PV watts/volts drops as house load increases

Hello,

I am in dire need of help regarding my system. I have 6x 545 solar panels and a 3.2KW chinese inverter [company: Fronus] with a 24v batteries. It has been 13 months since I installed it and it worked perfectly last year. As I live in Karachi, Pakistan, the weather is pretty hot throughout the year and we have great sunlight for around 10 months. I am technically not that well versed with electronics but have little basic knowledge of how things work.

My inverter settings are as follows;

Mode: SBU (Solar > Battery > Utility)
Back to grid volts for battery: 24.5v
Batteries: 2x Lead acid 24v bank (155AH each)
Battery charing source: Only solar

For past couple of months, I have been noticing, as my house load increases anywhere above 1.5kw to 1.9kw (if I turned on my air conditioner which takes around 5.5amp), PV production from the panels starts dropping to 0w literally within a minute and as I use SBU mode, the load shifts from solar to battery and then instantly to grid as batteries cannot endure such high load and drops their volts. As I turn off my Air conditioner, the PV production gets back to normal and starts charging batteries. So my actual problem is that DROP in the PV power production when the load increases, ideally it should not decrease the PV production. For instance, load is around 1300W and the production is around 2200W, but when load starts increasing anywhere above 1400W or 1500W, the PV power drops from 2200/2300W to 0. It should be stay stable or max out, right?

I have tried changing settings and whatnot, but I ain't able to fix this issue. I have tried contacting my installer company but they aren't much responsive as we got bad after sales service generally here. I will share some screenshots from the app that I use to monitor which might clarify the issue with graph curves.

Could the batteries be going bad? What type of batteries?

24.4 volts could be a low state of charge.

My guess is your batteries are shot. 1 or both.

chrisski said:

Could the batteries be going bad? What type of batteries?

24.4 volts could be a low state of charge.

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I got lead acid batteries, mentioned in the thread as well. How come batteries are correlated to pv production?

Mattb4 said:

My guess is your batteries are shot. 1 or both.

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For my own knowledge, do you mind sharing why batteries would cause this drop is PV production? For instance, load is around 1300W and the production is around 2200W as its charging batteries simultaneously, but when load starts increasing anywhere above 1400W or 1500W, the PV power drops from 2200/2300W to 0. It should be stay stable or max out, right?

bilalirfanpk said:

I got lead acid batteries, mentioned in the thread as well. How come batteries are correlated to pv production?

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The problem is lead battery.
Really a lead battery can only handel c0.2 discharge.
Moment you pull more it will make heat and the battery go faster bad
The other problem lead battery have a mass drop on volt if you draw a lot of power.
A lipo4 battery do not have this problem.

For your pv problem the inverter pull from the lead battery and the solar power
So all power go first to the inverter that is the reason it stop charging.

Simpel explain.
Electric is the same like water.
Water always thake the easy way out
This is with electric to .
So the inverter pull on it so that is the easy way out
So thare is no problem really
It work just fine .
The solar electric is use by your inverter and pull les on the battery .

Easy test
See what your inverter use with out solar power.
And see the draw of amps out of the battery.
Set your solar panels on again and see what draw now out of the battery.
You will see les amps from the battery will be pull

Suijkerbuijk said:

The problem is lead battery.
Really a lead battery can only handel c0.2 discharge.
Moment you pull more it will make heat and the battery go faster bad
The other problem lead battery have a mass drop on volt if you draw a lot of power.
A lipo4 battery do not have this problem.

For your pv problem the inverter pull from the lead battery and the solar power
So all power go first to the inverter that is the reason it stop charging.

Simpel explain.
Electric is the same like water.
Water always thake the easy way out
This is with electric to .
So the inverter pull on it so that is the easy way out
So thare is no problem really
It work just fine .
The solar electric is use by your inverter and pull les on the battery .

Easy test
See what your inverter use with out solar power.
And see the draw of amps out of the battery.
Set your solar panels on again and see what draw now out of the battery.
You will see les amps from the battery will be pull

Click to expand...

I believe you have misunderstood my question unfortunately. My question is related to drop in solar power production when I increase the house load on it and not the battery sir. My battery backups are totally fine as they are one year old only and never discharged under 50%.

bilalirfanpk said:

For my own knowledge, do you mind sharing why batteries would cause this drop is PV production? For instance, load is around 1300W and the production is around 2200W as its charging batteries simultaneously, but when load starts increasing anywhere above 1400W or 1500W, the PV power drops from 2200/2300W to 0. It should be stay stable or max out, right?

Click to expand...

No its not
Solar panels are not a stable power .
It go up and down and your mppt try to make a stable watts come out.
A cloud will stop it .

Really you have to know that solar panels we use are uv panels.
More uv power more power we have
That a sun is thare do not mean all the uv power come to.

