Earth Hour - possible in Poland?

Solar panel!

It still can be very tricky.
Hot water will shatter the windshield. Warm water might, depending on the temperature differences of water and the glass. If it doesn't then, in minus 20 it will freeze on the glass in seconds. To avoid that, the car engine should be running during the process, to heat the glass. In other words we're back to square one - you gotta warm run the engine for a few minutes before driving.

Pouring warm water in winter has also some negative side effects on the car's paint job. If the car needs to be repainted then I wonder what kind of greenhouse footprint does the painting have. Or how much greenhouse gas does it take to replace rusted car parts. of course, warming water up ain't free either. It does take energy to do that.

In addition, virtually all car manufacturers recommend running the cars engine for a few minutes before driving. This reduces wear an tear of the engine and other mechanical parts. Again, the production of these also consumes large amounts of energy.