You can make a horribly inefficient tool, but if it relies on green energy and uses green materials then it does not particularly matter how inefficient it is. It is a multiplicaiton issue. 0 X 1,000,000,000,000 = 0 and there is no way around it.
So yes, lets look into greener sources of energy and materials for the sake of being green. But let's look into more efficient printers for the sake of production capability.
The big issue with 3D printing is that it is far too slow for proper mass production on objects that can be injection molded or easily sculpted and welded into shape. Those operations can be done quickly and accurately, and in batches of tens of thousands of products. 3D printing is good for smaller batches of custom parts, large objects like buildings and airplanes which would normally require a lot of individual parts, and complicated objects with a lot of moving and/or embedded parts. It is great for bowing because airplanes can be made of less pieces, with lighter weight, less screws and maintenance, etc. It is great for joe consumer like myself because I do not need to drive to home depot to buy a single molly to hang a picture, and I can make custom lightswitch plates for my kid's rooms, custom legos for my son, and dollhouse furniture for my little girl. I can make custom cell phone cases, and if I ever get so complicated as to adding electronics then I can make custom docking stations for devices and cable connectors. The list goes on and on and on for fun things that it is useful for.
But if I was starting up a company, and I wanted to sell a few million game consoles it would be horrifyingly and frustratingly slow to 3D print all of those console cases, controllers, and accessories. It would be inefficient beyond belief! But if it was green or not depends on the type of power and materials used, not the quantity of time, power, and materials required.