Newbie to the forum please be gentle

[Jason2512]

Hi guys and girls, I am new to the forum and after some help please and when I actually get my head around solar I might be able to help others one day. I have 12 panels on my main roof wired up in series on 2 strings and I have just set up another 12 panels on my flat roof extension, my question is do I have to climb up on the roof to disconnect the original panels and wire up to the new ones or is there an easier way to save me going on the main roof this is where my lack of knowledge comes in could I connect my two strings together at the inverter to make one string and then just re wire the new panels on the easy to get to flat roof to make the new second string Thanks in advance for any info

 

[time2roll]

Usually these separate strings need to be facing the same direction and the same angle to place in parallel. Also with three in parallel fuses on each string are needed in the combiner box. If the MPPT has multiple input then each string might be to a separate input.

Otherwise no harm to make the connection down off the roof.

 

[Hedges]

All panels in one series string need to be facing same direction.
But perfectly fine to have to strings of different orientation. I prefer that - more hours of good production out of the MPPT.

Six panels in series is enough to give you a bad shock (trust me, I have experience with both AC and DC).
How are your strings wired in parallel? Wire nuts? "Y" cables? Busbars?

The issue is, you don't want voltage on screws when you put a screwdriver on them. That can be done, is called "hot work" and ought to involve insulated tools, insulated gloves, leather outer gloves, and some training to put the fear of Volta and Ampere into you.

Many PV panels have MC4 connectors (some have MC3) which can make this much safer because they are "touch safe".
Never connect or disconnect under load. Shut off whatever breakers the SCC or inverter has. Confirm circuit is off. Then you can unplug both ends of both PV strings from wires leading to SCC.

Get a DMM, check the busbars or wires for DC voltage between each other, and between them and ground. Repeat checking for AC voltage. (some devices backfeed AC onto the PV terminals.)

Run a ground wire from PV panel frames to chassis of SCC or inverter. That is so you don't get an AC or DC shock from the frames.

With zero volts on the busbar or other connection, then you can add wires with MC4 connectors for your new panels. After done with tools, plug the MC4 connectors from PV panels into the system.

... so yes, you may have to climb on the roof to unplug MC4 connectors, if that's the only way to disconnect PV hot wires from the things you're working on.

And as Time2Roll said, 3 or more PV strings should have a fuse for each.

 

[Jason2512]

Hi thanks for the replies I am still a bit unclear as to what I can do, if you look at the picture of my house the original working panels are wired up in series on two strings in the second picture they go in to my inverter can I unplug these and get a adapter to make one string then wire up my new panels on the lower roof and put in to the then free outlet

 

[TomC4306]

Hi thanks for the replies I am still a bit unclear as to what I can do, if you look at the picture of my house the original working panels are wired up in series on two strings in the second picture they go in to my inverter can I unplug these and get a adapter to make one string then wire up my new panels on the lower roof and put in to the then free outlet

This is a math question that requires specs of existing panels, specs of new panels, and specs of the 'inverter'? to which they are going to be attached.
Is this a grid tied system?
Does this system have batteries?

 

[Jason2512]

Hi thanks for the reply it is a grid tied setup and has a battery, I am currently running a Samsung ess all in one please see pic attached, this will be going soon and replaced with a growatt sph6000 and 2 growatt batteries, solar panels spec is in the second pic

 

[Jason2512]

This is the spec in the new panels

 

[Hedges]

As Tom says, need specs of what you've got.

Maybe a Y cable can parallel the two existing strings into one input. That assumes the two strings are same voltage, and have to see of 2x current is OK. The two arrays on roof appear different, so not sure they are the same angle. You provided one data sheet, are they the same?

Alternatively, the two strings could be put in series. Voltage would add, have to see if that is too high. (39Voc, so 12s would be 480V, 16% headroom at ambient temperature and remains under inverter 550V max even when cold.)

Also, wattage handling of one input.

Then, are the two inputs paralleled internally (so fuses would be required when you add one or more additional strings in parallel) or is there separate MPPT per input.


Will added panels be same orientation, or on opposite side of roof?

New Trina panels also < 40V, so 12s works.
Voltage close enough to old panel that you can parallel two strings with same number of panels.

Inverter processes up to 15A, allows 20A Isc. Two strings in parallel is just within Isc. Will exceed 15A sometimes so MPPT will run at higher voltage, not get all power. But only on cool days with direct sun.

Existing array 12 x 285W = 3420W, within inverter capability. Expect 75% to 85% max under most conditions, will occasionally hit 100%.

With 12 of the new panels, 6600W (STC) total array. Nicely overpanels inverter beyond 4600W, don't know if it can process extra to the battery. But should at least do 4600W for longer.

