Just want to run an idea past here... pick the collective seabreeze brains as it were 
I have ducted reverse cycle AC in the house but poorly designed/situated block for passive heating in winter.
The idea is to use a fan (run by solar) to pump the warm air in the roof space down into the house (via the existing ducted AC) during the day to increase the in-house temperature.
In theory I can add another inlet (with filter) in the roofspace and use an inline fan to blow the hot air around).. Bling the system up by adding it as another zone to switch it from the main AC switches.
To add more heat - if you had solar water you could run a radiator in front of the inlet to increase the heating effect.
Total running cost should be zero as all power is solar. 
Thoughts? 
(or has this already been done somewhere)
Check out HRV ventilation systems, on the website there is a diagram of what you want, a New Zealand company, nice blokes
Thats EXACTLY what I'm after.
