Adding panels to existing arrays

[jramerman]

Hi, I have 2 x PV arrays, each consisting of 3 x Trina 260W panels & a midnight classic 150 controller. At the moment I have 6 x deep cycle 100 Amp AGM batteries configured in series & parallel for 24V system. I did have 8 batteries but have removed 2 as they were not holding charge.

I would like to add 1 more panel per array and then add back in 2 batteries. I figure that maybe the 6 panels are not sufficient to charge all 8 batteries.

Is this feasible?

I am based in South Australia and am off-grid.

Johan Ramerman

[jramerman]

Just checked a few things about the Classic 150, particularly HyperVoc. If I have understood it correctly, I could not add more panels in this configuration. My panels have a Voc of 38.2. Correction Factor for my area is 1.14 (-6 to -10 degrees Celcius). So this means a voltage of 130.64 which is within the Classic 150 Mac Input Voltage. 4 panels would put it over the top.

So, I guess I need to review my setup and learn what I have to do.

[jramerman]

Adding to my query posted above;

having used the Classic Sizing Tool, it looks that I could create 4 x parallel strings of 2 panels in series and stay within the Maximum Input Voltage for the Classic 150. This configuration also seems to provide higher battery charging current, 25% (roughly) more PV array power. This would then allow me to add a couple more batteries.

Do I have all that correct?

[ClassicCrazy]

The Classic sizing tool is your best resource . But yeah putting the PV in lower voltage series and more in parallel is better idea since it will be closer to the battery voltage and the Classic will work more efficiently - less heat created to drop PV voltage to battery voltage.

Your battery situation seems to be the bigger concern.  If you don't have the wiring balanced that batteries might not be sharing the charge and loads evenly leading to some cells failing prematurely.  Also it is not a good idea to mix new and old batteries.  Ideally you would have all the batteries the same manufacturer and production age.

How far down are you discharging your batteries ?  Are you using Whizbang and ending amps to terminate the Absorb cycle ?

You can use this as reference for wiring your batteries.
http://www.smartgauge.co.uk/batt_con.html

Larry

[jramerman]

Thank you Larry for your reply. Much appreciated.

Just to clarify my 1st post, it was only 2 batteries not holding charge. They were older than the rest. The remaining 6 batteries are OK, and since I removed the 2 "bad" ones, the batteries charge to 100% quicker and holding the charge better. Sorry I don't know all the technical terminology. The remaining batteries are same manufacturer (Hard Core) but there is about 6 months difference in age. Unfortunately I don't have the funds to start afresh with batteries. I have a saving plan in place but I am also trying to get my head around the "best" batteries to get.

I will be changing the PV configuration to that which I propose as soon as I can, particularly in view of your reply "...putting the PV in lower voltage series and more in parallel is a better idea...".

Thanks for the reference to Smart Gauge. I did review that site when I re-did my off-grid system and have cabled up according to the 2nd method, but intend to do the "best" method ASAP.

I watch the battery discharge closely with 66% having been the worst I've had them drop down to. I usually power down the system if it gets to 70%. Not sure how to do that automatically though. I have a Whizbang Jnr in the setup, also have the battery temp cable attached and I have reviewed the various settings like absorb and EQ etc as per the manuals and battery specs, but again, I still have a lot to learn there.

My new solar system (set-up August 2017) appears to work somewhat OK (well to me at least with my limited knowledge), but I have no doubt that I can do a lot of tweaks on it to get the best out of it.

My finances are a bit limited though, which has meant I have not been able to do best practice in everything.

Again, thanks for your reply, I really appreciate it.

Regards

Johan Ramerman

[Vic]

Hi Johan,   nice to see you on the Forum.

A couple of things;

You may have a PV Combiner in use on this system,   but you have not mentioned it.   If you are not using one,  it is really needed for safety.   This is a Link to a US supplier,   just for reference.  You generally would want a Combiner that is rated for 150 VDC,   and use circuit breakers in it:

https://www.solar-electric.com/mnpv6.html

As an aside,   AGM batteries connected in parallel can be difficult to manage,  when used in off-grid systems.  AGMs  have a very low impedance.  This often means,  that one of the parallel strings can hog much of the charge and discharge current,   resulting in imbalances.  These imbalances can worsen with continued use.

And,  with off-grid systems   the charge time is limited by sun availability.

With AGMs that are used as a Grid Backup (on almost perpetual Float charge),   strings that are hogging current become fully-charged (often after many hours),   allowing the next most-needy string to get its full-charge,   and so on.

And,  obviously,   the inability to measure the SGs of AGM cells means that it is very difficult to determine actual SOC,   and adjust charge parameters,   based upon these measurements.   AND,   setting WbJr battery parameters cannot be based upon measured SGs,   etc.

Just FYI,   Vic

[jramerman]

Hi Vic,

Thanks for your response.  I have a rated combiner with 2 breakers in the system. I will update that if I add the additional strings.

Regards

Johan