Calculate acceptable over paneling.

McDubsy

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My system:
-1300W Trina solar array (4x325w panels) 40v/isc of 10
-Renogy Rover 100A MPPT, rated at 100A/150V max pv input. Also 1200w at 12v max pv input.
-12v 300ah battery bank
-Renogy 2000W inverter



I am trying to increase my solar array. I can easily wire 8 x 325w panel in series parallel and stay well below the 100a/150v max limits of the Charge controller.
It would take the pv wattage over the stated limit

My question is since the posted maximum input limits seem to not agree(100a/150v v.s. 1200w)...which should I follow?
 

rin67630

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You can exceed the max amps of the MPPT controller by factor 2 or 3 or even more, but stay well under the max voltage !
Factor 0.8 is the very maximum i would try.
 

timselectric

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25% to 50% is the norm. Beyond that, you will need to see if it will be cost effective for your situation.
 

Ampster

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Renogy Rover 100A MPPT, rated at 100A/150V max pv input. Also 1200w at 12v max pv input.
.......
There is an inconsistency between the 150V and the 12V above that needs to be clarified?
My question is since the posted maximum input limits seem to not agree(100a/150v v.s. 1200w)...which should I follow?
100 Amps at 150 Volts is 15,000 Watts.
 

rmaddy

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100 Amps at 150 Volts is 15,000 Watts.
It's 100A at battery charge voltage, not max PV input voltage. 100A x 12V = 1200W. Though the battery will likely be charged at a higher voltage so the actual max usable wattage is more like 1400+W.
 

rmaddy

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So what is the maximum PV Amperage? There was some ambiguity in the original post by @McDubsy
I assumed the 100A is the max battery charge current. The SCC may have a max short circuit current listed in its spec sheet.
 

Ampster

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The SCC may have a max short circuit current listed in its spec sheet.
Yes, @McDubsy will have to look that up. If the Isc of the panels is 10 Amp as he stated it to be. and if the SCC limit is higher I presume he can wire the panels in series and not worry about the panel Wattage? He will see some clipping, but to answer the question in this thread, that amount of over paneling would be acceptable? That seems to be consistent with the threads below where over paneling is discussed. @rin67630 essentially said that same thing earlier in this thread.
 
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Ampster

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Over paneling
Wattage
You said 50 percent was the norm and I asked 50 per cent of what and your response is:
Over paneling?
Wattage?
How would other readers use that?
I have seen typical AC to DC ratios of 1.25 to 1 but can't figure out how to make that be 50 percent?
Do you want to give an example?
 

MichaelK

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I have done the math for this somewhat differently. My observation is that most of the time charging starts around 12.5V, and that panels typically need to be de-rated to 85% for actual production.

So, my math would be (100A X 12.5V)/85% = 1470W of panels

I am not very concerned about charging voltages below 12.0V. That would only be for a very depleted battery, and even starting out at just 12.0V around sunrise, the state of charge will be going up faster than the amperage will, so I'd expect it to be at 13+V way before amperage gets anywhere near max.

The other issue though is that with 325W panels you don't get many options. Four panels is 1300W, and five is already 1625. A more viable alternative I think would be three 2-panel strings, one facing SE, one facing S and one facing SW.
 
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MichaelK

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That is a good way to make over paneling work for more production and less clipping.
I've done it this way for years now, because my arrays were designed to rotate. This method really works well on cloudy/rainy days, when production is really low, but light is more scattered. I find that the extra arrays mean a few more watts on marginal days, when output is next to nothing. But, I can still make 3.0kWh in the rain, so if I do my part, I can still keep my batteries close to fully charged.
 

timselectric

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You said 50 percent was the norm and I asked 50 per cent of what and your response is:
Over paneling?
Wattage?
How would other readers use that?
I have seen typical AC to DC ratios of 1.25 to 1 but can't figure out how to make that be 50 percent?
Do you want to give an example?
7500w of solar panels connected to a 5000w SCC.
50% over paneling
 

timselectric

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Never go over on VOC. There's enough magic smoke already released in the world.
Over paneling has nothing to do with DC to AC ratios.
It just provides more production in less than favorable weather conditions. The extra is clipped in favorable conditions.
 

Ampster

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Over paneling has nothing to do with DC to AC ratios.
A DC to AC ratio is just a metric that explains the mathematical relationship of array to inverter capacity.
Over paneling is a term used to describe putting more panels on an inverter and was the subject of this thread.
One could describe it like you did as a percentage above 100 percent. Over stringing is another term. There are some other technical terms as well some more specific than others. I think it is safe to say that with an DC to AC ratio of 1 to 1, no one would describe a system as over paneled. There would not likely be any clipping since panels rarely exceed their STC ratings.
 

sunshine_eggo

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I like what Victron has to say (but of course I would, because I'm their biatch):


There are two limits, when determining the maximum array size that can be connected to an MPPT:
  1. The Maximum PV open circuit voltage (Voc at STC)
  2. The Maximum PV short circuit current (Isc at STC)
Both values are specified in the datasheets of all our MPPT Solar Charge Controllers. Those two ratings of the PV array must not exceed these MPPT limits.
 

rmaddy

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A DC to AC ratio is just a metric that explains the mathematical relationship of array to inverter capacity.
Sorry but over paneling has nothing to do with AC or an inverter. It's only with regard to a solar charge controller and its rated max wattage which in turn is based on the charge controller's max battery charge current (times the battery charge voltage).

Granted, some "inverters" (all-in-ones) have a solar charge controller as part of the system but still, over paneling has nothing to do with the inverter portion or its rated output wattage. Two completely different and unrelated ratings.
 
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