Solar Panel Questions

[WStayton]

Hi All!

  I getting ready to order my Solar Panels - and, no surprise, I am looking at the bottom right for the price as well as the performance of the panels.]

  Right now, Sun Electric in Miami, Fl, is offering their model SV-T-200 HV for $1.34 per watt or $268 per panel.  I have, tentatively, settled upon ordering these units.

  First the specs:

   Power (W)                         200 Watts   
   Open Circuit Voltage (V)        33.20 Voc   
   Short Circuit Current (A)         8.25 Isc   
   Maximum Power Voltage (V)        27.50 Vmp   
   Maximum Power Current (A)          7.28 Imp

  I'm wrestling with exactly how many panels to get and exactly how to wire them up.  As I see it, I have a choice of:

  Sixteen each panels wired in eight sets of two panels per set, in series.

  OR

  Eighteen each panels wired in six sets of three per set, in series.

  Eighteen panels is the max that I have enough real estate to deploy on the South face of my dwelling roof.

  The Xantrex XW Solar Charge Controller is ordered and paid for, but has yet to be delivered but I BELIEVE that the unit will be happy with any voltage between Voc equal or greater than battery voltage and less than 120 VAC.

  If I put two panels in series, I will have Voc of 2 * 33.20 = 66.4 volts.

  If I put three panels in series, I will have Voc of 3 * 33.20 = 99.6 volts.

  Questions:

1) Is there any advantage/disadvantage to either configuration other than I will have two panels more of current in the 3 x 6 = 18 panels configuration.

2) Is the gradual degradation of the panels over time a matter of concern in the 2 x 6 configuration, in that it MIGHT let the Voc get below the battery charging voltage of 54 volts, ultimately?  With the max current voltage = 27.50 Volts, which is VERY close to the required Voc of 54, but I don't understand why/how they specify the Voc as the required voltage and not the Vmc - can anybody explain that anomaly to me???

  I suppose i ought to wait until the XW Charge Controller gets here so I can read the book and make a more intelligent decision BUT I have sat with my finger in my butt two times before when a VERY good deal popped up and by the time I got around to doing something about it, the deal was no longer available, so I am determined not to have that happen to me yet again, already! <grin>

  Really, the right answer is probably to order eighteen of them and then if I don't use more than 16 for the house, I'll have a couple of panels to rig a coulple of lights in outbuildings, etc., and if I can't get a definative answer fairly soon, that is what I WILL do!

  So what do you EXPERTS say - 3 x 6 or 2 x 9?

   All input is hereby solicited.

Regardz,

Wayne Stayton

[LowGear]

Hi Wayne,

What does this inverter prefer to produce 120 / 240 for immediate usage?  Those batteries aren't always going to need charging?

Casey

[bschwartz]

3 x 6 is my vote.
Higher voltage and lower current allows smaller diameter wire to be used from the combiner box to the charge controller.

[Thob]

I would put as many is series as possible to minimize the total current.  This will give you the minimum loss in the wires from the panels to the charge controller.  In other words, I vote for 3 * 6, assuming that fits within all the limitations of the charge controller.

[LowGear]

Hi Wayne,

I don't mean to be cheekie but you know I'm chasing this same inverter to determine if it can convert my generator power to grid tie in real time.  So I have gone over to a Xantrex seller and pulled the spec sheet for the XW6048:
http://store.oynot.com/xaxw48vin1.html

It seems to want 44 to 64 volts DC input.  Is the charger looking for or at a different input voltage?

Casey

[WStayton]

LowGear:

  "What does this inverter prefer to produce 120 / 240 for immediate usage?  Those batteries aren't always going to need charging?"

  I am not sure that I understand the question, but . . . what's new!!!  <grin>

  Between the Charge Controller and the inverter/charger, the "system" looks at what is neccessary - so if you are using DC to make AC, it diverts the output from the soloar panels to inverting. If their is no demand for DC for consumption, or if there is more output from the solar panels than is required for the DC to AC demand it uses the Solar output to charge the batteries, IF CHARGING IS REQUIRED.  If the batteries are "full", I THINK that it then looks at selling the surplus, inverted solar power back to the net.

