Something is better than nothing but assuming you get 100% of what they advertising for 8 hours of usable sunlight, that is 168 amp hours into the bank.
A 10 watt anchor
light for 8 hours of darkness consumes over 1/2 of that. Do you mean you have no other draws on the bank. No auto helm
, to depth sounder
, no fridge, etc? They add up pretty fast.
Because it has no regulator
does not mean it doesn't need one. If you leave it hooked up all the time while you are away from the boat, it will try to float the batteries at 15.4 volts, not really good.
Yes, when plugged in and using your battery charger, you would want it unhooked.
Still, if you have no other means of passive charging
capability, something is better than nothing.