Four 12V 150watt mono crystalline panels. Parallel vs. Series-parallel vs. Series?

Hey guys, just when I thought I might have the most efficient setup possible, I've come across the fact that you can actually run an MPPT controller ~12V. I have a 48V 30amp EPEVER MPPT solar charge controller with custom paramaters for my 12V 200ah diy lifepo4 battery.

Now I live in an area that has a lot of cloudy days, but the solar rack almost never has shade and is facing directly up at the sky with an air gap underneath to keep the panels cool under full sun. I normally get 16amps on cloudy days and as much as 25 amps on sunny days without even cleaning the panels. They're currently in series-parallel configuration but the wiring was originally rated for a full parallel setup.

Now I'm curious if the MPPT controller is rated for 30amps at 48V, would it be able to handle all the panels in parallel at 600watts peak? Or is my math wrong?

If it is possible, would parallel be preferable over series-parallel? Do you think I would see greater than 400watts under full sun?

I suppose I might be too wishful here... I'm assuming the MPPT amperage rating advertised is the maximum output on the battery terminals of the solar charge controller... So in that case series-parallel would be the most optimal I think.

But... If I switched to a 60amp mppt controller... Curious if that would achieve that greater 400watt+ charge...

OK after more thinking... My guess is that this is a worthy upgrade:

Renogy 12V 50A DC to DC Battery Charger with MPPT, On-Board Battery for Gel, AGM, Flooded and Lithium Batteries, Using Multi-Stage Charging, Solar Panel and Alternator https://a.co/d/dX3bYpv

If I ditch my 48V 30amp epever MPPT controller and 20amp renogy dc-dc charger, I could get this all-in-one and parallel my panels to get a maximum of 50amps from both the solar & alternator (at elevated idle)

I only wish there were a 60amp model.

But I think this would be Superior in shade and full sun since my battery is 12V and my 12V panels produce at a minimum ~14V even under shade...

What I'm confused about... Is if 300 watts at 24-32V has better low-light effiency over 600 watts at 12-18V. I would assume the higher voltage can achieve higher efficiency as long as half of the panel that is in series isn't shaded or blocked from the low-light.

OK here's what I'm going to do:

Since over-paneling is an issue for some SCC's without confirmation on which ones can be over-paneled, I'm playing it safe by installing an automatic-reset circuit breaker on the PV side of my circuit and going full parallel.

I'll still be limited to the 30amps of the epever SCC, but I'll get more amps under low light and shady conditions vs. Series-parallel, and still retain the maximum amperage.

The circuit breaker will trip if the SCC ever tries to short the inputs during a fault, preventing an overload of the crowbar-type shunt inside that's most likely rated for only 1.25x the maximum amperage of the SCC's output of 30amps.

This will also protect from lightning surges or other short circuit events, and prevent SCC runaway on the battery and BMS, but I'm also limiting the charge current to the BMS with a high current relay just to be extra safe.

Then all I have to do is install a bigger SCC later when I'm ready for more amps

Edit:nvm

Basically, under zero-shade conditions, my educated guess is that this is why series-parallel can be advantageous with 12-18V solar panels.

I drew a simple graph to demonstrate:

(red is parallel at max 600watts, green is series-parallel at max 300 watts) 4 150watt 12V panels

So with a 50amp MPPT controller, you could achieve both parts of this graph by automating the config based on light conditions with something like a raspberry pi.

Actually, to simplify it even more I could build the script around the idea of the graph based on voltage alone, since I just want to make use of the peak red output.

OK, stop. Take a breather. Grab a drink and sit down. You're getting yourself all sorts of confuzeled here.

What battery voltage are you running? That's going to determine everything.

600w / 12v = 50a SCC
600w / 24v = 25a SCC, you're perfect. No overpaneling happening.
600w / 48v = 12.5a SCC. You're not even half way there.

TheAlmightyOgreLord said:

I normally get 16amps on cloudy days and as much as 25 amps on sunny days without even cleaning the panels.

