I'm working on setting up a cheap solar-powered Bitcoin miner.  It's going to run one of my three U2's I have collecting dust by pairing a solar-charged 4000mAh battery bank, a USB solar panel charger to charge the battery bank along with its built-in panel, and a Raspberry Pi or TL-MR3020 router with OpenWRT to control the U2.  I'll add more solar panels so I can have a powered USB hub and the other U2s run later.  It definitely won't generate a lot of Bitcoins, but hey!  No more power costs of leaving my PC on 24/7!  It'll also be a fun little project.