Solar System DC Wiring and Panel Installation (Take 2)

The story so far... My previous thread on this topicwas shut down due to some passionate discussion by posters.A situation I am seeking to avoid this time around :angel:

I am seeking to gain your experience andknowledge, that can help me install my solar system. So whilst I appreciate robust discussion, I would please ask if you have strong opinions you dont let that get ahead of helping me find solutions

So far I have arrived at a string of 3 panels, with the option to add additional strings. The panels I am using will be the Trina Honey M Plus 300 watt. The inverter/charger I have is a Victron SmartSolar 150/45 unit.

From previous discussion the string of 3solar panels will be connected together using 6mm2 cable into a roof top isolator switch. The isolator switch will utilise 10mm2 cable that will go to a combiner enclosure that will contain non-polarised circuit breakers. The cable between the combiner enclosure and the data center (man cave) will be a 10mm2 cable (most likely I will run 2 cables.

So... a few more questions...

The Trina solar panels have the following specifications:-
Maximum Power Current-IMPP (A) = 9.19
Maximum Power Voltage-VMPP (V) =32.6
Open Circuit Voltage-VOC (V) = 39.9

Therefore, if I have a string of 3 panels, the amps will be 27.57, so would it be safe to use a 32amp DC non-polarised circuit breaker in the combiner enclosurefor eachstring of 3 panels?

After the 10mm2 cable reaches the data center and prior to connecting to the inverter/chargerI assume I should have either another isolator or circuit breaker? Which would be best?

Here is a picture of the roof onto which I will be installing the solar panels... Thanks toRedpacket for sharing his clever approach to laying the roof out in excel. From my initial estimates I'd say I should be able to get 2 rows of solar panels on the roof, but not sure I need to go to that much trouble... or should I? Thoughts?





As always, thank you for your advice and ideas, it is very much appreciated and that you do so respectfully.

A string implies series wired panels, your current calculation implies parallel - your controller would much prefer the former.

You're adding the currents (you do that with panels or strings in parallel).
With one string of three panels, they are in series, so the same current will flow in all of them, but you get 1x the current out (& 3x the voltage).
For cable calculations, my understanding is you are supposed to use the Isc value which is usually a little higher than the Imp.
For your Trina Honey M Plus 300W panels, the spec sheet I found shows Isc = 9.64A so that's the max current each string of panels could make.

The 32A ZJBeny BYH-32 isolator is a good one & has 4 poles per breaker eg 4x switches mechanically ganged together.
So you can run one string +ve & -ve through one half of the unit & you can run your next string through the other half.
Don't forget the metal sun shield plate/bracket.

Water ingress into roof top isolators has been a major problem for the industry, so you need to use glands which have two hole rubber inserts and a rubber washer for the body like these:
https://www.tro-pacific.com/collections/solar-accessories-tools/products/nylon-cable-gland-25mm
and
https://www.tro-pacific.com/collect...m25-2x6-sealing-insert-for-stm25-cable-glands

Any exposed cable has to be the solar rated PV1-F XLPE cross-linked polyethylene exterior. Otherwise 100% in sealed conduit.
If a person could walk on it, has to be in conduit. To go through into the roof, must use conduit + a dektite (bunnings).
Cable ties must be stainless.

Plan to pack as many panels on the roof as you can now. You can always install the rest later.
Given the sloping ridge (left) & valley (right) you could probably fit more panels if you orient horizontally - there are "even more special" right angle brackets so the rails can run vertically.
If that chimney is in the way, move it! (I'm seriously considering taking the brick chimney in my diagram down due to winter generation hit).
You'll need the juice & be running more & more with it - it's addictive you know, didn't anyone tell you?!

The 3 panels will be in series, so Imp of 9 Amps as per redpacket. For that you only need 4mm2 at the most. I have used 2.5mm2 for 4 panels in series in my installation (Imp 8A).

For two parallel strings, you will end up with 18Amp specification with likely just over 15A max.

For cable glands the rubber washers are critical (as per redpacket) as they come without rubber washers and are useless without them for waterproofing. Install them under the eves so they don't get direct water spray as well, where possible.

For breakers I have my polarised breakers orientated to protect the solar panels from the battery / charger. With a solar panel that is short circuit rated for less than 10A the solar output will never be able to trip a 10A breaker, so the breakers end up protecting the solar wiring / installation from faults that cause a backflow. With parallel strings the breakers then also protect one string from the rest of the solar panel output, in addition to any return fault.

I tend to use brekears rather than isolators but avoid switching them for isolation purposes as some breakers can end up with the contact surfaces being changed, enough to alter the trip / continuous handling current capabilities over the long term (years later). Use the solar isolator switched to turn off and then the breakers for secondary isolation / protection. Double pole as a preference. Solar isolators are required under the regulations to be accesible, whereas brekers can end up in locked enclosures / locations, so breakers do not always fit the regulations...

