Solar Panel Overkill

It is my understanding that the whole purpose of a controller is to stop too much power going into the battery. Just make sure that the controller is set to the right kind of battery. 280 watts doesn't seem excessive to me as you have to account for the possibility of many consecutive cloudy overcast days such as we have all become familiar with over the past year.

I bought one of these on the recommendation of Ramona from this site 18 months ago to charge my batteries from a 330 watt panel and it has worked flawlessly. I don't leave my fridge on all the time so my panel is probably even more over-the-top than yours would be.

At this price it is probably not worth cheaping out and getting a lesser unit.

au.renogy.com/rover-li-40-amp-mppt-solar-charge-controller/

By the way your dinghy is going fine in its second life :). Hope your project is coming along well.

Cheap out on the solar panel but buy the Renoloy controller. It's hard to buy any decent panels less than 200 watts now. If you have the space for the 280 watts panel go for it.

It's not the sunny days that are the issue. Your MPPT regulator will reduce charge to protect the battery. However, when you have a few cloudy rainy days, you'll appreciate the larger panel still providing some charge and the MPPT controller converting that to optimal battery charge.

I just looked at the Renogy controllers on line, would the 40 amp one be right for me ?. I'm a bit of a dunce when it comes to this subject.

I.would buy 2 x 280w panels, a good quality controller that exceeds the maximum rated amp output of both added together (should be on a sticker on the back of the panel or manufacturers specs) and at least one more battery.

Sounds like overkill, but panels NEVER put out as much as the manufacturer states, the sun don't shine everyday and it goes away at night. Then there is always going to be drama with electrical connections and the likes failing. Handy to have that extra output and storage.

To top it off make sure you have a conveniently placed voltmeter so you can watch what's going on. Even better, a battery monitor that records amps in and out. Some controllers come with both.

As part of this process, you might also want to do a calculation of total usage taking into consideration all the loads, not just the fridge, and your likely usage of the boat (day sails, weekends, extended coastal, crossing oceans, sunny tropics or cloudy Tassie). There are lots of spreadsheets you can search for to help with this. Apologies if you are already across this, but I don't think it has been mentioned so far.

The overall picture, and your outlay, might change a lot depending on whether or not you are also running other sizeable loads such as radar, autopilot, water-maker and HF radio. And of course there's the question of finding a place to put these panels. So while it is good to have reserve capacity, it would be a shame to overspend and have a clunky panel installation.

Cheers, Graeme

Sam fridge size is sort of irrelevant, it's more to do with size of compressor/ amps to run, how often it's opened & what's in it. Ie a cartoon of beer will mostly fill your new fridge & if it's warm it might take a day or two to cool down & the compressor will run regularly but If, you put that same cartoon of beer in the fridge and forgot about it for a few days, the whole mass becomes cold, so requires less cooling / fridge run. From my experience what you are talking about is feasible, but you will find the bottom of the battery with overcast skies or excess cold beer consumption

I always put beers in the fridge pre-chilled helping with reducing the compressor running times. However that means the beers are ready to drink immediately causing the frequently opening and closing of the fridge sooner, cancelling out the benefit.

Sam, I don't think you can have too much solar as long as your reg controller is up to the job. Id be more concerned about how, where and the weight of mounting it, especially if you're thinking of mounting it on the bimini.

No such thing as too much solar ( within sensible limits) in my view if you have a decent mppt charge controller.
Most even large yachts have panel shading issues which combined with overcast conditions some days ( weeks recently) can mean only a small percent of your panels rated output actually reaches your batteries.
100amp even lithium battery doesn't leave much margin for a bad few days.
In my view charging any lithium battery without a fairly sophisticated charge controller is asking for problems and thermal runaway on lithium batteries rates right up there with leaky gas lines in my view.
My 28 foot yacht now has 600w of panels running 300amp lithium in two ecoflow power packs. Two hard panels of 160w one on the coach roof and one on the targa bar. Two 140w flexible solar panels one on the bimini and one on the dodger. The Ecoflo units have built in computer controlled solar and shore power high speed chargers and 2400w inverters. We however also now cook via an induction cooktop drawing 1000-1500w as well as run our refrigeration and we occasionally fire up our 800w 20 litre electric storage hws which came fitted for shore power use when I purchased my boat.
Boy have things moved on even from my previous similar yachts 330 amps of AGM's with 240w of solar from only about 5 years ago and my earlier struggles to keep powering my compressor fridge with 200amps of lead acid batteries supplied via 96w of solar in 3 x 32w panels 22 years ago.

Actually thought it looked much bigger than that.
Must have been the mast top perspective.