Solar System Struggles - Need Advice!

[camaraderie]

Well...with 640 watts of panels...on average in a decent climate you will output around 160 amp hours a day. Since you can only safely run down your batteries to 87 amp hours (50%)... even with perfect batteries you are throwing away around 1/2 of your solar panel output to begin with.
Furthermore, you don't know your daily usage on average so you don't really know how many batteries you actually need though FOUR 6V's or 12V Group31's that are TRUE deep cycle...will handle all the output of your panels average. A battery monitor like the victron or trimetric will allow you to start your evening with full batteries and see what you use over the course of the night in various situations. Buy twice as many amp hours as you use in battery capacity. You might find you either need more panels or a generator to keep up with your actual usage..Good luck with it all.

[Tom48]

First, you have way more solar than storage capacity. A handy rule is 100 watts of solar per battery. Maybe in a less sunny area, 150. If you are running that big inverter, I assume you have a residential frig. Two little 87 amp batteries are probably not enough to pull that system from sunset til sunrise on even a perfect day. If you really have 2ga wire from panel to controller and from controller to battery, you have plenty. I'd say that is the heaviest install for 640 watts of solar that I've seen. Plenty good. You simply do not have enough storage capacity. I have only 380 watts of solar on two big,. 220 amp 6v batteries and as low as we run it at night, they are back to float by ten am on a clear morning. Heck I need two more batteries in my system. You could use four more. Nice solar system. I'm jealous.

On here a while back a member posted pictures of a fairly simple welded frame tucked up next to the stairwell where the two primary batteries sat, in a little FR3. HE POSTED PICTURES. Good luck.

[aircommuter]

I have built several solar systems including some with panels that are level.Using this system which I have tested and modified the first year and it has been performing very well for 12 years now. We run a/c units in the summer, coffee maker, lights, hydraulic system, and the 36” side by side refrigerator runs year around. Perhaps you can adjust your system proportionally to this one. Panels 3840 watts, morningstar 60 amp controller, 5500 watt 48v inverter, 24ea L-16 flooded batteries 300 ah . The biggest thing in these systems is battery capacity, and panel total wattage, laying flat is a major drawback. They have given you all the advice you need to check it out, I would test the panels individually also. But trying to drive a 2000 watt inverter with 2 little batteries is not going to last long because when have the power at your fingertips it is easy to over use it. Oh
I almost forgot it is on my boat, I also. Have a backup generator that auto starts when the batteries are getting low and shuts down when the batteries are charged plus 2 hours for absorption time. The generat doesn’t start every winter, it just depends of course on cloud cover duration. If you need more info just let me know.

[johnbryanpeters]

Originally Posted by meaningfulmiles

Batteries were purchased in September 2017, and have not reached less than 50% that I've noticed (we live in the unit). To clarify - 50% of what value? 12V or something else? The lowest our batteries have ever been is 10.2, that I'm aware of.

For lead acids, 12.1 VDC is 50% capacity, time to recharge. 10.2 VDC is damaging.

[Tom48]

Originally Posted by meaningfulmiles

Batteries were purchased in September 2017, and have not reached less than 50% that I've noticed (we live in the unit). To clarify - 50% of what value? 12V or something else? The lowest our batteries have ever been is 10.2, that I'm aware of.

When rested voltage, meaning no use and no charge for a significant period of time is below 12 volts you are below 50% and the batteries are being damaged.

At about $895 each there are some lithium batteries that will endure really deep discharge, but no lead aside battery, including AGMS will take that withoutdamage.

Rested voltage,at 10 volts is for all practical purposes DEAD AS A DOOR NAIL. They never fully recover from that and useful capacity will decline each time you drop tgem below 12.0 v.

[richp]

Hi,

One other note. The mention of tank heaters could be another red flag. They will suck battery like a champ.

But I agree that if the batteries got into the tens, it's time to go shopping for new ones.

FWIW.

Rich Phillips

[babock]

Originally Posted by Tom48

If you really have 2ga wire from panel to controller and from controller to battery, you have plenty.

It meets the 2% voltage drop rule but I would try to shoot for 1%, @ 14V and 40A that's a 0.25V voltage drop. That is fine on the input to the controller but the actual battery charge is going to suffer.

All that being said, it's likely a battery issue at this point. Batteries need to be replaced.

Here is a good read:
http://www.jackdanmayer.com/rv_electrical_and_solar.htm

[SLOArmada]

It definitely sounds like battery storage is your issue. If it is within your budget, (say ~1700 to $2000) consider getting some Lithium batteries. There are many advantages of lithium batteries, but for your case the two biggest ones are: ~60% more storage capacity pfor the same size (your limited size battery compartment), and lifetimes measured on the thousands of cycles for 80% dischsrge (as compared to lead acid which is measured in the hundreds of cycles to 50%). The latter an advantage for you since you are full time and discharging daily.

