I am a new PV householder - advice please. Unbalanced strings and wrong inverter

[sedgy34]

Maybe you could say to them you are not happy with the equipment being installed
you want an power one inverter as you can alter the start up voltage on the mppt

 

[SolarCity]

Personally, I don't think installing the panels in this way is the right thing to do.

However, that is just an opinion. Because I don't install panels in this way, I'm not sure exactly what the real world effect would be. What I do know is that slight changes of pitch on my irradiance meter shows up quite different readings.

 

[juniperz]

Maybe you could say to them you are not happy with the equipment being installed
you want an power one inverter as you can alter the start up voltage on the mppt

Well they are supposed to be coming up with a quote for Solar Edge with 16 Optimisers by tomorrow. I will have to see what the difference is.

 

[pww]

Well they are supposed to be coming up with a quote for Solar Edge with 16 Optimisers by tomorrow. I will have to see what the difference is.

Accepting that Solaredge is probably the best solution, but if your installers did not offer it (or knew anything about it?) originally - do you want to be their first 'guinea pig' solaredge installation in these particular circumstances?

 

[juniperz]

Accepting that Solaredge is probably the best solution, but if your installers did not offer it (or knew anything about it?) originally - do you want to be their first 'guinea pig' solaredge installation in these particular circumstances?

A good point of course, but I am running out of time and options. But how hard can it be plugging 16 optimisers into the back of 16 panels and plugging them in one string into an inverter? OK, I was joking - that's why you are the experts and I am just the unfortunate punter! Is there any technical configuration to do in the inverter, or does it set itself up? I must say that having the Solar Edge transmitting data to the web is sounds interesting...

By the way, this was the Growatt Tech Support answer to my question "Our 2 roofs face in the same direction but they do NOT have the same angle - the 12 panels would be at 30% to the horizontal, and the 4 panels would be at 35% to the horizontal. Can we still use the 3600MTL wired 8+8?"

"5% should not be that much that affect the overall performance. In some instances 4 panels may be able to produce more that the 4 others, but limit their power production to the low ones. I am assuming this will be a 8+8 config using a 3600MTL".​

So if the extra for Solar Edge is too much, we just settle for the Growatt with 2 MPPTs wired 8 + 8, since that is the contract we have signed up to.
I just need to decide how much is too much... Answers on a postcard.

 

[wstevew]

A good point of course, but I am running out of time and options. But how hard can it be plugging 16 optimisers into the back of 16 panels and plugging them in one string into an inverter? OK, I was joking - that's why you are the experts and I am just the unfortunate punter! Is there any technical configuration to do in the inverter, or does it set itself up? I must say that having the Solar Edge transmitting data to the web is sounds interesting...

By the way, this was the Growatt Tech Support answer to my question "Our 2 roofs face in the same direction but they do NOT have the same angle - the 12 panels would be at 30% to the horizontal, and the 4 panels would be at 35% to the horizontal. Can we still use the 3600MTL wired 8+8?"

"5% should not be that much that affect the overall performance. In some instances 4 panels may be able to produce more that the 4 others, but limit their power production to the low ones. I am assuming this will be a 8+8 config using a 3600MTL".​

So if the extra for Solar Edge is too much, we just settle for the Growatt with 2 MPPTs wired 8 + 8, since that is the contract we have signed up to.
I just need to decide how much is too much... Answers on a postcard.

Perhaps you should look at the predicted generation of your options and look at the returns based on cost and monitoring facilities you require.

1. Growatt as above
2. 12 panel system with a single tracker inverter.
3. Solar edge.

 

[Gavin A]

Maybe you could say to them you are not happy with the equipment being installed
you want an power one inverter as you can alter the start up voltage on the mppt

I've just checked, and both inverters have the same MPPT lower voltage of 120V

120V simply isn't low enough for 4 x 30.5V panels, because as soon as the panels warm up even a little the voltage will go outside the MPPT voltage range and shut down that MPPT.

Combining the 4 panels on that roof with 1-4 from the other roof is the only viable option with this inverter (or power one / sma equivalents).

tbh there's not going to be a lot of difference between a 30 and 35 degree roof, and the dual MPPT will minimise this impact. It's not ideal, but then any losses from doing this are likely to be lower than the reduction in efficiency from swapping to a seperate smaller inverter for that roof, so I understand this companies reasoning.

They probably should have explained this better themselves though.

 

[juniperz]

I've just checked, and both inverters have the same MPPT lower voltage of 120V

120V simply isn't low enough for 4 x 30.5V panels, because as soon as the panels warm up even a little the voltage will go outside the MPPT voltage range and shut down that MPPT.

Combining the 4 panels on that roof with 1-4 from the other roof is the only viable option with this inverter (or power one / sma equivalents).

tbh there's not going to be a lot of difference between a 30 and 35 degree roof, and the dual MPPT will minimise this impact. It's not ideal, but then any losses from doing this are likely to be lower than the reduction in efficiency from swapping to a seperate smaller inverter for that roof, so I understand this companies reasoning.

They probably should have explained this better themselves though.

Thanks, though when you say this inverter, which did you mean??
Is this why 12 + 4 Physical but 8 + 8 Wired is best for the dual MPPT Growatt?

 

[wstevew]

You could probably get away with a 6 and a 10 string on a dual tracker to minimise losses, but still close to the lower end of the tracker voltage range.

 

[Gavin A]

growatt 3600MTL

I'd think 10 + 6 might be better in this situation to minimise the number of panels affected, but I don't know this inverter so there may be some reason why not.

 

[juniperz]

You could probably get away with a 6 and a 10 string on a dual tracker to minimise losses, but still close to the lower end of the tracker voltage range.

Even if split 12 panels at 30% to the horizontal, and 4 panels at 35% to the horizontal?

 

[wstevew]

4 panels at 35 and 2 panels at 30 wired in series to 1 string. Approximately 180v

Then 10 panels at 30 wired in series.

Each of the above to an isolator and its own tracker.

Losses minimal as you have 10 panels not affected by the pitch difference.

But the tracker on the inverter needs to be right for the string.voltage and current.

 

[wstevew]

Another possible alternative. Maybe someone knows.

Would 72 cell panels like the znshine have enough voltage for a string of 4 panels?

 

[babba]

Another possible alternative. Maybe someone knows.

Would 72 cell panels like the znshine have enough voltage for a string of 4 panels?

Even better get an installer who knows what they are doing. I dont understand how people can take such risks to save a few quid ????

 

[wstevew]

Even better get an installer who knows what they are doing. I dont understand how people can take such risks to save a few quid ????

Oh how hindsight is a wonderful thing.