Solar Panels being clipped /limited on Inverter Input

[JonesyJT]

Hi There,

I have had a Sunsynk 3.6Kw system installed since end of may (15 x 385w, Sunsynk 3.6kw investor, 2 x 5.12Kw batteries). the PV's have been installed on 2 strings ( 10 + 5). What I have noticed is that the PV's only ever generate a maximum of 3.8Kw and seem to be getting clipped at this value, whereas they should potentially be able to generate 5.77Kw.

Installer initially said that is how they work, but on further questioning he clarified that once the batteries are up to 100% then the PV's would be clipped to 3.6Kw. However, this is still not the case, as with the recent sunny weather I have data showing the batteries to be less than 100% and the PVs being clipped to 3.8Kw.

Is this correct, or can this be changed via software/hardware settings?

TIA

 

[Al D]

I'm not sure what you mean when you say the panels are on two strings, 10+5. Are the panels connected in 10 in series on one string, and 5 in series on another string? And how are those strings connected?

If the 10 series connected panels are the only ones hooked up to your system, then you would only be getting 3.85kW from them, maximum. Connecting two strings with varying voltages is not something a professional installer would have done. I don't know what the string of 5 is connected to.

I think what the installer was trying to say about the 3.6kW is that the inverter will only be able to output 3.6kW AC, which you would use off of your charged batteries. It's possible the string of 5 is charging your batteries while the string of 10 is going to your house. Or vice versa. It's not something I'm used to seeing, but I'm not the expert, just a DIY guy.

You should look over the datasheet for this model and become familiar with it.

3.6kw Hybrid Inverter | Sunsynk

www.sunsynk.org

 

[400bird]

Hi There,

I have had a Sunsynk 3.6Kw system installed

So, you have a 3.6 kw inverter and your surprised (?) it is limited to about 3.6 kw? I'm surprised it's doing 3.8 not closer to 3.6

If you want more output from your 5.7kw of panels you'd need a bigger inverter. It is very normal to over panel and inverter, 20-30% over paneling is standard

 

[JonesyJT]

AI D - what I mean by strings, is that 10 panels are connected in series to input 1, and 5 panels are connected in series to input 2 - see photo of graphic. And as they are on 2 separate roofs, I have an installed capacity of 5.77Kw, but only ever reaching 3.8KW.

400bird - I understand what you are saying, but system provider explained that while battery is less than 100% then whatever the panels can chuck at it, it will use to charge the batteries. Once you get to 100%, yes I agree, it will limit them as once you extract the 3.6KW the remainder KW has to be lost in heat etc.

 

[wattmatters]

Is this correct, or can this be changed via software/hardware settings?

Some hybrid inverters have an AC output plus can send additional PV power to the battery over and above the AC output capacity (if it will accept charge). It's one of the nice things about some hybrid inverters but I've no idea if yours can do this.

Which is why this is a good idea:

You should look over the datasheet for this model and become familiar with it.

I won't download it because Sunsync require you to sign up to do that, but you should.

I would say it's likely there is a setting currently limiting its operation.

But since this was a put in place by an installer, then you really should be talking with the installer about the system settings and why it is not operating as it should.

 

[JonesyJT]

Hi wattmatters, yes I think that is what should be happening here. See screenshot below of another person and mine should be operating like that.
Having read a few posts on this site, it seems the Sunsynk is the same as Deye investors and I have downloaded the manual and found a setting which should allow max PV to charge the batteries, I will now check this on my system.

AI D - have been asking the installer to sort this out for over 4 weeks. he initially changed a setting but it didn't make a difference, so he is now going back to sunsynk, and I am still waiting for a reply, hence this post to see if I could resolve it.

 

[JonesyJT]

I managed to find the similar setting to the Max Solar Power (see below) and mine is set at 6500, which should mean the PVs charge the batteries at full capacity until the batteries reach 100% and then they will be clipped to 3.8Kw. Looks like there is an internal software bug, so will need to wait back from installer/sunsynk

 

[fromport]

Once you get to 100%, yes I agree, it will limit them as once you extract the 3.6KW the remainder KW has to be lost in heat etc.

An inverter that is "over fed" PV wise simply does not take more than it can take/handle.
A solar panel can be out in the sun, nothing connected to the leads and it is not "burning up" or anything because the power is not "taken" from it.

 

[Al D]

I suspect string 2 isn't coming through. Maybe it's turned off or not hooked up correctly? Shaded panel, open circuit, connected wrong, etc.

The 3.6kW should be the max output AC. The PV panels show 3.8kW DC. if you’re in a very sunny area, 10 panels at 385W each could produce the 3.8kW you're seeing. It's not clipped, you're maxed out on string 1, and string 2 isn't coming in.

