System Upgrade Advice

[SM-Viper]

Hello all!

Sorry for the long read.  I am working on a design to expand my current off grid solar system and could use some advise.  Currently, I have two 100w panels in series on the roof of my garage for 200w. These panels are charging (2) 6v 215AH lead acid GC batteries in series for 12v via Kid CC.  I have WBJ and all associated breakers connected. The total distance from inverter to batteries is 6ft using 2/0 wire.  The distance from PV array to cc is no more than 30ft one way.

I works fine now, however, I recently got a fantastic deal on (4) 245w Solar World 60 cell panels that I couldn't pass up.  Now I would like to rack them on the roof and connect them to my existing system.  I know, it's a small system, but my plan is to convert the whole 12v system to 24v by replacing the 12v 2000w inverter with a 24v 600-1000w inverter, and get four of the same batteries and put them in series.  The system will be used for off grid lighting, emergency backup, and other projects.

My intention is to place these new panels on the roof in a 2x2 series-parallel array.  I have a Soladeck combiner/pass-thru with (2) 15A fuses that can either use this as a combiner box, or pass-thru.  I plan to use 6GA wire from the PV array to the DC Disconnect box.  The only problem with that is not being able to easily access or shut down the strings individually.  This may not be a problem if I can use both of these strings at full power with my existing system until I'm able to upgrade it to 24v.  It's mid summer here in Ohio, and I'd like to get this done before winter.

My questions are:

1.) Can I use these new panels in 2x2 series-parallel with my existing 12v system without overpowering the Kid cc and any other part of the system?

2.) Should I use the Soladeck as a combiner box with the existing fuses I have, or use it as a pass-thru to a separate combiner box that is more accessible?

3.) I plan to drive a ground rod and connect it directly to the DC Disconnect box, and connect a ground wire from the PV array to that point to ground the panels.  It that right?

Here are some useful links:

http://www.rstcenterprises.com/soladeck/products/

http://pdf.wholesalesolar.com/module%20pdf%20folder/SW245datasheet.pdf?_ga=1.228215198.2021096968.1430238672

http://www.renogy-store.com/100W-12V-Monocrystalline-Solar-Panel-p/rng-100d.htm

Any advise or help with this project would be greatly appreciated!
Thanks!

-Sean

[Vic]

Hi Sean,

Seems that the Solarworld PVs have a Vmp of about 30.8 V  (or a bit lower if they happen to be the Multicrystals)  ,  and the Renogy 100d PVs have a string Vmp of about 37.8 V.   This difference it too large to run one SW 245 in parallel with two Renogy 100s.

And,  the  KID is  30 A maximum output CC.  Running even four of the SW 245s  on a 12 V system would really require a CC with 60,  or more Amp output capability.   Four of the SW 245s on a 24 V battery system would be about Max.  It is OK to over-PV the KID,  but running about twice the rated capability of the KID would waste a lot of power much of the time.

Here is a Link to the KID String Sizer:
http://www.midnitesolar.com/sizingTool_kid/index.php

More Later,   FWIW,  Vic

[SM-Viper]

Thanks Vic,

I forgot to mention that I want to replace the existing Renogy 100w panels in the system. They will not be in the new system.  Also, i was thinking (correct me if im wrong), that if I have two stings into a combiner with two breakers, (one for each string of course), that I could just shut one of the strings down and only run on one string until im able to upgrade the inverter and the batteries at a later time.

How doable would this be?

-Sean

[Vic]

OK Sean on not using the Renogy PVs.

It has been said here that the KID can withstand significant over-PVing.   Roughly doubling the max rated output current may be pushing it a bit ...

You could also shut off one string as you mentioned,   but this may not be necessary.


This is an in-transit day,  so this is a short reply.

Breakers are more convenient than are fuses.  You really should not connect/disconnect fuses that are carrying current.

Will let others cover the grounding thing ...  there are many variables here  --  it all depends.

Good Luck,  Later,  Vic

[Vic]

Hi Sean,

OK,  so your Soladeck Combiner on the roof should be fine,  as should those two 15 A fuses.  The cables that connect the Soladeck to your present CC should #14 AWG or larger.  So you could just leave  the Soladeck in place,  but it is not clear how you  will deal with the MC4 connectors on the PVs,  and if the run length from the Soladeck to the location of the CC,  you might want heavier gauge wire.

While it is always convenient to have circuit breakers for each PV string, generally, if there are fewer than three strings,  no overcurrent protection is required.

Two SW 245s per string with two strings should be fine,  and will also be appropriate for your switch to 24 V.

Almost never give any advice on Grounding.   There are a number of different grounding systems,  and,  there are a number of variables.  Local custom also can affect on just how one wants to do the grounding.

The systems here need safety grounding,  Lightning Ground,  and Grounding for Emission reduction.

FWIW,   Vic

[SM-Viper]

Alright. I have decided to install the Soladeck as a pass thru from the panels on the roof to the combiner box in the garage. Then, I will shut down one string most of the time with my existing 12v system. Then, later, when I get the equipment to upgrade to 24v, I will switch on both strings all the time.

About the grounding, #8 copper wire from panel rack to combiner box to dc disconnect, to a ground rod outside.

Any issues with this?

Thanks!

[tecnodave]

SM-Viper,

I know the kid controllers can handle over panelling. I have been feeding two kids with a whopping 1980 watts between them and they self regulate to 30 amps, also they have current limiting based on temperature. I've had some really hot days here in California but 103 degree days and over paneling has not caused any problems. 18 months now.  They are pretty bullet proof.

I have really serious fog here sometimes so I over panel to get full charge thru the fog.

td