  All of these functions are infinitely tweakable if you are smart enough to do it and industrias engoug to do it.

  I also THINK that if there is no AC demand, the batteries are "full" and you are not selling power to the net, it will just present an open circuit to the solar panels.


   "It seems to want 44 to 64 volts DC input.  Is the charger looking for or at a different input voltage?"

  The installation manual says:  " The Xantrex XW SCC maximum power point tracking algorithm maximizes the output energy of PV arrays as long as  the operating voltage is within the MPPT operational window.  Ensure that the PV array used in the system operates within the MPPT operational window. . . . "

  The Installation manual then goes on to give a table where it tells you that if the Voc is between 120 Vdc and 140 Vdc the SCC reduces the output current to "limit protect" the unit from Voltage Spikes.  It then say if Vmpp or Voc are more than 140 Vdc it shuts down the unit.

  It also say Voc < Vbatt = SCC not operating
   and  Vmpp < Vbatt  = normal SCC operation
   and Vmpp < Vbat to 120 Vdc = Maximum harvest of solar energy

  The inverter/charger itself is looking for a Vdc between 46 Vdc (low batt cut out) and 70 Vdc (high batt cut out) but the SCC would seem to manage and panel input between Vbatt and 120 Vdc to give the batteries what they want/need.

  The input Vdc in the surce you sited DOES NOT agree with the manual from Xantrex by a couple of volts, so beware of what you read on the net, it may not be applic able to the product shipped to you when/if you make a purchase.

  As I said, I do not have the SCC manual yet, so that is from what is said about the SCC in the inverter/charger manuals.

  All of that has a big "I THINK" in front of it!!!!

  I hope that answered the question(s), if not, more explanation on the question(s), please!

 
  About the 2 x 8 vs 3 x 6:

  I reached the same conclusion that everybody has voiced here - 3 x 6 is best due to wire size considerations and, I THINK, due to panel degradation considerations putting the output for 2 x 8 at/very-near the low voltage operating limit, where with 2 x 9, I am comforatbly within the limitws at all times.  With 4 panels in series, I wind up with a Voc that is above the 120Vdc taper off of the SCC, so I THINK that I am better off with 3 in series and thus avoid any hint of a Vdc overvoltage condition.

  Thanx for the input, everybody - it helps to just organize your thoughts enough to put them down on paper, and then, the opinions/discussion are icing on the cake!!

Regardz,

Wayne Stayton

[mike90045]

The XW MPPT 60A charge controller has a sizer tool, to plug in your PV panel model, and local temps.  As panels get cold, their output voltage increases to the point that on a cold morning, as the string of panels is lighting up, you can fry the controller.     140VDC max, sets an overvoltage flag, voids warranty, @ 150V it dies.
Sizer is at :http://www.se-renbu.com/support/xwsizing/Default_SE.aspx    Since the panel does not show in the choices, call sunelec and ask what the parent model was, these are rebranded from something.
  I hope, 3 PV's in series would be OK, be it depends on your low temps.  That will give the most efficient feed from the array.


The XW-6048 inverter/charger  only has AC inputs.  It's a honking powerful inverter (12KW surge for 10 sec) and it's internal charger runs from 240VAC    and can feed 100 amps into the batteries for charging.      No DC input for charging.    AC1 input is for grid (which I don't use) AC2 has relaxed Fq requirements, for generator 240VAC input   It supports many features, and has a nasty manual.  Also needs a $200 System Control Panel to get into its programming.

[LowGear]

Hi Wayne,

Actually I don't think that is Japanese or Chinese.  But it certainly isn't conversational English either.

So Wayne has his answer until the unit arrives but has or does anyone know of this unit being used to grid tie a diesel powered generator?

