I liked this video on it. Basically, a play on the ideas of cyberpunk, but rather than using grim art as a warning, it instead focuses on radical optimism and envisioning a world we should strive to create. Building off the the ideas of renewable power, hence the solar, it posits that technology used in the right way can bring us to a beautiful and healthy society, freed from the capitalist systems that are poisoning our environment and selves.
I think the realities of physics will make true interstellar travel hopeless, so to me solar punk as an aesthetic is the more real idea of humanities possible utopia, should one ever exist. With that, I think it also pretty strongly ties the art with action. These facts giving a more grounding for praxis than start trek.