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

[JulianC]

Each panel is wired to an optimizer, then the optimizers are connected in series strings as per usual

 

[jason121]

Each panel is wired to an optimizer, then the optimizers are connected in series strings as per usual

reading these comments on the solar edge, i am thinking of using them on job with 2 roofs slightly different angles.
I know segen stock thems anywhere else ?
Also is there any other wiring to them besides the DC side ?
and can you excess information from any location thru the web.

 

[JulianC]

Got mine from Segen. No additional or unusual wiring required. However, the main inverter is transformerless so array frame bonding may be required depending on which version of the DTI guide you're working to! Didn't connect up the communications side of things on our job 'cos the customer didn't have an internet connection but as I understand it, you can access the monitoring through the interweb from anywhere (someone with more experience please correct me if I'm wrong)

 

[daytona600]

the best car made in china , would not compare to the worst car made in europe
get them to fit a real inverter suitable for the application ideally a poweredge due to string layout or dual MPPT sma/powerone

 

[juniperz]

I did manage to stand them down over the weekend, so nobody turned up yesterday. Apparently "senior management" are investigating. I had suggested something like a Solar Edge Inverter 3680W 16A AC Clamped - SE-3680 and 16 lots of Solar Edge 250W Power Optimiser + the 16 Suntech 245w panels that are in my garage. Though why I, the punter, has to suggest this {insert deity} only knows.

 

[daytona600]

you signed a contract with them they should supply exactly as ordered or equivalent or better in lieu
example girlfriend ordered a new kitchen , after fitting she noticed work tops where different you know what women are like with kitchens
she phoned to complain next day the MD of the company turned up with one of those huge amercian freezers
free as way of letting her down

 

[Worcester]

and Daytona600 is as good as his word too, he's not just saying it, he practices it as well.

 

[juniperz]

Busy week... The installer has come back saying they will install the quoted GroWatt inverter, use fire retardant board etc.
I am going to struggle to get out of a signed contract where they have offered to comply with the contract.
Whats the worst that could happen with
Growatt 3600MTL (2 MPPTs)
12 x 245w panels on a 30% roof
4 x 245w panels on a 35% roof
Could be wired 8+8 according to Growatt tech support, though that was before I knew about roof angle, and they haven't answered my recent question.

In another thread, FB said

As Gavin says: in summer it won't matter.
But with low sun in winter (or early/late in the day at other times of year), the difference in angle will make a big difference to panel output, so the bypass diodes will be working overtime.

By my reckoning, a 5-degree difference (35 v 30 degrees) in angle affects as follows:

Mid-day, June sun: 0.5%

Mid-day, March/Sept sun: 5%
(comparable to morning/afternoon summer sun)

Mid-day, December sun: 20%
(comparable to early-morning/late afternoon spring/autumn sun)

Will that amount to much over the year?
Is bypass diodes working overtime a big problem?
Thanks...

 

[sedgy34]

Busy week... The installer has come back saying they will install the quoted GroWatt inverter, use fire retardant board etc.
I am going to struggle to get out of a signed contract where they have offered to comply with the contract.
Whats the worst that could happen with
Growatt 3600MTL (2 MPPTs)
12 x 245w panels on a 30% roof
4 x 245w panels on a 35% roof
Could be wired 8+8 according to Growatt tech support, though that was before I knew about roof angle, and they haven't answered my recent question.

In another thread, FB said


Will that amount to much over the year?
Is bypass diodes working overtime a big problem?
Thanks...

When did you sign the contract as you have 7 days cooling off period

 

[juniperz]

When did you sign the contract as you have 7 days cooling off period

It's nearer a month ago.

 

[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.

 

[babba]

Oh how hindsight is a wonderful thing.

Is that what its called now ?

 

[Earthstore]

I do think Babba has a point, there have been so many threads recently where customers have come here for help because for whatever reason they have chosen an installer that is not competent, I have also noticed that the professionals are becoming less helpful, and I have to say I am included in this.
Maybe customers could choose more wisely, I know it can be difficult as it is quite technical, but I feel the public are buying on price only.
Remember, penny wise and pound foolish.

 

[SolarCity]

There does seem to be a lot of threads like this but I don't think it is fair to say to a customer "you are buying on price alone and you got what you deserved." We all know that paying more doesn't guarantee competence - we can all name firms which are useless yet charge ludicrous prices. As far as a customer is concerned, they see MCS and REAL badges and that should be enough.

My personal opinion is that training isn't good enough and the MCS isn't strict enough with regards to competence.

This is not the customer's fault.

 

[juniperz]

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 ????

I will try not to be offended :cool3: This wasn't about saving a few quid. I thought I had a competent installer, and signed a contract. I then chose to look at the installation half way through, and found a problem. They have offered to rectify their mistake (installing wrong inverter) and use fire retardant material for the board, so I can't void the contract (or whatever the expression is). The good people here on the forum have been extremely helpful while I try to get this sorted out. Without the internet I would have been stuffed.

 

[sedgy34]

When is your installation date

 

[juniperz]

When is your installation date

Well it was last Friday, but I stopped them half way through when I discovered the problem. I am waiting for them to come back with a proposal inorporating Solar Edge + optimisers today, then when I have made a decision (the alternative being to revert to the quoted Growatt inverter wired 8+8 or 6+10) I will ask for next Friday since I will be home then. Friday 13th. Gulp.

 

[sedgy34]

What modules have they given you, sorry I havnt been following what the issues were.

 

[juniperz]

What modules have they given you, sorry I havnt been following what the issues were.

