Classic 150. 4 strings of 6 24V 153W panels. Sizer looks like this:
(https://i.postimg.cc/k4WcxXs5/Sizing-chart-4-strings-153-watts-per-panel.jpg)
So, common problem. I'm underpaneled on cloudy/rainy days. Before purchasing another controller for some additional panels, I'm pondering the viability of adding additional strings to the existing configuration (there is room on the combiner for more strings). If I, for example, double the number of panels, obviously the sizing calculator is not going to like it. However, if I don't exceed to the voltage limit, and the current draw stays the same and within limits, can this not work? I see that there is a current limiter parameter on the Classic.
Therefore, on paper this appears to work. Is there a hole in my theory?
(double the panels)
(https://i.postimg.cc/J7vryrgX/Sizing-chart-8-strings-153-watts-per-panel-2.jpg)
(https://i.postimg.cc/5ywRNSTn/min-max-volta-amps.jpg)
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BONUS QUESTION: I just now noticed that Maximum Volts on the controller is set to 100. Hadn't ever changed the default. My panels typically produce ~135v. Holy misconfiguration Batman! Am I artificially limiting the power of this system?
The volt limit is for output to batteries.
Larry
I see, said the blind man.
Hi Steve,
Yea, did notice the quite high Vin readings on your LA Macro Thread. Wanted to mention it, but, if would have been a bit off-Topic.
This high Vin will reduce production, somewhat just from reduced CC efficiency.
AND, probably more important, is that the CC will spend a reasonable amount of time Resting, due to Hyper Voc.
Overpaneling will also generally raise the average input voltage. Especially, if you were thinking of essentially doubling the number of existing PV size.
The string Sizer already "thinks" that the CC is overPVed, but, much is probably due the the high Vin ...
Add a Classic? Restring the existing PV array?
Later, FWIW, Vic
I see. That makes sense. So let's say for the purposes of my core questions the panels were re-strung and voltages were lower. Like below. Can you get away with doubling number of panels given the points I made in the OP?
(https://i.postimg.cc/kGPRZsgy/string-calculation-for-solar-panel-array-for-combiner.jpg)
Strings of four of these PVs, with a Classic 150 and a 48 V Li battery looks essentially perfect, IMO.
MN usually recommends 1.2 X maximum Classic utilization.
If you doubled the present array size on a single Cl 150 will probably result in an "EXCESSIVE" judgement from the Sizer.
You might try that. It is a transit day. Later, Vic
Thank you Vic. Yes, I certainly expect the sizing tool to complain. But I don't think I will actually ever draw the current, because a) there is an amperage limiter on the classic, b) I can size either one or both of the fore and aft circuit breaker tied to the controller to trip at a certain point, and perhaps c) the BMS of the battery pack probably has a current limiter (although I need to determine what that limit is.
And of course the circuit breakers on the combiner for the extra strings can be flipped off except on cloudy/rainy days. I of course not want to rely on that policy exclusively. :>
Also if you tilt the array to the best winter angle, come summer, the angle will be wrong and you won't be at max efficiency.
Quote from: mike90045 on July 31, 2020, 02:52:10 AM
Also if you tilt the array to the best winter angle, come summer, the angle will be wrong and you won't be at max efficiency.
Mike makes a good point. Also changing the Azimuth of the PVs, to face more to the East or/and the West will spread solar production, more evenly throughout the day, reducing the max current.
Vic
Good points.
Also, I got this reply to the same question posted on an Amazon page where the Classic 150 is sold.
"I have this exact overpanneled situation and the Midnite 150 handles it just fine. It just doesnt exceed 96 amp output, so you lose some potential charge, but it doesnt hurt the CC. It seems to ramp up to 96ams, then cycle back down, then ramp up again, over and over. I dont know the energy loss (if any) this cycling costs. I only get this effect in the spring when the sun is more direct and the panel temps are still cool. With summer heat I dont notice it maxing out, or with the less direct rays of winter sun. I burned up a cheapy CC before getting the 150, so I was a little gun shy going into this upgrade. I have been very pleased and will get another when I expand."
The unknown is if the responder knows about the limit settings on input/output current, which I assume may mitigate the controller ramping up current like that. It is a shame that Amazon has dumbed down its product reviews so much that it often doesn't allow you to comment to a an answer that's been posted.
ps - I found out that the max current the batteries BMS will handle is 120A. And with two units in parallel, the BMS won't be the throttle point. I'll have to rely on the other tricks.
That responder must have a !@ V system ... The current ramping, may well be the Classic, Thermal Limiting.
IIRC, boB mentioned, previously, when large overpaneling was being considered, that when overpaneling to a large degree, that there could be a situation in Solar Mode (at least) where the fast current limiting in the Classic might not be able to reduce the output current quite quickly enough protect it from violating Safe Operating Area conditions of the FETs (a paraphrase). Not to try to place too many words into bob's mouth. Hope that he will chime in, on this ...
There could be other unusual/Fault situations where the Classic might not have enough time to safely limit output current, quickly enough.
The Classic is a tough box, and might well survive doubling the existing PV array, at least for quite some time.
I had a similar question to boB, in 2011, IIRC. Wondered about running 5.88 kW STC array on a 48 V battery (93 V String Vmp) to a single Classic 150. He said that maybe I should try it. Never did try it, but, decided to add a second Classic and divide the PV array in two. Each of these Classics just loaf along at about 40 - 43 Amps maximum. Am happy to have made that decision.
YMMV, etc, FWIW Vic
So, we're saying that, after the world ends, all there will be is cockroaches... and classics.