Casey

[Tom Reed]

The xw 60 amp charge controller will handle the output from about 2900 watts panels @ 48 vdc before you exceed the 60 amp output rating of the charger. So that would be about 14 panels. So you will need a 2nd controller and/or a larger controller to handle 18 panels.

Then you need to calculate the voltage increase from your lowest expected local temp and apply that to the 3 panel strings to see if this will exceed the input voltage rating of the controller (140 v).

[WStayton]

Hi All!

  Well, I called Sun Electronics and they said that they had an agreement with the manufacturer that, since they were selling what are technically "blem"s panels, not to divulge the manufacturer but that if I looked at just the model number I would be able to match it up!  Thanx a lot!

  So, I started down the list of panels in the Xantrex Calculator, checking every 200 watt panel to see if the specs matched.  At about panel # 37 or 38, I FINALLY matched up to a Sovello SV-T-200 panel.

  The calculator kicked out the following:

     Pmax @ STC             204.9 W    
     Pmax @ PTC             186 W     
     Vmp at Pmax              27.5 V    
     Imp at Pmax              7.28 A    
     Voc @ STC               33.2 V    
     Voltage change    -109 mV/C

  It also spit out:

    Voc at -10F                   110 Vdc
    Vmp min at cell temp 35C   68 VDC

  The latter two are for a three panel in series configuration.

  There was also a note that said:  "Note: For installations in compliance with National Electric Code (NEC), the maximum array Isc should not exceed 48Amps."  I think that this limits me to four strings of three panels, since anything that I hook to NYSEG will have to be in accordance with the NEC and with four strings I have             STC   2458 Wdc   44 Adc    
            PTC   2238 Wdc   40 Adc

   I THINK that this is only a problem in the winter, when the panels are cold, and in the summer when they are hot I would think that I would have lots of room, but I'm not sure if NYSEG will let me have the panels there and then hook them up or not depending on the month of the year - probably not!

  For the cases of five and six strings, it says only that the Charge Controller will regulate them to a max of 60 amps-dc - no notes not to do it, other than the note about NEC requirements.

  I can't really see investing in a second Solar Charge Controller to control two strings of three panels each, so I guess that the 18 panels I ordered is overkill by six (!) panels - I can see having two or three for use on outbuildings, but six is definately "wretched excess".

  I have thought about trying to squeeze a third row of panels on to the roof, which would allow me to have a max of 27 panels, and 24 would fully populate TWO Solar Charge Controller's, however, at 18 panels I am already up to a shade over five grand with the shipping and my piggy bank isn't bottomless!  <grin>  So, I guess I will have to cancel a few panels - maybe cut back to the 12 that one controller will handle and an additional 3 for use on outbuildings, for a total of 15, instead of the 18, as originally ordered.

  Seeing that footnote about NEC requirements WAS an eye-opener!  <smile>

  Anyhow, thanx for the handholding - you AGAIN have kept me from doing something financially dumb!

Regardz,

Wayne Stayton

[mike90045]

Yeah, the bit about the NEC forcing a de-rate on the charge controller is lame.  It's certified to run at 60A, and will limit itself to it's safe zone (temp & amps) but NEC copied and pasted their generic de-rate clause 
So at -10, it's only 110V output, I wonder if you tried 4 in series, what that comes up to at -10?

Outback has the 80A controller,
Midnight Classic 150  http://www.solar-electric.com/mnclassic.html  is 96 amps, and with the "hyperVOC" it will take 198V on the input (w 48V battery bank)  That may be the ticket.

[WStayton]

mike90045:

  The only problem with using the OutBack, or any other equipment except Xantrex, is that nothing else communicates on the XanBus to let everything know what everybody is doing with which and to whom!  <grin>

  I'm sorta reluctant to give up the XanBus capability if I can work around it . . .

