Two strings, inverter question.

[bris]

I just picked up a 3.9 kw kit, 20x 195w panels. When The seller saw my roof layout he informed me the inverter that was with the kit would not be suitable as the instalation was spread over two roofs at right angle to each other. The lay out will be 7 panels on the smaller roof and 13 on the other so he suggested i should get two inverters as it would need two strings and the inverter wouldn't handle the MPPT tracking well enough because the one string is much bigger than the other.
I am now back at the drawing board as far as inverters are concerened. Firstly is he right, is one tracker not up to the job.
Secondly I was thinking of the Sunny boy SB1700 for the smaller string 1365 watt and the SB2500 for the larger string 2535 watt would the SB2500 be enough for the bigger string, would the extra 35watt make a difference.
I don't mind having to get two inverters if it does a better job so it's not an issue if it works out better.
Finally, he gave me two AC isolators for the kit but only one DC isolator as he said the two inverters could go into the on DC as it was designed for two, should I use another one and keep them seperate.
Thanks for looking, ant answers are greatly appreciated.

 

[Graeme Harrold]

An inverter with two MPPT's is usually split 50/50 of the overall power. Yes you have quite an imbalance and the two inverter route is one choice you have.

You will need 2 DC isolators as each inverter will require one, even with two strings on 1 inverter, you would need 2 (unless the strings were combined with a splitter).

Get your installer to salvage the situation, as they will be able to match your kit to the roof and inverter.

 

[solarfred]

You may struggle to get one string for 13 x 190wp panels but I don't know what panels you are using. If you go for the two SB's then a 1200 is big enough for 7 x 190wp panels.
Always use a DC isolator for each string so you can isolate the strings independently to test for problems. You can't do this if it is all paralleled up into one inverter. Maybe worth downloading free SMA designer software to get you started. You can input two unequal strings into a dual input (twin MPPT) Inverter and it works very well but the overall parameters must not exceed the inverter input limits. I would go for individual inverters or change the panels if they will fit and get lower voltages.

 

[daytona600]

what make of 19owp panels are you using , depending on type you could use SB4000TL-20 sma , PIKO 3.6 kostal , PVI-3.6-OUTD powerone all have 2XMMPT trackers

 

[bris]

I am using JR solar 195w panels ( JRM195M ) they are accredited panels. I was hoping to avoid a TL inverter because of the earthing requirment needed. I tried using the Sunny design software but not sure how to use it, and the panels are not on it, although there are other 195w panels on it.

My preffered method is to use the two inverters SB 1700 and SB2500 but solarfred doesnt think the SB2500 can do the 13 panels on one string, how can I check this.

I have had conflicting info from three different installers, this is why I am here, consulting the experts.

I want to get it right before I buy the inverter(s) so if everything is in place I can just tell the installer this is how I want it.

It's not that I don't trust the installers but most are new to this and I don't want them making their learning mistakes on my system, so if everything is in place they can go ahead and install it.

 

[solarfred]

The VOC of those panels = 44.5 x 13 = 578 v. If that total is higher than the input limit of the inverter you will have to find another way. I think you may find it is too high.

 

[daytona600]

sunny design lists virtually all pv modules , and jr solar can,t find on google , must be i assume branded cheap chinese modules
send them back and get decent modules with inverter to suit with twin mppt trackers or 2 inverters

 

[bris]

The panels are listed as Wenzhou Jingri, JRM on the MCS site, the cert number is BABT 8550-01. They are Jingri solar for search purposes. I have saw a couple of installs using these panels and the results are pretty good, so I have no reason to doubt the panels. The panel states the VOC as 43.8 X 13 = 569.4.

Still left with what inverter to use though if the sb2500 can't handle the 13 panels, what will.

Just looking through the specs of similar sized panels and the VOC is pretty much the same on them all, so the problem I have would still be there whatever panels I had.

 

[BruceB]

DELETED AS ANSWERED BY PREVIOUS POST.

Be aware that HF transformer inverters and transformerless inverters are more efficient that the bog standard sunny boys.
Regards
Bruce

 

[solarfred]

sunny design lists virtually all pv modules , and jr solar can,t find on google , must be i assume branded cheap chinese modules
send them back and get decent modules with inverter to suit with twin mppt trackers or 2 inverters

Try Jingri Solar - too late !!

Can you get larger cell panels on like 245's where the voc is lower and amps higher. You need around 37 voc

 

[bris]

Would it make a difference if I was to make it 6 panels on one roof and 14 on the other. Probably not but it is the only other layout I can have. There must be an inverter out there that can handle the two unequal strings, even if it is a transformerless one.

 

[solarfred]

OK try two strings paralleled up into 7 + 7 into one input of an Aurora 3.6OUTD and one single string of 6 into the other input.That should solve your problem. The voltage will be lower than ideal in string 1 but the Aurora is a decent bit of kit. It will be available in the next few days clamped at 16 amps so you will be OK with your DNO. Not only that you can get a bluetooth remote display also. Others here will have better designer tools and may advise further.

 

[northernsun]

quite possibly, if you have 14 modules then you can split these into 2 string of 7 and have them on the one inverter, then have the 6 on the other inverter. As long as the 2 strings are equal you can have them on the single tracker inverter- sb2500 or sb2000hf- sorry havnt checked which, i've not got acess to my pc at the moment. You may be able to use the 2000hf for the single 13 string but again I cant check at the moment.
The 4000tl is the way to go for a dual tracker from sma, but obv needs bonding.
sorry for being a bit vague!

 

[Bright_Light]

Have a look at the SMA Sunny Boy 4000TL. Twin MPPT, we have used this inverter on similer sized systems with a split roof design. Read up on installation of TL inverters first if you have not installed one - earting arrangements canbe very different to a standard inverter (earth stake/earthing the array frame etc)