I fitted a Panel when I got Odysseus, purchased from China for £120 and £40 delivery arrived 4 days later Via Ebay:-
110 watt glass in an aly frame which I mounted on a S/S frame over the cockpit, Odysseus is in France and in the summer sun the output is 9.3 amps this keeps all things running all the time. I fitted a regulator, if you do not you will boil the batteries. When sailing with all things on I have never run out of power.
I have 3 110 amp batteries
If you put a panel (plastic) on the deck be mindfull that contrary to the manufactures Guff they break be warned.
Hope this helps.
Odysseus