What options are there to keep the windshield more or less ice-free during extreme cold (-30 degrees) without using the heater of the car?
We are currently on a road trip through the Baltic states and car heater broke. It is blowing only cold air. The motor temperature is okay (around 85 degrees) and the cooling liquid is filled up, has no air bubbles and heat is transmitted through the pipes going from the cooling unit. According to the only car mechanic we could find, the problem is deeply hidden in the car (the valve that mixes warm and cold air is probably broken), so it would take long to fix it.
We have however only limited time and need to be back in Russia in 2 days. Driving with warm clothing and stoping for coffee frequently etc is alright, but since the windshield fogs up and the interior's moisture freezes from the inside, it is impossible to see anything and therefore also impossible to drive the distance to the next bigger town (about 160km).
We have tried de-icing spray (alcohol-based), which of course quickly evaporates and leaves a thin layer of water which...freezes. Leaving the (cold) fan on blows dry air over the windshield and very slowly creates a spot that is cleared. As it seems, our best bet would be a portable car heater that runs on 12V. Those seem to be sold out in the town we are staying at the moment. We are hoping to drive to Tartu, which should be large enough to have such a 12V car heater in stock.
What other options are there to temporarily de-ice the windshield from the inside?
In case it matters: the car is an Opel Corsa from 2008, using gasoline as fuel.