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This makes me think you're running a 12v system, so swap out your 30a SCC for a 60a and leave everything else alone. Your SCC can do 30a so if the highest you're seeing is 25 you've still got a little headroom left and you're only getting about 50% of your panels ability for some other reason. With 600w on a 12v setup you should be maxxing out your SCC hard. You're going to want to do some troubleshooting on those panels because I suspect you're only getting one of your strings actually doing anything.

TheAlmightyOgreLord said:

Now I'm curious if the MPPT controller is rated for 30amps at 48V, would it be able to handle all the panels in parallel at 600watts peak? Or is my math wrong?

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If your SCC is rated for 30a and 48v, that means it can provide up to 30a of OUTPUT power to the batteries, and will work with a 12v, 24v, OR 48v based system, or:
30a * 15v (12v charging voltage) = 450w max usable panels
30a * 30v (24v charging voltage) = 900w max usable panels
30a * 60v (48v charging voltage) = 1800w max usable panels

So, like I said, stop and grab a drink, you've gone down a math rabbit hole because of a math error.

Yeah I came back here to just admit defeat and not embarrass myself, but it appears I already did the latter lolol...

Math was wrong. You're right. Either way I'm always generating max 600watts with the higher voltage (V x A = W)

I've changed up my plans, but since I am indeed already overloading the 30amp MPPT with a potential 50amp PV charge, I'm still installing a 48V 15amp auto reset circuit breaker (~720watts capacity) and wiring the entire string of panels in series to get 72V max. The 30amp mppt I have is confirmed to handle up to 100V, so this should be optimal since shading isn't an issue and the panels are facing directly up at the sky.

I'll also halve the amount of wiring going through the roof this way and make up for voltage losses under diffused radiation.

As far as the SCC... I think the reason why I only see a maximum of 30amps output @ battery voltage (my battery is a 12v 200ah) is because the 30amp rating is it's maximum output. So yeah I've been overloading it lol... But it hasn't burned up yet! And it doesn't get super hot either... But you might have a point about the troubleshooting of the panels. They're all visibly fine, a bit dirty from not being cleaned for 6 months. As I wire them in series I'll do some readings at the MC4 connectors with my multimeter.

SCC is an epever 30amp tracer BTW, the first model without the LCD display and rs485 data connector (needed custom tuning for lifepo4). Everywhere online it says 100V input maximum, 30amp input and 30amp charge output. From my deep research, the 30amp input rating is due to the crowbar-type breaker built in to the SCC for surge currents, some sources confirmed they can only handle + or - 15% of the rated input amperage. What I have trouble finding is if the 30amp output rating is for 12 or 24V?

Thank you for chiming in friend

TheAlmightyOgreLord said:

What I have trouble finding is if the 30amp output rating is for 12 or 24V?

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Yes, the 30a rating is regardless of what voltage you're running at, so you can get 12v @ 30a, or 24v @ 30a, or even 48v @ 30a. The output rating doesn't change.

TheAlmightyOgreLord said:

wiring the entire string of panels in series to get 72V max.

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You should see more than that from 4x panels without the SCC drawing a load, in bright sun you should be seeing somewhere around 88v.

Rednecktek said:

Yes, the 30a rating is regardless of what voltage you're running at, so you can get 12v @ 30a, or 24v @ 30a, or even 48v @ 30a. The output rating doesn't change.


You should see more than that from 4x panels without the SCC drawing a load, in bright sun you should be seeing somewhere around 88v.

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Thank you for that info, I'm looking forward to my readings under diffused sun with them all in series since on a cloudy day I'm only seeing 14V at 8.3amps (sun at a ~70° angle) from all 4 panels in series-parallel.

20-ish volts is what you should see per panel in sunlight, trying to do troubleshooting in the clouds doesn't work very well. I'm assuming you're reading this at the wires with a multimeter and NOT on the EPEver screen? EPEver has a known issue where it likes to lock up at lower voltage in the morning and just refuse to change that, so your charging is really nerfed. I've replaced all my EPEvers because of this issue.

