Off Grid System PV Wiring help of 3 parallel to 2 series...

[Greg Burton]

I am going to be getting six 400 watt solar panels and the classic sizing tool stated to do 3 parallel and 2 series. How exactly would I would wire this up and I think I would use a combiner box as well? This will be feeding a Classic 150 to 24v battery system and a 4000w inverter (coming soon).

I have done some research and the wiring part is not sinking in.

Any help would be greatly appreciated...

[ClassicCrazy]

Look up the Midnite Kid manual - I think they have some good pictorial diagrams in there to show wiring up series / parallel strings .
Also look on  youtube - sure there are all kinds of tutorials on there - Alt E has a lot of beginners videos.

Larry

[tecnodave]

Bur1196,

Basically wire the 2 panels in series for each string, build 3 strings , combine the negatives to one common feed wire in the combiner. You will need breakers or fuses on each of the pairs of panels.
I would advise using a MidNite MNPV-6 combiner as this will allow for future expansion. You can use the smaller MNPV-3 combiner, but expansion of the system will be more difficult and expensive. Look at the name plate on your solar panels....there is a recommended maximum fuse size for each type of panel.
Buy MNPV circuit breakers that are 1.56 times the fuse size listed on the panels. The code requires the breaker to be 1.25 times the maximum current that the panel and 1.25 times maximum current if this device can supply that current for 2.0 hours or more...(that makes this device a "continously operated device" ). (solar panels are continuously operated device).....so the math 1.25 times 1.25 is 1.56 times rated amps. Connect the output of the combiner box to the p.v. Input of the Classic. That is pretty much it for a very basic panel array. If you live in a lightning prone area then a "surge protective device" at the combiner output or at the Classic input to protect from lightning. Suggest the MNSPD-150  Wire the Classic directly to the battery, do not combine the wiring with the inverter......we need to have the controller see the battery voltage, not the system voltage. The inverter running will pull down the voltage somewhat, the Classic needs to "see" the true battery voltage.  Install a circuit breaker between the Classic battery output and the battery negative. If you use a MNPV breaker here it would be sized at 1.56 times maximum battery current. If you use the MNDC type breaker it would be sized at 1.25 times the maximum battery current. The difference is that MNDC breakers are "rated continually operated device" and does not need to be derated. The MNPV breakers are not "rated continuously operated device" and so must use the 1.25 X1.25 =1.56 rating . If using the MNDC breaker the post (end) marked positive(+) MUST be connected to the battery!

Pretty simple but if you need more clarification do post more questions here...there are lots of folks here that will help you with the issues.

David

[Greg Burton]

ClassicCrazy: The Kid diagrams help a little, thank you...

tecnodave: I am not planning on expanding (on that particular solar array) but it might be a good idea to go to the 6 instead of the 3 just to be safe...I have attached what I have come up with on the wiring. Thank you again for your input...

I am thinking of using the MNPV6HV-MC4 (since it is already pre-wired and ready to go) and if my diagram is correct, I would wire the two outputs to the box and then go from there (plus this will allow me to expand in the future as well)?

[tecnodave]

Bur1196,

Your diagram is not too clear and I'm not sure what you are proposing.  For each string of panels panel 1 will be wired + connector to breaker in combiner box.   - connector to positive connector of panel number 2 and the - connector of panel 2 to negative buss in combiner.

Repeat that three times and you will have three strings of two panels each.

The MNPV6HV is a high voltage combiner made for grid tie type installations and not suitable for the Classic in off grid applications....use the standard MNPV-6 combiner instead....it uses 150 volt DC single breakers,  the HV version uses ganged breakers for a 300 or 600 volt application.....not needed here as your max voltage will be less than 150 volts

I communicate with an iPad which has no drawing editor so I cannot post a diagram. The Kid manual has very good diagrams for panel connections.

David

[Vic]

Hi bur..,

In the Classic Manual - 2056,  page 26   has a good wiring diagram.  Choose the latest Classic / Classic SL manual:

http://www.midnitesolar.com/documents.php?productCat_ID=21&productCatName=Charge+Controllers+-+Classics&model=CLASSIC 150&product_ID=256&act=

Regarding sizing PV breakers,  you can use a breaker that has an Amp rating that is equal to the  Max Fuse rating on the label on the back of the PV.   Or Isc X 1,25 and round up if necessary.

You might not really need an Combiner with MC-4 connections.   All depends on the layout of your PVs.

Breakers (or fuses)  are there to protect the cables from overheating,   or fire.  So the output breaker from the Classic + battery cable needs to be sized to that cable size.  There is a cable size verses breaker size in the Appendix of that Classic  Manual.

