greenhouse Winter Green House heating

Curious to know if anyone has practical experience with heating a green house over the winter months.  In particular, would love to know if anyone is playing with solar heating and thermal mass storage.
Ha... You keep asking questions that I have researched for years.   I have learned to deal with my GH and situation to make the most of it.  This would include extending the season by 3 months and making the most of heat and light to grow seedlings with little to no expense.    If I were to build one on the ground and did not have to deal with flooding I would have more experience than the Google knowledge I know.
Look into RMH  (rocket mass heaters)
Rairdog, I too like to read up on my goofy ideas.  Problem is so many people like to write about things that they too are only speculating at.  My favorite example is underground green houses.  Yes, they have their function but some of the claims are over the top.  The cost of heating is one of those.  While the earth does help maintain temperatures much higher than outside, heating them further must take a ton of energy because the earth also acts like a heat sink.  Is why under ground homes cost less to cool in the summer time.

So the result of reading up on a thing is often that I become more and more confused the more I read.