It's effectively free if you have no other opportunistic use for it. For example it's free if you don't have a smart electrolyzer attached to it. If you do have one, then it's not free. (Likewise it's not free either if you have no wasted overgeneration.)
It's a sacrfice but of something we can easily sacrifice, excess of solar energy we have no means to store but we still need to produce if we want to go 100% renewables.