maybe they can just, you know, burn their trash in incinerators for electricity
They do that already, it produces about 1% of the total electricity.
In the end it'll also boil down to proper design. I've seen illustrations of houses that uses water heated by the sun to warm to home, maybe they do that there. I mean, the sun still shines during winter, except if there's a blizzard.
Much easier: windows facing the sun. It helps, but it's not enough.
Wow, and even the incinerators are not enough. And yes properly designed windows, design the house for maximum sun absorption and heat retention. Unfortunately I don't think those living in flats have much options. I have family in Italy and they complain about the cold and are not running the heater continuously to save on gas (this was even before prices skyrocket). I can imagine it'll be much frigid in Germany. Hope they sort that all out before winter.
Or they could just buy lots of red hot chilli peppers, store them to last up to spring. It warms the body without having to burn anything. Just add 3 chilli peppers to a noddle soup and its good. Add peppers to every food thats to be eaten. Food is importanter than gas in the long run.
I don't know if you're serious about the chili part. That just trick your body into thinking you're hot. That's why Thais love them, they sweat and then it evaporates and cool them down. But yes, food is definitely important in helping keep the body warm. Maybe they can adjust the heating to be lower than they're used to and just put on an extra layer or two of clothing.
