Wow! This is really cool. We have a greenhouse we set up last year, and our big question has been what's the best, "greenest", and cheapest way to moderate the wide temperature swings and keep the greenhouse warm on winter nights.

Just reviewed the info at Solar Greenhouse Heat Sink - Solar and this is brilliant. We were actually thinking of using an old computer fan, but we had not put the rest of this idea together.

Thanks so much for posting this!