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We have on our boat what we think is a 100 w solar panel.We dare not risk the batteries going flat as we have an electric toilet so we want to fit a larger one..Can we draw on the huge amount of knowledge on this forum and ask if we replace it with a 300w panel would it be a straight drop or would the whole thing need rewiring?

Many Thanks

Keith and Pauline

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that will depend upon several things, a 300W panel may certainly be bigger, so you need to check available space.

your solar charge controller will need to be rated to match the panel voltage and output (for the 100W panel, you may only have a 10A controller- this would need upgrading to the current and voltage rating for the new panel. wiring from controller to battery, check this is up to the expected curren toutput from the new panel, ditto the wiring from panel to controller, a 100W panel could get away with 4mm cable, the 300W panel might need 6mm.

also check the panel type, a monocrystalline panel will start accepting charge a lot earlier in the day than a polycrystalline, and will even work somewhat on dull days, my monocrystalline 50W panel starts charging about 6AM at the moment, while my bigger panel needs direct sunlight to start outputting.

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Hi Keith To add to Grendel if a rigged panel leave a 2 inch gap on the under side between the roof and panel for cooling, you can get plastic mounts from caravan dealers that make a neat job of mounting them .And make sure you have a separate fused connection direct to live side of battery isolation  switches, this will keep your battery's fully charged when moored John

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Depending on the age, construction and location of your existing panel, it may be better to add another one rather than replace the existing one

There is then a school of thought that suggests they should be wired in a parallel not series, and each solar panel should have its own charge controller

This allows each panel to perform to its best, and gives a bit of resilience against failure  

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Hi Thanks for all the replies.We have only had the boat since June and the previous owner died so we have no point  of contact.We think it is a Phototonic 100w with a 30 amp controller so given what has been said it should take a 300 w panel.Don't think that it is that old as Kingsley Farrington bought it in ,2019 part refurbished it but only use it twice.So far it has been a whole lot of trouble but that is boating for you.We figured that someone on the Forum would know.You guys have a  wealth of knowledge and experience.

Many Thsnks

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