Issues with Off Grid Solar System

[Aussieboxy]

Hi all,

New to the forum & have an issue I am finding difficult to resolve.

I have a basic off grid solar system with 6 x 175W Panels, 2 x 30A convertors wired in parallel & 8 x 200AH Deep Cycle 12V batteries wired in parallel.

My problem is that a few weeks ago my batteries got drained & now they don't seem to hold a charge. I have taken them off individually & charged them on a battery charger.

Whilst the sun is shining I get full voltage but as soon as it's off the panels I'm down to under 11VDC. Whatt meter tells me they are taking some sort of charge when the sun is on the panels.

Is it possible that one of the batteries has gone bad & is dragging the rest down?

Any suggestions or idea's would be appreciated.

Cheers

 

[snoobler]

Welcome to the forum.

6*175W = 1050W of solar

1050W/12 = 87.5A peak - maximum charging current (limited to 60A due to charge controllers)

8*200Ah = 1600Ah of 12V batteries

1600Ah / 60A = 27 hours of FULL POWER charging.

If you get EXCELLENT sunshine, it should take you at least 5 days to completely recharge your bank to full provided YOU USE NO POWER WHATSOEVER FOR THOSE 5 DAYS.

Here's what I KNOW:

• You have two too little solar for that much battery. Every day it's been in use, the batteries have sustained damage.

Here's what I suspect:

• You have been consistently exceeding your daily solar production resulting in infrequent full charges. This has further degraded the batteries due to not being fully charged most days.
• You may not have a working understanding of the proper way to manage lead-acid batteries or the arithmetic of off-grid systems.

Important questions:

1. What is your location?
2. How old is this system?
3. Are these batteries flooded lead-acid, AGM or gel?
4. How much energy do you use per day?
5. What do you call "full voltage"?
6. Where do you measure "full voltage?

 

[Hedges]

Whilst the sun is shining I get full voltage but as soon as it's off the panels I'm down to under 11VDC. Whatt meter tells me they are taking some sort of charge when the sun is on the panels.

Is it possible that one of the batteries has gone bad & is dragging the rest down?

Certainly possible one or more of the 8 batteries has a bad cell.
I assume they don't have accessible terminals between cells.

You said you charged them individually.
Isolate them, see if any have decent voltage. If so, reassemble with just those and try to use system in a way that gets them fully charged on any sunny day.

Are these wet cell?
If so, for any which are low voltage, try equalizing.
Check specific gravity of cells for any batteries which are decent, see if they need equalization.

If some batteries have decent voltage or can recover to decent voltage with equalizing, use those but don't mix in any that are low, would drag the good ones down.

With battery bank 5x one day's PV production, so long as you normally drain only 20% DoD (or make that 15% DoD for inefficiencies), system should be good. You have lots of extra capacity for multiple days without sun. However, takes a long time to recharge. Would be good to add PV or generator in that case.

With strings of PV panels having different orientations, you can get more hours without exceeding peat watts of charge controller. (more so in the longer days of summer than short winter days, however.)
If you had a 24V system, same charge controllers would handle twice the watts.

You should have a low-voltage cutout so batteries never get discharged below a target level.
Some charge controllers have a relay which can be programmed according to voltage. If you add one, maybe that could be wired to an enable line for your inverter or other loads.

 

[Aussieboxy]

Thanks Snoobler & Hedges.

You are right Snoobler, I don't have a sufficient working understanding of how to configure these types of systems. Like some others I have tried to do it on the cheap. To answer your questions:

1. Location: Brisbane
2. Age of system: Got panels second hand so unsure. MPPT Controllers are 12 months old, 4 batteries 12 months old, 4 batteries bought second hand.
3. Batteries are AGM
4. Power usage is minimal. 1 95L Waco Fridge/Freezer, a few 12V Led lights & every few days a 75W TV for a few hours via a Victron 12-240 inverter.
5. Full voltage is essentially enough to keep the fridge going overnight which at the moment it doesn't.
6. Voltage measured at batteries.

What voltage should I expect with a fully charged 12V AGM, & how can I tell if one is dead?

Really appreciate your assistance.

 

[Hedges]

Here's the manual for my batteries:

http://sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

Exact specs may very slightly for different model AGM.
This manual suggests an equalization process to try to save an otherwise dead AGM.

