Help please - additional PV 400w panel conflicting with the existing 2kW system

Hi all, total newbie to the forum. I sincerely hope that those in the know-how would be able to assist me. On my semi-detached house we have an existing 2kW system (8 panels, 250w each), this was installed 9 years ago, with the inverter SMA Sunny Boy 2kw (SB 2000HF-30), and recently we added a 400w single panel over our porch just to add bit extra as we are planning to have a battery installed in the near future. It appears that the inverter can accommodate a 2nd string.

During the installation the electrician attempted to connect the single additional panel into the 2nd string, however the inverter didn't like that at all and it wouldn't power up for some strange reason, then the installer connected it through the existing isolator box (so two seperate feeds into it and then the single feed going out to the inverter, still the inverter didnt like that. Then he placed an optimiser onto the new panel and then it worked. He was really puzzled about all this especially why the 2nd string wasn't accepting this single panel, but it worked.

Achieved larger generation than usually we would at this time of year, but in the last couple of days with this sunny weather I noted that in the morning (8am) when was really bright outside (sun is still to the side of the house and not fully shining onto the main 8 panels) the system was producing only 200w. I am monitoring this via Solo PV monitor. I thought that it should be definitely more than 200w. I had a large piece of cardboard and covered the new singe panel over the porch, and monitor indicated a drop to 10w. This indicated that only new 400w panel was generating any electric albeit being in the shade (as the sun hasn't come yet to that side of the house which is apx around 10.30am this time of the year (we are facing SW). New panel remained covered and after about 5min main panels kicked in and monitor showed 800w generation. I uncovered the new panel and production increased by 60w, and started to increase as the sun was moving. As soon as the new panel came into the sun massive increase in production and most of the day we were generating 2kWph. Unfortunately, house roof goes in the shade around 5.30pm but we manage to clock 12.5kW. So the system works to its full potential/capacity when all the panels are in the sun, but something is preventing the main panels starting in the morning.

This is happening now constantly in the morning and even yesterday when we had that mini 1 day heatwave, I did this cardboard cover re-set of the one over the porch and then the main top 8 panels got awaken and started to produce 800w and increased as the sun was coming around.

In the late afternoon when the new panel goes first in the shade the generation accordingly drops and the main top panels carry on working fine until they go in the shade and start shutting down (no optimisers have been installed on them).

As it was really cloudy today the generation was only showing 200w, covered the porch panel, generation dropped to 10w, and after 5min the top panels kicked in and showed around 300w while the one was still covered. Uncovered the porch one and production increased to 430w, remained like that for a bit and the cloud cover increased and production dropped down to 160w apx.

So I am really confused why the main panels would not start producing on a low lux levels while the 400w panel would be generating something while being in the shade and on a cloudy day without direct sunlight as well. Like I said once the all of the panels are in the sun (well appears once the porch single panel comes in the direct light all system works fine as it should).

I have informed the installer/electrician of this and he is finding it really strange, but he hasn't had a chance to come around to have a look yet.

Any thoughts on this strange issue, could it be they way the new panel is connected through the existing isolator as that was the only option due to the inverter not accepting the 2nd separate string, but why the generation from a smaller separate 400w panel would record production by the inverter but no production from 8 (250w) panels? Something is preventing the main system kicking in when its clear that the smaller panel is trickling small amount of energy.

Sorry for such a long explanation just trying to give you a full picture of the issue.

This inverter looks like it has just one MPPT, that means both strings need to be identical, hence not surprised connecting to 2nd string did not work. Not sure from your description how the second panel has actually been connected. I guess the original 8 panels are all in series on string 1, string 2 is not used ? - The new panel i guess is connected in series or parallel with the original 8 in string one ????

plugsandsparks said:

This inverter looks like it has just one MPPT, that means both strings need to be identical, hence not surprised connecting to 2nd string did not work. Not sure from your description how the second panel has actually been connected. I guess the original 8 panels are all in series on string 1, string 2 is not used ? - The new panel i guess is connected in series or parallel with the original 8 in string one ????

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Thank you very much for your reply, really appreciated. On the bottom of the inverter there are two more plugs/slots (-ve and +ve) as per the photo for the 2nd string?

Or just because there are available connectors there maybe it means that my 9yr old inverter doesn't have a second MTTP internally, is that how it works perhaps?

