I would check with Gubler Orchids (www.gublers.com), they have been using a system like that for many years now.

This link might be useful
http://www.reuk.co.uk/Solar-Greenhouse-Heat-Sink.htm

Don't be over optimistic, as you don't get energy from nothing. At best, you might get a little heat stored which will even out temperature drops, but no system is going to heat your greenhouse in the depths of winter from solar energy. The only serious 'alternative energy' system would have to be a heat pump with an extensive network of ground heat source tubes.

True, the Gubler system works because they are in the high desert of California, and their annual average temperature is just about right for growing orchids. Areas with lower average temperatures will have to grow plants that can take chillier conditions, or add some artificial heat.