As strange as it may seem, given my usual ramblings on MPPT charge controllers and batteries, I concur with Rogeriko (almost).
The defining factor here is that the surplus panels that can't produce power through the Outback are just the right Vmp rating (24.0V) to provide maximum power boost with no controller when the batteries are flat. But only when the batteries are flat at 24.0V and only when the panels are used singly and in parallel with short, high current capacity wiring.
By the time you get to 27.3V (float level) the panels will be so far off their Vmp point and in the near vertical drop on the power curve, heading towards the Voc point where they produce no power at all.
In fact, they're a little bit on the low side in terms of Vmp to be truly usable singly. This is because to connect them to the battery without a controller, you need reverse current blocking diodes installed on each panel that is in parallel. This will reduce the available Voltage by 0.5-1.0V (depending on how good a diode you use). Otherwise, by the time your Outback has pushed the bank up to 27V and more, the uncontrolled panels will be drawing reverse current and loading the system.
But then I'd have reverse blocking diodes on all the PV strings at the point where they combine to prevent partial shading losses from one string to the next, even on the strings connected to the Outback input. This applies where you have more than 2 strings in parallel or where part of the array is at any risk of partial shading from trees or the like.
But the diodes will mean that these panels will only deliver full power when the bank is on death's door at 23.0V. If that's not what you're after then you have to go for at least 2 panels in series and a charge controller, preferably a MPPT one.
Hot weather will also stop the single panels from working at all. Above 25C their Voltage probably drops away by 0.1V per degree C and so by 30C, you're down another 0.5V...
Unless your panels are connected by
massive wires just 50cm long, you'll lose another couple of points of a Volt in the wiring.
So it's looking more and more marginal that single 24.0Vmp panels can significantly charge anything but a 24V battery bank that is heading for the scrap yard

Now, taking in all the little Voltage losses above, panels that have a Vmp of 26.0V at 25C would work a charm without a charge controller (but again only as a bulk phase booster).