FWIW,  Vic

[tecnodave]

Bur1196,

Looking again at your diagram ......at 56 volts these are 96 cell panels and the Classic will do just fine with all the panels in parallel.  It will require 6 panel breakers but will releive the Classic of down converting the 112 volts DC to 28.8 DC to charge the batteries (that would be a down conversion ratio of 4-1).  Using a all parallel wiring the voltage conversion ratio will be 2-1.  This will create less heating in the Classic and give it a longer life due to the lower temperatures. MidNite does state that the Classic will be fine with the strings of two, but it will create more heat with a higher string voltage.

I have two Classic's and two Kids and I have done the side by side tests of 96 cell panels all in parallel vs in strings of two and the results repeated each time. No additional power was noted using the higher voltage strings and the Classic and Kid controllers ran hotter.

I repeated the tests with my 72 cell Sharp panels using strings of 2 for 72 VMP in verses strings of 3 for a VMP of 105 volts in.  Results were the same. System with the higher voltage ran hotter and did not produce more power

There is an ideal ratio of input voltage to battery voltage.  Basically you cannot use a ratio of less than 1.3 and have good performance . It's somewhere between 1.8 times battery volts to about 2.7 times battery voltage.  Above that ratio you will burn up power making extra heet.

I run my PV input voltage at 2.0-2.7 times battery voltage.

For the 72 cell Sharp and Suntech panels, two in each series string.   2.5 to 1 voltage conversion
For the 96 cell Sanyo multilayer panels,   all in parallel.........2-1 voltage conversion

Disadvantage of all in parallel......more breakers....bigger combiner
Advantage of all in parallel.....less heat....less wear and tear on Equiptment,  no fans running constantly! Maybe slightly better efficiency due to the power not being lost as heat. Longer life from Classic's and Kid's

I had to custom build my big combiner........14 spaces...a one off....TDPV14...

David

note the TDPV14 box is not a commercial product, I built that for my needs. Kinda like my TDAC20BX
custom buss for square d QO line breakers that serves as my AC distribution box for inverter/generator

[Greg Burton]

Bur1196,

Looking again at your diagram ......at 56 volts these are 96 cell panels and the Classic will do just fine with all the panels in parallel.  It will require 6 panel breakers but will releive the Classic of down converting the 112 volts DC to 28.8 DC to charge the batteries (that would be a down conversion ratio of 4-1).  Using a all parallel wiring the voltage conversion ratio will be 2-1.  This will create less heating in the Classic and give it a longer life due to the lower temperatures. MidNite does state that the Classic will be fine with the strings of two, but it will create more heat with a higher string voltage.

I have two Classic's and two Kids and I have done the side by side tests of 96 cell panels all in parallel vs in strings of two and the results repeated each time. No additional power was noted using the higher voltage strings and the Classic and Kid controllers ran hotter.

I repeated the tests with my 72 cell Sharp panels using strings of 2 for 72 VMP in verses strings of 3 for a VMP of 105 volts in.  Results were the same. System with the higher voltage ran hotter and did not produce more power

There is an ideal ratio of input voltage to battery voltage.  Basically you cannot use a ratio of less than 1.3 and have good performance . It's somewhere between 1.8 times battery volts to about 2.7 times battery voltage.  Above that ratio you will burn up power making extra heet.

I run my PV input voltage at 2.0-2.7 times battery voltage.

For the 72 cell Sharp and Suntech panels, two in each series string.   2.5 to 1 voltage conversion
For the 96 cell Sanyo multilayer panels,   all in parallel.........2-1 voltage conversion

Disadvantage of all in parallel......more breakers....bigger combiner
Advantage of all in parallel.....less heat....less wear and tear on Equiptment,  no fans running constantly! Maybe slightly better efficiency due to the power not being lost as heat. Longer life from Classic's and Kid's

I had to custom build my big combiner........14 spaces...a one off....TDPV14...

David

note the TDPV14 box is not a commercial product, I built that for my needs. Kinda like my TDAC20BX
custom buss for square d QO line breakers that serves as my AC distribution box for inverter/generator

Ok, I think this is starting to make more sense. If I am correct, I can run each solar panel (positive lead) to its own breaker in the MNPV6 combiner box (the negatives will connect to the negative busbar) (or to simplify - get the MNPV6-MC4-LV and just connect the MC4 wires accordingly). Then I will have to run two wires from the combiner to the charge controller which will be the Classic 150 and then go from there...Also, I forgot to mention, attached is what I am planning to get for the solar panel but I might change to the Panasonic HIT model since I can run in parallel easily (it'll be slightly higher voltage)...

Thank you again for spelling this out to me, its finally starting to click

[mike90045]

Look up the Midnite Kid manual - I think they have some good pictorial diagrams in there to show wiring up series / parallel strings .
Also look on  youtube - sure there are all kinds of tutorials on there - Alt E has a lot of beginners videos.

