In my reading the difference between 710 and 702 is that 710 would apply to a PV/battery system that never connects to the grid, whereas 702 would apply to a system that normally is connected to the grid but operates as a standby generator in an outage. That said I've seen a lot of people try to apply only 710.15 to systems that are normally grid-tied.
Perhaps one might argue about which to apply differently for an 'AC coupled' backup system in which the battery inverter is not directly connected to the DC output of solar panels.
It's a little unclear what kind of system you're asking about, although your phrasing seems to refer to a normally grid-connected system.
my problem is that 702 is for stand-by systems. Solar systems, by definition, aren't in standby mode at any time. They falls under 705, as parallel power source in standard operation and 710, stand-alone when grid power goes out.
All solar installations that I've seen in the past couple years, are all using batteries with built in inverters. There's hardly any DC in these systems other than the panels themselves. The batteries aren't stand-by either, they are being charged during the day and depleted during night time.
My main concern is that the only requirement for complete solar system (including batteries) is to meet 710.15 for single load, rather than have some type of load management although all solar systems have a built in transfer switch, in their gateway, to disconnect from the grid in case of power outage which is covered in 702 for standby systems.
