Is there a way to protect beer from freezing in a garage with no electricity

I have kept my beer in my garage during Northwest Iowa cold winters. Usually when the outside temp gets to about 0-5 degrees my beer in the garage will start to freeze. So, since my garage is about 10-15 degrees warmer than outside my best guess is at about 15-20 degrees it will start to freeze.

At -10°C I think you will need some sort of heating element. If you don't have electricity, you could try doing it swamp cooler style.

1. Put the bottles in an insulated container - an old refrigerator unplugged, a plastic cooler, or a DIY insulated box would all work (like a fermentation chamber). Put a thermometer in there to check on the temps.
2. Put a heat source in the insulated container, some heated bottles of water (steel or aluminum bottles would be good since they're conductive) or bricks heated in the oven or something like that, swamp cooler style. Don't put the hot stuff too close to the bottles, you will want to avoid getting the beer hot.

This seems like a lot of work to me, because you'll have to heat the heating source manually with the stove or oven or something, so you're probably better off finding a closet to store them in. But this approach will work, as a well-insulated box will maintain temp pretty well for many hours, as long as you monitor it for a while and figure out how long your non-electric heat sources give you before it cools down.

On the few occasions I have had beer freezer it led to a permanent haze forming in the beers. Otherwise the beer was fine.

Without a power source even a well wrapped/insulated container of beer will lose its temp and get to the ambient -20 you describe.

You only option is to find a place inside or get power out there to the beer.