1000 watt off grid system on the drawing board...

[SgtPepper]

Hello, i'm stock piling the components to build the above system at home, I should be ready to go in September. I was hoping if someone could answer a few questions and check my maths??

I've got a classic lite 150,
6 x 2v Sonnenschein dryfit 800 amp hour A600's  ( i'll wire in series for 12 v of course,)
5 x 200 watt mono crystalline panels with VOC of 46.44 and ISC of 5.67

I was planning on wiring the 5 panels together in parallel, they have MC4 connectors. Is this the most efficient way to wire them for the 150? Does anyone had some ingenious ideas for a cheaper alternative to Y connecters for parallel connecting? I was thinking about  simply making some one ended MC4 leads and connecting all of the positives and negatives to their own common bus then going from there to the classic lite.

The batteries and classic lite will be situated right underneath the array which will be ground mounted next to the house so cable lengths will be short, about 2m max.

My maths say a 40amp breaker between pv and classic lite is the one to use, is this right?

Well thats it in a nut shell, thanks in advance.




 

[zoneblue]

Hello, i'm stock piling the components to build the above system at home, I should be ready to go in September. I was hoping if someone could answer a few questions and check my maths??

I've got a classic lite 150,
6 x 2v Sonnenschein dryfit 800 amp hour A600's  ( i'll wire in series for 12 v of course,)
5 x 200 watt mono crystalline panels with VOC of 46.44 and ISC of 5.67

I was planning on wiring the 5 panels together in parallel, they have MC4 connectors. Is this the most efficient way to wire them for the 150?

If your array isnt far away then you ideally want the array voltage to be  about one nominal bigger then the battery bank. So for you 12v bat, 24ish for the array. So yes, all 5 panels in parallel is best. So long as the pv isnt too far away, in which case you start to horse trade controller losses against cable losses.

Does anyone had some ingenious ideas for a cheaper alternative to Y connecters for parallel connecting? I was thinking about  simply making some one ended MC4 leads and connecting all of the positives and negatives to their own common bus then going from there to the classic lite.

No for that many panels in paralell you need string fuses to prevent a fire if one panel shorts. G get mc4 extention cables, cut them in half and wire each panel to the combiner, one fuse or breaker per string.

The batteries and classic lite will be situated right underneath the array which will be ground mounted next to the house so cable lengths will be short, about 2m max.

My maths say a 40amp breaker between pv and classic lite is the one to use, is this right?

The sizing of this breaker isnt too critical, as the pv cant generate bucket loads of current. Obviously you dont want it too small, so go bigger rather than smaller. So 5 x Isc, 40amps is about right.

Try NAWs forum as well.

Well thats it in a nut shell, thanks in advance.

[/quote]

[SgtPepper]

Thanks for the quick response and good info  , would the fuses at each panel need to be dual pole? and would 10 amp be too high?

[SolarMusher]

Single pole 15A 125/150Vdc max, Midnite or Outback, take a look at the MNEPV15.
Erik

[Vic]

Hi SgtPepper,

In addition to the fuses/breakers needed for EACH of the PV modules,  as noted here,  you will also need a circuit breaker on the output of the Classic -- between the Classic and the battery.  Depending on the standards used for your  location,  this breaker may need to be about 100 Amps and rated for DC.  Fuses and breakers need to be sized to protect the wire used for the circuit,  so,  you will want to use appropriate breaker for the gauge  of the wire used.  Depending on conditions,  the maximum output current that you could expect from the Classic is in the range of 72 Amps or so,  continuously,  so make certain that the wire and breaker are sized correctly,  with an appropriate safety factor.

The String Sizing Tool is on the MidNite site:
http://www.midnitesolar.com/sizingTool/displaySizing.php

This is useful for designing your system.  Good Luck,  Vic

[SgtPepper]

Thanks again for the answers

Single pole 15A 125/150Vdc max, Midnite or Outback, take a look at the MNEPV15.
Erik

Mmm Maximum series fuse rating on the Panel says 10amp, I was thinking that 8 amp would be ok? The polarity of these breakers is important which way around should they go?

Hi SgtPepper,

In addition to the fuses/breakers needed for EACH of the PV modules,  as noted here,  you will also need a circuit breaker on the output of the Classic -- between the Classic and the battery.  Depending on the standards used for your  location,  this breaker may need to be about 100 Amps and rated for DC.  Fuses and breakers need to be sized to protect the wire used for the circuit,  so,  you will want to use appropriate breaker for the gauge  of the wire used.  Depending on conditions,  the maximum output current that you could expect from the Classic is in the range of 72 Amps or so,  continuously,  so make certain that the wire and breaker are sized correctly,  with an appropriate safety factor.

The String Sizing Tool is on the MidNite site:
http://www.midnitesolar.com/sizingTool/displaySizing.php

This is useful for designing your system.  Good Luck,  Vic

Cheers Vic, the battery charging current will be 69.4 amps, I've got an 80amp Midnite breaker I was going to use between the CC and Bat, positive end to batt of course.
In addition to the single breakers on the positive lead at each panel, I was planning to put a Dual pole 40amp breaker after the whole string positive end towards the array of course, is this necessary with all of those breakers there? 

Try NAWs forum as well.

Finally worked out what the NAWs forum is , Cheers for that great lot of info there!

