it's pretty cute, and at first blush i thought it even made sense.
I'm sure it is effective.
That said, something is ass-backwards, , lemme see,
The physics of this is quite involved, and I'll readily admit I don't fully understand it.
Insofar as I do understand it, explaining it would be tedious and overly wordy,
suffice to say, a green house results in 'excess' heat that does warm the air.
Moving that warmed air via counter-convection using additional mechanical power
even though the energy for that power is derived from solar, is super inefficient.
Air has very low thermal mass. Very low.
What would be better, would be to use a solar hot water collector, run some tubing
from the collector through the thermal mass storage and circulate the water with
a small pump and pv panel. You'd gather a whole lot more heat that way.
keeping the small hot water collector in the greenhouse would neatly side step
all the normal headaches involved with a closed loop solar hot water system,
as it wouldn't likely be subjected to freezing temps. It could be a simple drainback
system. Further, there would be no need to run the pump 24x7, only when the sun
shines, so there is no need for a battery. The energy storage would be the thermal
mass storage (pebble bed) and maybe a small drainback water tank.
Further, to retain heat in ANY greenhouse, it's best to cover the green house at night.
Seriously. I've done this experiment, and have been able to make ice in a small solar
oven by placing a black uncovered pot with water in it and pointing it at the black sky
(outside the 'milky way') at night, when the ambient temp didn't drop much below
50 degrees F.
On a clear night, the heat radiating to deep space from the green house will give up
a LOT of energy. Covering the greenhouse at night prevents this heat loss.
the solar hot water collector wouldn't have to be anything fancy, nor 'store bought',
you could build it yourself.
here's some ideas:http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm#Collectors