Why am I not seeing 700-800Watts coming into the charge controller from my solar panels?

Question

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rbertino asked Sep 28, '23

Why am I not seeing 700-800Watts coming into the charge controller from my solar panels?

Setup

100/20 MPPT Victron CC.

Four 250 W Solar used Canadian Panels. all clean tested at 33v / panel out of poss 38V.

Panels wired in series / parallel so not to exceed amps

3 Odyssey 12V AGMs in series

Question/Concern

I'm only getting 275W at peak sun with clean panels,

Following a post by snoobler, https://community.victronenergy.com/questions/111676/getting-very-low-watts-from-charge-controller.html?childToView=111685#comment-111685

would like to just confirm if my CC is limited on charging power coming in based on amp x current battery voltage?

so if current battery voltage is 13, then 13*20 = 260W would be the max allowable power through this CC?

I have an additional 100/20 MPPT Victron CC, 3 AGMs and 4 panels. Is one solution to set up a facsimile and simply distribute the load or is there a different / better alternative?

2nd question:

Also, I spoke with battery tech support at Enersys regarding my Odyssey 12V AGM31 and he had me set the low cutoff at 11.1, suggesting these deep cell batteries like to be discharged to low levels. from what I'm reading on this forum, the cutoff should be like 12.05 or higher??

thanks for the help here.

charge current limit

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Modifications Space

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Answer 1 · 2023-09-29T03:27:10Z

kevgermany answered · Sep 29, 2023 at 03:27 AM

On the first question, yes the output current limit of the controller will restrict power. Your calc is not correct for batteries in series. Use the serial voltage. E.g. 39V in your example. Be aware that SOC of the batteries and light levels will also affect output.

On the second question, usual advice is to follow maker's instructions. Failing that max discharge of 50%. It's a trade off to minimise battery cost. The lower the voltage you discharge to, the shorter the service life/number of discharge cycles. It would be interesting to see the expected discharge cycles to this level compared to 50%. Time before recharge also has a big effect.

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rbertino commented · Sep 29, 2023 at 10:30 PM

yes, my bad (rookie) they are in parallel to keep at 12V. Thanks for the confirm. I reduce from four panels to 2 today and at approx 12V they were producing 240W. I will add a second 100/20 Victron and 3 additional batteries (same exact AGMs). It appears I should limit discharge to approx 12.4 which is approx 50%

thank you for the comments and help here!

Feel free to comment on my reply to snoobler if you have any suggestions. thanks again

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Answer 2 · 2023-09-29T04:00:34Z

Matthias Lange - DE answered · Sep 29, 2023 at 04:00 AM

You wrote that the batteries are in series (to 36V) but on the picture is looks like they are in parallel (12V).

In that case you are limited to around 250-300W charging power.

You need a bigger MPPT or a second one.

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rbertino commented · Sep 29, 2023 at 10:29 PM

yes, my bad (rookie) they are in parallel to keep at 12V. Thanks for the confirm. I reduce from four panels to 2 today and at approx 12V they were producing 240W. I will add a second 100/20 Victron and 3 additional batteries (same exact AGMs)

thank you for the comments and help here!

Feel free to comment on my reply to snoobler if you have any suggestions. thanks again

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Answer 3 · 2023-09-29T04:30:10Z

snoobler answered · Sep 29, 2023 at 04:30 AM

290W @ 12V (20A * 14.5V):

Those are about 110Ah batteries meaning they should be charged with about 11A max per battery in parallel (you said series, but they are in parallel), so the most you want to charge with is ~33A - that's about 2 of those panels on a controller that can handle > 33A.

Voltage cut offs are tricky. The voltages that reference to % charge are always for RESTING voltage, i.e., a battery that hasn't been charged or discharged for 10-24 hours depending on specification. If you cut a battery off at 12.05V while under load, the battery voltage will rebound. If the goal is to limit the battery to 50% discharge, the best thing is to get a BMV/Smartshunt programmed for 330Ah and then figure out where your voltage is when it reads 50% - use that as a cut off.

IMHO, best option would be to add a 4th battery, add the second 100/20 and put two panels on each 100/20 yielding 40A of charging against 440Ah of capacity.

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rbertino commented · Sep 29, 2023 at 11:41 PM

Thank you.

See current panel wiring below but have now reduced to 2 panels and still getting 240W when batteries read 12Vh. I'm starting to get this stuff - maybe.

My plan is to do as you suggest and remove the 3rd battery and connect it to the fourth with a second CC.

Question: I recently purchased another 100/20 from amazon and still have time to replace. should I get the 100/30 to increase power coming in to approx 360W?

See panel specs below to see if you suggest any different setup. They are used panels so I’m assuming I’ll get approx 200W or 20% less than stated. I am getting 33V per panel.

Regarding the smartshunt, victron appears to be $130. do/can you recommend an alternative at a lower price or should I stick with Vectron so it communicates efficiently.

Thanks again for all your help. Tremendously appreciated.

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