I think you are stating things a little generally without taking boat specific aspects into account. I also think some of the rest of your post gets a little misleading, especially when it comes to the quote on panel output. You can't make comments on panel output that generically and then talk about different controllers. The controller has a lot to do with the output.
I think a 160 watts would likely be fine for a C310. Our boats have a small fridge with OK insulation that ends up being fairly efficient. When I did my power consumption work sheet I cam up with an estimated usage of 50-125 amp hours per day. Of that 40 amp hours were to run the fridge. In reality that is closer to 25-35 amp hours per day. Our biggest power hog is the autopilot. So long days of sailing using the autopilot uses the most power per day. We have been pretty consistent with using about 40-50 amp hours per day while at anchor.
Our solar setup is two Renogy semiflexible panels at 100 wattts each in series into a MPPT controller. We are typically topped back up to 100% SOC by 1-2 PM every day. When we were in Oriental we had 4 days of rain and overcast. Even with that there was enough power generated by the panels that we didn't get below 60% SOC during that time (we have 460 amp hours in our bank supplied by 4 6 volt golf cart batteries). We've been living offgrid with this system for over 6 months now.
As far as the 160 watt panel that the OP is looking at, that's around 9 amps at 17 volts. Going into an MPPT controller that would be close to 11 amps at the appropriate voltage. With 4 hours of decent sun every day that would be 44 amp hours. So that would be close to 100% SOC. Of course this if rough math and the real math gets a little more complicated when you include bulk vs. absorption, charge efficiency, etc. But he would be in the ballpark of at least keeping at 85% SOC daily which is where most cruisers live.
I think the POs biggest issue is the two 4Ds that make up his house bank. The best money to spend on his electrical system is to get ride of those and get some real batteries like 6 volt GCs or maybe Firefly AGM. Then he can get true deep cycle performance and start thinking about other upgrades.
Fair winds,
Jesse
your point is taken and understood, but this subject, like a lot of subjects on this forum, it is seldom "boat specific".. it could be any brand or model of boat.
and yes, 160watts may be enough, but it leaves little excess... for the extended stretches of extremely gloomy winter days, and yet the power draw goes on... maybe the OP never experiences this kind of weather where he is, and maybe he will never sail his boat to where this kind of weather does happen, but I dont know this.
my "general" idea/opinion is given from experience. when someone is going to put that much money into a system, why not put a few more dollars in so that there is plenty of power available for the times that you cant foresee, or for when the batteries get older and cant hold as much charge.... it is my thought that you should plan and build a system for what you may want to add next year, not just for the needs that is based on the usage of yesterday, or what was used today.
and as general as I was, there really is no need to be any more specic at this time, when the OP is still speculating.... when he starts asking for specifics, then we can help him out. but it isnt rocket science, so if ANYONE plans a system at a 50% working load of the panel rating, uses quality components, and assembles it correctly, they will have a nice system that they will be happy with for a long time.
its completely fine for the OP or anyone elses to build their system in any manner they choose, but when someone is asking for recommendations and experiences, I will always recommend what I know without a doubt will work for them, based on what they say their requirements are. and error on the safe side, rather than having any chance of them coming up short.
there will never be a time when someone says, "darn it!, I sure wish I didnt have so much power available from my system"... but a lot of us have heard someone grumble about all the money they spent on their system, but wish they would have spent the 2-300 more and got the bigger or better stuff....
It's a lot of reading, but real world. Right up our alley.
