Solar panel setup opinions/advice wanted…

jrobertp

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One of my biggest questions to get the most out of my setup right now….
I have my 4 solar panels in series - parallel. (2 sets of series, then paralleled). My Renogy charger can only handle 520w of solar. So my understanding is that I can only add one more panel, but then I would have to run all 5 panels together in series… in real world usage on an Rv, where I may have to deal with shade on the roof, am I truly gaining by adding a 5th panel, or am I adding more worry with shaded panels than it’s worth?

I have a 26‘ toy hauler rv trailer that I’m setting up to be able to take boondocking…. we Camp regularly with hookups available but also a few times a year with no hookups. Our longest trips are 8 consecutive days.

in my setup I have:
- Jita 300ah 12v battery (in the manual it states that it’s a 200A bms and that it has an internal heater)
- Renogy rover 40A mppt solar charge controller
- 4 100 watt hqst monocrystaline solar panels
 

sunshine_eggo

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One of my biggest questions to get the most out of my setup right now….
I have my 4 solar panels in series - parallel. (2 sets of series, then paralleled). My Renogy charger can only handle 520w of solar. So my understanding is that I can only add one more panel, but then I would have to run all 5 panels together in series… in real world usage on an Rv, where I may have to deal with shade on the roof, am I truly gaining by adding a 5th panel, or am I adding more worry with shaded panels than it’s worth?

520W is the maximum it can deliver. It doesn't mean you can't put more on it.

Overpaneling by 20-30% is generally acceptable to most manufacturers provided you don't exceed PV input limits,e.g., for a 100V/40A controller, series Voc can't exceed 100V (should have head room for cold weather too) and PV amps shouldn't be more than 40A unless otherwise stated.

2S3P or 3S2P would be very workable. Given flat roof panel performance on an RV with shading potential, I wouldn't hesitate to do 2S4P.
 

rmaddy

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in real world usage on an Rv, where I may have to deal with shade on the roof, am I truly gaining by adding a 5th panel, or am I adding more worry with shaded panels than it’s worth?
If you have shading issues then you do not want to put all 5 panels in series. If one gets shaded you lose power on all of them. Putting all 5 in parallel will handle the shade a lot better. The biggest issue with 5 panels in 5P is you won't have very good low light performance.

Post the specs of your charge controller (max PV input voltage) and the full specs of the panels.

If you can add 2 more then 6 panels in 2S3P or 3S2P would be a much better option. 600W at 12V would be up to 46A on your 40A controller. But with the panels being flat and with you having some shading, you will rarely, if ever, see close to 600W. If you ever get more than 520W the extra will basically go to waste but it won't be a problem.
 

jrobertp

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520W is the maximum it can deliver. It doesn't mean you can't put more on it.

Overpaneling by 20-30% is generally acceptable to most manufacturers provided you don't exceed PV input limits,e.g., for a 100V/40A controller, series Voc can't exceed 100V (should have head room for cold weather too) and PV amps shouldn't be more than 40A unless otherwise stated.

2S3P or 3S2P would be very workable. Given flat roof panel performance on an RV with shading potential, I wouldn't hesitate to do 2S4P.

I would love for that to be possible… but I fear the 520W is the maximum input, not max delivery…
 

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Bud Martin

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It will limit the power when over panel to the max the charger can use.

PV Overvoltage:
if the PV voltage is larger than maximum input open voltage 100VDC. PV will remain disconnected until the voltage drops below 100VDC.

PV Overcurrent:

The controller will limit the battery charging current to the maximum battery current rating. Therefore, an over-sized solar array will not operate at peak power.
 

jrobertp

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It will limit the power when over panel to the max the charger can use.

PV Overvoltage:
if the PV voltage is larger than maximum input open voltage 100VDC. PV will remain disconnected until the voltage drops below 100VDC.

PV Overcurrent:
The controller will limit the battery charging current to the maximum battery current rating. Therefore, an over-sized solar array will not operate at peak power.
Thanks. That’s great info… I didnt make the connection between the different way it handles over current vs over voltage
 

bradbill

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If you have shading issues then you do not want to put all 5 panels in series. If one gets shaded you lose power on all of them. Putting all 5 in parallel will handle the shade a lot better. The biggest issue with 5 panels in 5P is you won't have very good low light performance.

