The tanks were 58f this morning after a cloudy and rainy day and cold night. I was concerned about that but not with those results.
Not sure I used that site you linked perfectly but I get the idea from it that, yes indeed, this water could stabilize a very large green house even with just the typical 1 layer of 6 mil greenhouse film.
Most of our coldest nights follow clear sky quality solar days too, so this thing is good.
A poster on another site suggested putting the tanks in on air tight and strategically insulated structure and moving water using heat exchangers to heat a detached greehouse. I am not sure heat exchangers are efficient at low temps but need to look into it. Probably better to use the surface area of the tanks and blowers. Not sure yet.
