Thanks, I think we posted the same links around the same time.
Looking at the layout, I think an easy option is a short loop of wire to a switch clipped on the transmission tunnel trim panel but hidden where it's only accessible with the glovebox popped open.

It took me roughly whole day to do it properly. But I had small setback when one contact of the sunroof snapped off because of tired plastic and I had to repair it in a way it won't break any more.

Also, I didn't pry off the A pillar trim to snake the wires this time, because the last time I was routing microphone into the rear view mirror area I've put some meaty wires there for 'future extensions', so this time I just reused the wires, so it saved some time too.

There is no need for second person to remove old sunroof and install new sunroof. If you bring totally prepared car with all parts I can guide you no problem.

The torque you mentioned for some bolts are not important I think.

I think you can also install the switch inside that small compartment in the knee panel. It will be easier to reach there and it won't be visible. I already use that space for AMI (http://forum.a8parts.co.uk/showthread.php?t=7109), but there's still plenty of space for a switch.

Yes. This is correct. The logic almost follows the same as ignition on/off with the exception of the resting heater. If you want to run the resting heater, which works with the ignition off, then the fans must be connected to the battery, not the solar panel. To the best of my knowledge this is the only reason the relay is controlled by the HVAC unit and not the ignition state.

It is also slightly unusual in that the HVAC unit grounds the relay, rather than providing a +12 feed to it as you rightly state +++

I wouldnt get overly excited about a bypass switch as the incredibly rare occasion when its both wet and very sunny and a tiny bit of moisture gets in the car, if your A/C is working correctly it will sort it out in seconds.

Likewise, the concept of using the solar panel to trickly charge the battery i find dubious as the power output is so relitively low, and the battery on the A8 so very good. If you find you //need// to trickly charge your battery, it likely needs replacing or you have a current drain you shouldnt have....

Of course its all good for novelty value if thats your priority +++

I'm rapidly filling that up with other stuff (XcarLink, Bluetooth, A/V interface, DVB-T for starters) and also don't want to add any more wires to it; fitting it back is going to be tricky enough as it is. :(
And the glovebox is on the "right side" (left) so that I can do it easily and independently of these.

Thanks for recommending me this upgrade Ian -- I remember I hesitated as my car is light blue colour, almost silver colour, and I was concerned that solar panel won't look good on it. But you said that it will be such a talking point on light colour car. So I made the upgrade and you're right -- this is such a talking point!

Novelty!

I need to have my 110ah battery always charged to the brim as I have installed heated windscreen last year. When HVAC unit sends heating request to the monster transformer in the boot it also starts to measure the voltage on the battery. Measuring voltage allows HVAC to abort heating process prematurely if voltage drops below acceptable levels to avoid draining battery completely. To have long and effective 'heating session' on D2 we need two things: 1. 110ah full size battery; 2. fully charged to brim battery, so it'll keep proper voltage for extended periods of heating.

Here is the solar charger device from the company which makes the best trickle charges in the world:

http://www.ctek.com/gb/en/chargers/D250S%20DUAL
http://www.ctek.com/Archive/ProductP...%20DUAL_EN.pdf
http://www.ctek.com/Archive/ProductM...%20DUAL_EN.pdf

Yes, it will take forever to charge drained battery, but 30W+ of power is enough to top up battery from 90% to 100% during several hours of UK sunshine. And that 10% creates the difference when heating. At least I believe so ... :) :) :)