 

[snoobler]

1. G'day. Solar for Brisbane:


Assuming you have your panels facing due North and tilted at 62° from vertical (28° from horizontal), you would typically multiply the hour number by your array wattage, e.g., June would be 4.13h/day * 1050W = 4337Wh/day. Since your MPPT limit you to 60A peak, it's going to be more like 4.13h/day * 720W = 2974Wh/day. Note that these values assume the panels are sitting in the sun and unshaded from sunrise to sunset.

1600Ah*12V = 19200Wh (assuming your batteries meet spec)

19200Wh / 2974Wh/day = 6.5 days to fully charge your array

2. mix/match of batteries of different sources and ages may be an issue.
3. Thanks - so no equalization. Stuck with what we got.
4. Is the Victron powering the AC devices listed?
5. Your definition of full voltage is utilitarian. The actual definition of full voltage is a bulk/absorption voltage of ~14.4V and a float voltage of ~13.2.
6. Good.

A fully charged AGM should peak at somewhere around 14.4V, stay there for 2-3 hours and then drop to around 13.2V and stay there until there is insufficient solar to maintain them.

If you leave a fully charged AGM sitting for 24 hours with no loads or charging applied at 25°C, they should settle to 12.8-12.9V.

1. Boost/bulk/absorption voltage usually refer to the same value. What is your MPPT set to?
2. What is your MPPT float value?
3. What model of MPPT?
4. At high noon, what is your battery voltage, how much current is each MPPT charging with, and what "mode" is each charger in?

 

[snoobler]

Here's the manual for my batteries:

http://sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

Exact specs may very slightly for different model AGM.
This manual suggests an equalization process to try to save an otherwise dead AGM.

Bookmarked.

That's impressive. 15.5V on an AGM. Most "equalize" only at something slightly higher than typical absorp.

 

[Aussieboxy]

1. G'day. Solar for Brisbane:

View attachment 33039
Assuming you have your panels facing due North and tilted at 62° from vertical (28° from horizontal), you would typically multiply the hour number by your array wattage, e.g., June would be 4.13h/day * 1050W = 4337Wh/day. Since your MPPT limit you to 60A peak, it's going to be more like 4.13h/day * 720W = 2974Wh/day. Note that these values assume the panels are sitting in the sun and unshaded from sunrise to sunset.

1600Ah*12V = 19200Wh (assuming your batteries meet spec)

19200Wh / 2974Wh/day = 6.5 days to fully charge your array

2. mix/match of batteries of different sources and ages may be an issue.
3. Thanks - so no equalization. Stuck with what we got.
4. Is the Victron powering the AC devices listed?
5. Your definition of full voltage is utilitarian. The actual definition of full voltage is a bulk/absorption voltage of ~14.4V and a float voltage of ~13.2.
6. Good.

A fully charged AGM should peak at somewhere around 14.4V, stay there for 2-3 hours and then drop to around 13.2V and stay there until there is insufficient solar to maintain them.

If you leave a fully charged AGM sitting for 24 hours with no loads or charging applied at 25°C, they should settle to 12.8-12.9V.

1. Boost/bulk/absorption voltage usually refer to the same value. What is your MPPT set to?
2. What is your MPPT float value?
3. What model of MPPT?
4. At high noon, what is your battery voltage, how much current is each MPPT charging with, and what "mode" is each charger in?

Hi Snoobler,

1. Unknown
2. Unknown
3. Refer pics
4. High noon battery voltage was 13.4V. Charging current was only 3A on each controller.

 

[Hedges]

Although in a sleeker package, that charge controller resembles one we were suspicious of before, thought it might be PWM by any other name:

What components am I missing for solar setup

Yes, either kind should work.

diysolarforum.com

What components am I missing for solar setup

Yes, either kind should work.

diysolarforum.com

100A 12V/24V MPPT Solar Panel Regulator Charge Controllers Auto Focus Tracking - Vogue Buy

Features: ✅Advanced maximum power point tracking (MPPT/PWM) technology, the efficiency is not less than 99.5%. High-quality components improve the system performance, and the maximum conversion efficiency is 98%. Super fast-tracking speed and guarantee tracking efficiency. ✅Large-screen LCD...

vogue-buy.com

Buttons, screws, USB in same place.

