deserves to be critiqued on the vision it promotes. The tweet I used as a discussion starter might be inflammatory, but I think the core point it makes is worth discussing.