I have idled all my diesels (2 different ALH TDIs and a Jeep CRD with the VM engine) for 8 hours at a time using them as a mobile rest stop.
The Jeep (filled up prior to going to sleep) used 2 gallons over 8 hours to keep the AC running.
The TDI used about half that, so 1 gallon over 8 hours, or about 16 ounces an hour to keep the AC on.
I also have used my TDI as a portable power source (on the same trip, as it happens) running a modest inverter inside, plus 2 iphone chargers (1amp @ 5v), 2 ipad chargers (2.1amp @ 5v), 2 Garmin GPS units, an XM radio, a CB radio, and an Escort radar / laser shifting system and detector.
The voltmeter on the radar detector never dropped below 13.6, so the alternator still had plenty of capacity.
The thing to remember is that the TDI doesn't need much power to run, not anything like a gas engine does. After an alternator failure years ago, I actually drove for about 30 miles with just the battery and everything was fine - Granted I had everything else shut off that didn't need to be on, but I still made it home. The TDI is a LOT tougher than you think.
There also is a lot of misinformation about the turbo - There aren't any "pressure seals" as such that NEED faster-than-idle operation to work. If that was the case, why wouldn't every single TDI be drinking oil while stopped in traffic or at a light? I have actually disassembled and rebuilt a VNT turbo. The oil is 'kept in' by simple path-of-least-resistance methods. The thrust bearings at the ends of the center shaft are VERY precisely machined to fit the shaft, and that keeps the oil in the center. Meanwhile, the drain hole around the main brass bearing is comparatively huge, so the oil easily wants to flow there. The slightest bit of incoming pressure creates the oil cushion for the center shaft, so the turbo IS spinning at idle, and not wearing on anything. Idling may not be good for other things in the engine or for the environment... But it doesn't bother the turbo.
Meanwhile, considering that just ONE of the coal-fired power plants in this country (and there are 542 of them) puts out about 3.5 million TONS of CO2 per year (and the 10 worst are ALL putting out about 16 million tons EACH) I don't think idling ONE tiny little TDI amounts to a hill of beans.
Want to help the environment? Get the EPA to restrict the tailpipe of just ONE coal powerplant to the same level that they go after diesel cars... And you will have effectively removed 3 million cars (of emissions) from the roads. Now think about that scale against all 542 coal plants.