See attach files.
How things works

bilalirfanpk said:

I believe you have misunderstood my question unfortunately. My question is related to drop in solar power production when I increase the house load on it and not the battery sir. My battery backups are totally fine as they are one year old only and never discharged under 50%.

Click to expand...

I think you do not understand how it go.

Your energy from the solar panels are not stopping.
It go directly to your inverter.
And its all use and do not go to the battery.
So its not registered that the battery is charging
That is the reason to test out with and without the solar panel connect .
Than you can see whare the power go to .
If the pv volt go down really down.
Than the only reason is that pv volt is disconnect.
If its disconnect the only reason i can think of is this.
To high pv volt on the mmpt part.

For the rest how hotter the panels how less it will make.
The max watts and amps on a panel are base on 25 Celsius..
It can that you panels are to hot so you never gone have the max watts come out .

You see , al of things can set your max watts from your panels go down
So you can never go base on a calculation of panels watts that you real can use.

Suijkerbuijk said:

No its not
Solar panels are not a stable power .
It go up and down and your mppt try to make a stable watts come out.
A cloud will stop it .

Really you have to know that solar panels we use are uv panels.
More uv power more power we have
That a sun is thare do not mean all the uv power come to.

See attach files.
How things works

Click to expand...

We have great sunlight with clear skies where I live. You can check the solar radiation here in my city.

Get a digital clamp meter, set to read DC amp. Take a set of readings from the DC + cable or cables depending on number of strings. The meter will show if the pv PANELS ARE PRODUCING POWER. That's step one. Seems to me you have very small FLA batteries. Get a discharge test done on the batteries by a car mechanic. I would expect you will find the batteries are at end of life. For reference i have lived completely off grid for 25 yrs with a 1000a C5 24 v FLA set up. I do know about batteries. Unless you test and measure stuff you are just guessing.

offgridandy said:

Get a digital clamp meter, set to read DC amp. Take a set of readings from the DC + cable or cables depending on number of strings. The meter will show if the pv PANELS ARE PRODUCING POWER. That's step one. Seems to me you have very small FLA batteries. Get a discharge test done on the batteries by a car mechanic. I would expect you will find the batteries are at end of life. For reference i have lived completely off grid for 25 yrs with a 1000a C5 24 v FLA set up. I do know about batteries. Unless you test and measure stuff you are just guessing.

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Thanks for your valuable suggestion. I have a pair of 155AH FLA (Flooded Lead Acid; if that's what it means?). Its been one year only since I bought and used them. I have daily discharged them maximum to 24v as its 50% SOC and then later shift load to grid automatically. It shouldn't go bad this early technically but I sure will get them checked.

bilalirfanpk said:

Thanks for your valuable suggestion. I have a pair of 155AH FLA (Flooded Lead Acid; if that's what it means?). Its been one year only since I bought and used them. I have daily discharged them maximum to 24v as its 50% SOC and then later shift load to grid automatically. It shouldn't go bad this early technically but I sure will get them checked.

Click to expand...

What for type of battery are those.
Not all fla battery can handel 50% soc .
Agm battery can do 50% easy
Lipo4/lithium do 99% easy

remember most FLA AH ratings are 20hr discharge rates or .1C so for your 100ah battery thats a 10a load nominal.
Pul more and battery go les longer in use to Internal heat .

Suijkerbuijk said:

What for type of battery are those.
Not all fla battery can handel 50% soc .
Agm battery can do 50% easy
Lipo4/lithium do 99% easy

remember most FLA AH ratings are 20hr discharge rates or .1C so for your 100ah battery thats a 10a load nominal.
Pul more and battery go les longer in use to Internal heat .

Click to expand...

Those are lead acid flooded batteries. I discharge them daily to 55% SOC and not less. Maybe batteries are dying but I fail to understand that why weak batteries would cause a drop in PV production on a sunny day with clear skies and zero clouds.

There is another possibility If your SCC gives an alarm and losses indication of PV production momentarily before recovery you may have a bad connection or panel.

I would suggest that the issue is how you interpret the data. Assuming your PV panels work and also the inverter; then if the battery is in poor condition and unable to hold a charge; as you increase the load all PV production is going to support the load. You don't have sufficient power to support the load AND charge the battery.

If you were to fully charge the battery to say 29V. Then turn of the charging source, then turn off the PV input and connect the load, See how the battery acts then. I suspect the battery will discharge very quickly indicating that the battery is unable to hold a charge. This is typical behaviour for a knackered FLA set up.

As with most things in life there are differing qualities in the batteries available. With FLA the more lead in the battery the longer it's life. Cheap batteries have less lead and less life. Buy cheap and buy twice is a accurate truism.