[SolarMusher]

Hi Sgt,
Follow manufacturer recommendations for fuse rating and use 10A per string. You will need a combiner box (see midnite products) to mount these Din Rail breakers. Polarity is, up to controller (PV+ IN) and down from PV. In fact as Vic said, you need an Input breaker from PV (150Vdc/60A Din or panel mount for 6AWG) and an output breaker (150Vdc/80A Din or panel mount for 4AWG) to battery bus bar. If your PV V0c output is above 150Voc, you will have to install 300Vdc breakers in a 300Vdc combiner box.
150Vdc breakers are single pole and 300Vdc are double pole.
A+,
Erik

[SgtPepper]

Excellnt Erik, thanks. I've got heaps of good wire ranging from 4mm right up to 8mm thick, that measurement is the wire diameter not the insulation as well. 

[Vic]

Hi Sgt ..

The Output Current is not an absolute,  it depends upon the temperature of the PV modules,  battery voltage,  the intensity of the sun,  reflections from snow or from water etc.  Those are some of the "conditions"  that I was referring to.

An 80 A output breaker is probably OK,  may be a bit of a low value.  The MidNite DC breakers are rated for continuous current conditions,  which helps reduce the possibility of nuisance tripping of the breaker.  Some countries and localities have specific safety factors which can increase the size of the wiring and the size of the breaker.

Regarding the rating of the PV input breakers,  sometimes,  with no data provided,  we guess based on some of the data,  but as Erik mentioned,  always follow the manufacturer's recommendations --  10 A in this case.

A 40 A PV input breaker (into the Classic) should be OK,  and a double pole unit should be OK,  just make certain that all of the breakers are rated for DC circuits.  The MidNite MNEPV,  and MNEDC breakers are so rated.

Good Luck,  and have fun,   Vic

[SgtPepper]

Thanks Vic, i'll go ahead and order my breakers now. 

[SgtPepper]

Hi Sgt,
Follow manufacturer recommendations for fuse rating and use 10A per string. You will need a combiner box (see midnite products) to mount these Din Rail breakers. Polarity is, up to controller (PV+ IN) and down from PV. In fact as Vic said, you need an Input breaker from PV (150Vdc/60A Din or panel mount for 6AWG) and an output breaker (150Vdc/80A Din or panel mount for 4AWG) to battery bus bar. If your PV V0c output is above 150Voc, you will have to install 300Vdc breakers in a 300Vdc combiner box.
150Vdc breakers are single pole and 300Vdc are double pole.
A+,
Erik

Well real life got in the way for a few months, but i'm now back on track and am now putting together my off grid system.
I'm building my PV combiner at the moment and the above info from solar musher has confirmed a lot. I just wanted to confirm the polarity direction of the 5 string fuses I have, Are the positive ends towards the controller or positive ends towards the panels?
I have 5 200watt panels in Parallel. Between the combiner and the controller I have a dual pole breaker also as protection.

[vtmaps]

I'm building my PV combiner at the moment and the above info from solar musher has confirmed a lot. I just wanted to confirm the polarity direction of the 5 string fuses I have, Are the positive ends towards the controller or positive ends towards the panels?
I have 5 200watt panels in Parallel. Between the combiner and the controller I have a dual pole breaker also as protection.

A dual pole breaker?  Is that a GFP, or are you breakering both PV (+) and PV (-)?

By the way, the way that Midnite says to install their combiner breakers for each string of PV makes no sense to me and many others.  Midnite says to put the breaker (+) on the PV (+) from the string.  This is how you would do it if the purpose of the breaker is to be a switch for each string.

However, the purpose of the breaker (according to NEC) is to protect against overcurrent flowing backwards through a PV string.  In that case the breaker should have its (+) side connected to the common (combined) bus bar.

This has been brought up before on this and other forums, but has never (in my opinion) been addressed in a satisfactory way.  A good discussion is here:  http://midniteforum.com/index.php?topic=17.msg696#msg696

--vtMaps

[zoneblue]

Interesting read. Ive pondered this issue from time to time, and ended up wiggling around it here because my string fuse spec is 20A. (Isc*(n-1) = 17A).

"string shorts are extremely rare". Thats my sense, that the issue isnt ever tested very much if at all. Those "shorted string" grid tie array fires you see, are possibly caused by the high string voltages involved.

But the thing worth noting from that thread is around shutting the classic output breaker off under load. For that reason i recently changed the din classic breaker to a carling panel mount, which i understand to be less polarity sensitive.  They are labelled line and load, but the distributer here said that they werent polarised. Is that right?

But before swapping the 60A CBI out, it was regularly switched under load, with no obvious issues.  Conclusion? that the rare pv string breaker trip should trip just fine, despite its orientation. OTOH.. if youre running 120V strings, this could be worth further inspection.

[SgtPepper]

Thanks for the replies guys.


@ vtmaps: Yes i'm breakering both (+) & (-), & Yes that is my understanding, the string fuses are to protect an overcurrent flowing backwards, so, correct me if i'm wrong please, the (+) side of each string breaker should be pointing towards the panels??

[vtmaps]

Yes that is my understanding, the string fuses are to protect an overcurrent flowing backwards, so, correct me if i'm wrong please, the (+) side of each string breaker should be pointing towards the panels??

Although it doesn't make sense (to me), I suggest you do what I did with my Midnite combiner:  Follow the instructions.  These things are designed and listed to work as shown in the instructions. 

So the (+) side of the breaker is connected directly to the PV (+) from the string.  The (-) side of the breaker is connected to the (+) buss where all of the strings are combined.

--vtMaps