Any domestic solar PV experts here?

[EdH]

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 appeared that the inverter can/could accommodate a 2nd string.

During the installation the electrician attempted to connect the new 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) and still the inverter didnt like that either. Then he placed an optimiser onto the new panel and then it worked for some strange reason. He was really puzzled about all this especially why the inverter wasn't accepting this single panel, but it worked and we left it to that.

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 (although sun is still to the side of the house and not fully shining onto the main 8 panels no shade on them in the morning whatsoever) the system was producing only 200w. I am monitoring this via Solo PV monitor. I thought that it should be definitely more than 200w given the brightness. I had a large piece of cardboard and covered the new singe panel over the porch just to see what would happen, and monitor indicated a drop down to 10w. This indicated that only new 400w panel was generating any electric at that time 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 with the cardboard and after about 5min main panels kicked in and monitor showed 800w generation from them. I uncovered the new panel and production increased by 60w to 860w and started to increase steadily as the sun was moving. As soon as the new panel came into the sun around 10:40 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 that day. 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 just one the new panel).

As it was really cloudy today the generation was only showing 200w, I covered the porch panel again to test it, and the 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 200w while being in the shade and on a cloudy day without direct sunlight as well and with the installed optimiser. Like I said once the all of the panels are in the sun (well it appears that 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.

 

[Skyliner33]

I can't help with the problem sorry.
However just wondering if you have a FiT tariff? I have thought about adding an extra panel to mine but didn't I didn't think you could add capacity afterwards?

 

[EdH]

I can't help with the problem sorry.
However just wondering if you have a FiT tariff? I have thought about adding an extra panel to mine but didn't I didn't think you could add capacity afterwards?

No worries mate, yes on the tarrif but the increase will be negligible (400w). I will wait for the installer to get back to me.

 

[Ozi]

I’ll start by saying that I’m no expert. But have been reading up recently for a new system. Currently have a 1.5KWH system installed around the same time as yours, and from what I’ve read, the tech in those panels is somewhat different to new modern ones.

As I understand it, you’d normally have panels which all have the same output. So adding a new larger panel alongside the old 8 with smaller outputs could be part of the issue.
And then theres the shade issue. New panels are able to work more efficiently with shading (I.e if one is partially shaded, the others can still work at full output) whereas older ones aren’t like this and shading on one can drive down the output from all.

So could a combination of these two factors be causing your problems? But that’s just based on what I’ve read. An expert may be able to diagnose the actual issue.

Would be interested in your answer to @Skyliner33 ’s question too, as I might add a couple more to my existing system if it doesn’t screw with the FIT rates

 

[Skyliner33]

No worries mate, yes on the tarrif but the increase will be negligible (400w). I will wait for the installer to get back to me.

Have you checked the terms? I think you might be breaking the contract you signed. Its a 20% increase in capacity. Be careful the energy company might spot the increase in generated.

 

[EdH]

Have you checked the terms? I think you might be breaking the contract you signed. Its a 20% increase in capacity. Be careful the energy company might spot the increase in generated.

My inverter is capped at 2kw and contracted as such, 8 panels of 250w (2kW peak), on occasions I have seen them keeping at the peak and then drop down to 1.6 -1.7kW, so this additional 400w (peak) will top-up to the maximum allowed 2kW.

So technically I am topping up the natural loss of the panels to my contracted capacity of 2kW and not exceeding the production per hour.

 

[Skyliner33]

So technically I am topping up the natural loss of the panels to my contracted capacity of 2kW and not exceeding the production per hour.

The energy company might not view it the same way. I am interested in this as I would like to add a bit more capacity.
Also interested if you get the new technology panels to work with the older ones. I think mine are about 10 years old, as an estimate.

 

[EdH]

The energy company might not view it the same way. I am interested in this as I would like to add a bit more capacity.
Also invested if you get the new technology panels to work with the older ones. I think mine are about 10 years old, as an estimate.

