while the idea of the solar staker looks good to me, I think that a single solar array powering multiple devices (including PCs) is much more convenient and efficient.
one PC consumes at least 400 W, so you need something like 2x 250w mono-crystalline solar panel, add the solar charger, the converter, and you easily pay at lest $500

There is no need for a full PC for a dedicated staking machine. There are other projects already doing this with a Pi running linux and a web gui for the user. You could add a small battery to a setup like this and the cost for all hardware would still remain very low.
http://www.voltaicsystems.com/blog/powering-a-raspberry-pi-from-solar-power/ The example here uses a 9 watt solar panel.
This seems like more of a fun hobby to do something like this over a product non -geeks may want to use. When the device only uses 5 volts of power in first place most people will not complain about that or look for alternative power solutions.