I did a search in "greenhouses" for Missouri and didn't find anything so maybe this has never been posted.
Missouri ext service has a design for a winter growing solar heated greenhouse. Barrels of water as thermal mass. They do use one small fan to blow air between the two layers of poly covering but passive otherwise and a small pv set up could probably run the fan. It's only 60cfm and looking at 12vdc computer fans, a 100 cfm pulls 1/2 amp. Very minimal. It's in Mt Vernon at about 37 degrees latitude and is a freestanding unit. I think if it was put against the south wall of a heated building, the fan might be unnecessary or you might take air from the building for the fan. Maybe from a crawl space or basement if there is one.
Of course you can't grow maters in it but most any cool weather/hardy crop has been grown. As far as I know, this thing is still operational. The PDF was written after 12 years of use though they did have to rebuild part of it due to wood rot.
PDF article with specs.
http://aes.missouri.edu/swcenter/research/Solar-heated%20greenhouse.pdf
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