Aaaa, what do I do now? There is always variations in generation to be honest as the weather has been crap so far and not many sunny days. 2020 we had much better summer and the generation was superb then, so I don't know how could they see difference to be honest, one month I could generate more and then next month much less.

 

[Skyliner33]

Aaaa, what do I do now? There is always variations in generation to be honest as the weather has been crap so far and not many sunny days. 2020 we had much better summer and the generation was superb then, so I don't know how could they see difference to be honest, one month I could generate more and then next month much less.

I agree, some years are better than others. This hasn't been great so far.
I have thought about adding more panels, but because of the worry about capacity, which I have to input for each FiT reading always been a bit worried. Then the complications of getting panels that would work. My inverter has 2 spare MC4 connectors on it as well.

SO I would be really interested if the companies will detect it.

 

[EdH]

I agree, some years are better than others. This hasn't been great so far.
I have thought about adding more panels, but because of the worry about capacity, which I have to input for each FiT reading always been a bit worried. Then the complications of getting panels that would work. My inverter has 2 spare MC4 connectors on it as well.

SO I would be really interested if the companies will detect it.

Hmmm, i don't know to be honest, I am going slightly up, and I am not generating more than I should as my inverter is only 2kW so I really don't know how would they notice an icrease as my system was meant to do that generation anyway. Of course if I was going 1kW and up then yes that would be bigger increase. On a good day I only generated around 11kW or so due to the orientation of our house and early shading in the late afternoon, this Friday was the best 12.5kW. But today will be 3kW at the most due to cloudy day.

And then if you install optimiser on each panel that will increase their productivity anyway, so I am really not sure how can they detect minimal increases.

 

[Skyliner33]

Hmmm, i don't know to be honest, I am going slightly up, and I am not generating more than I should as my inverter is only 2kW so I really don't know how would they notice an icrease as my system was meant to do that generation anyway. Of course if I was going 1kW and up then yes that would be bigger increase. On a good day I only generated around 11kW or so due to the orientation of our house and early shading in the late afternoon, this Friday was the best 12.5kW. But today will be 3kW at the most due to cloudy day.

And then if you install optimiser on each panel that will increase their productivity anyway, so I am really not sure how can they detect minimal increases.

I'm not sure either.
But if you up the panel capacity by 20%, then surely over a year your kWh generated would be up by almost that amount (assuming you rarely get 2kW). Maybe its just me being overcautious but I would imagine that a jump of almost 20% after 8 years might be noticeable. That's what I was thinking when I was deciding ion to investigate adding a panel.

 

[EdH]

I'm not sure either.
But if you up the panel capacity by 20%, then surely over a year your kWh generated would be up by almost that amount (assuming you rarely get 2kW). Maybe its just me being overcautious but I would imagine that a jump of almost 20% after 8 years might be noticeable. That's what I was thinking when I was deciding ion to investigate adding a panel.

Have a look into this, i have been doing some research. Section 6 is of interest, as I was planning to replace the whole system with 8 x 400w panels (have 5 panels under FIT tarif, and 3 panels non-FIT tarif) which will give me a 3.6kw overall capacity.

Maybe I am mis-reading this, but section 6 doesn't say that you cant replace the system.

Feed-in Tariffs: Guidance for FIT Generators

This guidance is relevant for both MCS-FIT and ROO-FIT accredited installations. Version 18 has been redesigned to improve readability and accessibility, with a new title that better reflects its focus.

www.ofgem.gov.uk

 

[Skyliner33]

Have a look into this, i have been doing some research. Section 6 is of interest, as I was planning to replace the whole system with 8 x 400w panels (have 5 panels under FIT tarif, and 3 panels non-FIT tarif) which will give me a 3.6kw overall capacity.

Maybe I am mis-reading this, but section 6 doesn't say that you cant replace the system.

