[Arinoth]

Ah gotcha,

Personally I'd try to skip the UPSes themselves, and just use the batteries. That way you have the straight DC to DC, though you may need to bump up or bump down the voltage depending on what your solar panels output, monitor the amount of current that's trickling in so you don't overheat your batteries by "quick charging it constantly", power inverting it when you want to deliver it back out to AC, and something to monitor/control all this. Unless you have a charging circuit (which the ups has inside of it, or say battery chargers do), you could overcharge your batteries, damaging or possibly making them explode.

Like I've said, I've done this on small scale (except for outputting to AC), so that's why I'm trying to weigh in from my own knowledge/experience with it.