Other problem is most of the existing off grid solutions, are designed as DIY install kits with 12/24/48V batteries, and lower voltage solar arrays.
So using one of them in an existing grid system means rewiring the panels, with thicker cable as well.
I did come across this which takes 48V DC input
http://solar.schneider-electric.com/product/conext-xw-230v-50hz/And the matching MPPT which converts <600V solar arrays into 48V DC
http://solar.schneider-electric.com/product/conext-mppt-80-600/It seems to me the small scale off the shelf home storage solutions are either all in one bricks that include everything, or a mains connected battery which is really just a UPS (with obvious double conversion losses). I don't like the all in one solutions, especially as it makes in impossible to keep the expensive batteries somewhere cool, without taking the entire unit inside.
What is really needed is the ability to treat the battery bank as another variable voltage/amps input like the solar array is. Then you can just choose the battery capacity/voltage that suits your needs. Would require a proper standard to work properly.
Companies have made UPSs with modules, for the really huge units anyway. Need more power output, add a second inverter, battery banks are separate cabinets and you can have multiple, same for power input/switching/bypass. Why can't we have a scaled down version that lets you pick and choose what modules you want inside the big white box ?
Given the ongoing development in battery technology, the part most likely to be obsolete is the battery charger and any related BMS (battery management system). Batteries are crazy expensive at the moment, so the builds involving assembled technology (eg mail ordered kits) carry a risk of bricking the batteries, should you over charge/discharge them, let them get too hot, etc. One company recommends people new to offgrid power, buy cheap batteries to start with for this reason.