It's in the first post:
"I was quoted for a Growatt-3600MTL with 16 Suntech STP 245S panels. We have a large roof, but it is hipped, so the installer proposed 12 panels on the house roof and 4 on a garage roof with same orientation and similar roof elevation. I did a bit of research on the inverter, even had a reply from Growatt saying that the panels should be connected 8 + 8.

So, today they came to install. The electrician has done all the internal wiring but they need to come back Monday to finish the panels and complete the electrical side.
2 Problems:
1) I just looked at the inverter in the attic and found it is not Growatt, but Samil SR4K4TLA1 (also badged Solar River and also known as Samil 4400w)......"

Might get back here at lunchtime

 

[sedgy34]

sounds like growatt prefer balanced strings for there inverters were possible, ive just seen some pics on here and i would make them re doo the work as they dont know how to install neatly!!! also we fit suntech 250s so why cant they 12 modules would get you 3kw but the 4 on there string not sure if that will work, also the board the inverter fixed too is not fire retardent is it, these clowns dont know how dangerous DC actually is.

you should speak to the manufacturer of the inverter to see if 1 string of 4= 980w will work


also dont pay them until everything is working and most of all LABELLED

 

[wstevew]

Is there a regulation thar says an inverter must be mounted on a fire retardent board.

I read a document from SMA that claimed that in theory the constant heat from an inverter will over time dry out wood and could cause a fire. But they concluded the heat from their inverters still would not be enough but were still concerned about wood dust which can ignite at lower temperature.

 

[Gavin A]

I believe it's a manufacturers instructions thing

 

[wstevew]

Thanks

 

[jerriais]

It is good practice to install on a fire proof board, especially when installing in a loft. We use it for every job except if we're on a non-combustible surface. Only trouble is it's not so strong so will usually need to be backed up with ply on the reverse side.

 

[juniperz]

I finally got a revised price from the installer - it was going to cost an extra 10% of the total cost to go for Solar Edge + 16 optimiers, so I have decided to stick with them removing the incorrect inverter and installing the one they quoted for - I don't think I would have got the return on that 10%. They are also going to mount on fire retardant board and do proper labelling.
I have given them this question (paraphrasing some of the advice from here - I hope I phrased it correctly):

"We will have 4 panels on the 35% garage roof and 12 panels on the 30% house roof. I know that we should not have these wired as 4+12 into the 2 MPPTs as the 4 would not generate enough voltage. We have talked about wiring the panels as 8 + 8, but with the roof pitch difference, I believe that it would be better to wire as 6 +10 as this would reduce the losses because 10 panels would not be affected by the pitch difference."​

 

[sedgy34]

If I were you I would check with inverter manufacturer technical helpline just for peice of mind as you seem to be doing the installers job for them

 

[juniperz]

Yes, I am doing that by email to Texas (Growatt is the manufacturer). They had suggested 8+8 before I realised that there was a roof pitch difference (picture me on a roof or two, with a protractor and a spirit level - much easier with scaffolding in situ!). The comment: "... 6 +10 as this would reduce the losses because 10 panels would not be affected by the pitch difference." actually came from Growatt, but I thought I would give the installer the chance to respond.

I do sometimes feel I am doing their job for them, and I thank you all here again, for providing me with (just) sufficient knowledge to do so.

 

[juniperz]

A new development - they have just told me that they cannot get stock of the originally quote Growat 3600MTL, and have offered "Power One Aurora PVI 3.6(16A limited), which (according to our design software) should be suitable to be wired either 4+12, 6+10 or 8+8, as this has a lower tracking voltage".

I remember someone on here suggesting Power One, so I am assuming I should say yes to this.
They send me a datasheet as PDF - I have found a link to it here.
COMMENTS APPRECIATED.

 

[jason121]

go for it beats the growatt

 

[Gary K]

Snatch his hand off for that offer.- Could be one of the most efficient inverters available

 

[jerriais]

How much is the pitch difference? I'm actually attending a Solar Edge technical conference today and would certainly say they are what you need in this case. Also I really doubt they would add 10% to the overall system cost.

Sent from my HTC Desire S using Tapatalk 2

 

[pww]

Actually this is about right. The solaredge inverter is similar in price to, say, an Aurora one. In this configuration you need 16 power optimisers which would make up most of the 10%, then you need to allow for the addtional back room work (solaredge registration etc). Still think the extra would be worth paying, but OP seems not to be convinced.

 

[juniperz]

How much is the pitch difference? I'm actually attending a Solar Edge technical conference today and would certainly say they are what you need in this case. Also I really doubt they would add 10% to the overall system cost.

Sent from my HTC Desire S using Tapatalk 2

Sorry, I have only just seen this.
"We will have 4 panels on the 35% garage roof and 12 panels on the 30%

Actually this is about right. The solaredge inverter is similar in price to, say, an Aurora one. In this configuration you need 16 power optimisers which would make up most of the 10%, then you need to allow for the addtional back room work (solaredge registration etc). Still think the extra would be worth paying, but OP seems not to be convinced.

Yes, this was their rationale - similar inverter prices plus the 16 optimisers.

 

[sedgy34]

they will have to change the startup voltage on the inverter for the string of 4 but still a result for you.

 

[babba]

yes looks like the four panels might as well not be there as they not going to start up the MPPT! as stated above .

Tricky one they should of either used a Mastervolt 600 for the four panels then a single tracker inverter for the other 12.

or gone for solar edge the dip sticks !!!

Makes me laugh really does

But we like a laugh.

 

[juniperz]

But we like a laugh.

Glad I caused some amusement! (I don't mean that is an offended way).