Hacksaw, I don't know where the cutoff is for practical solar, but no question if there is little sun there is little solar energy to harvest. Just as when there is little or nothing flammable around, relying on a found fuel technology makes no sense. Each has its appropriate place and its limits.

Where I live we have in excess of 200 days of sun, and I wouldn't rely on solar in the rain and fog of winter either. But even in winter here we have more than a few glorious days of bright blue skies and full sun between storm fronts, we call them bluebird days, that offer a solar opportunity.

The travel literature indicates summers are pretty nice up your way. If your closed vehicle is pointed south and it is hot inside when you come back after a few hours, you probably have useful solar. When the sun is melting ice and snow, you probably have useful solar. If agriculture has a growing season in your area, you probably have useful solar.

Survival choices should probably focus on what works. I would never suggest trying to use solar when it doesn't work. But when it does work, why take the solar option off the table?