Disclaimer : This is what I have learnt in the short time I have been involved in this type of installation ... I m not an expert ... please free to correct me.

Solar panels : Correctly selected according to the MPPT charge controller (max voltage and current to be taken into account) ... installed with the correct bonding and earthing.

Correctly sized wire ... Fuse protection and lightning/surge protection and a means to disconnect the system ... in the correct location ... the equipment must be DC rated.

Batteries : Fuse protection for the batteries and a disconnecting device which is accessible.

Remote viewing capabilities including the SOC (state of charge) and the DOD (depth of discharge).

If more than one bank of batteires is installed ... it would be a good idea to install battery balancing ... some battery suppliers require temperature monitoring ... otherwise in some cases you have no warranty claim ... best to verify this before you have a claim ... there seems to be issues with AGM batteries ... I am busy on a site where the AGM battery supplier advertises a 12 year expected life span ... the data sheet indicates 5 years ... but the warranty on the batteries is only 1 year ... when I called the supplier in JHB ... the first question when I enquired about a warranty claim ... "is there temperature monitoring at the batteries" ... no temperature monitoring ... no claim.

The batteries must be positioned in a well ventilated area and best to keep them at ambient temperature ... otherwise it reduces the lifespan of the battery.

I dont have any experience with lithium batteries ... hopefully someone with more experience can offer some input.

What I have learnt is that you need to understand the the C rating ... many batteiries offer a 0.5 rating ... a 1 rating is much better ... something to consider when comparing prices.

Make sure that the batteries are compatible with the inverter and has for remote control and monitoring with the inverter software.

The inverter ... There are so many diffrent brands now availble ... it is better to stick to the utility (eeeishkom) approved brands ... beware of the dodgey imports.

Understand the diffrence between an off grid ... UPS and hybrid type (a more detailed explanation can added)... this will determine whether or not you have to register your unit with your electricity supplier ... so that your meter can be upgraded to prevent you from making the old type turn backwards.

Make sure the inverter is correctly sized for the application ... I see it so often ... where the customer tries to save money which results in a system which is not suitable for the application (undersized) which results in backup times being reduced dramatcally even to a point that the system shuts down as a "fault" condition.

There is no such thing as " I will switch off devices when there is load shedding or a power failure" ... in most cases there is no means to identify that there is a power failure ... so how will you know if there is a power failure ... maybe with a load shedding schedule you can ... but I see this has caused issues with customers and installers since we started installing generators back in 2008 when load shedding started. (You would think by now they would have fixed the issue by now)

Labeling ... notices and separation of essential and non essential circuits is critical for the safety of the users.

(COC) Certificate of compliance ... yes the installer must provide one for the installation.