Solar install not going well

keno-daytrader

Need some advice on our PV installation. Almost a month ago we had an install of 10x 420w panels on West facing house roof, and 6x 420w panels on South facing Garage.

Upon commissioning of the 2 strings, the garage string was fine but the house array was showing an over voltage of 5v and shutting down the inverter.

On this inverter the max rated mmpt voltage is 550v, so the house string was producing 555v.

So the garage string is producing fine but house string is unplugged. Haven't heard from them in 3 weeks, so made contact last week. I thought the solution was to remove a panel, unplug a panel or change the inverter. However the solution from their end is to change this string from series to parallel. I'm fully educated on the difference now between amps and volts of series and parallel 😉. Promised me they would be here last Thursday, but a no show and no call or text.

I've tried to research series Vs parallel but really can't get a clear answer for my situation. No shading anywhere and I'm worried that parallel won't produce like series will.

Any advice?

Jonathan

What inverter do you have?

hurikane

Is it a company from the north that did the install?

graememk

What solar panels do you have, the voc must be very high if your getting 555v from 10 panels... Unless they put 16 on a string?

What inverter do you have

keno-daytrader

The company is not from the north.

The inverter is a 5kW, but I don't want to name and shame the company.

The open circuit voltage on these panels is quite high at 59.4v.

There are 2 mmpt's on the inverter, one has 6 panels on it, the other has 10 panels, but the 10x one is currently unplugged.

Jonathan

What exact model of inverter and panel do you have?

keno-daytrader

https://www.boards.ie/discussion/comment/121714868#Comment_121714868

Rec 420w alpha pure R panels. Inverter is NAC5K-DS

graememk

Wow, yeah the voc is really high. Perfect for small arrays that will get the inverter up and running quickly..

But for large strings not so much. As your limited to 9 panels

bullit_dodger

On the (somewhat) positive side - as we get further into the year and the temperatures improve you'll be less likely to hit the over voltage as the panels "like" the cold. That said, you should defo push ahead and get it fixed by the installer.

It's not great as they do it for a living. They should know the specs and the limitations of the equipment they are installing. That said, people are entitled to make a mistake and as long as they rectify it and you get a working system that performs to spec, that's ok. It's not wrong to do stuff in parallel, but it's a bit unusual. I'd push them for what options they are suggesting.

Change the inverter, swap the panels to different make/model, etc

Buffman

OP, having had a quick look at the specs it looks like someone didn't bother spending a few minutes doing the basic calculations or may have confused the inverters max DC input voltage of 600V with the max MPPT voltage of 550V or panel Vmpp and Voc.

But whatever the case, having a design string Voc of 594V was never going to work on that inverter with a 550V MPPT max, luckily the inverter protected itself and didn't go bang.

Not to be doing their work for them but they will have to plan any parallel connections very carefully to avoid going overcurrent as with the panel Isc of 8.73A and max inverter MPPT Input of 12.5A their are potential issues with any parallel connections, as even only 2 panels in parallel will be at Isc 17.46A.

Also, just to be a bit pedantic, I see the inverter max recommended PV power is 6500W but you've got 16x420W for 6720W total on it. I know the strings are on different orientations so in real world use it won't matter as you'll never get 6720W, but I'd get it confirmed in writing from them that it won't have any warranty issues.

IMO the easiest solution all round is to reduce the 10 string to 9 sting for a string Voc of 535V and a new total of 6300W.

keno-daytrader

https://www.boards.ie/discussion/comment/121716509#Comment_121716509

Thanks for the input. I agree on the minus one panel. My preference is to just unplug 1 panel and leave it there. No cutting of rails back and removing rail brackets and having to replace tiles, which I dont have and probably wont match.

I must say it has been a disappointing experience so far.

bullit_dodger

https://www.boards.ie/discussion/comment/121717122#Comment_121717122

Yeah, I'd be feeling the same. However, keep with it. Many of us here (myself included) had teething issues at the start when the installation was new and here we are years later with little/zero complaints. You'll be in the same boat as ourselves shortly enough.

keno-daytrader

This board has been a huge help and education, we will get there.