Feed-in Tariffs: Guidance for FIT Generators

This guidance is relevant for both MCS-FIT and ROO-FIT accredited installations. Version 18 has been redesigned to improve readability and accessibility, with a new title that better reflects its focus.

www.ofgem.gov.uk

I think in a way it does:

Feed-in Tariffs (FiT)​

The other reason not to swap out existing inverters is if you are on the Feed-in Tariff scheme, you are not allowed to uprate your inverter. The safest plan is to leave the existing inverter as is, and add any new power through a separate inverter which will have its own separate generation meter and will not invalidate your FiT payments.

If you add more PV panels, you will not be eligible for any export payments under the Smart Export Guarantee (SEG) if you are getting the FiT deemed export payments. The FiT is composed of two parts:

1. A payment of up to around 50p / kWh that is paid based on quarterly generation meter readings (the generation side).
2. A deemed 50% payment of up to around 5p / kWh (the export payment).

Adding More Solar Panels to Your System: What Changes?

Can you add more solar panels to your PV system? Yes, but here's what you need to know about grid permission, tariffs, inverters and more.

blog.spiritenergy.co.uk

 

[EdH]

I think in a way it does:

Feed-in Tariffs (FiT)​

The other reason not to swap out existing inverters is if you are on the Feed-in Tariff scheme, you are not allowed to uprate your inverter. The safest plan is to leave the existing inverter as is, and add any new power through a separate inverter which will have its own separate generation meter and will not invalidate your FiT payments.

If you add more PV panels, you will not be eligible for any export payments under the Smart Export Guarantee (SEG) if you are getting the FiT deemed export payments. The FiT is composed of two parts:

1. A payment of up to around 50p / kWh that is paid based on quarterly generation meter readings (the generation side).
2. A deemed 50% payment of up to around 5p / kWh (the export payment).

Adding More Solar Panels to Your System: What Changes?

Can you add more solar panels to your PV system? Yes, but here's what you need to know about grid permission, tariffs, inverters and more.

blog.spiritenergy.co.uk

Sorry I forgot to mention it, that I would need two seperate inverters, keep the existing one 2kw (works for now) and install another one for the rest of the system. So the existing one will be connected to FIT payments as it is now and second one just fpr private use. But the question is can I "swap" the existing panels for the new panels with the exact same total capacity of 2000w? Reading official OFGEM guidance it doesn't say that you can not?

 

[Skyliner33]

Sorry I forgot to mention it, that I would need two seperate inverters, keep the existing one 2kw (works for now) and install another one for the rest of the system. So the existing one will be connected to FIT payments as it is now and second one just fpr private use. But the question is can I "swap" the existing panels for the new panels with the exact same total capacity of 2000w? Reading official OFGEM guidance it doesn't say that you can not?

Why would you want to just swap the panels for same capacity?

 

[EdH]

Why would you want to just swap the panels for same capacity?

the existing capacity (2kw) is derived from 8 panels of 250w, which on our semi-det house cover the whole of the roof. 8 panels of 400w are almost the same size of the existing, so in that instance I would increase the production. Connect 5 "new" panels to the existing inverter (that way i would be within 2kw FIT "cap"), connect the rest of "new" panels to the new inverter.

 

[Skyliner33]

the existing capacity (2kw) is derived from 8 panels of 250w, which on our semi-det house cover the whole of the roof. 8 panels of 400w are almost the same size of the existing, so in that instance I would increase the production. Connect 5 "new" panels to the existing inverter (that way i would be within 2kw FIT "cap"), connect the rest of "new" panels to the new inverter.

Ah I see. Have you not thought about asking the installer and the FiT company?

 

[EdH]

Ah I see. Have you not thought about asking the installer and the FiT company?

the installer hasn't got a clue (well, he said that "everyone is upscaling their systems at the moment, and providing that they stick with the accredited inverter size it should be fine"), sent EDF email two weeks ago, no reply as they are busy with all transfers from the failed suppliers. Hence I went onto OFGEM website to read upon it.

 

[sparkzer]

I completely missed this thread, otherwise i would have piped up sooner. i don't confess to being an expert, but i did work for an inverter manufacture for a number of years and did work with installers to commission the inverters for both PV and wind applications.