BTW have you checked the water level in the cells. Hot weather increases evaporation. If the water/acid solution level drops and exposes the lead plates then harm is done and the charge available is reduced.

Mattb4 said:

There is another possibility If your SCC gives an alarm and losses indication of PV production momentarily before recovery you may have a bad connection or panel.

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I will look into connection and panel individually as well. Would you mind guiding me to which exact bad connections should I be looking at?

offgridandy said:

I would suggest that the issue is how you interpret the data. Assuming your PV panels work and also the inverter; then if the battery is in poor condition and unable to hold a charge; as you increase the load all PV production is going to support the load. You don't have sufficient power to support the load AND charge the battery.

If you were to fully charge the battery to say 29V. Then turn of the charging source, then turn off the PV input and connect the load, See how the battery acts then. I suspect the battery will discharge very quickly indicating that the battery is unable to hold a charge. This is typical behaviour for a knackered FLA set up.

As with most things in life there are differing qualities in the batteries available. With FLA the more lead in the battery the longer it's life. Cheap batteries have less lead and less life. Buy cheap and buy twice is a accurate truism.

BTW have you checked the water level in the cells. Hot weather increases evaporation. If the water/acid solution level drops and exposes the lead plates then harm is done and the charge available is reduced.

Click to expand...

As per inverter's design, its meant to support the load first and charge batteries with leftover power provided by the panels. So ideally it should keep supporting the load and ignore the batteries while sufficient PV power is available as I mentioned earlier. My actual problem here aren't my batteries but PV dropping its power whilst the house load increases on a clear day and bright sun. I want to understand if is there a co-relation between weak batteries to PV power production? If PV is producing 2400W while the houseload is 800W, why does PV drop to 0 when the house load increases to 1500W or more despite having no clouds, bright sunlight? That's what I am trying to understand here.

And yes, I topup water every month and make sure it doesn't drop below low levels.

bilalirfanpk said:

I will look into connection and panel individually as well. Would you mind guiding me to which exact bad connections should I be looking at?

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The first place to check is the MC4's and if you have any inline fuse MC4's they are a prime area of bad connection. Also check for loose terminal screws in any combiner box or disconnect.

Mattb4 said:

The first place to check is the MC4's and if you have any inline fuse MC4's they are a prime area of bad connection. Also check for loose terminal screws in any combiner box or disconnect.

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Great, let me get that checked.

One of my 12v chargers does exactly like your describing and I narrowed it down to a bad connection to the panels. I didn't find the exact location of the bad connection since this array in on an awning and hard to get to and I will be replacing those panels in a few weeks.

It's more than likely a bad mc4 connector as they are old and need replacing. I moved the cables around and get it back working.

The lower the load the better they work. If I put them all in series as soon as any real load is pulled from the panels it drops to almost 0 output and then comes back.

4s problem (all 4 panels wired in series making 48v)
2s2p works fine (two panels wired in series making 24v and then the other 2 panels wired in series for 24v and then paralleled staying at 24v)

So odds are good you have a bad mc4 connector or a melted cable.

Crowz said:

One of my 12v chargers does exactly like your describing and I narrowed it down to a bad connection to the panels. I didn't find the exact location of the bad connection since this array in on an awning and hard to get to and I will be replacing those panels in a few weeks.

It's more than likely a bad mc4 connector as they are old and need replacing. I moved the cables around and get it back working.

The lower the load the better they work. If I put them all in series as soon as any real load is pulled from the panels it drops to almost 0 output and then comes back.

4s problem (all 4 panels wired in series making 48v)
2s2p works fine (two panels wired in series making 24v and then the other 2 panels wired in series for 24v and then paralleled staying at 24v)

So odds are good you have a bad mc4 connector or a melted cable.

Click to expand...

Sounds exactly like mine. I have all 6 panels connected in series for the max output I believe, that's what my installer told me.

If your going to fix this yourself I advise getting the right tools together before tinkering with it.

You need a box of mc4 connectors (will need these to replace any bad ones).

Good wire strippers because you have to cut out the bad connector and strip the wire to install the new connector.

A good crimping tool to attach the metal ends that go in the mc4 connector housing.
This is what I bought but it shows currently unavailable.

I just ordered in some more Staubli MC4's to replace some of the cheap ones I used in the past on my arrays. Things are working but it is a pain to deal with intermittent fault conditions. Staubli are not cheap at $5.50 a pair. I am also replacing some of the cheap Y connectors I have with Staubli brand ones.

It is amazing how many issues are caused by wires, connectors and fuses bought cheap.

Could be a bad connection, hope it is. I would still test stuff seperately. Just because a computer (inverter) says it is so don't mean it's true. Independant check with multi meter to confirm is a good way to go. But look for signs of burning around the MC4 connections, usually evidence is there to see. I assumed you had checked this first.