Sharp drop in PV production in the afternoon

[Billybob16]

Hi everyone,

I'm experiencing a sharp drop in PV production in the afternoon on a sunny day, no shading, no clouds, see screen shot of solar assistant. Sharp drop around 1pm then some rise in late afternoon around 4pm. Strange

I'm wondering if anyone besides me have been experiencing this. The days are sunny with no clouds. Looking closely I think I can see a slight haze. Could it be airplane chemtrail/contrails. Looking closely I see a slight haze in the blue sky, I'm in midwest Missouri off grid. This is really bothersome and perplexing.

I have a 7.5KW PV system that I have recently installed. 3 SPF5000ES inverters, 2 with series array of PV conected, approximately 400V input each, 6 - 48V/100A lifepo4 batteries. Array is south facing at 34 degrees, I'm at 38 longitude.

Any ideas or have you been experiencing anything like this.

Thanks, Bill

 

[fega72]

Probably your batteries are fully charged around 1pm? This is my one: fully charged around 9am

 

[timselectric]

I agree, batteries are probably full by then.
Output is only going to match usage, up to its limits.

 

[Supervstech]

That is the most likely.
Ac season hasn't hit most of the US yet, so production isn't needed.
Another issue might be panel temps.
Sunlight peaks can warm panels and reduce output a little.

 

[Ampster]

The easiest way to prove the hypothesis that your batteries are charged is to measure Voltage and/or put loads on the system to see if solar production increases.

 

[Billybob16]

You are correct about the batteries being fully charged around that time. However I have the inverters set to run off solar if available then batteries. While the batteries are charging the solar is also providing house power. When this drop in production happens the system begins to draw from batteries due to low solar production. My solar assistant monitoring program shows both the drop in solar, draw on batteries as well as state of charge. Due to drop batteries will be consumed during the afternoon. This just can't be right. I don't think it can be temp as this is still winter here.

Any other thoughts?

Thanks

 

[Ampster]

Any other thoughts?

Yes, give us some data. Voltage, current used for loads over time and at the the times that you have production and production falls off.

 

[aentrop]

Sounds like you could have your float voltage set too low. Once the bulk charge which is constant current completes it should switch to constant voltage mode and you may need to increase the CV value up some.

 

[Ampster]

Sounds like you could have your float voltage set too low.....and you.may need to increase the CV value up some.

He is using LFP batteries. Most people do not recommend using Float for LFP. I didn't see any reference to the voltage settings so how did you conclude that the Constant Voltage setting was too low?

 

[Billybob16]

Here are 5 screen shots covering data charts for 3 days. They include PV voltage, pv current, pv power, load, buss voltage, battery voltage. Note when pv current drops voltage stays the same but pv current/power drops. Battery voltage also drops due to it no longer charging from pv. Inverter temps are running between 10C-30C. The growatt inverters are set solar/battery/grid, option 5 to LI with bms comunication. Only 2 inverters have PV input which is a mathing split string, all have battery. The 2 strings are acting the same.

It sure looks like something in the afternoon atmosphere.

Thanks for all of you that are contributing your thoughts.

Bill

 

[Ampster]

It sure looks like something in the afternoon atmosphere.

That notch looks like possible shade. Any insight you can share? Thanks for all the charts. Do you have any data on battery voltage and loads?

 

[Billybob16]

Yes I do in the one chart listed here. Panel temp at peak today was 102F, 92 was the norm, all charts except the combined chart showing today up to 4pm. I think (fega72) had it correct regarding batteries being charged with little needed production after that. There is a direct coralation to load and solar production looking at the combined chart with battery power just below it. It apears that the inverters (mppt) are not keeping up with the load demand, maybe not applying all the power that they could and using battery as solar is surly available. Maybe a setting, setup or software issue. I really don't want to wast solar production or use the battery at all during the day if I can help it. It's as if it is using the batteries as a load buffer but not applying all available current as it thinks it's not needed due to SOC of batteries.

Interesting issue, the charts sure help to see what's going on. I really like this PI Solar Assistant.

Thanks, again, Bill

 

[labeeman]

Here is a chart of my current from the charge controller and around 12 PM the current goes to 2.5 amps due
to the batteries getting charged up.

 

[TorC]

Looking at those charts, I'd first say it looks like the batteries get charged up, the current from PV drops, and then there's some reaction time for the MPPT to keep up with the load, which goes back up in a big spike in the mid afternoon. Assuming no grid tie, I don't think you're leaving more than maybe a few watthours on the table at most, but I suspect that's made up for by the solar keeping going longer. Unless you find evidence the batteries aren't fully charged byat the time current load exceeds available PV for the remainder of the afternoon, I'd say you're extracting all the PV power your system can make use of.

 

[Lt.Dan]

Is the inverter or MPPT getting hot and throttling? Mine will do this.

 

[Billybob16]

Is the inverter or MPPT getting hot and throttling? Mine will do this.

It is going up to 80-82F

 

[Billybob16]

Looking at those charts, I'd first say it looks like the batteries get charged up, the current from PV drops, and then there's some reaction time for the MPPT to keep up with the load, which goes back up in a big spike in the mid afternoon. Assuming no grid tie, I don't think you're leaving more than maybe a few watthours on the table at most, but I suspect that's made up for by the solar keeping going longer. Unless you find evidence the batteries aren't fully charged byat the time current load exceeds available PV for the remainder of the afternoon, I'd say you're extracting all the PV power your system can make use of.

I don't think the batteries are charging fully, they get to 99% then the inverters reduce charge amps to around 6-10. This included chart shows the battery voltage and current.

 

[Billybob16]

Looking at those charts, I'd first say it looks like the batteries get charged up, the current from PV drops, and then there's some reaction time for the MPPT to keep up with the load, which goes back up in a big spike in the mid afternoon. Assuming no grid tie, I don't think you're leaving more than maybe a few watthours on the table at most, but I suspect that's made up for by the solar keeping going longer. Unless you find evidence the batteries aren't fully charged byat the time current load exceeds available PV for the remainder of the afternoon, I'd say you're extracting all the PV power your system can make use of.

I don't think the batteries are charging fully, they get to 99% then the inverters reduce charge amps to around 6-10. This included chart shows the battery voltage and current

I don't think the batteries are charging fully, they get to 99% then the inverters reduce charge amps to around 6-10. This included chart shows the battery voltage and current.

 

[Billybob16]

Is the inverter or MPPT getting hot and throttling? Mine will do this.

I don't think so unless 82F or is considered hot

 

[Billybob16]

Here is a chart of my current from the charge controller and around 12 PM the current goes to 2.5 amps due
to the batteries getting charged up.

View attachment 87962

I think that is what's going on here. Your chart looks very similar. Does your system run on both solar and battery at the same timw?