Given the controller you've got, I'd wire them in 2 series wired strings of 3 - so present 2 pairs internally. That'll give you the option to parralel the strings to feed your charger, or feed a GTI by series wiring the 2 strings (so a string of 6).

Redpacket said:

You're adding the currents (you do that with panels or strings in parallel).
For your Trina Honey M Plus 300W panels, the spec sheet I found shows Isc = 9.64A so that's the max current each string of panels could make.

Click to expand...

Thanks for clearing that up, makes sense and helps me scope everything out.

Redpacket said:

The 32A ZJBeny BYH-32 isolator is a good one & has 4 poles per breaker eg 4x switches mechanically ganged together.
So you can run one string +ve & -ve through one half of the unit & you can run your next string through the other half.
Don't forget the metal sun shield plate/bracket.

Click to expand...

Thanks mate, have already sourced both of the above. Wasn't sure if I could use the BHY-32 for two series strings, but sounds like it is doable. I had purchased two BHY-32 units, but can use the second one for strings 3 and 4

Redpacket said:

Water ingress into roof top isolators has been a major problem for the industry, so you need to use glands which have two hole rubber inserts and a rubber washer for the body like these:

Click to expand...

Yep, have these. Actually purchased a 3 hole gland so the earth cable could go down the same flex conduit as the power cables to the combiner box. I assume that is ok, running earth wires in the same conduit? I also have some 2 hole glands for just the power cables from the panels. Assume the rubber washer should be on the outside :s

Redpacket said:

Any exposed cable has to be the solar rated PV1-F XLPE cross-linked polyethylene exterior. Otherwise 100% in sealed conduit.
If a person could walk on it, has to be in conduit. To go through into the roof, must use conduit + a dektite (bunnings).
Cable ties must be stainless.

Click to expand...

I will install 32mm orange conduit in the ground between the combiner box on the house and the data center, and will run the grey flexible from the roof isolator down inside the house wall to the combiner box (will probably mount a PVC box on the house wall). Thanks for the tip on the stainless cable ties.

Redpacket said:

Plan to pack as many panels on the roof as you can now. You can always install the rest later.
Given the sloping ridge (left) & valley (right) you could probably fit more panels if you orient horizontally - there are "even more special" right angle brackets so the rails can run vertically.

Click to expand...

Yep, have seen the rotatable brackets. Will start with planning on horizontally mounting and see where it goes. Have already started my Redpacket inspired spreadsheet, and may even go for a SketchUp design

Sean said:

Given the controller you've got, I'd wire them in 2 series wired strings of 3 - so present 2 pairs internally. That'll give you the option to parralel the strings to feed your charger, or feed a GTI by series wiring the 2 strings (so a string of 6).

Click to expand...

Hey Sean... any chance you could provide more info, or a diagram... would be a massive help.

It's 1AM here, so no diagrams at this time of night.

3 panels, all holding hands, left to right etc, the 2 ends (pos and neg, are presented adjacent to your combination box)

Another 3 panels, exactly the same as above, so you've now got 4 wires presented, 2 plus 2 neg, join the negs together and the pos together for feeding your MPPT charger .... or ...... join a pos to a neg, and feed the remaining pos and neg into a gti

Make sense ?

completelycharged said:

The 3 panels will be in series, so Imp of 9 Amps as per redpacket. For that you only need 4mm2 at the most. I have used 2.5mm2 for 4 panels in series in my installation (Imp 8A).

Click to expand...

Thanks mate, makes me more comfortable as I have a truck load of 4mm2, and was terrified I'd have to tell the wife it wont be used

completelycharged said:

I tend to use brekears rather than isolators but avoid switching them for isolation purposes as some breakers can end up with the contact surfaces being changed, enough to alter the trip / continuous handling current capabilities over the long term (years later). Use the solar isolator switched to turn off and then the breakers for secondary isolation / protection. Double pole as a preference. Solar isolators are required under the regulations to be accesible, whereas brekers can end up in locked enclosures / locations, so breakers do not always fit the regulations...

Click to expand...

Awesome feedback, thank you. As per my other replies, I am planning on using the ZJBeny isolators on the roof, then run individual string cables in individual flex solar rated conduit down the inside of the house wall to circuit breakers in a combiner point. Having the circuit breakers accessible without climbing on the roof will be good.

gregoinc said:

Yep, have these. Actually purchased a 3 hole gland so the earth cable could go down the same flex conduit as the power cables to the combiner box. I assume that is ok, running earth wires in the same conduit? I also have some 2 hole glands for just the power cables from the panels. Assume the rubber washer should be on the outside :s

Click to expand...

Yes you can run earth in same conduit.
Yes rubber washer on outside.

gregoinc said:

I will install 32mm orange conduit in the ground between the combiner box on the house and the data center, and will run the grey flexible from the roof isolator down inside the house wall to the combiner box (will probably mount a PVC box on the house wall). Thanks for the tip on the stainless cable ties.

Click to expand...

