Inserting something like this into the duct work of a normal heating or cooling system is fairly simple. The real issue is they increase construction costs and most buildings are built by people that don't use them. Further, they don't look like something out of a Norman Rockwell painting.
> most buildings are built by people that don't use them
Having rented for the past 6 years in 4 different houses, I've become convinced that this is one of the most significant factors for why so many house aren't enjoyable to live in.
Even if the overall design and layout of the house is good (I'm talking about the Christopher Alexander sense of good design), there are always small and not-so-small features that would never have been built that way had the person designing or building the house been intending to occupy it. Or had they moved in, said problems would be remedied in short order.
A problem of insertion into ductwork of a passive-design system component, is that when the heating system runs at night, it will cause air to pass through the panels, and thus cool the building at night in winter.
Since the solar panel-system is passive in design, insertion into ductwork would be a new design issue.
