The evolution of large amplitude circularly polarized Alfven solitons in the solar wind is described via dispersive MHD simulations in the expanding box model. Solar wind expansion causes the soliton amplitude to decay, initially following the standard WKB law, which together with the plasma cooling causes the propagation speed to decrease as well. At long times, the soliton disrupts, giving rise to relative density fluctuations which are enhanced as compared to those which develop when evolution is within the framework of homogeneous MHD.