About using a four battery "string":

   I don't think that will work, since the STP max voltage is 33.xxx , 110 + 33 Plus .1*40C, is more than than 140 V and painfully close to 150 V.  I think that it would gaurantee a problem in cold weather - the Xantrex website won't even consider giving you the data for four panel strings of this panel, so I THINK that means they don't recommend it.  And, I would rather NOT have a failure that has to be repaired on my nickel!  <grin>

  Regardz,

Wayne Stayton

[mike90045]

All the xanbus does, is possibly share the BTS sensor data (I've heard both ways, it does and doesn't) and co-ordinate the recharge from multiple sources (genset & MPPT charge controller).
Since genset will / should only run when batteries are really low, the inverter/charger will be a full programmed rate for your bank.  And if your are burning genset fuel, it's assumed you have little sun     The Midnight Classic MPPT has it's own 3 stage system, and if it senses the genset has brought the battery up, it throttles back.

I'd not let the perception that one brand is better then several, because I've got a mixed system and it's just fine.   And you save needing to buy and wire 2 controllers.  (well, you save some, because the Classic does cost more) You loose a bit because you loose the redundancy of 2 separate charge controllers.  If you have a monitoring system already configured, and reliant on the xanbus, I guess that's a vote to stick with the one brand.

[WStayton]

mike90045:

  About the Xantrex XW6048:

  Doesn't the Inverter/charger use the Xanbus to communicate with/through the the XW solar charge controller to charge the batteries from its (i.e. the Inverter/Charger's) battery charger???

  I had thought that if I put something other than a Xantrex charge controller in the system, the Inverter/Charger would just default to some "safe" charger algorithm and you wouldn't have access to the various "flavors"/varietes of charging programs???

  Or am I again laboring under a misconception?


About the MidNite Solar Classic 150 MPPT Charge Controller:

  When I look at the site you posted, I find:

Model Number   150   200   250   250KS   
Op Volts Input   150VDC 200VDC   250VDC   250VDC   
Bat Chg Volts   12-93 Volts   12-93 Volts   12-93 Volts   12-150    
Max Current O/P
at 25°C (77°F)   96A @ 12V   74A @ 12V   60A @ 12V   40A @ 120V   
                          94A @ 24V   70A @ 24V   62A @ 24V   
                          83A @ 48V   65A @ 48V   55A @ 48V   
De-rated Current
at 40°C (104°F)   80 Amps   66 Amps   52 Amps   33 A
   
Environment   -40°C to 40°C (-40°F to 104°F)   

   And you say:  "Midnight Classic 150  http://www.solar-electric.com/mnclassic.html  is 96 amps, and with the "hyperVOC" it will take 198V on the input (w 48V battery bank)"

  Where did the 198V input come from???  The 96A/80A unit shows  150 V for the max input in the chart above . . . It LOOKS, to me, like the only way you can get to a higher input voltage is to use one of the smaller current versions of the unit, no???


  So, if I put the Midnight unit in the mix and just wire the Xantrex Inverter/Charger as though it wasn't there, from a data standpoint, what will the Xanterex do for Generator/Line Charging?  Does it care that you don't have a Xantrex Solar Charger in the path???  Will the Inverter/Charger still let you taylor the charging functions to your particular battery bank?

   If the Midnight will allow the Xantrex Inverter/Charger to perform all of its functions, despite not being able to communicate with the Solar Charger, I THINK I am willing to spend the $100+ extra for the Midnight instead of a Xantrex solar charger.

  You seem to be good at turning things upside down - a least for a simple mind like mine!  <grin>

  I await you response!

  Thanx for the input, BTW - its good to have an EE looking at what our doing so you don't do something stupid!!!! <smile>

Regardz,

Wayne Stayton

[Tom Reed]

Wayne, These components are built to be fairly modular. The inverter/charger will only charge from utility or generator power. It is triggered off of battery voltage, hence if the solar can't keep the voltage up and there is no utility power the generator is started to correct the low battery condition. The key to making all these items work nicely together is the calibration of the different components internal voltage meters and proper settings in the components. As long as the components don't all require separate programmers mix and match can work. You will need 2 different temp sensors on the batteries for the 2 different chargers though.