Original 8 are connected in series (I think as one goes in shade early evening all generation drops significantly), end cable goes into an isolator and then into the inverter. So yes, I presume that this is the string 1.

The new single panel has its own separate cable, and the intention was it just to connect it into the available slot for the 2nd string in the inverter (as per photo). Once connected the inverter didn't want to know, didn't want to power up having both strings connected.

Strange how it doesn't perform well on the low light and then full capacity when much brighter either on a brightish cloudy day and when really sunny?




New (panel) cable (left one on the photo) then goes into the existing isolator (with black dial switch) where it joins the cable from the 8 panels (right one), and then the single feed goes into the inverter. So the isolator is the only place where both connections meet, and then single cable from there into the inverter. I really don't know would that make a series or parallel connection then? Is that the issue you would think?



This is the feed from the isolator box. Those two empty plugs were presumed to be used for a 2nd string initially from the new panel. When plugged no reading/input was registered at all. And then that second option was implemented (join the feed via existing isolator).





I hope this makes sense, and once again thank you very much for your assistance. Please feel free to private message me your number if easier to explain that way.

By process of elimination i think i can make some assumptions as to what has happened. That inverter is designed for a maximum of 2000W output. You now have 2400W of panels connected, so on Sunny days expect the inverter to take evasive action to limit damage to its components. This inverter states a maximum of 2100W from the panels so if you are seeing dead on 2000W of output chances are that the inverter is limiting the DC input from the panels, no biggy but just bare in mind.

Next is the Inverter strings, the reason for the extra two plugs is to allow for a second string. SMA and all inverters i have seen are very specific how panels should be connected, as you have 2000W on string 1, i cannot see a scenario where you could use string 2, it is in effect redundant. This is pretty standard so i am surprised the electrician thought he could connect one panel to it..... this does not make sense.

SO that leaves how has the panel been connected.

I have never connected mixed panels to an existing system so not sure what would happen. Parallel connection is largely out as electrically this would cause the big array to be in conflict with the single panel in virtually all circumstances. Series connection is possible but as this panels had very different electrical characteristics from the originals i dont know how the inverter would react, as stated never even attempted it.

So now we are back to the Optimiser, you have not offered any specs to this unit so i am guessing. I suspect its still a series connection but imagine having an optimiser in the inverter and one on a panel. I can imagine some "arguments" going on between them, lol

Question is, overall, are you getting more power ?

The characteristics will have changed so that is not a surprise.

plugsandsparks said:

By process of elimination i think i can make some assumptions as to what has happened. That inverter is designed for a maximum of 2000W output. You now have 2400W of panels connected, so on Sunny days expect the inverter to take evasive action to limit damage to its components. This inverter states a maximum of 2100W from the panels so if you are seeing dead on 2000W of output chances are that the inverter is limiting the DC input from the panels, no biggy but just bare in mind.

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Aha, ok I understand this. Yes, I am seeing it dead on 2000w now remaining constant on the sunny days, while before it would be in the region of 1600w or there abouts, sometime lower on the hot days. I understand also that due to the inverter capacity/limitation i am loosing some from the new panel.

plugsandsparks said:

Next is the Inverter strings, the reason for the extra two plugs is to allow for a second string. SMA and all inverters i have seen are very specific how panels should be connected, as you have 2000W on string 1, i cannot see a scenario where you could use string 2, it is in effect redundant. This is pretty standard so i am surprised the electrician thought he could connect one panel to it..... this does not make sense.

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So, as the inverter is capped/limited to 2000w, each string should be equally split in essence (1000w each) to work properly. So inverter recognises that there's already a string with 2000w connection and shuts off the second string, and therefore I can't plug this additional panel then? Say for example that I had 1600w existing system on 1string and then plugged new 400w panel to the 2nd string, would the inverter, accept that? Am I understanding it correctly. Not sure why he thought that was a possibility with the current setup (2000w + 400w)?

plugsandsparks said:

So now we are back to the Optimiser, you have not offered any specs to this unit so i am guessing. I suspect its still a series connection but imagine having an optimiser in the inverter and one on a panel. I can imagine some "arguments" going on between them, lol

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Sorry I don't have any details on this, just that the optimiser was installed on the back of the panel (panel cable into the optimiser and then cable from the optimiser up to the roof joining into the isolator meeting with the cable from the existing panels and then into the inverter.

