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Author Topic: Help with my Sofar inverter  (Read 923 times)
charlesd
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« on: March 25, 2020, 04:17:55 PM »

Hi
I'm hoping someone might be able to provide a bit of advice.
My inverter a sofar 6ktlm  has 2 dc inputs these both come from the dc isolator switch as 2 pairs of cables with the connectors to plug in to the inverter.
The dc supply from the panels (ground mounted in the field) comes in one cable there are 5.5kwh of panels and I assume the one cable going into the isolator then gets connected to the 2 pairs of cables coming out and that they should "share" the load into the 2 inputs on the inverter.
However this does not appear to be the case I have attached a photo of the set up so hopefully it will make sense and a photo of what the software reports as input voltage for the PV1 and PV2 inputs. It seems that all the input goes into the second input with nothing going to the first.
I think this is meaning that i'm limiting the production to around 3.5kwh because the max for 1 input 11amp i think is being met.
I have experimented by removing the second input connectors and the inverter wont turn on so assume that there is nothing coming in on the PV1 input but cant see how that can be.
The whole lot was installed mid may last year and I believe i was getting higher output through last summer but issues with the wifi connection and a new router meant i wasn't really monitoring very well now i have access to the monitoring and the sun has come out I think I've spotted a issue.
Thanks
Charles



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Fintray
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« Reply #1 on: March 25, 2020, 04:32:05 PM »

I have a single cable from my PV system, but it has 4 cores as the panels are split into 2 arrays; so would expect yours to be similar as I can't see why the installation company would have put it into both inputs if it wasn't 2 arrays.
Are you sure there is not a cable break somewhere at the panels?
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charlesd
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« Reply #2 on: March 25, 2020, 05:09:17 PM »

Hi
Its definitely just one supply coming up the cable I laid it myself the panels are in 2 strings of nine then connected together and to the cable which is then terminates at the isolator box I'm pretty sure everything is OK at the panels end because I'm getting way more than if only one string of panels was working and based on the (hopefully correct ) understanding that as each string is in series a break would mean I'd lose the input from all 9 panels in that string.
My working theory at the moment is either the PV1 input is broken on the inverter or that there is an issue with the connections for that inputs cables.
I think I can test theory one by turning everything off then disconnecting both inputs and putting those connected to PV2 into PV1 and seeing what happens. If nothing then the inverter is the issue and if it work then the cables are the problem does this make sense ?
Charles
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Fintray
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« Reply #3 on: March 25, 2020, 05:30:04 PM »

If I'm looking at the correct information for your inverter it shows 2 MPP trackers each with a maximum DC power of 4000W so I would have expected the PV arrays to each have a dedicated MPPT input rather than commoning them together then sharing them across the 2 MPPT inputs.

Downloaded the installation manual for your inverter and it shows 2 PV arrays each supplying one of the MPPTs, it also states that the operating current during normal operation must not exceed the limits specified in the technical specification. It could be that one of the MPPT inputs has failed.
« Last Edit: March 25, 2020, 05:48:23 PM by Fintray » Logged

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daveluck_uk
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« Reply #4 on: March 25, 2020, 05:56:41 PM »

 Deleted because I should have read fintrays post more closely.

+1 for invidual mppts










« Last Edit: March 25, 2020, 06:00:54 PM by daveluck_uk » Logged
charlesd
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« Reply #5 on: March 25, 2020, 07:56:11 PM »

Thanks for the suggestions.
I've decided to move the inputs from pv2 to pv1 while it's dark.
If I get some voltage showing on that input in the morning when the sun comes up then I guess it's not the inverter input. If not then I guess that's where the problem lies.
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charlesd
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« Reply #6 on: March 26, 2020, 10:17:31 AM »

So swapping the inputs just and all is still working but with voltage reporting on the PV1 input so from this I deduce that both inputs on the inverter will work if there is some voltage to them. so it would appear that there is a fault with the cables I briefly removed the cover of the DC isolator last night once it was dark and checked there are definitely only two incoming wires from the armoured cable coming from the panels and this goes into one side of the isolator switch with 2 positive and 2 negative connections coming from the other side of the switch to the connectors which are then plugged into the inverter. The cabling in the switch all looked to be tight and nothing had come loose that I could see.
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Fintray
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« Reply #7 on: March 26, 2020, 10:22:51 AM »

If you have a multimeter you could just test each cable to see which has the fault or switch off the isolator and use opposing + & - in the MPPT inputs till you find which cable has the fault.
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nowty
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« Reply #8 on: March 26, 2020, 11:47:23 AM »

Charlesd

You have paralleled up the strings at the panel end, ran it down two wires to the isolator. So far, so good, but you cannot then split them up again and connect them up to the two individual MPPT inputs. You should only have two wires coming from the isolator which goes into one of the MPPT inputs. Some inverters (like my SMA ones) allow you to parallel up the MPPTs but you still only connect to a single MPPT. Your inverter does not do this so is working as designed.