Have you seen inside? Does it have a good size inductor?

The voltages are shown in the manual picture you provided:

"Equalization" 14.4V
Float 13.7V

 

[snoobler]

Those are "MPPT Solar" brand PWM charge controllers. They are not MPPT. You were swindled.

3A EA at 13.4V = 6 * 13.4 = 80.4W.

How are your PANELS connected to the SCC? Are they in series? If so, that won't work with a PWM controller. You MUST parallel the panels to the charge controller, and they MUST be 12V panels, i.e., a Vmp somewhere around 18V.

 

[Hedges]

If the 175W panels are "12V" nominal, their Isc will be a bit over 10A. Their Voc will be something over 20V
Three of them in parallel would risk putting more than 30A through the charge controllers on a good sunny day, which could kill them.
(Had they been MPPT, they would probably limit the current by their control circuitry, but PWM can't limit)

Initially test with one or two PV panels per charge controller.
Once proper operation is confirmed, you could connect three PV panels in parallel if their orientations are significantly different so not all face directly at the sun at the same time.

Charge controller instructions say max 23 Voc from PV panel for 12V battery, so a "24V" nominal panel shouldn't be used; it would exceed 40 Voc.

 

[snoobler]

Good point on panel current. Worth posting the panel specs as well.

 

[Aussieboxy]

Not surprised I was scammed. They are from China.

So should I replace the Charge Controllers?

 

[Hedges]

Not surprised I was scammed. They are from China.

So should I replace the Charge Controllers?

They may work for you, if Vmp of the panels is suitable.
You would probably get more power using MPPT charge controller, especially over various temperatures and battery voltage.

See if any of the batteries are good and if the charge controllers can charge them properly.
Have to deliver enough power to replenish what is consumed, of course. Also voltage has to get high enough with enough current to fully charge. That's where the PWM charge controller may or may not do it, depending on Vmp of the panels under your weather conditions and the loads you operate at the same time.

Have a link to PV panel specs?

 

[Aussieboxy]

I have attached pics of the panels. I have 2 x 175W & 4 x 200W connected in parallel with the connectors shown.

 

[snoobler]

Those panels are not compatible with your PWM charge controllers UNLESS you have a 24V system, which you don't.

The most you'd get out of the 175W panels is about 75W.

The most you'd get out of the 200W panels is about 85W.

So rather than 1150W of panels, you can only harvest about 500W in perfect conditions.

 

[schmism]

So rather than 1150W of panels, you can only harvest about 500W in perfect conditions.

Its like a dumpster fire of news for your system.

For an updated SCC

https://www.amazon.com/Renogy-Charge-Controller-Compatible-batteries/dp/B01MSYGZGI/ref=sr_1_8?dchild=1&keywords=mppt&link_code=qs&qid=1611043709&sourceid=Mozilla-search&sr=8-8&tag=wwwcanoniccom-20

2 of Something like that is what your looking for.

 

[Hedges]

The 175W and 200W panels are close enough in voltage to parallel.
Connect two of each in series, then parallel those three pairs:

(175W + 175W) || (200W + 200W) || (200W + 200W)

Total 1150W (STC) at 71 Vmp
Into 12V that's 100A, into 15V that is 80A.

Considering panels usually put out somewhat less than STC rating, an 80A charge controller would usually capture all the power, but here's one for 100A (good for up to 150Voc of panels)

Epever 100A Solar Charge Controller | SanTan Solar

store.santansolar.com

With three PV panel strings in parallel, should have a fuse for each. The following link includes 15A fuse, but you need 10A according to panel label.

15A MC4 Inline | SanTan Solar

store.santansolar.com

Using a suitably sized MPPT charge controller will double the power produced, compared to the PWM charger which Snoobler noted is incorrect for your panel and battery voltages.
Still need to see if your batteries have been damaged or if they recover to proper voltage.

 

[snoobler]

And wrapping back around to the original issue:

8 * 12V * 200Ah = 19200Wh

Assuming you get fantastic sun during the winter with perfect panel placement (4 hours):

19200Wh/2000Wh/day = 9.6 days with ZERO power use to recharge your batteries.

 

[schmism]

Assuming you get fantastic sun during the winter with perfect panel placement (4 hours):

19200Wh/2000Wh/day = 9.6 days with ZERO power use to recharge your batteries.