Underground = orange HD = OK
In walls, ceilings, roof spaces, under floors & any building cavity, solar cabling must be in orange HD conduit or same flex & marked SOLAR every 2m (sharpie).
Outside, it's the gray MD, orange HD inside building cavities (as above), gray MD inside a room where you can see it.

Probably a silly question, but hey lets see... I assume that all the cables between the solar panels and the isolator and combiner box need to be equal length? So what I am saying is the positive and negative DC cables from each of the3 panels in series needs to be the same length? Does it matter if they are not, or is it important they are the same length?

Doesn't really matter, certainly not in the few meters, or less, I'd guess you'd be seeing.

+1 the small differences in voltage drop won't matter in the scheme of things.

The only time that varying cable lengths on opposite sides of the circuit matter, is usually gonna be data transmission wires. Other than that, there's really not an issue. The only thing is, when you do your voltage drop calcs, you need to accommodate for that.
If from panel->controller is 5m, and 1 cable is 5m the other 7m, then that's 12m length, not 10m. So the 12m length will have a higher voltage drop. Not much, in this example, but it's still there.
Just remember it's both sides of the feed that accounts for voltage drop

Thank you gents. Looks like I have some work to do, digging trenches, laying conduit, mounting solar panels, and running cables.

Just out of curiosity, the MC4 connectors... I have an MC4 crimping tool, so are the MC4's just crimped, and no need to solder?

They are just crimped. There is no need to solder if you crimp them properly. There is also screw on MC4 where you dont have to crimp at all.

The Crimped one is what i prefer all day

daromer said:

They are just crimped. There is no need to solder if you crimp them properly. There is also screw on MC4 where you dont have to crimp at all.

The Crimped one is what i prefer all day

Click to expand...

Thank you sir, I figured as much.Looks like I have some crimping practiceto do

Also, am looking at the following enclosure for my combiner box (to be mounted on the house wall). I am planning on the combiner box containing a circuit breaker for each series string and a combiner to take the panels down to the cable to run to the home DC. Having never built a combiner box I figured a poly-carbonate enclosure would better than metal?

http://direct.dksh.com.au/Product/Solar/consumer-unit-enclosure-8-pole-1000vdc-ip65

Any poly box with a DIN rail mounting will be fine, that's just an empty enclosure - it's says number of poles, it means number of ways, as in how many standard width modules can be fitted.

That looks expensive.

gregoinc said:

daromer said:

They are just crimped. There is no need to solder if you crimp them properly. There is also screw on MC4 where you dont have to crimp at all.

The Crimped one is what i prefer all day

Click to expand...

Thank you sir, I figured as much.Looks like I have some crimping practiceto do

Click to expand...

Mating crimps are supposed to be from the same manufacturer as the panelor at least on the manufacturers recommended list.
See here (end of section 2): http://solarjuice.com.au/wp-content/uploads/2018/01/installation-manual-of-standard-module.pdf

If you use cheapie or not quite right ones you can get heating & failureissues.

You need the special crimper too like this one:
https://www.ebay.com.au/itm/MC4-Cri...olar-Crimp-Crimper-2-5-4-6mm-Kit/172842444513
sometimes called "A-2546B"
notice it's got (hard to see) side bit to put the metal crimp piece in & hold it while you tighten - trust me, this is really useful!

---

Sean said:

Any poly box with a DIN rail mounting will be fine, that's just an empty enclosure - it's says number of poles, it means number of ways, as in how many standard width modules can be fitted.

That looks expensive.

Click to expand...

As long as it's IP rating is good & you can mount it without drilling holes in it!

Redpacket said:

Mating crimps are supposed to be from the same manufacturer as the panelor at least on the manufacturers recommended list.
See here (end of section 2): http://solarjuice.com.au/wp-content/uploads/2018/01/installation-manual-of-standard-module.pdf

If you use cheapie or not quite right ones you can get heating & failureissues.

You need the special crimper too like this one:

Click to expand...

Thanks Redpacket, took a look at that doco... It's probably because I dont know what I am looking for, but I am stuffed if I can find any of the MC4 connectors on page 5 available for sale, or they have different part numbers :huh:

Redpacket said:

As long as it's IP rating is good & you can mount it without drilling holes in it!

Click to expand...

Stupid question time... If I dont drill holes, how would I get the PV string cables into the enclosure? I had planned on mounting it on the house brick wall, with the 25mm solar UV flex tube coming in the back.

The old way of waterproofing for fixing enclosures to a wall was to use a soft non setting compound to push around and over any screws that had been used to fix anything to a wall. Blimey, just had a google and this looks like the stuff.. last time I used some it was a few years back...
https://www.cablejoints.co.uk/sub-product-details/3m-scotchlok-connectors/prysmian-r391
Not sure how it fits into the local wiring regs though...

The cable glands and rubber washers for the solar in / power out... they are IP6 rated if done right (rubber washer !!).

I have used hot glue to seal around some glands where they may be prone to cable movement, but that is a non regulation fix I have done for myself on my own equipment where rain can't reach and was also lacking in rubber washers and had lots of hot glue sticks.... lol.