I probably wouldn't have taken the leap if not for the posters and all the information that has been posted here.👍😎

slave1

See if they can throw a micro inverter onto the extra panel for all the grief, may as well make it work for you

keno-daytrader

https://www.boards.ie/discussion/comment/121718614#Comment_121718614

That's a great idea and one I actually hadn't thought of, but in my case it's not plausible. My inverter is in the Garage, and AC from the inverter is routed back to the house via sub board in garage.

All the DC wiring from the house panels are routed down the gable of the house into an esb duct which carries it to the garage/inverter.

We designed it this way because of a very high level of airtightness of my house, I simply didn't want them breaching the house with cables. 😉

I'm still battling with my original delema regarding parallel vs series. If the inverter can handle the increase in amps of a parallel string. The dc cable run is about 15m to the inverter with 6mmsq cable. Will 10 panels in parallel out perform 9 panels in series???

Buffman

https://www.boards.ie/discussion/comment/121717122#Comment_121717122

Ye, no worries, shouldn't be any need for cutting rails or anything as they can stay in place no matter what.

I can understand wanting to leave the panel in place for aesthetic reasons but if it was my house it would annoy me to be just left idle as it just seems like such a waste not to have it producing power and you should be entitled to a refund on it if it can't work.

https://www.boards.ie/discussion/comment/121718721#Comment_121718721

As I hinted above I think there would be issues with running anything in parallel with the existing equipment. Using your panel specs as an example, 10 in parallel will have a design Voc 59.4V and Isc 88.9A, so pretty crazy/useless figures when your inverter specs has MPPT Min voltage of 100V and Max DC Input Current of 12.5A. As above, even only running 2 panels/strings in parallel would have an Isc of over 17A, still above the 12.5A MPPT max.

All I can say is keep onto them as the longer it's unresolved, the more money it's costing you having 9 or 10 panels out of action. Hope you get sorted.

graememk

I'd be looking to see if they have a different type of panels with a lower voc.

As for paralleling panels if you had a a string of 5 in parallel, the max the inverter could pull from that paralleled string is 12 amps

And at a nominal power, at 50v per panel, string voltage of 250v your max power out would only be 3000w

keno-daytrader

Thanks lads, I'm going to get on to the owner Tues morning, it will be over month since install, it's just not good enough, and the parallel idea sounds bizzare to me now. I'll update this thread hopefully soon.

10-10-20

How did you get on with this?

I was thinking that paralleling two strings into one MPPT would not be a bad solution overall provided that all 14 panels match precisely and both the wiring and MC4 connectors are capable of taking the increased current. But the challenge comes about if one panel fails and you can't source a matching voltage and current, then you'll have unbalanced strings and that's not really a runner. I think that's the main justification for not having parallel strings.

keno-daytrader

The company finally returned to rectify the problem. What they have done is use a "hybrid" or series/parallel method of wiring the string. (I've read about the method and it is a proven method)They have run 5 panels in series, then the other 5 panels in series, then run these 2 strings in parallel to form 1 string back to the mmpt.

So from the original 10 panels the voltage has halved and amps have doubled.

The 16 panels seem to be producing very well. We have had no bright sun yet so the test for me will be when the inverter starts clipping hopefully it won't shut itself down because of too many amps.

I received the final invoice and they have indeed provided us with a discount. I know things go wrong sometimes and we obviously fell thru the cracks, but they rectified their mistakes in the end and it worked out for now. I'm happy with that, as they are a long established company with stellar reviews.

I'm hoping I won't have to chase them as I'm sick of chasing 😭😭, last thing now is for them to upload all Doc's and pictures to the SEAI for our grant, nothing done as of yet.

10-10-20

https://www.boards.ie/discussion/comment/121786963#Comment_121786963

Right, makes sense. You could also do a optimistic purchase of a spare panel and stick it in the attic/shed, just as insurance.