Post the specs of your charge controller (max PV input voltage) and the full specs of the panels.

If you can add 2 more then 6 panels in 2S3P or 3S2P would be a much better option. 600W at 12V would be up to 46A on your 40A controller. But with the panels being flat and with you having some shading, you will rarely, if ever, see close to 600W. If you ever get more than 520W the extra will basically go to waste but it won't be a problem.
Not if the panels have bypass diodes!
 

rmaddy

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Not if the panels have bypass diodes!
Which part of my statement is this in reply to? I guess you are referring to the first two sentences about panels in series. I believe it does apply even with bypass diodes. Let's say part of one panel is in shade and it loses 1/3 power while the bypass diodes allow the other 2/3 to keep working. All of the other panels in series will also effectively lose 1/3 of their power as well. At least that's my understanding.
 

bradbill

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Which part of my statement is this in reply to? I guess you are referring to the first two sentences about panels in series. I believe it does apply even with bypass diodes. Let's say part of one panel is in shade and it loses 1/3 power while the bypass diodes allow the other 2/3 to keep working. All of the other panels in series will also effectively lose 1/3 of their power as well. At least that's my understanding.
That is incorrect. Lets say you have 3 20v 5A panels. Each one is 100W.

If one of the panels gets shaded, you will still have 40v@5A instead of 60V@5A. You will actually get slightly less than 40V becuase of the voltage drop across the bypass diodes.
 

sunshine_eggo

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Not if the panels have bypass diodes!

Which part of my statement is this in reply to? I guess you are referring to the first two sentences about panels in series. I believe it does apply even with bypass diodes. Let's say part of one panel is in shade and it loses 1/3 power while the bypass diodes allow the other 2/3 to keep working. All of the other panels in series will also effectively lose 1/3 of their power as well. At least that's my understanding.

You're both right.

It depends on the partial shading. If the shading is only over a zone covered by one or more diode, but it still allows the operational portion of the panel to continue to put out the same current as the rest, then the impact on the remaining panels in the string will be minimal if measurable at all.

However, if all three zones split by the diode of a typical panel are under partial shading, then the entire string is severely compromised.

This amount of shading on a panel will reduce the entire string to zero:

1642138830237.png

Shading any ONE of the single cells in the three zones shown will shut down 1/3 of that panel and should not significantly affect the rest of the string:

1642139072107.png

One can plan for the worst case shading, but one does not get to choose their shading on a vehicle in all cases.
 

rmaddy

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When I first started learning about solar panels it was pointed out many times that panels in series are bad if there is any shading and panels in parallel are much better when one panel is shaded since it won't impact the others. But I think that whole basic idea assumed panels with no bypass diodes. Correct?

When working with panels with bypass diodes, panels in series are no longer impacted as badly when one panel is (partially?) shaded. If a panel has shading within one zone then it seems that the rest of that panel works fine and the other panels in series are not affected at all. Correct?

However, if all three zones split by the diode of a typical panel are under partial shading, then the entire string is severely compromised.
This one still gets me (assuming both of my previous paragraphs are correct). If one panel in the series has all zones in shade, why does it affect the other panels? Why don't the bypass diodes of the fully shaded panel still do their thing and allow power through the other panels?
 

bradbill

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You're both right.

It depends on the partial shading. If the shading is only over a zone covered by one or more diode, but it still allows the operational portion of the panel to continue to put out the same current as the rest, then the impact on the remaining panels in the string will be minimal if measurable at all.

However, if all three zones split by the diode of a typical panel are under partial shading, then the entire string is severely compromised.

This amount of shading on a panel will reduce the entire string to zero:

View attachment 79596

Shading any ONE of the single cells in the three zones shown will shut down 1/3 of that panel and should not significantly affect the rest of the string:

View attachment 79598

One can plan for the worst case shading, but one does not get to choose their shading on a vehicle in all cases.
What you are saying is correct for one panel.

