I will talk about light dark sector particles that weakly couple to ordinary particles but strongly couple to each other. Such particles can be produced from the Sun and fully thermalized with its own temperature. The resulting dark fluid accelerates under its own thermal pressure and attains a highly relativistic bulk velocity outside the Sun. Compared to the free-streaming case, the resulting outflow predicts higher number density and smaller average energy per particle at Earth. I will describe how this generic phenomenon arises in a dark sector comprised of millicharged particles strongly self-interacting via a dark photon. The dark plasma wind emerging in this model has novel predictive signatures that can be probed in upcoming experiments.