G'day Dr Jones,
Well you say ya mate lives in an apartment which I would imagine it would be in a multi level building. Now where would be the space to mount the PV panels externally to get the maximum exposure on a southerly direction. A 48 volt array is generally used for large off grid installations and the cost is way up there. OK if your mate does want a off grid array then a 24 volt array would make sense. All of those big pv panels are rated at 24 volts so by say getting 2 0ff 175 watt ones and mounting them in parrallel, then say get some decent deep cycle batteries to make up 250AH array ( at a min). Then all that will be needed is a charge controller to stop the batteries being over charged. 24 volt inverters are a heap cheaper but even with a 250 ah array and only 350 watts of PV a ongrid charger will be be needed to ensure the batteries are charged properly.
I'll explain our setup which has been going on now for close to a decade.
14 off of those 90 watt Kaneka high voltage panels all mounted in parrallel going into a Outback FM60 MTTP controller
2 off 175 watt 24 volt panels directly mounted to the batterybank.
12 off 600AH sonnenschein 2 volt deep cycle batteries in series.
SA32 Selectronics Pure sinewave inverter
80 amp ultra smart traction batterycharger ( think souped up forklift charger)
That array cost us 17K back in 2002 and the only problem I had was the original MPPT died so we got the FM60 under insurance.
Fridges working off inverters can be a big killer for batterybanks so if the grid is around it does make sense to leave fridges connected. most other appliances will work fine but it all comes down to how the array is setup. What if one doesn't get any sun for a week or so, if batteries are left to drain to a real deep cycle they won't last long at all.
My advise would be start small and learn but have that said small array capable of being upgraded with more solar and more batteries. So that would mean buying a decent 24 volt inverter and always check on the idle current power draw.( Both of my 24 volt inverters have less than a 6 watt power drain). If one does want to use a MPPT then by putting the panels in series and programming the MPPT to suit the array is the way to go.
Like I said above deep cycle batteries will last a long time if looked after and for a 24 volt array the cutoff should be set at 23 volts min. Keeping the battery specs for charging is also needed so have a real good read about deep cycle batteries and learn what they do require.
I do apologize if I came over rough in my first post, but wanting to be grid independent is a disease and only gets worse over time so getting it right first time can bring a lot of enjoyment that can last a long time or it can all go wrong and leave the wallet empty......
Cheers Bryan