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l00semarble avatar image
l00semarble asked

Am having trouble specifying panels for the MPPT RS 450/200 with high working PV Voltage

I want to use a high working PV voltages because my panels will be ground mounted at about 100m from the closet with the MPPTs and inverters. I want to transmit power over the long distance at highest possible voltage (close to 400v) for minimum losses and cable size.

The issue is that to actually maximize the output of the MPPT RS 450/200 you have to divide your panels into 4 arrays as it has 4 separate trackers. The MPPT is capable of a maximum output wattage of 11,520w which is 2,880w per tracker.

I was planning on using what I can find in large format panels. My supplier (In Costa Rica) can get me right now:

Jinko JKM535M-72HL4-TV 535w panels

49.1 VOC

40.63 MPP V

13.85a Short Circuit I

13.17a MPP I


So if I want to use these on the MPPT RS I could put 6 in series to each tracker (24 total panels) and put 3,210w into each tracker. This would over-panel the MPPT by about 11% which I am fine with and Victron is fine with as well. It seems perfect but the problem is the voltage of each array would only be 295 VOC/244 MPP V.

So the working voltage I would transmit over the long distance would be only 244v when I was hoping to do around 400v.

I am wondering if I should consider only using 3 trackers on the device. I believe this is permissible while still being able to get the maximum rated output of the MPPT. Can someone confirm? . In that case I could put 9 panels in series into three trackers (27 total panels) and get 442 VOC/366 MPP V and same array MPP I of 13.17a. This would put 4,815w into each of three inputs thus a total of 14,445w so 25% over-paneled. This could be significant wasted capacity in the dry season but during rainy season I would appreciate the over-paneling.

Or I could do 8 panels in series (24 total) into 3 trackers at 393 VOC/325 MPPT V at 9% over-paneled.


Thoughts?

MPPT ControllersMPPT SmartSolarmppt rs
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Michelle Konzack avatar image Michelle Konzack commented ·

What kind of cable do you use with 100m distance?


I had a similar problem with a customer (needed 130m) and we used Aluminium EarthCables AXPK 4x16mm² and used two conductors in parallel to reduce the power losses.


0.03 × 130m × 2 × 14, 4A ÷ (2 x 16mm²)

= 3,6V drop over the 130m


P.S.: we had only 4 SmartSolar MPPT 250/100-Tr VE.Can available, the Solarpanels have 36Vmpp and we used 5s2p with 520Wp panels.

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Alexandra answered ·

@l00semarble

Use three trackers. They can even be assymetrical.

Just remember your max VOC is 8x your battery float voltage. And you haven't broken the 20A short circuit limit on each string.

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l00semarble avatar image
l00semarble answered ·

Was considering EG4 batteries which have a float voltage of 56.5v so 8x is 452v so that ends up not being a constraint. But I was aware and will keep that in consideration.

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l00semarble avatar image
l00semarble answered ·

Actually 9S panels at 442 VOC is close enough to have to check with temp coefficient even though tropical climate. Our lowest recorded temperature on my mountain in some years is 69F/20.5C. I figured I would use 68F/20C as my design temp. So that means 5 degC of compensation at 0.28%/DegC off the STC of 25C.

.28%/degC * 5degC = 1.4%

49.1VOC * (1+1.4%) = 49.818VOC

49.818VOC * 9S panels = 448.4VOC String

So I'm just squeaking in at the limit. Technically even 19C would give me 449.6VOC. 18C and I blow up my controllers! This temp is unheard of and even if somehow it was that cold it certainly would not be sunny at the same time.

I would love to hear from anyone not using all trackers.

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Alexandra avatar image Alexandra ♦ commented ·
@l00semarble

Also note panels have a 3% tolerance - so you are too close to the edge there.

There are also other effects like cloud edge, so dial back a panel on the tracker.

Unequal use of trackers is not a problem fr the RS Range.

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