We built a barn on a sandy hillside in SE Massachusetts. 10" poured concrete walls, tarred and blue foam before the backfill, completely dry. The ground level has room for tractor, attachments, tools, and it stays a pretty even temperature except in the coldest part of winter. We built a water collection system - the cistern is next to the foundation - gravity irrigates the vegetable garden. A 12" I beam lengthwise supports 3x12 joists, which allow us to put the cars on the deck above. All the wood from a local sawmill. Its nicer than the house, so we spend a lot of time in it, including holding concerts, dances and jams with the neighbors. This of course was before the economy tanked.
I like jesemd's idea above for the OP. 4000sf is a big number, and a lot of concrete, but a steel truss supported shed roof (peak at the back wall) would definitely do the trick, be nearly invisible from behind the grade, and offer good exposure for the solar panels. There seems to be plenty of elevation. Not sure why to cover with dirt though: an engineer could evaluate cost to hold the extra weight and maybe you'd be better off with more conventional roofing.