For your stated battery compartment size you could probably fit 200 to 250 Amp hrs of lithium, giving you a usable 160 to 210 Amphrs.

[johnbryanpeters]

However, Lithium batteries have serious limitations in both hot and cold environments.

[carlsbad]

If you’re a little tech savvy, a $50 wattmeter for RC planes can be easily wired inline. Tons of how-to videos on YouTube.
If you are rich, buy a Victron or similar. The little wattmeter is accurate - shunt accurate.
Take a voltage reading after sundown when you aren’t charging. If the battery is full and it dies quickly then:
A)You are using more power than you think.
B) you possibly have a bad battery.
C)you need more battery capacity.

You have a lot of solar. You should be able to solve it quickly.

[SLOArmada]

Originally Posted by johnbryanpeters

However, Lithium batteries have serious limitations in both hot and cold environments.

Yes, lithium batteries are more temperature sensitive than lead acid. Don't use or store them above 135*F, and don't charge them if below 25*F. (Discharging below 25*F is OK)

[ScottBrownstein]

You are not really giving the mppt controller much to work with in a parallel setup. Give it 75 volts at much lower current and it will work better. Otherwise PWM would be just as good.

Agree if you can hook up "remote sense" to the bank you would do better.

Still not enough battery capacity.

[HangDiver]

Originally Posted by meaningfulmiles

The lowest our batteries have ever been is 10.2, that I'm aware of.

We can all talk about solar panels, solar controllers, wire gauge, etc. until we're blue in the face. But the best help we can give the OP is where the problem really is:
Their batteries, while relatively new, have been depleted and are damaged.

The solution now is to help the OP with battery replacement options that will help them with full-time living in their RV - and the proper use of their inverter. If you have experience with this (I don't) what are your solutions?

Rich J.

[garbonz]

Battery battery Battery. Good rule of thumb for system balance is 1 amp hour of battery per watt of panel.

OP has a lot of batteries to buy.

Needs a victron or trimetric monitor.

The rest comes after.

[tomkatb]

Spring and summer Costco had Interstate gc2 6 volt batteries for$85.

You need the max amp batteries you can install. 400+ amps.

Or a big lithium? 10x cost of wet cell batteries.

[ScottBrownstein]

Recent posters are correct. You need a battery monitor. If you went to those low voltages you have killed your batteries. If I recall, you said you don't use them much but they are bad. You used them too much...a couple of times and now you probably have 15 AH of useful capacity.

New batteries AND a trimetric or equivalent

[Skyliner]

Originally Posted by tomkatb

Spring and summer Costco had Interstate gc2 6 volt batteries for$85.

You need the max amp batteries you can install. 400+ amps.

Or a big lithium? 10x cost of wet cell batteries.

The cheap costco $85 batteries are not the best batteries you can get at membership bulk store. They have 207 amp hour capacity.

For slightly more money at Sams Club you can get their EGC2 golf cart battery which has 230 amp-hours. For my 3 banks (two 6 volt batteries wired in series), that amounts to 69 amp hours of extra capacity in a battery that is identical in size to the costco battery. More capacity means less depth of discharge (DOD) which means greater lifecycle.

The EGC2 battery is usually offered on sale around May for $99 versus its regular price of 117.

I'm not a fan of Sam's Club but in this instance I recommend their ECG2 battery over Costco's battery.

[camaraderie]

Originally Posted by Skyliner

For slightly more money at Sams Club you can get their EGC2 golf cart battery which has 230 amp-hours. For my 3 banks (two 6 volt batteries wired in series), that amounts to 69 amp hours of extra capacity in a battery that is identical in size to the costco battery. More capacity means less depth of discharge (DOD) which means greater lifecycle.

You may be right...you may be wrong.

You are assuming that a battery from one mfr with 230 rated amp hours has more capacity than the Costco battery with a different rated capacity. Your mistake is thinking that there is one standard test procedure and that all mfr's ratings are comparable to other mfrs. ...WRONG. They lie and they each test differently or PROJECT results without doing the testing.
Mfr. ratings should only be used to compare between THAT mfr's products. Of course battery construction, assembly and plates can make a huge difference too...suppose your Sams would give 300 cycles vs. Costcos 500 cycles?? Ditto..they all lie there too. No standards.
Both companies GC batteries are excellent values in my opinion...but far from the best in their class in terms of actual amp hours delivered over their life cycle or construction. If I were full timing and doing a lot of boondocking I'd want to invest in something more robust but it is hard to beat their values for typical RV use.

[aircommuter]

If you are going to modify your battery compartment and you want to get a battery that will pay you back for the initial cost you may want look at the Rolls Surette battery line. They have thicker plates and they are the first I recommend to my customers when I build a system. Once you checkout their website you will see that they are a professional battery maker for solar applications.

[spock123]

Checking out batteries tonight and came across solid-state batteries. That would be awesome if the could be made cheaper. I saw something that said they would charge in a minute. I had to upgrade my laptops hard drive and I went with a solid-state drive