PSOC vs. bank size vs. solar

[OldManMirage]

A question to those who have knowledge.

Concerning the PSOC issue, is it better to have a smaller bank and more solar or vice versa ?

Let's use a 220amp bank comprised of 2 6V 220AH batteries as an example. FLA or AGM, not lithiums. What would you want for solar ?

I know it would also depend on load so let's use the 50% capacity daily. As if we were cruising with a frig system, a couple of fans and other such things an average 30 footer would have.

[sailorboy1]

Assuming the battery bank size is enough, it is better to have more solar. Never go wrong with more solar!

More solar means you run off solar more during the day and more chance you got fully charged. For battery health and charging if solar can get the batteries to absorption and charge acceptance limit by around noon you probably will get charged fully. It takes 4-5 hours in absorption to get fully charged.

BTW - I was fully charged yesterday on my 481Ah bank. This morning I am -95Ah, 80% SOC. Last night we ran the freezer and refrigerator, a few fans, LED anchor light, and watched 3 hours of streaming.

[sailormed]

220Ah discharged at 50% is 110Ah to fill up batteries in the next day of sunshine (should be a bit more, say 10%). So 120 Ah to produce in 5 hrs. Experience is that you get 5 hrs of 100% efficient input from any solar installation on any given normal sunny day.
120/5= 24 Amp. Your installation should produce 24 amp = 24 x 12 = 300 W of solar.
This is a minimum of course, not taking rainy days etc......

[sailorboy1]

Originally Posted by sailormed

Experience is that you get 5 hrs of 100% efficient input from any solar installation on any given normal sunny day.
120/5= 24 Amp. Your installation should produce 24 amp = 24 x 12 = 300 W of solar.

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.

[PaulCrawhorn]

Ballpark, 200W of solar per 100Ah of capacity should help you be "mostly solar" even if it's cloudy some days.

But really, the most panels you can fit without wrecking the boat's lines, looks up to you, but windage is important.

No matter how large your bank, should not matter, so long as "most cycles" you cut your consumption to below your income for the day.

Or, if you have a FF source on demand, you can use that in the early AM to get your bank up to 80-85% before the solar kicks in for the long hours of CV/Absorb required to get you to 100% Full by evening.

Ideally that is "most days" or at least a couple days a week.

LFP gets rid of that PSOC concern COMPLETELY, but of course not the need to keep consumption to below your income for the day, just averaging over longer number of days

[rslifkin]

I'd say solar sizing is mostly based on your power usage, not the bank size. A bigger bank to cover more cloudy days will require more solar for catch up if you're not using any other source of charging to help catch up.

But in general, if you're using 100ah overnight and need to replace that, it doesn't really matter if you're putting 100ah into a 200ah bank or a 600ah bank, it'll take about the same amount of solar to get things topped off during the following day.

As far as peak output from solar, I've seen brief peaks of 100% rated power (even slightly over), but it's rare that I see much more than 90% output sustained for any period of time even on a crystal clear, sunny day. Occasionally 95% on a perfect day with the boat facing the ideal direction, etc.

[thomm225]

Just to give you some idea.

At this time, I have the same setup as your post.

Two 6 Volt 220ah Golf Cart (flooded) Deep Cycle Batteries in series for 12 volts, 220ah total. (Season All; $135/ea)

I plan to install a 95-100 ah 12 volt battery on the other side (position 1) as those cables are long enough to reach as backup.

I'm not running a frig just fans over night, 400 Hz inverter, computers, HDTV. lights, VHF, depth, autopilot, etc

So far this is satisfactory but I have only been out with these new 6 volt batteries on nice Sunny days

I have 115 watts of solar panels feeding two PWM controllers. 40 watts of solar panels that I hook up directly to the batteries if I need to. They are usually in the lazarette lockers while sailing.

For 9 years I used two 90 ah 12 volt so-called deep cycle batteries in parallel for the same load as above but in the morning I'd have somewhere around 11.5-12.1 volts available.

If either battery was a bit low my inverter low voltage alarm would go off around 3 am or so. I like my ac fan best and use that even though I have a 12 volt fan

[flightlead404]

Originally Posted by sailorboy1

BTW - I was fully charged yesterday on my 481Ah bank. This morning I am -95Ah, 80% SOC. Last night we ran the freezer and refrigerator, a few fans, LED anchor light, and watched 3 hours of streaming.

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.

[ranger58sb]

Originally Posted by OldManMirage

Let's use a 220amp bank comprised of 2 6V 220AH batteries as an example. FLA or AGM, not lithiums. What would you want for solar ?

Can't speak to your solar question, but...

FWIW, can't say I'm a fan of only two 6V batteries in a critical 12V bank. One battery goes south, no 12V.

Four 6V batteries at least gives you a quick temporary Plan B. As would two 12V batteries -- although there are fewer deep cycle 12V options. (Lifeline comes to mind, though, but not inexpensive.)

-Chris

[thomm225]

Originally Posted by ranger58sb

Can't speak to your solar question, but...

FWIW, can't say I'm a fan of only two 6V batteries in a critical 12V bank. One battery goes south, no 12V.

Four 6V batteries at least gives you a quick temporary Plan B. As would two 12V batteries -- although there are fewer deep cycle 12V options. (Lifeline comes to mind, though, but not inexpensive.)

-Chris

Which is one of the reasons I'm installing a 12 volt 95-100 ah 12 volt battery on the other side of my switch.

For backup power if I run my 6 volt batteries too low or if I have a failure .....

[rslifkin]

I figure my backup plan if one of my 6v house batteries goes south is to re-purpose one of the engine start batteries into a tiny house bank and let both engines start off the other battery. And then head for the nearest place I can get replacement house batteries.

[OldManMirage]

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.

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

[OldManMirage]

Originally Posted by sailorboy1

Assuming the battery bank size is enough, it is better to have more solar. Never go wrong with more solar!

More solar means you run off solar more during the day and more chance you got fully charged. For battery health and charging if solar can get the batteries to absorption and charge acceptance limit by around noon you probably will get charged fully. It takes 4-5 hours in absorption to get fully charged.

BTW - I was fully charged yesterday on my 481Ah bank. This morning I am -95Ah, 80% SOC. Last night we ran the freezer and refrigerator, a few fans, LED anchor light, and watched 3 hours of streaming.

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

[OldManMirage]

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

[rslifkin]

Originally Posted by OldManMirage

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

FLA or gel will tolerate PSOC better than AGM. But no lead-acid chemistry (save for the fancy carbon based options like Firefly) really enjoys PSOC. Ideally, you want to have enough solar or other charging sources that they get topped off most days (a day or 2 of PSOC during bad weather and then a top off after that won't hurt too much).