Passively heated greenhouse

I'm considering building partially underground green house. I'm thinking I could use something like 18" plastic tubes to store water and as a frame to support the roof on 3 sides. The tubes could be filled with water to passively store solar heat. Any thoughts?

hi....For many gardeners, it is not economical to heat small greenhouses with electricity, because the value of the plants grown during the winter does not offset the cost of the heating. Also, there may not be a source of power nearby, resulting in additional cost to run electricity to the greenhouse in the first place. http://www.storeitoffsite.com/offsite-backup.php