On the face of it t looks like your installer has wired your new 400W panel in series with the existing string of 250W panels. this is not a good idea, a string like this will be limited to the lowest wattage inverter(s) in the string (in effect your inverter is seeing 9 x 250W panels)

Regarding why your new panel wouldn't allow the inverter to power up, i think it may be to do with the minimum voltage required - I'm speculating at to the ratings of your old panels and your new one but I'm guessing your old panels on their own have a string voltage of about 250V. Your new single panel however has only a voltage of about 35V and your inverter has a min voltage of 175 and a max of 700. ideally, when you are using both strings, you want to balance them however the inverter does have a minimum 'start up voltage' (on yours 220V) before it will wake up.

Moving on to what you can do....

You could change your roof panels as you suggest however your inverter can only handle up to 2100W, regarding the concern over exporting more than you are allowed, you could fit an export limiter - it basically monitors power going out to the grid (at your meter) and if that is greater than your set amount it communicates with the inverter and dials it down so it outputs less. This is a great idea as you can run a bigger inverter, more panels etc and in effect generate far more tan you are allowed to feed back - whilst you cant feed it back, you can use it in your home, so lets say your generating 4000w, and your house usage is 3kw (assume cookers on for example) it will export 1kw back to the grid. when you turn off your cooker, your usage house usage drops to 1000w, the export limiter will dial back your inverter to 3000w, 2000w will go back to the grid and the remaining 1000w will be powering your house.

Adding a battery storage system will again allow you to get more from your system, for example in that same example as above, an inverter outputting 4000w, a house using 1000w battery charging gets priority over export, so potentially 3000w going into the batteries when can then get used overnight.

Hope this is of interest,

 

[Skyliner33]

I completely missed this thread, otherwise i would have piped up sooner. i don't confess to being an expert, but i did work for an inverter manufacture for a number of years and did work with installers to commission the inverters for both PV and wind applications.

On the face of it t looks like your installer has wired your new 400W panel in series with the existing string of 250W panels. this is not a good idea, a string like this will be limited to the lowest wattage inverter(s) in the string (in effect your inverter is seeing 9 x 250W panels)

Regarding why your new panel wouldn't allow the inverter to power up, i think it may be to do with the minimum voltage required - I'm speculating at to the ratings of your old panels and your new one but I'm guessing your old panels on their own have a string voltage of about 250V. Your new single panel however has only a voltage of about 35V and your inverter has a min voltage of 175 and a max of 700. ideally when your using both strings, you want to balance them however the inverter does have a minimum 'start up voltage' (on yours 220V) before it will wake up.

Moving on to what you can do....

You could change your roof panels as you suggest however your inverter can only handle up to 2100W, regarding the concern over exporting me than you are allowed, you could fit an export limiter - it basically monitors power going out to the grid (at your meter) and if that is greater than your set amount it communicates with the inverter and dials it don so it outputs less. This is a great idea as you can run a bigger inverter, more panels etc and in effect generate far more tan your allowed to feed back - whilst you cant feed it back, you can use it in your home, so lets say your generating 4000w, and your house usage is 3kw (assume cookers on for example) it will export 1kw back to the grid. when you turn off your cooker, your usage house usage drops to 1000w, the export limiter will dial back your inverter to 3000w, 2000w will go back to the grid and the remaining 1000w will be powering your house.

Adding a battery storage system will again allow you to get more from your system, for example in that same example as above, inverter outputting 4000w, house using 1000w battery charging gets priority over export, so potentially 3000w going in to the battery's when can then get used overnight.

Hope this is of interest,

Yes, its of interest.

However I believe that, although its called a Feed In Tariff, and there is a meter that measures the number of units generated that no actual electricity is fed back into the national grid. I am certain that this is the case with my system, and I also have a SUNNY BOY inverter. Although it looks different to the one in the OP post.
I will try to find all the paperwork for my system tomorrow after I get home from work to add some more information.
I also would be interested in generating more electricity, especially a battery storage system as, like most people my energy usage is higher in the evenings when its dark.