That's my guess. I would try testing string 2 with a DMM at peak daylight.

Edit: just be careful working with live power. Don't make the measurements if you're not tech savvy and comfortable doing so. You are dealing with a lot of power at those two leads. That can harm or kill you.

Also, if that picture of the schematic is viewable on your device, you could just monitor the readings at peak daylight. That's the safest option and doesn't require you to disconnect anything. Do this first.

 

[wattmatters]

An inverter that is "over fed" PV wise simply does not take more than it can take/handle.

Perhaps your system has that limitation but there are most definitely hybrid solar PV inverters which can both supply their max rated output on the AC output side, while also sending power over and above that to charge the battery.

 

[fromport]

Perhaps your system has that limitation but there are most definitely hybrid solar PV inverters which can both supply their max rated output on the AC output side, while also sending power over and above that to charge the battery.

I know!
I have a 12kW DC PV input and 8kW AC capable inverter (MegaRevo)
The posting I was referring to had this statement " once you extract the 3.6KW the remainder KW has to be lost in heat"
Maybe I didn't understand the question ?!

 

[wattmatters]

I suspect string 2 isn't coming through.

I had that thought (e.g. a DC isolator left open) but the image shown earlier shows power on both MPPTs, plus the dead flat production curve through the day. It wasn't a lot of power so I presume it was early or late in the day, maybe cloudy.

 

[Al D]

I had that thought (e.g. a DC isolator left open) but the image shown earlier shows power on both MPPTs, plus the dead flat production curve through the day. It wasn't a lot of power so I presume it was early or late in the day, maybe cloudy.

We can't be certain that the same configuration was used for both sets of pictures OP provided. He mentioned changes were made by the installer at some point.

 

[wattmatters]

The posting I was referring to had this statement " once you extract the 3.6KW the remainder KW has to be lost in heat"
Maybe I didn't understand the question ?!

I think this was referring to the case when the batteries are fully charged and so no more output can be diverted to them, so the total system output is capped to the AC output of the inverter. In which case any unrealised capacity of the PV array(s) is simply not generated with the excess irradiance just sent back into the environment as heat.

 

[fromport]

I think this was referring to the case when the batteries are fully charged and so no more output can be diverted to them, so the total system output is capped to the AC output of the inverter. In which case any unrealised capacity of the PV array(s) is simply not generated with the excess irradiance just sent back into the environment as heat.

since the remark had KW (kilowatt) I took that as the author thought the inverter was forced to convert to heat.
Let's leave it at this.

 

[sergea]

AI D - what I mean by strings, is that 10 panels are connected in series to input 1, and 5 panels are connected in series to input 2 - see photo of graphic. And as they are on 2 separate roofs, I have an installed capacity of 5.77Kw, but only ever reaching 3.8KW.

400bird - I understand what you are saying, but system provider explained that while battery is less than 100% then whatever the panels can chuck at it, it will use to charge the batteries. Once you get to 100%, yes I agree, it will limit them as once you extract the 3.6KW the remainder KW has to be lost in heat etc.View attachment 107168

Your PV will produce only if there is a load. 5.77kW is in ideal lab condition only. and the MAX PV DC is 4680W on the 3.6K inverter . There is no way you can get this theorical 5.77kW from the PV.

And to make it worst the MPPT channel with the string with 10x384W panel will generate 4680W /2 max = 2340W max.
Second MPPT channel will generate in lab condition 5x385W = 1925W. So max in lab condition is 2340W + 1925W = 4265W

You say you get 3.8kW max, it doesn't seem to be a problem here. I think.

 

[robby]

What's the mystery?
The Inverter is putting out 3.6KW as rated.
In the third picture the house is getting 2.7KW and the Battery is being charged at 840W.
The Inverter is using 3.8KW to do this and about 200W is being lost in the conversion.
Any extra power the panels could produce during the peak is being clipped by the MPPT reaching their limit.
Nothing is going to fix this because there is nothing to fix. The benefit your getting is that those sloping sides before and after the peak would be a lot steeper if you had less panels. So you are getting a fair amount of benefit in the mornings and late afternoon on sunny days and also a lot of benefit on days that are a bit cloudy.

 

[wattmatters]

The Inverter is putting out 3.6KW as rated.

It's rated 3.6 kW for AC output but is also capable of additional DC power output to charge the battery on top of the AC output. Except it's not doing what it should in that respect.

 

[robby]

Where exactly did you read this info?

 

[wattmatters]

Where exactly did you read this info?

Not sure what you mean. It's a common feature of many hybrid grid tied solar PV inverters.
e.g. a Sungrow SH6.0RS has a 6 kW (230 V) AC output and can charge a battery at up to 6kW as well. It's rated to connect up to 13 kW of solar PV.