Does the inverter has inbuilt optimiser inside? If it does, that could well be a conflict between the two then? But wonder why? It does seem strange that in the morning original panels ar not producing despite being exposed to the sun, although on a really shallow angle, while the new single panel is in shade from the sun is producing 200w. Once I cut light to it the main panels after 5min or so start working and generate apx 600w, then by uncovering the single panel production jumps to 800w. If I didn't do this"reset" i wonder when the original panels would actually start?

plugsandsparks said:

Question is, overall, are you getting more power ?

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Well, I think that I am. Once all panels are receiving direct light my constant production is 2kW and remains like that providing that's strong light, even now is coming through the clouds strongly and it's showing 2000w. It's just that slight loss in the morning which drew my attention to this issue. Before I was clocking around 10-11kW in the summer, on Friday (heatwave day) it generated 12.5kW.

Maybe I will just need to live with it, but then what will happen in the autumn/winter when the lux levels will be much lower? It appears that the new panel with optimiser is almost shutting down the original panels on the low light, but then when the new panel goes into the shade later late afternoon the main panels carry on production until they get into the shade. So it appears that it's mainly in the morning.

Edin Hrustanovic said:

Aha, ok I understand this. Yes, I am seeing it dead on 2000w now remaining constant on the sunny days, while before it would be in the region of 1600w or there abouts, sometime lower on the hot days. I understand also that due to the inverter capacity/limitation i am loosing some from the new panel.



So, as the inverter is capped/limited to 2000w, each string should be equally split in essence (1000w each) to work properly. So inverter recognises that there's already a string with 2000w connection and shuts off the second string, and therefore I can't plug this additional panel then? Say for example that I had 1600w existing system on 1string and then plugged new 400w panel to the 2nd string, would the inverter, accept that? Am I understanding it correctly. Not sure why he thought that was a possibility with the current setup (2000w + 400w)? -

Sorry I don't have any details on this, just that the optimiser was installed on the back of the panel (panel cable into the optimiser and then cable from the optimiser up to the roof joining into the isolator meeting with the cable from the existing panels and then into the inverter.

Does the inverter has inbuilt optimiser inside? If it does, that could well be a conflict between the two then? But wonder why? It does seem strange that in the morning original panels ar not producing despite being exposed to the sun, although on a really shallow angle, while the new single panel is in shade from the sun is producing 200w. Once I cut light to it the main panels after 5min or so start working and generate apx 600w, then by uncovering the single panel production jumps to 800w. If I didn't do this"reset" i wonder when the original panels would actually start?

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Strings should be balanced and achieve minimum voltage to turn on, plus you have just one MPPT. One panel will do nothing but drag the rest down. You have 8 panels and you need a minimum of 220V to turn on the inverter you are already at around 8 panels just to get the thing started. Hence i cannot see how string two could be used, its possible i suppose it allows for 16 X140W panels but they would need to have the same Sun action to work efficiently

I am equally baffled. I would not even attempted what you have done without Sunnyboy underwriting the design as the extra panel induces a change of electrical characteristics in the main string which the MPPT will have to deal with, also of course the optimiser also needs to get some light to turn on as such i could not predict what would happen at start up.

Edin Hrustanovic said:

Well, I think that I am. Once all panels are receiving direct light my constant production is 2kW and remains like that providing that's strong light, even now is coming through the clouds strongly and it's showing 2000w. It's just that slight loss in the morning which drew my attention to this issue. Before I was clocking around 10-11kW in the summer, on Friday (heatwave day) it generated 12.5kW.

Maybe I will just need to live with it, but then what will happen in the autumn/winter when the lux levels will be much lower? It appears that the new panel with optimiser is almost shutting down the original panels on the low light, but then when the new panel goes into the shade later late afternoon the main panels carry on production until they get into the shade. So it appears that it's mainly in the morning.

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Switch on will be the biggest change, but if you are getting more power overall throughout the year then you could say it works.....
I dont know how much difference there is in when sun gets to each panel but if you are loosing more through delayed switch on , then you will have to look at a microinverter solution

plugsandsparks said:

Strings should be balanced and achieve minimum voltage to turn on, plus you have just one MPPT. One panel will do nothing but drag the rest down. You have 8 panels and you need a minimum of 220V to turn on the inverter you are already at around 8 panels just to get the thing started. Hence i cannot see how string two could be used, its possible i suppose it allows for 16 X140W panels but they would need to have the same Sun action to work efficiently

I am equally baffled. I would not even attempted what you have done without Sunnyboy underwriting the design as the extra panel induces a change of electrical characteristics in the main string which the MPPT will have to deal with, also of course the optimiser also needs to get some light to turn on as such i could not predict what would happen at start up.

