PSOC vs. bank size vs. solar

[contrail]

Originally Posted by flightlead404

Roughly 20% of the charge on our 420Ah bank is what we consume overnight also. On a H38 in south Florida with a fridge, freezer, small fan, anchor light, and a few hours of netflix/LED TV running off a small 300A cigarette lighter plug in inverter.

I have 3x210W panels but wired in series at the moment due to cabling constraints.

We are also running 3 laptops for work and every now and again, like yesterday, when its a little cloudy we don't get to 100%. If we get a few days in a row, and we're into the evening hours with less than 75% charge I'll run the generator for a couple hours to bring it back up.

Panels wired in series??? Or did you mean parallel?

[contrail]

To the OP: A lot depends upon the your intended boat usage, which is not specified. If you will be daysailing out of a marina, you want a good house bank, but don't really need much solar, as you will recharge at the dock.


If your cruises will be weekend cruises, returning to a dock, Thomm's system will do the trick, although in a very minimalist way which may or may not be suitable. Note that he is heavy into electronics and computers, but very light when it comes to anything else, such as refrigeration, but that makes sense for the type of sailing that he does.



If you will live aboard, with some pretty serious cruises, Sailorboy's model will work well, and that is what he does. Note that the idea of using some multiple of an average day's usage becomes insufficient if you are on the move for days at a time. Your consumption will be higher, with nav gear and autopilot, for starters. You will either need bigger batteries, or more charging, whether with a realistically convenient generator or more panels, or wind, or whatever. And, if you are always at anchor or on a mooring, it's nice to have some margin for when its grey for several days in a row. If you cut things too close, you will suffer the tyranny of replenishing the charge in your batteries, on a too frequent basis.


With regard to batteries, all lead acid batteries will accept a charge at a rate that slows the more fully they are charged. For that reason, bigger batteries will accept more amps at a higher state of charge, which is an argument for a larger bank. But, whatever type of battery you use, you still need a sufficient charging source, which is an argument for more solar! You can never have too much of either.


I would be inclined to tell you not to change anything until you have done a little cruising, which will tell you if you need more capacity or more charging, or both.Go from there. A-nd, it is worth noting that with effectively double the capacity of lead acid, double the cycles, and at half the weight, Lithium is becoming competitive, price wise.



Let us know what you do!

[OldManMirage]

Unfortunately I'm dealing with the constraints of both the boat and the budget, a double whammy !

The boat limits where and how much battery capacity I can add, and the budget limits what kind. I did just have a revelation that I can put 2 GC2 batts where there are currently 2 group 24's. Well, as long as I can somehow muscle them into place, there's a little bit of weight difference between the two. But that more than doubles what I have now.

I've already decided that I'll be running the engine now and then in order to keep the batteries maintained, and I plan to upgrade my alternator slightly in order to help that aspect.

Just trying to make the most out of what I've got with what I have.

[sailorboy1]

Originally Posted by OldManMirage

Same question here - you have separate frig/freezer units ?

Mine are separate units. BUT couple of years ago it was 1 unit, freezer, and a spillover system. The 2 separate units use maybe a little more power, like maybe 10Ah/day, but keeps the food colder.

I don't know if FLA tolerates PSOC better than AGM. In talking with other off grid cruiser people each seems to last about the same. But if you think about how abused a battery can get a golf cart is pretty hard use. My last 2 sets of FLA 6V cart batteries lasted over 3 years each and I abused them. That worked out to around $13/mo on 1 set and $6/mo on another. Unless you really need a battery that doesn't need to be watered I feel the AGM advantages are nothing but marketing.

With that said, My current set of batteries are FireFly carbon foam. I don't know if they could be called AGMs, but they definitely are SLA. They cost 4 times what the golf cart batteries would have cost and I only got because I got tired of having to think about the PSOC all the time (I haven't plugged in to SP in over 6 months).

Batteries are consumables on a boat! Use and abuse them and just understand them have to be replaced regularly. To you orginal question. if it a decision between more batteries and more solar the answer really is BOTH. You are going use the same power and have to make it up (the solar part). So it becomes if it is better cycling down to 50% on a smaller set or only to 75-80% on a larger set.

[kmacdonald]

I have a huge frig, separate portable freezer, LED lighting and do fine with 320 watts of solar. In winter or way up north it's lacking. I also have 326 AHr lithium battery. They charge at nearly 100% efficiency. LA batteries charge at about 75% efficiency so that will make a significant difference. Using a greater % of LA capacity of course will increase that charge efficiency. Another reason to discharge LA well below 50% SOC.

[kmacdonald]

Originally Posted by OldManMirage

Unfortunately I'm dealing with the constraints of both the boat and the budget, a double whammy !

The boat limits where and how much battery capacity I can add, and the budget limits what kind. I did just have a revelation that I can put 2 GC2 batts where there are currently 2 group 24's. Well, as long as I can somehow muscle them into place, there's a little bit of weight difference between the two. But that more than doubles what I have now.