You can an either.

1) Change the inverter for one which accepts more current but you still may be curtailed a bit, example SMA ones limit at 15A.

2) Split the two strings up and run a separate cable from the panels into another isolator so you can have each string into its own MPPT (BEST OPTION).

3) Wire the panels into one 13 panel string (15 or more will destroy the inverter through over voltage, you might get away with 14, depends upon your panels). The other panels sadly wont be used in this case.

4) Just accept that it works with a 11A max input and if the day is cloudy you will still gain max power out of all the panels (EASIEST OPTION).

(1), (2) and (3) assumes you have permission from the DNO to connect more than 3.68kW to the grid.
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charlesd
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« Reply #9 on: March 26, 2020, 01:51:01 PM »

Hi Nowty
Thanks for your help and please dont think i'm being awkward because its clear that pretty much everyone on here understands this better than I and ultimately I may have to accept your option 4. But I know this has worked in some way before. The inverter has settings that restrict the output to grid to the 3.68kw via a clamp on the meter tails. when this was happening last summer and before I changed routers and lost contact with the thing I would regularly see this function happen and was notified of it so I would have to have been producing more than 3.68+whatever i was using for this to happen.
I have managed to find a graph from very early on after the installation and will attach it. It seems to show to me that both inputs were running in parallel


There is also a section in the manual which refers to connection in parallel outside the inverter as a setting see copied text below

10. Set Inputmode
Input mode selection: inverter has 2 MPPT channels, the 2 MPPT can
operate independently, also can operate in parallel. If the PV strings are connected in parallel
outside the inverter, you should choose the "in parallel mode", otherwise use the default
setting. Press “Back” button to enter “1.Enter setting” interface, press ”OK“ button to enter
main setting interface. Enter “10. Set inputmode” by pressing “Up” or ”Down“ buttons. Press
“OK” button to enter setting interface. Choose “In parallel Mode?” or “Independent Mode?”
by pressing “Up” or “Down” buttons, then press “OK” button. “Success” or “fail” is displayed
after setting.

Interestingly the current setting seems to be "Independent mode"

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nowty
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« Reply #10 on: March 26, 2020, 03:10:07 PM »

I had a quick flick through your manual, I thought it did not do parallel MPPT but yes I have had another look and as you copied to your last post, it does, so then it should be set to parallel and not independent. It does not say exactly how you connect the string to the inverter but usually you just connect one set if you have already paralleled them up.
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Home battery storage of 40+ kWh's.
Hot water storage of 15+ kWh's.
Heat storage of 15+ kWh's.
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EV BMW i3 (another 30+ kWh's of storage).
280,000+ litres of water harvested from underground river.
Countrypaul
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« Reply #11 on: March 26, 2020, 03:16:37 PM »

I had a quick flick through your manual, I thought it did not do parallel MPPT but yes I have had another look and as you copied to your last post, it does, so then it should be set to parallel and not independent. It does not say exactly how you connect the string to the inverter but usually you just connect one set if you have already paralleled them up.

Why would the inverter have a parallel mode if you were only to connect one set? Surely a parallel mode would require both connections in order to be parallel?
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charlesd
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« Reply #12 on: March 26, 2020, 03:18:04 PM »

Using Fintray's suggestion swapping the cables about I have identified that one positive and 2 negative cables work fine one positive cable is not working so next step is to see if I can find out why.
This is more difficult since I have to isolate the DC at the panel end (box in the field) before opening up the dc isolater at the inverter end.
I'll do more looking and see what I can work out.
Unfortunately the sparky who helped me with all this has retired now and is no longer local and I doubt i'd find another electrician keen to pop out at the moment.
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charlesd
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« Reply #13 on: March 26, 2020, 03:20:11 PM »


Why would the inverter have a parallel mode if you were only to connect one set? Surely a parallel mode would require both connections in order to be parallel?
Its always had both sets connected up I am guessing here but perhaps it was never set to parallel mode but worked fine with both inputs being the same but one cable has developed a fault
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nowty
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« Reply #14 on: March 26, 2020, 03:37:01 PM »

I had a quick flick through your manual, I thought it did not do parallel MPPT but yes I have had another look and as you copied to your last post, it does, so then it should be set to parallel and not independent. It does not say exactly how you connect the string to the inverter but usually you just connect one set if you have already paralleled them up.

Why would the inverter have a parallel mode if you were only to connect one set? Surely a parallel mode would require both connections in order to be parallel?

Cos that's what it says in the manual.

If the PV strings are connected in parallel outside the inverter, you should choose the "in parallel mode"

If you connected them together outside of the inverter you would only have one pair of cables to connect to the inverter.

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12kW+ of PV installed and 60+ MWh's generated.
Home battery storage of 40+ kWh's.
Hot water storage of 15+ kWh's.
Heat storage of 15+ kWh's.
6kW Ground source heatpump.
EV BMW i3 (another 30+ kWh's of storage).
280,000+ litres of water harvested from underground river.
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