Solar Panels Query

[Skvez]

River Song,

Given that this isn't your house you should probably avoid messing with the system at all before SHTF.
For after SHTF you can ignore the whole system except the panels where you have a lot of pre-fitted panels on the roof.
You will then need to re-wire the panels and supply a charge controller, batteries and either DC wiring or an inverter (possibly both).

You really need to discover the nominal Voltage of each individual panel.

A "3kW system" will never produce 3kW in the UK, even on a sunny cloudless day in July at noon.
The biggest mistake people make with solar is to expect it to produce 100% of what it's theoretically rated to be capable of producing.
I did a post a few years ago on a solar panel I few into a data acquisition system recording data every 10 minutes across a whole year. It shows realistic levels of power expected in the UK compared to the panels rating.

Even if you were getting 3kW, it's very easy to exceed 3kW with a cooker or an electric shower.