Solar blankets would be a great invention in places like New York. First of all, a homeless person could easily save for one and still sleep outdoors without losing heat. They would also come in handy on long trips. Simply lay it out in the sun before the night and use it to feel at home on the road. And camping trips! You would lay it out during a time you are hiking or doing some other activity and then have a toasty night. Simply made, almost microscopic solar panels would be stitched into the blanket and absorb solar enerygy.
Is this to complicated and not worth the trouble? And I am just gessing when i say, they would cost quite a bit.