Year round greenhouse in Maine

     I’m planning a building with greenhouse this summer in Gouldsboro, Maine (usda hardiness zone 6A). It will have a 48’x48’ footprint. It will be divided into two 24’x48’ structures with the long axis oriented east/west.

The north half will be an insulated two floor workshop/storage space with a single slope roof and the 32’ high ridge on the south side. It will have a frost protected shallow foundation with cast in place pex for heat, and a 4’ skirt of 2” xps foam buried around east, west, and north sides.
     
     The south half will be a lean-to greenhouse framed with pressure treated simple post and beam type construction, with a 45 degree sloped roof which will meet the ridge of the north half and run south down to a 6.5’ wall. The top 6’ of that roof will be a roll roof under 15 - 400 watt solar panels. The greenhouse will have a second floor deck attached to the south side of the insulated building. The perimeter walls will be icf’s  2’ above grade and 4.5’ below grade, and their footings will be cast onto granite ledge which will be cleared of subsoil so it will be an open ledge floor. The roof will be light scattering twinwall polycarbonate, and the walls will be clear twinwall polycarbonate. There will be a 60’ long drainage pipe from the northwest corner to allow the water that is persistent at the footing drain to drain out to daylight. There will also be a 160’ trench for power and water from our house. All pipes in trenches will have 2” xps foam board buried over them because we don’t get too deep before hitting ledge no matter where we dig. Combined with the perimeter of three sides of the greenhouse, that’s 536’ of wet trench that I’m thinking of as a good source of geothermal. Should be around 48 degrees F.
     
     I’d like to find a way to use the pv panels to the maximum for maintenance of this building’s needs, because any extra goes back to the grid and each year the power company zeroes out my credits on the house pv, so I’d like to avoid annual donations to the corporation that owns the power company.
     
     I’d like to build as much passive temperature control as possible into the greenhouse, not only because its cheaper, but because I think it’s the most reliable. I’m thinking of 62 gallon pickle barrels with sand, water, or Glauber’s salts, raised beds with raised walkways between to create a heat sink below, a horizontal curtain I can pull from the south wall top to the deck on winter nights...
     
     Can anyone advise me on how to get the best out of this situation?