If new panels are on other face of roof (assuming East/West not North/South), peak is reduced and hours are extended.

Should be good with 12s of old panel, 12s of new.

 

[Jason2512]

Hi thanks for the reply the new set of panels are on the flat roof below the main roof on same angle as main roof you can just work them out in the picture of my house above the spec on the new panels is in pic above

 

[Hedges]

Oh, right. You did say you put them up already.
And I can't count - 12 panels in upper array.

Double-check datasheet, but I think growatt sph6000 says 2 MPPT trackers, 550V 12A each. So that should also accept two strings, 12s panels each.

 

[Jason2512]

That is the data sheet on the growatt. So by the sounds of it I can get a y connector for the set on the main roof to bring both the strings together at the inverter and basically wire up the new set the same way, meaning I do not have to climb up on the main roof

 

[Hedges]

Not a Y connector, that would put 2 existing strings in parallel, and with 2 new strings also in parallel, about 40A total into existing inverter. Too much current. For new inverter that would be 20A into each MPPT, also too much current.

In series for twice the voltage. My math says it is OK but double check yourself by math and measurement.

Without climbing up on the roof, I think you can:
1) Shut off inverter for zero current flow
2) Unplug MC4 connectors from inverter
2a) Measure voltage of each string, see if about 240V
3) Connect PV strings in series with MC4 connectors
3a) Measure voltage of new string, see if about 480V
4) Connect new long string to inverter.

5) Turn on and confirm operation

6) Turn off inverter
7) Confirm voltages of new array two strings, similar to above, connect in series and reconfirm voltage AND POLARITY!, connect to inverter.

Make sure polarity of new string matches old. Probably does because I think you used pre-assembled PV cables with MC4 connectors. When I connect to other wire for extension I often get it reversed.

 

[Jason2512]

Is it these I would need to get

 

[Jason2512]

My inverter says I am only producing 181v which seems low and producing 2.8kw

 

[NCislander]

With your planned upgrade, would recommend placing PV circuit breakers onto PV feeds just before Inverters. Helps for times like these working with systems. Allowing you to ioslate loads prior to changes/troubleshooting efforts.

 

[Jason2512]

Hi thanks for the reply I do have circuit breakers on each string

 

[Hedges]

My inverter says I am only producing 181v which seems low and producing 2.8kw

6 x 40Voc/panel = 240Voc
6 x 32Vmp/panel = 192Vmp

12 x 285 = 3420W STC
2800W / 3420W = 82% of STC

All of those seem reasonable.

Is it these I would need to get

Only if connecting strings in parallel.

And, when using MC4 connectors, ONLY use same brand, or pair of different brands that are UL listed for use together. Incompatible knock-off "MC4" connectors fail and cause fires.

I can't tell you for sure how to identify brands on your panels. Might be in documentation. "Stabuli" is the inventor and only source of genuine MC4. As for your extension wires, unless sold as Stabuli by a reputable store, they are probably something else.


My suggestion was to not use Y or other parallel connectors. Instead, connect the two 6s strings in series for 12s.


Disconnects are useful. Fuses/breakers are required for 3 or more parallel strings, but your inverters won't allow the current of 3 parallel strings. With your panels connected as 2 strings of 12 panels each, fuses and breakers aren't required.

Hi thanks for the reply I do have circuit breakers on each string

Double check voltage and other ratings. My suggestion of series connection will increase string voltage to 550V; are breakers rated for that? (if two 300V poles are ganged, that can work up to 600V)

Are the breakers rated for DC?

Are they "Polarized" (may show +/-) or non-polarized? Special care to get polarity correct when using polarized. Connect "+" to PV+, "-" to PV-

 

[Jason2512]

Hi again I bit the bullet and climbed up on the roof was not as bad as I thought but not nice for the wife. I now have 2 strings wired up in series at 5 o’clock one pumping out 433v the other 435v measured at the inverter I have not turned
It all back on yet was just wondering if everything will be ok.

 

[Hedges]

Should be.
Double check max Voc rating of inverter. In case data sheet we're looking at isn't correct one for that model.
Double check polarity, so inverter doesn't get reverse voltage.
Double check whether DC breakers, if polarized type, have PV connected with correct polarity. (twice the voltage now, so more difficult to interrupt current.

Try one PV string at a time before both.

But it should be OK. Just check everything twice. I sometimes connect things wrong.

 

[Jason2512]

thank you so much for this you are a amazing chap to spend your time helping people out like this I really really appreciate it. My breakers are rated at 450v do you think I should change them before I fire it up