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Do I need a better controller?

DenverGuy

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I have a 100W panel, 12V system, two 100Ah batteries, and a P30L 30A PWM controller. I am going to upgrade by adding three 100W panels for a total of four, and I will add 2 more batteries for a total of four.

I think I need to beef up the controller. The vendor says that I don't have to, but I am not convinced.

Should I add a second 30A controller, or should I buy a new 40A MPPT controller (cable lengths are short)?
 
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Assuming 12V system.

With PWM, it is critical that the 4X Isc of the panels is NOT > 30A. 30A is also an input limit.

Your Vmp is probably somewhere around 18V, so Imp is about 5.6A. 4 * 5.6A = 22A.

This means that your 400W of panels will likely never produce more than 22A * 14.4V = 320W

These numbers indicate that the 30A PWM will suffice.

MPPT will make it possible to eliminate that penalty and maximize the output of your panels. 30A is sufficient, but if you plan to add panels in the future, 40A or larger might make sense.
 
MPPT will make it possible to eliminate that penalty and maximize the output of your panels. 30A is sufficient, but if you plan to add panels in the future, 40A or larger might make sense.
Plus the cost difference between a 30a and a 40a is pretty negligible so you might as well do a little future-proofing while you're at it.

Pro tip: If the controller has USB ports, it's NOT a real MPPT, it's a PWM with a lying sticker. :)
 
Plus the cost difference between a 30a and a 40a is pretty negligible so you might as well do a little future-proofing while you're at it.

Pro tip: If the controller has USB ports, it's NOT a real MPPT, it's a PWM with a lying sticker. :)
just curious why is that?

My SCC's use RS232 RS485, and ethernet but do not have USB. in order to program them i had to get a Serial to USB adapter to plug the SCC into a computer to program it. is there something about USB that inherently prevents it from being used on a MPPT design?
 
I am going to upgrade by adding three 100W panels for a total of four,
Not sure why you are fixated on little 100W panels. Maybe space limited?

If not, then you should consider big cheap solar panels. Assuming you are going to pay $100 for each new panel and end up with 400W, consider this:

New REC 300 watt Mono 60 cell Solar Panels for $165.00 each

Buy 2 of these for just over $300 and you'll end up with 600W of solar and only have to mount and wire up 2 panels.

Just a thought.

 
He's talking about USB charge ports. :·)
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gottya! I was thinking USB vs serial etc. for programming purposes. not nocking his knowledge I thought maybe I had missed something by pure dumb luck. Yes I might as well be Amish when it comes to a lot of current computer things.
 
gottya! I was thinking USB vs serial etc. for programming purposes. not nocking his knowledge I thought maybe I had missed something by pure dumb luck.
Yeah, charge ports. Things like This Liar and This Liar and This Liar may SAY they're MPPT, but they're not and people get suckered too often.


Yes I might as well be Amish when it comes to a lot of current computer things.
I work with sailors, you're a computer genius!
 
Long Answer here. Getting back to the original question: It depends on the VOLTAGE (V-mp) of your panels. For example:

If V(mp) of your "100 watt" panels is 18.1 volts, the current at rated power (standard test conditions, which are very "sunny") would be about 5.52 amps per panel. A "PWM" controller will disconnect and reconnect the panels many thousands of times per second, so that the average charging voltage matches your battery requirement (typically around 14.2 volts, or maybe 14.4 if you have programmed it to do that).

At 14.2 Volts charging Voltage, the maximum power into your battery pack under "standard conditions" is only 5.52 Amps times 14.2 Volts (not 18.1 volts.) That is only 78.5 watts. The rest of the "available power", about 21.5 watts, is all left in the panels (and un-utilized) during those moments of disconnection. That power is WASTED in comparison to a theoretical 100% efficient MPPT controller feeding hungry batteries.

If V(mp) of your panels is closer to your battery charging voltage, the percentage of 'waste' is smaller. If V(mp) is much higher and further away, the percentage of 'waste' increases quickly.
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With just one panel, the cost of an MPPT controller ($150 and higher) is not justified. But with 4 panels at this Voltage, a PWM Controller can give you only 314 watts in standard test conditions. In comparison to the rated power, you're really only getting a bit more than "3 panels". The "100% efficient MPPT controller" gets you the other 86 watts.

