New Cabin with off grid solar

MMark · September 2021

A month ago, I bought a cabin that is off the grid. It is propane and solar. There are 6 PVs (3 more than 7 yrs old, 3 newer than 7 yrs old). It has a Outback 60 Inverter and Outback charger controller. It has 8- 6 volts batteries (2-3yrs old and the rest older than 7 yrs old). When I bought the cabin the solar system worked fine. During the last month I have had repair work done on the cabin, involving electric saws. During that time the voltage on the batteries, as per the Outback system, have shown a sightly lower and lower voltage(12.9 to 11.9). Last week I checked the battery water/acid and in 2 of the 8 the was no water above the plates, the rest were all down to just above the plates. It took about 3 gallons to refill the batteries. At the time of refilling, the batteries were at 11.9 volts. I turned off the electricity supply to the cabin. I let the panels recharge the batteries (the panels were supplying 36 to 45 Volts peak during the day) and after 4 days the batteries were at 12.3 volts. I then ran the generator for an hour, the batteries showed 13.9 volts during that hour, after, the batteries showed 12.4 volts. I checked each battery and they varied from 6.0 to 6.47 volts. (I have since found out that the previous owners were not at the cabin for 2 years prior to my purchase.)

I have a question: Are my batteries toast? Do I continue to try to wait for the batteries to recharge and try different things or do I just go and buy 8 new batteries? If I get new batteries, do I have to reset my Outback set points?

Photowhit · September 2021

You have and will want to continue learning about solar electric systems and how they function.

I would suggest buying a hydrometer and checking your batteries 'Specific Gravity' (SG), I suspect it will be best to replace the batteries if you understood them now. But if people were able to run power tools off them, you may have some functioning batteries... So maybe best to pickup a hydrometer now and check the batteries. It will help with the learning.

You will want to know what your system voltage is. You may have a 12, 24, or 48 volt system. Yu will also want to know what size array you have. Built at least 7 years ago, you may have up to 250 watt panels.

A moment about terms, Wattage is a measure of power, it is made up of volts x amps. Voltage or amps by it's self doesn't tell people much. The basic formula for wattage is Amps x Volts = Watts. Amps can be used as a momentary value, but is regarded over time. So if someone (or meter) says 12 amps, that is a momentary value if continued for an hour is 12 amps per hour.

I would suggest getting a hydrometer and measuring your batteries SG, you can get a glass hydrometer for batteries at an autoo parts store for around $10. There are easier ones like this one sold by Northern Arizona Wind and Sun;

main product photo

MidNite Solar Battery Hydrometer | MNHydrometer | Northern Arizona Wind & Sun (solar-electric.com)

Now I'd suggest looking at your system and see what you can tell us about it.

What is the system voltage?
You can tell this by the output of the charge controller or the model number of the inverter.

If you can, tell us the size(wattage) of the solar panels.

Now do you know what your needs / power usage is?

Is this a weekend cabin or a 24/7 home?

If you can get them fully charged, it would be god to do an equalizing charge. Best guess is at 7 years, you have some dead batteries. Golf cart batteries are good for 4-5 years more is a bonus. BUT you might not need that much reserve power depending on your usage, and the size of the array in terms of having a balanced system.

Here are the basics of battery charging,

The voltage you are seeing is the system voltage and not the battery voltage. If you are connected to charging or a load it will effect the system voltage.

During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

BULK;

First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

ABSORB;

Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries.

The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

FLOAT;

Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

The morning voltage may reflect a load present that is effecting the voltage level. With sealed batteries, you would want to disconnect the battery from the system and allow it to 'rest' for a while to get an accurate idea of it's SOC (State Of Charge) from the voltage.

BB. · September 2021

Welcome to the forum MMark,

More or less, if you get 3-5 years from a "Golf Cart" battery bank in daily use--You are doing fine. You can get upwards of 7 years from a summer cabin battery bank. Especially if it gets cold in your area (cold FLA flooded cell lead acid batteries age slower when cold).

Also, exposing plates (not keeping up with distilled water when needed)--Is also a battery killer.

For "proper" charging--You want to charge up to ~14.75 volts and hold that voltage for ~2-6 hours (deeper discharge, longer absorb time)... Less than reaching and holding ~14.75 volts for X hours, is not fully charged.

At this point--Your bank is pretty much toast. In theory, you could replace any batteries that are not reaching charge or discharging quickly vs the other batteries--But that will only typically buy you months or a year--Not a long term solution.

At this point, I recommend that you get all of the data/configuration information you can about the present system...

Solar panels (Vmp, Imp, Watt rating of each panel), how they are wired (series/parallel, if different panels, you may have three "brand A" in series, three "brand B" in series, and wiring in parallel). Is solar array facing south? Is it tilted towards sun?
the number and type of batteries (like 8x 6 volt @ 200 AH golf cart batteries wired in 2x series by 4x parallel for a 12 volt @ 800 AH battery bank, etc...)...
Rating of AC inverter (if you have one). 2,000 Watt @ 12 VDC input...
Roughly where the cabin is located (nearest major city such as Las Vegas NV) to figure out hours of sun per day by season.
Backup genset and AC battery charger?

And what are your expectations... Amp*Hours or Watt hours per day (i.e., 500-1,00 WH per day for a simple cabin LED lights, tablet and cell phone charging, simple RV water pump--Or 3,300 WH per day--Add a full size refrigerator, possible clothes washer, LED TV, Laptop Computer, etc.). And is this weekend, seasonal, full time, or what?

Going through the system... Making sure that you have good/tight/clean electrical connections. That the array is properly configured... You might want add circuit breakers to reduce the chance of fire (if they where left out of the original design). Even the size of the copper wiring can be an issue (long runs of 12 volt wiring have voltage drop issues, an 800 AH battery bank can easily output 1,000's of Amps into a dead short--Fusing/Breakers can be a good safety measure).

In the "olden days" when solar panels were expensive (20+ years ago) and batteries were cheap--People tended to add more batteries to get "more power"--Today with "cheap" solar panels, and expensive battery banks--It is almost always worth adding more solar panels to a system--This gives you "more energy harvest" and keeps the battery bank "happy" (properly charged, avoiding deep discharges for longer life, etc.).

And solar power is still expensive--Sometimes it is better to run solar for "quiet time" (over night, on quiet days)--And possibly using a cheap genset (or a nice Honda or similar) when needed (running power tools to fix up cabin, shop tools, etc.) when more power is needed for just a few hours/days at a time).

Anyway--More questions than answers at this point. Your thoughts?

-Bill

New Cabin with off grid solar

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