It’s not portable, or even available yet, but the solar icemaker prototype created by students at San Jose State University (see full story on the icemaker here) is literally cooler than cool. They used pressure differentials created by rise and drop in daytime temperatures to create a “zero carbon footprint” ice maker.
At something like 5 feet cubed for dimensions, and only capable of producing ice at night, it’s not going to replace the ice tray any time, but it could be really important in places that don’t have easy access to a power grid for food refrigeration and space cooling. Best of all, it looks like something that the dedicated DIYer could put on his or her “To Build” list without having to hit the books much beforehand.
They are currently at work on the product, as well as several others related to solar energy. See the San Jose State U program site here, it looks very interesting, and it’s great to see renewable energy being taught in higher education.