Raspberry Pi can do a lot of neat things, and the server this Hacker News user built is just one of many. It runs entirely on solar power, and it comes with instructions on how you can too.
The neat part is that this device is being run entirely on a solar panel. As some commenters on the hacker News thread are pointing out, the solar panel pictured is probably overkill for some users' needs.
Check out the source link below for instructions on how to build the server, and be sure to check out the Hacker News thread for a lot of valuable input on alternatives to save even more money and power.