No MPPT controller is 100% efficient - the real ones are generally around 91-94% efficient at converting "panel power" (in lower Amps at High Voltage) into more battery charging Amps at lower battery charging voltage. In this scenario, with a decent real-world controller, you would get around 368 watts (I assumed 92% efficiency). Your "real world MPPT" gain, in comparison to the PWM scenario, is only 54 watts (about 1/2 panel).
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But there is another important factor which we should add into this scenario. 4 panels into a PWM controller, at 5.52 Amps each, is a total of about 22 amps. (And with a PWM controller, that's all the Amps you can ever get). But, if you combine your panels in parallel near the panel mounts (to avoid running 4 sets of very long wires down to the Solar Controllers), you will have 22 amps in the long wire - with substantial power loss in the wire. They must all must be wired in parallel.

With an MPPT controller supporting multiple panels, you can put panels in Series - doubling the Voltage at the same current (2 'parallel' sets of 2 'series' panels, or 1 set of all 4 panels in Series.) In this scenario all 4 panels in Series, you could have just 5.52 Amps in the long wire (at 72.4 Volts V-mp). My own MPPT configuration is approximately like that, with 4 slightly bigger panels (at slightly higher Voltage, slightly higher current) all in Series.
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The last thing I want to advise is: If your batteries will all be "full" before 2 PM with either type of controller, then it makes no difference (which one you use). You only need MMPT when you need to squeeze that last 15-25% from your panels, or when V(mp) of your panels is much higher than your battery charging Voltage.
 
I have a 100W panel, 12V system, two 100Ah batteries, and a P30L 30A PWM controller. I am going to upgrade by adding three 100W panels for a total of four, and I will add 2 more batteries for a total of four.

I think I need to beef up the controller. The vendor says that I don't have to, but I am not convinced.

Should I add a second 30A controller, or should I buy a new 40A MPPT controller (cable lengths are short)?
I'm just trying to figure out things myself, so at the risk of looking dumber than I really am (I really hope my wife doesn't read that part!?)....

Some of you experienced guys feel free to correct my thinking!!! I'm going with the idea that the batteries are FLA. Four 12v/100Ah batteries will provide 2400Wh of power before being discharged down to 50%. Four 100W panels will provide roughly 400Wh of charge per good sun hour. Making a not-so-conservative WAG here at the maximum good sun hours being five, that would work out to 2000Wh of recharging capability before any system losses are considered. To me (and I'm far from smart about solar power) it appears that the battery bank capacity exceeds the capacity of the panels to recharge them fully from the 50% SoC. For a more balanced system and better battery health would it be better to cut back to three batteries....or to go with five (or better, six) panels?

For some reason I've got it in my head that a 2:1 ratio of panel power to battery capacity is "about right"....something like for a 100Ah battery two 100W panels work well. ?

Also, in regards to going with an MPPT controller, isn't there a threshold where MPPT makes a big difference...and in this case it seems the OP definitely is crossing that threshold???

And, I agree with going with more powerful panels if possible...better, cheaper, and, well, better!(y)
 
For some reason I've got it in my head that a 2:1 ratio of panel power to battery capacity is "about right"....something like for a 100Ah battery two 100W panels work well. ?
This line of thinking revolves only about recharging battery(s). One also has to consider what loads will be running during the solar charging hours. If one is away during the day that is one thing but if one is home and cooking or keeping oneself cool or entertained the loads can be enormous.
 
With very high loads during the day I can see where more pv power would be required...a major variable in the equation. A guy by the name of Richard Graylin has a spreadsheet that includes a section for specifying day or night usage by percentages. I've tinkered with it and the day/night percentages really make a difference in the results of the spreadsheet.

Disregarding my 2:1 ratio statement and going back to my calculations regarding the OP's proposed battery/panel capacities...are my calculations anywhere in the ballpark as to being correct? Do they make any sense? :)
 
Disregarding my 2:1 ratio statement and going back to my calculations regarding the OP's proposed battery/panel capacities...are my calculations anywhere in the ballpark as to being correct? Do they make any sense? :)
I understand your calculations and reasoning. I am unable to extrapolate a good panel to battery ratio based on the amount of information the OP has provided. Your 2:1 could be perfect or it could be unsuitable for his energy use patterns.
 
I understand your calculations and reasoning. I am unable to extrapolate a good panel to battery ratio based on the amount of information the OP has provided. Your 2:1 could be perfect or it could be unsuitable for his energy use patterns.
Ok, thanks. I was just curious if I was skipping down the right rabbit trail with my ciphering. :)
 
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