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The bottom lines of the datasheet says:
1a) If more PV power is connected, the controller will limit input power
1b) The PV voltage must exceed Vbat + 5V for the controller to start. Thereafter the minimum PV voltage is Vbat + 1V
2) A PV array with a higher short circuit current may damage the controller
This seems a bit confusing. If the controller limits input power and the input voltage needs to be higher than Vbat then why should the PV array short circuit current be of any concern.
The Voltage and the current limits need to be taken separately.
Voltages:
The maximum PV Voltage that this controller can have across its input is 100V. This must never be exceeded. In cold weather the PV Voltage can be higher than its 25°C rating.
Also, the controller has a minimum Voltage at which it can work. PV Voltage needs to be 5V over the current battery Voltage to begin working, then once working, 1V above battery Voltage. It's better to give it more headroom that this and the PV MPP Voltage could be lower than battery Voltage in poor conditions outside.
Run series strings of PV if you can but you must keep below the 100V limit.
Current:
The maximum Battery (output) current that this controller can deliver is 20A. This is a friendly limit because the charge controller limits its self to this value or some lower limit if chosen in the settings. Adding more PV (to a certain point) will not damage the controller because it will not take any more power from the PV array than it can deliver to the battery.
You do need to be careful that the PV (input) current does not exceed the maximum rated PV (input current) which is also 20A for this controller. So don't put three PV arrays in parallel whose Isc (short circuit current) is 8A for example, this 24A could damage the controller. This scenario rarely comes about, because if you have an array configured to deliver that much PV current, then you are into a larger charge controller anyway.
Power, the product of Voltage and current:
On a 12V battery, this controller can charge at 240W (20A). Having 300W or more of solar PV will not damage the controller, it will only take 240W from the PV.
Having extra PV is useful on cloudy days when the PV does not produce its full power, a 500W PV array might make 200W, so this is still OK. As above, it is possible to have too much PV current, but it's not a scenario that many people run into.
