> My point was that 3d printing lightweight plastic structural parts where they are needed, will be to space based solar power, what mixing concrete on a construction site is when compared to having everything transported to the site via cement mixers. Sometimes it makes sense for the project to mix on site, other times it won’t.

I argue that any kind of large scale structure fabrication is fundamentally different than the preparation of raw inputs, like your concrete example. A large orbital 3D printer is a complex industrial machinery that needs servicing, constant supervision and human involvement, it's more akin to the Hubble telescope than to an concrete mixer. The costs to operate it in space are orders of magnitude higher than on the ground even in the most optimistic orbit cost reduction scenario, short of space elevators and the like.

Until we have self replicating and selfrepairing orbital robots, any space project will need to contend with the fact that human labor in a spacesuit in orbit is inconceivably more expensive than a guy riding his bike to the factory in sweatpants, breathing the free air our planet seems to have aplenty and drinking the water that falls from the sky from time to time. And this is, I repeat, a fundamental stumbling block no matter how far launch vehicles advance, space will always be insanely hard compared to surface.

So you better have a damn good economic case for printing structures in orbit which are 1000x more expensive than the same structures built on earth. The savings from the support structure and the lack of foldable mechanisms necessary to deploy into orbit could be significant, but definitely less than a single order of magnitude.