Eric's Thermal Storage Tank

This is a tank built by Eric for his solar space heating system.   The pictures were submitted by Eric (ericjeeper) to the http://HomesteadingToday.com   Alternate Energy forum, and copied here with permission -- thanks Eric.

The tank has no structural walls other than the dirt -- can't get much simpler than that.

The tank is lined with 6 inches of extruded polystyrene (pink) foam.  Early indications are that the heat loss from the tank is low. 

Obviously, you need to have soil that allows this to work -- cohesive enough to make good walls, and not to wet.

The liner is PVC, but EPDM would likely also work well.