For a 2s2p setup you Should be seeing about 40-44v per string and about 16a under load charging the battery. Under load the strings should drop down to about 36-ish volts per string and 16-ish amps in total, or 576-600w trying to come into the SCC. The SCC being only capable of outputting 30a cuts that down to 14.5-ish volts and 30a output (an SCC is basically a DC-DC converter after all) so only 435-ish watts can actually get into the battery.

I still say get yourself a decent 60a SCC and chuck that 30a EPEver. You don't need to sell a kidney for something in blue, but an HQST or Rich Solar would utilize all the panel you have and still not worry about cooking the SCC or leaving anything on the table.

My readings were initially from the epever screen, then I used my multimeter at the junction (busbar) to verify the reading is indeed accurate. The only inaccuracies I've experienced overall with this specific controller is the battery percentage reading, but it doesn't matter to me much since I have a low voltage cutoff relay set for 12.6V that has a bright red digital display I can glance at when needed.

That sounds about right for 2s2p. I think the solar panels are really dirty... And the mc4 connectors could use some cleaning out. Just disconnecting the main positive 8guage mc4 junction and reconnecting it brought the series-parallel array back up to 38V 8.6amps under mixed clouds/sun (kinda like witcher 3 weather lol)

I'm going to clean out out the mc4 connectors after sundown with CRC electronic cleaner, and I have a pair of two 12guage mc4 extension cables to make the whole string in series... Didn't quite reach far enough when I went up there to reconfigure it.

Since all 4 panels are placed next to each other in one line as if they're one large panel, they're very likely to always be under equal shading conditions... I live in an area where 70% of the year we get that stormy witcher 3 weather... So raising the voltage I think I'll see good results.

I read somewhere else on this forum that the MPPT algorithm is useless anywhere from 14-18V and really only shows efficiency in the higher voltage ranges... Also mentions that due to that, most cheaper MPPT controllers (like my first model epever) have a basic PWM mode that is used in that lower voltage range to try and squeeze what little it can.

You're right about the 60amp upgrade though... That's my plan. I'm just curious to see what I can squeeze out of this charge controller before I make the jump to 60amps... I've had the thing for 4+ years now it hasn't failed me yet. It just doesn't like the lower voltage ranges.

I'll write down those models you recommend. Thank you!

Even though its close to the maximum... What do you think about this controller?

VEVOR 50A MPPT Solar Charge Controller, 12V / 24V Auto DC Input, Solar Panel Regulator Charger with Bluetooth Module, 98% Charging Efficiency for Sealed(AGM), Gel, Flooded and Lithium Battery Charging https://a.co/d/4BK4BAs

I just had a weird idea... Is there any reason not to just cheap out for simplicity sake and install a small jumper wire at the solar panel junction to put both parallel strings in series instead of reconfiguring the whole solar rack?

Kind of like this. I worded it the wrong way, but disconnecting the + and - of the two strings and joining them together with a junction connector like a bolt and nut secured away... Then leaving the last pair of + and - as the main feed. This would open up the ability to switch back to 2s2p from 4s using a switch (pardon my awful drawing skills)

TheAlmightyOgreLord said:

I just had a weird idea... Is there any reason not to just cheap out for simplicity sake and install a small jumper wire at the solar panel junction to put both parallel strings in series instead of reconfiguring the whole solar rack?

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Don't. EPEver's are notorious for getting stuck at lower voltage at sunup and getting stuck there. Get any brand other than EPEver (I prefer HQST or Rich Solar for value) and get more amperage (that Vevor should be fine) and leave the panels alone other than cleaning them.

Rednecktek said:

Don't. EPEver's are notorious for getting stuck at lower voltage at sunup and getting stuck there. Get any brand other than EPEver (I prefer HQST or Rich Solar for value) and get more amperage (that Vevor should be fine) and leave the panels alone other than cleaning them.

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yep, I had to get rid of mine. They would get stuck at battery voltage sun up and also when a cloud would go by! I ended up going Victron.