West/South uneven split system

[daruvalla]

I've recently had a 3.6 Kw system commissioned involving a 7 panel 230W string on a west facing roof and an adjacent 9 panel string with the same panel type on a south facing roof.

The system has been installed with a Deihl 3800s inverter and the two strings have been connected from what I understand together in series before going into a single input on the inverter (single MPPT).

The system seems to be generating power (about 1-2 Kw per day at this time of year) but I am concerned that the efficiency of the system is reduced due to way the two unbalanced strings are joined into one (ie. the west facing 7 panel string compromising the output of the south facing 9 panel string when there are different levels of light on each orientation earlier in the day and vice versa later in the day).

I was under the impression that joining two unbalanced strings into a single MPPT input is not good practice and inefficient?

I haven't tackled the issue with my installer yet as I wanted to keep an eye on the output for a while and get more information before I do so. Am I right in assuming that this system should have been installed with an inverter with 2 seperate MPPTs for maximum efficiency, or failing this 2 seperate smaller inverters?

 

[Earthstore]

Yes you are correct.
They should be split using either dual MPPT or two small inverters, because the "shaded" panels will pull the other panels down to their performance.
Speak to your installers when you can, they should help you out.

 

[SolarCity]

You need an inverter with dual MPP tracking for two reasons: You have two uneven strings (7 panels and 9 panels) and each string is at a different orientation.

It really needs sorting.

 

[Eco Chap]

As above. Bad design leading to bad performance.

Give your installer a ring. We've used SMA 4000TL's for 2 seperate roofs in the past, failing that 2 seperate inverters or micro inverters.

Joe.

 

[moggy1968]

It is the current that is most affected by the different orientations. the way to mitigate this is to connect the two strings in PARALLEL. However, you can only do this if the 2 strings are balanced for volatage, i.e have equal numbers of panels. A number of inverters are available which can utilise 2 trackers which would be more suitable. Kostal Pico 3.6 is one, Aurora power one 3.6 another, Or as above an SMA4000TL (although this would require DNO notification) although they were like rocking horse poo to get hold of which mayexplain why they didn't use them. They are also more expensive than the Diehl which may be a nother reason why they didn't use them!! Personally I would go with the 3.6 on a system like this.

As above, it's a pooly designed system!!

 

[daruvalla]

OK so I have contacted the installers (actually the company's head office as they sub-contract out the work to local installers) to raise my concerns about having an incorrect inverter for the system they have installed, and they have come back saying that they have run my set-up through the PV SOL software program and this indicates that I do have the correct inverter fitted and there is no issue with it! I have again challenged this and asked them to go back and check with a technician who is familiar with split roof unbalanced systems to explain to me why its OK for my system to be set up contrary to all other advice I have been given.

Does anyone who has or have used the PV SOL program know if it can be used to design systems to take into account 2 different roof orientations with uneven numbers of panels? I suspect they may be just using the program to work out the 1 array of 16 panels on the south pitch roof?

 

[SolarCity]

Did you tell them that both strings are running into one input? If you did, and they couldn't see anything wrong with that then they don't know what they're doing.

 

[daruvalla]

Did you tell them that both strings are running into one input? If you did, and they couldn't see anything wrong with that then they don't know what they're doing.

Yes I did mention this to them, but unfortunately it just seems that I'm talking to a customer services operator who's not clued up on these things. I've asked to speak to someone in the company who knows technically about these things and I'm awaiting a call back.

 

[dansk]

to answer about pv sol, yes you can do split arrays and if they had done that pv sol wouldnt have suggested a single mpp inverter. so the operator has made a mistake.

 

[moggy1968]

rubbish in rubbish out!
you cannot use a computer program to replace sound technical knowledge, as this demonstrates.
I suspect they may struggle with your request to speak with someone technically competent as they may not have anyone!!

 

[Markc]

We fitted several Deihl 3800S inverter's but not one on a split array system. They are just not right for that system but like many things it will work. Your output in kWh per year will be significantly down if compared with a correct twin MPPT inverter. PVSOL can be manipulated to show it works however if compared with a better MPPT inverter then annual yield will be higher.

Unfortunately I think it shows lack of knowledge.

 

[moggy1968]

hello Mark C, just spent some of my profits from nov on a rather nice 1981 88"
(sorry guys, very off topic!)

 

[Markc]

hello Mark C, just spent some of my profits from nov on a rather nice 1981 88"
(sorry guys, very off topic!)

Nice one. PM me more details if you want. Runner or Project? My 71 is on the road but the 77 is stripped to chassis. But yes very off topic. Sorry!

 

[daruvalla]

Have finally managed to speak to someone in the company who appears technically competent and they have agreed with apology that the system has been designed incorrectly.

They have offered a solution after running PVSOL again with the correct south/west split system, to provide a SolarEdge inverter with seperate power optimisers on each panel (as the scaffolding is still in place). They seem to prefer to fit this over the alternative solution of fitting two smaller inverters. They didn't mention the possibility of fitting a twin MPPT inverter when I asked which is strange, so I guess it must be a cost decision.

Not sure if anyone has any knowledge on how efficient a SolarEdge system with power optimisers would be for a south/west split system compared to two seperate inverters?

 

[dansk]

Have finally managed to speak to someone in the company who appears technically competent and they have agreed with apology that the system has been designed incorrectly.

They have offered a solution after running PVSOL again with the correct south/west split system, to provide a SolarEdge inverter with seperate power optimisers on each panel (as the scaffolding is still in place). They seem to prefer to fit this over the alternative solution of fitting two smaller inverters. They didn't mention the possibility of fitting a twin MPPT inverter when I asked which is strange, so I guess it must be a cost decision.

Not sure if anyone has any knowledge on how efficient a SolarEdge system with power optimisers would be for a south/west split system compared to two seperate inverters?

SolarEdge is the muts nuts, i really like it and the monitering portal is excellent. Thats a really good offer.