What rmaddy is saying is that one panel will affect the other individula panels which will not happen. He is saying if you lose one panel, you lose all the panels which is not correct. If you have the crappy HighTec 200W panels, as an example, yes you will lose the whole string since they don't have bypass diodes.

If you put a diode in series with two other panels in series does it wipe out the other 2? Of course it doesn't. That one panel with bypass diodes that gets shaded looks exactly like a diode in series.
 

jrobertp

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For my particular case I have the HQST 100 watt Monocrystalline panels. Mine are the more square version… 32.5 x 26.4”
They do say they have the bi-pass diodes…

I was able to find someone who had the same Renogy controller setup and he did fine with a 3s2p. He said in the real world he rarely went over current. As @rmaddy mentioned, It seems if you do go over current it wastes the extra current through the heat sink. The manual says it would shut down if the heat sink reaches 85c (185f). However in his test he could not use 5 panels in series, because it did go over voltage and immediately shut down…

Thanks for all the help, at least I can feel confident adding two more panels to squeeze just a little more out of my setup. (if i can find them, my particular version seems to be out of stock)
 
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bradbill

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was able to find someone who had the same Renogy controller setup and he did fine with a 3s2p. He said in the real world he rarely went over current. As @rmaddy mentioned, It seems if you do go over current it wastes the extra current through the heat sink. The manual says it would shut down if the heat sink reaches 85c (185f). However in his test he could not use 5 panels in series, because it did go over voltage and immediately shut down…
An MPPT controller will just reduce the output. It doesn't put any excess through the heatsink. The heatsink is there for the output mosfet stage. Since nothing is 100% efficient, the heatsink is there for the percent energy that doesn't make it to the battery. For example, if you had 500W of output with a 95% efficient solar controller, there are 26W that is converted to heat. That is what the heatsink is for.
 

Bud Martin

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For my particular case I have the HQST 100 watt Monocrystalline panels. Mine are the more square version… 32.5 x 26.4”
They do say they have the bi-pass diodes…

I was able to find someone who had the same Renogy controller setup and he did fine with a 3s2p. He said in the real world he rarely went over current. As @rmaddy mentioned, It seems if you do go over current it wastes the extra current through the heat sink. The manual says it would shut down if the heat sink reaches 85c (185f). However in his test he could not use 5 panels in series, because it did go over voltage and immediately shut down…

Thanks for all the help, at least I can feel confident adding two more panels to squeeze just a little more out of my setup. (if i can find them, my particular version seems to be out of stock)
The load PULLS the current as needed up to the limit of the charger through the conversion process to charge the battery, as the battery gets fuller then the current draw will drop, MPPT SCC is basically a smart Buck Converter. PV panels do not Push current, I.E. your home has AC outlet than can SUPPLY 120V up to 15A, which is 1800W of power, so if you plug in 100W lamp into the socket, the socket is not going to push 15A into the lamp.
 
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sunshine_eggo

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Been away for a bit. @bradbill and @rmaddy had me questioning my understanding to the point that I've been in my back yard with 2X Renogy 100W panels, a voltmeter, an ammeter and a shade.

@bradbill is right. I was wrong about how a single panel going to zero would affect the other series strings.

I am now questioning the fundamental assumption that series is terribad compared to parallel for shading tolerance in typical circumstances.
 

sunshine_eggo

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Do those panels have bypass diodes?

I didn't open the back to confirm, but they behaved as though they did:

Voltage:
Shade each zone, and I got a reduction in voltage

Current:
Shade each zone, no change in current until the final zone was shaded
 

rmaddy

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I didn't open the back to confirm, but they behaved as though they did
Renogy's website states their 100W panels have bypass diodes.

It would be really interesting to see real numbers on actual voltages and amperages (and resulting wattages) on 2 panels in series vs 2 panels in parallel with various shading patterns applied to the two pairs of panels. That might help narrow down which shading patterns would indicate using serial panels versus which patterns are better handled by parallel panels.
 
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