Larry

The quality of youtube is sometimes doubtful, but topics from Midnight Solar and Alt E should be good.   Watch out for Bubba and his solar arc welder

[tecnodave]

Bur1196,

Ok this is not the same, these LG panels are 72 cell and the working voltage is too low for a parallel connections. You will need to wire them 2 in each string to get high enough voltage for the Classic 150.

These LG panels are some of the highest rated panels available right now. 72 cell panels are far more common than 96 cell panels.

Do be aware you cannot mix different voltage panels on one controller. So decide now before you buy just what you want to do.

One bad thing I will say about the Sanyo HIT panels is that they are difficult to mount. They have their own system of mounting and common track rail is difficult to mount on. I had to fabricate my own mounting system so as not to pay more for the rack than the cost of the panels.

If I had lots of money to spend and money didn't matter I would get the LG panels.
LG is the rebranded name of Heath-Zenith corporation, they have been around a long time. Their products are well engineered.

Some things I do not scrimp on.......I have a been through a dozen or more of inadequate controllers that didn't work out well........its brand new MidNite gear purchased from NAWS for me, no used units.......reliability counts.  I cannot find good used controllers.

Solar panels are a different matter.......I bought brand new Suntech 275 and 285 watt 72 cell panels for $50.00 each from a housing contractor just finishing a 42 house sub-division. He bought containers full of panels from China to build with and had a dozen left over. He didn't need them.

I shop craigslist and eBay on a daily basis and get smoking good deals on grid tie leftovers and upgrades........

BUT.......with off grid.....there are no leftovers.....no decent used controllers etc.

I have worked in industry for 50 years before retiring so I have a skill set that few people possess.
I weld all materials including aluminum, copper, brass, do machining, electrical contracting etc. build houses etc.

As a newby I advise you to keep it simple and within your skill set.

I cannot upload a drawing from my iPad.......its a communicator......but it doesn't like to share with my Lenovo computer. Apple and Microsoft do not like each other......

Please do get the manual and the diagrams are in there.

Your diagram is showing panels in 2 series strings of three panels each
What you need is three strings of two panels each for the best efficiency and long life of your system.

Please get togather a complete list of planned gear including specs before asking about anything specific. It's hard to guess just what you are envisioning without knowing more details of what you propose.

David

[Greg Burton]

Bur1196,

Ok this is not the same, these LG panels are 72 cell and the working voltage is too low for a parallel connections. You will need to wire them 2 in each string to get high enough voltage for the Classic 150.

These LG panels are some of the highest rated panels available right now. 72 cell panels are far more common than 96 cell panels.

Do be aware you cannot mix different voltage panels on one controller. So decide now before you buy just what you want to do.

One bad thing I will say about the Sanyo HIT panels is that they are difficult to mount. They have their own system of mounting and common track rail is difficult to mount on. I had to fabricate my own mounting system so as not to pay more for the rack than the cost of the panels.

If I had lots of money to spend and money didn't matter I would get the LG panels.
LG is the rebranded name of Heath-Zenith corporation, they have been around a long time. Their products are well engineered.

Some things I do not scrimp on.......I have a been through a dozen or more of inadequate controllers that didn't work out well........its brand new MidNite gear purchased from NAWS for me, no used units.......reliability counts.  I cannot find good used controllers.

Solar panels are a different matter.......I bought brand new Suntech 275 and 285 watt 72 cell panels for $50.00 each from a housing contractor just finishing a 42 house sub-division. He bought containers full of panels from China to build with and had a dozen left over. He didn't need them.

I shop craigslist and eBay on a daily basis and get smoking good deals on grid tie leftovers and upgrades........

BUT.......with off grid.....there are no leftovers.....no decent used controllers etc.

I have worked in industry for 50 years before retiring so I have a skill set that few people possess.
I weld all materials including aluminum, copper, brass, do machining, electrical contracting etc. build houses etc.

As a newby I advise you to keep it simple and within your skill set.

I cannot upload a drawing from my iPad.......its a communicator......but it doesn't like to share with my Lenovo computer. Apple and Microsoft do not like each other......

Please do get the manual and the diagrams are in there.

Your diagram is showing panels in 2 series strings of three panels each
What you need is three strings of two panels each for the best efficiency and long life of your system.

Please get togather a complete list of planned gear including specs before asking about anything specific. It's hard to guess just what you are envisioning without knowing more details of what you propose.

David

Again, I do appreciate your time and wisdom...

If I go with the Panasonic panes (specific model attached), are you saying that I would need to just attach all 6 them to the combiner directly (1 panel for each breaker - all parallel connections) and that the voltage (58v) is high enough for it to work?

If I go with the LG panels then I would have to wire in series and parallel (which I am confused on how to wire them together). The specific model is attached as well.

So basically I need to know how to wire 6 panels (either Panasonic or LG - no I am not mixing them) to a combiner box.

Thank you again!

Greg