Won't the regulators on the solar system prevent them overcharging?
Short answer: NO.
Longer answer: when charged, they are two very low current "things" in series.
If one of them is ever so slightly less resistance than the other, it will have a higher voltage across it.
Imagine if you will, two 1K resistors in series across your 24V line.
They'll have 12V across them, each. And that's true.
But what if one is 900 ohms and the other is 1100 ohms?
It won't be 12V any more, it'll be 13.2 across one and (24-13.2) = 10.8 across the other.
Now, what if it isn't 24V, but equalize voltage while you're charging... with lets say 29V across your bank, that should be a "safe" 14.5V across each, right??
With the same imbalance (only 10%) we're now up to 16V on one.... and 10% is unrealistically tight for tolerances in capacitors of that size!
edit: for clarity, when I say "resistance", I'm talking in general terms.
Lets say one of your capacitor banks is 450F and the other is 550F.
When they're charging, one will charge faster than the other, given it's a series circuit (two in series) so the one that's a lower capacitance will reach full charge before the other... and even if they charge equally (which they won't), one will likely have a higher leakage current... there are many ways in which an out-of-balance of two components will manifest itself.
Not saying it will, just saying it CAN. It depends how risk-averse you are!