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Old 04-15-2021, 12:28 AM   #1
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MPPT Operating Voltage

I've been researching RV solar electrical systems, planning on upgrading our future RV. I can't seem to find an answer, or real world performance answer to my questions.

I will have 2 170W Zamp panels mounted on the roof, and I believe from the factory they will be wired in parallel through the Zamp 3 port roof port (170W Zamp V(mp) = 18V, I(mp) = 9.4A; V(oc) = 23.8V I(sc) = 95.A)

I am planning on also getting a 200W Renogy suitcase (200W Renogy V(mp) = 17.7V, I(mp) = 10.35A; V(oc) = 21.2V I(sc) = 11.72A)

I understand that for different panels, for max efficiency, each array should have it's own controller (so one for the 2x Zamp in parallel, and one for 1x Renogy).

I was planning on the Victron MPPT (100/30 for the Zamp and 75/15 for the Renogy). I read on the datasheet that in order for the controller to turn on, the PV voltage needs to exceed Vbattery + 5v. After the controller is on it just needs to be Vbattery + 1V.

My questions are:

1) Is there any advantage to running an MPPT on a single panel?
2) Do I want to look at Vmp or Voc for the MPPT operating (turn on) voltage? I don't want to have to wait for panel voltage to get high enough to turn on the controller.
3) Is there anything else to consider for the Zamp panels for Parallel vs Series? I know series is higher voltage, so less voltage drop in the lines, but parallel is better for shading.
4) Are these panels similar enough to warrant running through a single MPPT? Series/Parallel?

Thanks in advance!
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Old 04-15-2021, 01:11 PM   #2
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With those "12v" panels, you could use a PWM solar charge controller which is quite a bit cheaper and still get similar output/charge to your batteries.


MPPT will give you (should) slightly better performance as it can convert (for example) 16-17v into whatever your battery stage is asking for (for example, 13.6v) and boost/scale the current a little.


How large is your battery bank?
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Old 04-15-2021, 01:26 PM   #3
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Put the panel in series to get the voltage up. More production from the MPPT.

Separate controllers for dissimilar arrays or array orientations.
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Old 04-15-2021, 01:46 PM   #4
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Quote:
Originally Posted by BradS7535 View Post
1) Is there any advantage to running an MPPT on a single panel?
2) Do I want to look at Vmp or Voc for the MPPT operating (turn on) voltage? I don't want to have to wait for panel voltage to get high enough to turn on the controller.
3) Is there anything else to consider for the Zamp panels for Parallel vs Series? I know series is higher voltage, so less voltage drop in the lines, but parallel is better for shading.
4) Are these panels similar enough to warrant running through a single MPPT? Series/Parallel?
1. Yes. On the panels you describe that have strings of 36 solar cells in series, a MPPT will improve performance between 25 and 30 % vs a PWM charge controller. The percentage improvement goes down slightly if you use series connected panels where there is a larger DC to DC conversion taking place in the controller.

2 and 4. Yes, if you want to wire multiple panels in parallel to a single MPPT charge controller, you can do this, as long as all are the same type of solar cell (mono or poly crystalline), and all have 36 solar cell in series architecture. If so, they will all have very close Vmp values.

3. Output of each group of solar cells wired in series will drop if any one of the series connected solar cells of a panel is shaded. Parallel will minimize losses caused by anything partial shading panels, which can be a problem on a RV roof with things like the TV antenna, AC shroud, even vent pipes and vent covers. Whatever you can do to position the panels and/or park the unit to minimize shading is critical to maximum power production.

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