Author Topic: Self-protection in MPPT algorithm and over-paneling  (Read 453 times)

Llaves

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Self-protection in MPPT algorithm and over-paneling
« on: June 30, 2021, 11:45:24 AM »
Since panels typically operate below the STC Pmax, if one designs the system to keep the charge controller output current below the rated value when operating at STC Pmax, the system will typically be operating below, or even well below, it's rated continuous capability. Since the output power curve rises monotonically to the peak power, then falls monotonically, it would seem the search algorithm could stop if it reaches the rated output capacity of the charge controller before reaching the max power point. I was told by someone who seemed to be knowledgeable about MidNite Solar products that the Classic has this property - it will not blow itself up trying to output more current than it can handle. Is that true? I do understand that transients, such as the sun coming out from behind a cloud, will drive the output over the limit until the MPPT algorithm can react, but hopefully the reaction time to the transient is short enough to be survivable. As panels get cheaper and cheaper compared to the balance of the system, it becomes cost effective to have enough panels to drive the charge controller at max output more of the time, even if that means "wasting" some input capacity during peak times.

To make this concrete - ideally I'd like to connect 5kW (STC) of bi-facial panels to a Classic SL-150 charging  nominal 48V LiFePO4 batteries. At STC that would be right at the limit. However, on a clear cold winter day with snow on the ground the system might well produce 5-10% (or more?) over STC. (I've seen a few percent over STC in these conditions with my now-ancient BP160 panels.) Would the Classic survive this? Is this just a stupid design choice?

mahendra

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #1 on: June 30, 2021, 12:04:30 PM »
I think the classic input and output amps in menu's charge settings.
Main menu-charge-limits- enter and set to desired limits for output and input.
I don't think you can exceed voltage limits though.
1.5kw on Midnite classic 150(whizbang jr.) networked 0.660kw on classic lite 200 ,180ah CALB Lifepo4 48v battery bank,123SmartBMS bms(top balanced) Outback vfx3648

boB

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #2 on: June 30, 2021, 05:33:10 PM »

5 kW on a 48V system is probably not too badly  overrated.

I would worry maybe putting a 50 kW array on one Classic though  🙄

YMMV.

boB
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jimbo

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #3 on: July 31, 2021, 04:46:05 AM »
^^^What about on a 24v system? Our winters are very cloudy and production can be extremely low.

boB

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #4 on: August 01, 2021, 02:07:08 AM »
^^^What about on a 24v system? Our winters are very cloudy and production can be extremely low.

It's pretty much how much you want to over-panel the system.  24V system can have twice the power of a 12V system and half that of a 48V system given the same battery current...

How many watts of panels are you thinking of putting on there ?  Yes, winter and cloudy weather can sure be over-paneled quite a bit.

And how low of temperatures there in the winter ?  One thing for cold weather is that the panels will run at a higher voltage so you want to make sure it will be under the PV rating of the controller.

But for a 24V system, I  would think that something like 3kW of panels might be OK. Maybe even a bit higher.

  If you were using a Classic 150 say, I would wire the PV array at a lower voltage, say maybe near 100 volts (ish)  Voc  or 48V nominal panel voltage.  That will help a bit for the Classic being able to back off its power without getting too high of input voltage and also a good margin between the PV's maximum power point voltage and the actual battery voltage if you have partial shading, long-ish wire runs etc.

K7IQ

Bob D

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #5 on: August 10, 2021, 05:47:37 PM »
FWIW, I have 3500 watts of panels connected to a Classic 150.
The system arrangement is 2500 watts facing solar 11:00, and 1000 watts facing solar 15:00.
Because of the two orientations, the Classic is never overloaded.
Essentially it give me a "wider " array, sort of emulating a bit of tracking.
I still get the benefit of additional panels on marginal days, and the extended time because of the different orientations allows a the battery to have a full absorb cycle.

Classic 150, Magnum 4024, 12-215W panels, 12-85-13 forktruck battery

mahendra

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #6 on: August 11, 2021, 12:28:05 PM »
Yes this strategy seems to be more cost effective.and efficient that  actually trackers while at.the same time it caters for days with poor solar irradiated.
1.5kw on Midnite classic 150(whizbang jr.) networked 0.660kw on classic lite 200 ,180ah CALB Lifepo4 48v battery bank,123SmartBMS bms(top balanced) Outback vfx3648

jimbo

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #7 on: August 27, 2021, 01:44:21 AM »
^^^What about on a 24v system? Our winters are very cloudy and production can be extremely low.

It's pretty much how much you want to over-panel the system.  24V system can have twice the power of a 12V system and half that of a 48V system given the same battery current...

How many watts of panels are you thinking of putting on there ?  Yes, winter and cloudy weather can sure be over-paneled quite a bit.

And how low of temperatures there in the winter ?  One thing for cold weather is that the panels will run at a higher voltage so you want to make sure it will be under the PV rating of the controller.

But for a 24V system, I  would think that something like 3kW of panels might be OK. Maybe even a bit higher.

  If you were using a Classic 150 say, I would wire the PV array at a lower voltage, say maybe near 100 volts (ish)  Voc  or 48V nominal panel voltage.  That will help a bit for the Classic being able to back off its power without getting too high of input voltage and also a good margin between the PV's maximum power point voltage and the actual battery voltage if you have partial shading, long-ish wire runs etc.

Sorry for the late reply (never got an email)

I replaced a PWM controller with a midnite classic and didn't change the panel configuration so my voltage is very low with Vmpp of 36v charging a 24v battery. I know this is not recommended but has been great for 9 years now (still equalizes as 31.4v).  Minimum temps are -1 or -2 Celsius a couple of times a year and this is early morning only.
Do you still think 3kw of panels is a max? That is only 10% more than rated. Our winters a very cloudy and misty. Some days my 2.7kw of panels produce 1.1kwh for the day.

PS: I'm looking at adding another classic soon and may parallel the panels to double the input voltage.

australsolarier

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #8 on: September 13, 2021, 08:52:05 PM »
one of my midnite 150 has 7.5kwp hooked up. they are in different orientation though.

jimbo

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #9 on: September 13, 2021, 09:03:06 PM »
Is the classic maxing out for a few hours a day in summer?

australsolarier

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #10 on: September 13, 2021, 09:31:23 PM »
maxing out doesn't happen too often. the reason for this is there are 4 more overpowered midnites in the system and the the battery is usually charged before overpowering occurs.
on the 12V system i have experienced maxing out for longish periods. the midnite seems to take this quite well. if you are worried about the max out amps, you can reduce  the amps.
bye the way, i am over powered with mostly horizontally oriented panels. the reason is those panels work best in cloudy weather, when you need most panels or power.

as far as i understand you can hook up an unlimited amount of panels. midnite doesn't say so, but that is probably to cover their backs.  victron limits overpowering by recommending the max panel amps should not be bigger than max bat amps.

running the midnite at max amps heats it up quite noticeably. all my midnites have external computer fans installed that run constantly. (changing a fan inside the midnite is a major operation.

jimbo

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Re: Self-protection in MPPT algorithm and over-paneling
« Reply #11 on: September 13, 2021, 09:45:32 PM »
Thanks, that is good to know.