Switch on will be the biggest change, but if you are getting more power overall throughout the year then you could say it works.....
I dont know how much difference there is in when sun gets to each panel but if you are loosing more through delayed switch on , then you will have to look at a microinverter solution

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aha, ok. So whats my options, was this an bodged job/attempt to increase my production, and furhtermore we have also planned to have a 5.3kW battery installed in the near futurure? I am well dishartened now to be honest, was the installer over too optimistic. Is it worth replacing the existing 8 (250w) pannels for 5 (400w) to match the newly istalled one. The existing ones are 10yrs old as well as the inverter. Really dont know what to do now???

or to simply get him to remove the newly installed one on the porch, and stick with the existing system and then when the battery comes just connect it and thats it and forget the increase?

Options:
1. Getting more power than before ? - Do nothing
2. Getting less power than before? - Put it back the way it was, consider microinverter instead of optimiser for single panel.
3. Sell existing system as a complete package but if you get FIT you may loose it.
4. Upgrade to more powerful panels but these could be physically larger so may not fit, change inverter to match say 8 X 400W and loose the odd single panel.

If you upgrade get a proper design, its a very complicated area and as such manufacturers produce design software to help installers get it right but Sun action is very important, so is shading so if there are any trees in the way give them a good prune.

If you go down the battery route consider a hybrid inverter system as there is less chance of a cock up and they are a little more efficient. Again get it designed using manufacturers design tool and give the Sun the first call on the panels, keep the panels clean, then put your feet up.

plugsandsparks said:

Options:
1. Getting more power than before ? - Do nothing
2. Getting less power than before? - Put it back the way it was, consider microinverter instead of optimiser for single panel.
3. Sell existing system as a complete package but if you get FIT you may loose it.
4. Upgrade to more powerful panels but these could be physically larger so may not fit, change inverter to match say 8 X 400W and loose the odd single panel.

If you upgrade get a proper design, its a very complicated area and as such manufacturers produce design software to help installers get it right but Sun action is very important, so is shading so if there are any trees in the way give them a good prune.

If you go down the battery route consider a hybrid inverter system as there is less chance of a cock up and they are a little more efficient. Again get it designed using manufacturers design tool and give the Sun the first call on the panels, keep the panels clean, then put your feet up.

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Aha, so if I was to keep as it is, what the micro-inverter would do in respect of the single panel then?

Yes, on FIT so any large increase over 2kW would be lost, hence my thoughts to keep it to 2kW (5 X 400w).

And most importantly if you are ever in mid Wales, you will have a beer from me for all this help.

So could micro-inverter solve my issue instead of optimiser fora single panel in the meantime until we decide if to change the whole setup?

Yes, if you are not getting more power, then a microinverter replaces the Optimiser. The microinverter connects directly to your Fusebox bypassing all existing solar. However i am sure with your luck there will be some un-foreseen issues, sat here on my Laptop......lol - would keep the existing solar guys as at least they have a modicum of knowledge of your set up and might take the Optimiser back.

plugsandsparks said:

Yes, if you are not getting more power, then a microinverter replaces the Optimiser. The microinverter connects directly to your Fusebox bypassing all existing solar. However i am sure with your luck there will be some un-foreseen issues, sat here on my Laptop......lol - would keep the existing solar guys as at least they have a modicum of knowledge of your set up and might take the Optimiser back.

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hahaha, I am really surprised he is a really good guy very reputable in my area (rural mid-Wales) with solar pv installs, so I am really surprised that it has turned out this way with my setup to be honest. I am sure that he would swap the optimiser for an micro-inverter.

Shouldn't micro-inverter go into main Inverter in order to distribute the electric to the house?

Edin Hrustanovic said:

hahaha, I am really surprised he is a really good guy very reputable in my area (rural mid-Wales) with solar pv installs, so I am really surprised that it has turned out this way with my setup to be honest. I am sure that he would swap the optimiser for an micro-inverter.

Shouldn't micro-inverter go into main Inverter in order to distribute the electric to the house?

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There are a few choices, one way or another it will connect at 240V AC into your house wiring system. It really depends where the panel is wrt existing fusebox and electrics, its a separate device totally