I've already decided that I'll be running the engine now and then in order to keep the batteries maintained, and I plan to upgrade my alternator slightly in order to help that aspect.

Just trying to make the most out of what I've got with what I have.

Two Sam's Club golf cart batteries are the best bang for the buck. About $100/each. Solar is cheap so get what you can comfortably fit. If you don't have refrigeration 200 Watts should be fine. Depends on location.

[zstine]

Originally Posted by sailorboy1

in 10 years of solar, including 5.5 full time on the boat, I have never seen 100% input from solar.

But I will agree that 300W on a smaller boat will probably be enough as I had that amount for 6 years.

My Kyrocera panels regularly exceeded their rating. I had a pair of 265w panels for 530W, but often saw 540w to 550w produced according to the MPPT charger.

[OldManMirage]

Originally Posted by kmacdonald

Two Sam's Club golf cart batteries are the best bang for the buck. About $100/each. Solar is cheap so get what you can comfortably fit. If you don't have refrigeration 200 Watts should be fine. Depends on location.

I agree with the Sam's Club, especially since there's one right down the street.

The Admiral really expects a frig so I'll be loaded up on panels. And the upgraded alternator. It'll work out.

[gregabbiss]

The maths should start from a different place. Presuming you are intending to be self sufficient at anchor.

Start with how much power you need per day, sized your battery pack so that you can survive 2-3 days with poor solar performance and then size your solar so that you can recharge this amount of AH if one good day or perhaps a little more.

This will allow you to have sufficient for a few days of poor weather and recover quickly.

Under normal sunny conditions you will have a full battery by midday each day and will have power to spare (hot water anyone?) power never gets wasted and worse case the solar chargers will shut down your solar.

So start with your power needs, then see how you can afford , dollars and space, to fulfill that and if need be compromise. But if you can, don’t.

[OldManMirage]

I get where you're coming from, but I figure I'll never have all the power I want on a 32 footer. So I'll do like Scotty from Star Trek and "give her all she's got" room for, and then see what I can do with it.

I really want the frig for sure, both for the Admiral and myself. Having ice for my sundowner or a cold beer is just a plain "must have." Anything less simply would be uncivilized. If it comes down to running the engine every other day to get the needed juice then so be it.

I can and will add more solar than I have. I'm going to be crawling around the below the cockpit this weekend and maybe some inspiration will strike and I'll see a way to mount 4 golf cart batts instead of 2.

I could get AGM 31's, lay them on their side and slip them under the cabin sole to sit on top of the ballast. I could put 4 of them there, maybe more. And that may end up being the best way to go. Not sure why I'm reluctant to do that. The cost would be ok I think. And it would be a good use of space that will likely not be good for anything else. The bilge is aft of that, and its plenty big and deep.

It'll work out, one way or another.

[flightlead404]

Originally Posted by OldManMirage

Ok, that's some good real numbers. Question - when you say Fridge, Freezer are those 2 separate compressors/units ?

Yes I have a front loading fridge and freezer, two separate units. They are a pretty standard fitment on larger Hunters. Unsure of the brand/model.

[flightlead404]

Originally Posted by OldManMirage

And as to the batteries I'm guessing FLA's would be better since the AGM's hate PSOC ?

If that was directed at me, I have two Lifeline GPL-4DA AGM Deep Cycle, C20 rate 210Ah each.

They are pretty new, installed Oct 2020, but I may have damaged them a little bit when I put in the solar. I installed the solar and promptly left for a month. Turns out in full sun the solar controller puts out just enough voltage to kick the shore power charger into a fail state. I had left fridge and freezer running. When I got back to the boat the batteries were at 37%. I suspect they had been cycling up and down through a low PSOC getting lower and lower each cloudy day.

[flightlead404]

Originally Posted by contrail

Panels wired in series??? Or did you mean parallel?

Currently series due to some constraints about how I'm running the cables.

[flightlead404]

Originally Posted by contrail

To the OP: A lot depends upon the your intended boat usage... Note that the idea of using some multiple of an average day's usage becomes insufficient if you are on the move for days at a time. Your consumption will be higher, with nav gear and autopilot, for starters....

This is true and I forgot to qualify that my above numbers were sitting on the hook in south florida/keys.

We recently left Stock Island and did 4 full day sailing legs to Lake Worth. We ran all the instruments and a/p on those legs. I did not note the SOC at the end of each day (mental note to do that next time) however, each day we typically ran then engine for 1-4 hours at the end of the day (except the 1st day) as the wind died or we had to motor in an inconvenient direction. So, that topped us up nicely and gave us warm water to boot.

[PaulCrawhorn]

A good alternator setup with external adjustable VR will be what saves you on Extended cruises off grid.

Big investment, but then you don't need to mess up your boat's lines with too many panels.

The best battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH @12V pair from BatteriesPlus or Sam's Club.

NAPA relabels it here: https://www.napaonline.com/en/p/NBP8144

Deka self-labeled also sold at Lowes.

If you don't worry too much about PSOC, and need to replace them every 2-3 years, is that so bad?