Since they wanted to put it on a Navy ship, it sounds like they'll need an entire flotilla with solar panels to power it. Not to mention countless banks of capacitors to discharge the whole thing. Would make more sense to have it on an orbital platform, catching solar rays before they get filtered by the atmosphere. Of course nuclear is still a far superior option in that case as well.
Edit: Sounds like the railgun project is a no-go. They downsized it from "let's use a railgun to shoot projectiles" to "we can use our existing deck guns to shoot those same projectiles." That means they either ran out of money or had a serious breakthrough with the tech and the project's gone black only to reappear fully functional in some conflict in a couple of years.
Starved of funding and purpose, the Mach 6 gun isn’t going to sea any time soon.
www.popularmechanics.com