I use a 7-Watt PowerFilm solar cell.

https://www.powerfilmsolar.com/products/rollable-solar-panels/7-watt-rollable-solar-panel

It is flexible enough to be rolled and I can walk on it when I have to with no damage. It easily fits on the rear deck.  It would probably not overcharge the battery my 25 AmpHr battery, but just to make sure I use a charge controller. The one I use is the Sunforce 7 Amp Charge Controller

https://sunforceproducts.com/products/regulateur-de-charge-solaire-de-7-12-v/

This is overkill, but it’s low cost ($15 to $20), available from a number of places, such as Amazon and Home Depot, and I have never found a smaller one.  West Marine has a different brand of charge controller with the same specs and at about the same price.

Vic Roberts

#2032

I am trying to do the calculations for a bilge pump in my Ensign. I have had success with a 35 amp-hour battery, running most of the summer, but won't hold a charge after a summer or two because it it not being topped-off (charged). I have a 2.0 amp pump; assume it runs for 2 minutes a day (in Rhode Island, it's more likely to run 14 minutes in a 24 hour period and sun the next 6 days). My question: how large (wattage) of a solar panel should I purchase to maintain the battery without over-charging it? I am hoping someone has a reliable configuration for their boat.