Source: http://lifehacker.com/5967840/make-a-raspberry-pi-solar+powered-ftp-server
There are lots of great #Raspberry Pi projects you can make. Add to the growing list using the small computer as an FTP server—a solar-powered one, no less.
CNET has the instructions for setting up your mini FTP server. With it, you can access your digital files from anywhere 24/7—and the solar panel means your electricity bill won't be affected at all.
Basically you just need a solar panel with a rechargeable battery pack in a case. You can buy the parts from Cottonpickers (based in the UK, but shipping worldwide).
Once you've got your sun bed set up, follow CNET's straightforward instructions for setting up the static IP, VNC, and so on. You can hook up an external hard drive for file sharing.
In theory, you could use the solar panel case for any Raspberry Pi project, including setting up a personal web server.
How to make a Raspberry Pi solar-powered FTP server | CNET UK viaTechCrunch