Yeh but realisticly dont we need to cut that in half because your only looking at 50% depth of discharge. so those 200ah become 100ah and then your time-to-recharge = ONLY 4.5 days.

 

[Hedges]

Yeh but realisticly dont we need to cut that in half because your only looking at 50% depth of discharge. so those 200ah become 100ah and then your time-to-recharge = ONLY 4.5 days.

That was with "24V" panels and PWM charge controller into a 12V battery.
With his 1150W of PV panels x 4 days = 4500W, and 20 kW battery bank at 50% DoD, just over 2 days when used with MPPT.
(Not counting inefficiency of lead-acid; I've heard 70% more or less. So make that 3 days)

If self-discharge isn't so high as to waste a considerable percentage of production, I think such a bank is reasonably sized.
If the batteries are a type which would only last a couple years with daily deep discharge, having this sized for 15% to 25% depth of cycle each day should let it last 10 years. (but some quality LA batteries are much longer life.)

What it does need is to have sufficient PV to fully recharge after discharge, because LA wants to be kept full.

 

[snoobler]

Yeh but realisticly dont we need to cut that in half because your only looking at 50% depth of discharge. so those 200ah become 100ah and then your time-to-recharge = ONLY 4.5 days.

In his original post, he indicated they were completely depleted, and he'd been unable to get them fully charged since.

 

[Hedges]

He needs to see if any of the batteries are still good, and if any can be brought back up.
8 panels in parallel, comes up to what he thinks is full voltage while charging and immediately drops back to 11V when not charging.

Disconnect all of them, log the voltage of each.
Check specific gravity of each cell, assuming wet-cell, and perform equalizing charge on any batteries with excessive differences between cells.
After charging all batteries, put back in service only the ones that settle to full voltage. Discard any that don't recover with equalization.

Even if these are sealed batteries, before scrapping the bad ones make an attempt at deep discharge recovery/equalization according to instructions for that battery type.

"I have taken them off individually & charged them on a battery charger."

What was their rest voltage after each was charged and allowed to sit?
Was this one battery at a time, leaving the others installed in the system, and returning the individually charged battery to the system with discharged bank?
Need to assemble a bank with all good batteries. An auto store can test "cold cranking amps". Not as much information as amp-hour capacity, but enough to say if battery is decent.

"Whilst the sun is shining I get full voltage but as soon as it's off the panels I'm down to under 11VDC. Whatt meter tells me they are taking some sort of charge when the sun is on the panels."

Apparently different result in the system with PV SCC as compared to battery charger?
Maybe not delivering proper voltage for full charge. Maybe loads pull it down. Maybe one or more bad batteries as you were thinking ... but then they would have show up as bad when charged individually.

"Whilst"
There's the problem! He's apparently British. Although the sun never sets on the British empire, it never rises in Great Brittan.

Seriously though, some problem with with charging or with the batteries. As Snoobler pointed out it'll take weeks of sunshine to recharge a completely discharged bank as presently configured. I've found that bring back a dead battery takes much longer than the amps and amp-hours suggests.

 

[schmism]

In his original post, he indicated they were completely depleted, and he'd been unable to get them fully charged since.

Point.

If I also understand lead based batteries they also want a .3C charge rate to avoid.. sulfation? (somthing about low charge rates is bad)
so 200x8 = 1600ah*.3 = 480a charge rate for ideal operating conditions.

So if you wanted to make an attempt at fixing this.... The only way I see you getting close to that kind of charge rate is to hack together 4-5 power supplies from the link in my description and run them off a generator. The PS go for about $20 each on ebay so another $100 and a 5kw genset you might make a run at being able to charge at something like 400a @14.6v (note that these charge rates result in current amounts that exceed normal wire sizeing that normal DIY folks deal with)

I dont know what it means to have a .05C charge rate (80A into a 1600ah pack) for the long term health of those FLA bats

 

[snoobler]

Few FLA/AGM can handle 0.3C.

.1 to .2C is typical. My T-1275 are limited to .13C. Rolls indicates that 0.05C can be used and still avoid excessive sulfation. I usually try to target 0.15C as solar charging typically starts well below that, and absorption is reached before 0.15C is achieved.