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Old 10-12-2016, 11:05 PM   #1
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I thought I was being clever :(

I have 4 solar panels - 2x155w (8.4amp @ 18.4v) and 2x80w (4.6amp @ 17.7v)

I used to run these in parallel to my pwm controller. I'd get about 20amps @14.4v out to the battery. Not great but not too bad either given these are flat panels and the don't tilt.

Then I purchased a fancy victron mppt controller (100/50) that can handle much higher input voltage to minimize loss.

Cool, so I wired up in series.

So sunny day around 1pm and I am scratching my head on why I'm only seeing like 10 amps to the battery through the victron?!

Now I am reading that when you wire in series the voltage is indeed additive however the current output must be the same for each of the panels.... otherwise it's a least common denominator issue with the current.

So what I now have, it seems, is 4 x 17-18v panels that are capped at a lowest common denominator maximum current of 4.6 amps each - so I am throwing away amperage output on 2 of my larger panels.

Does this sound right? Should I go back to wiring in parallel to avoid current drop since voltage is similar (+/- 1v) on all 4 panels but current (amperage) differs (4.6-8.4amps)?

To complicate things further I also read that "Mixing solar panels with different electrical characteristics is not recommended if you use an MPPT charge controller. Different wattages make impossible for the controller to find the optimal operating voltage and current, since they are different for each panel type."

What a mess advice on how to optimize performance would be welcomed!

I like that I can see real time power usage via the victron on my iPhone though
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Old 10-13-2016, 03:46 AM   #2
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You might want to send a PM to lewster, or other experts, if they don't chime in here. I believe he travels from the west coast to Florida in the fall, however, so I am not sure how active he is right now on the forum.

Good luck!

PS -- See Post #89 here for instance:

http://www.airforums.com/forums/f382...er-129842.html
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Old 10-13-2016, 05:00 AM   #3
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I am no expert on the topic but if your panels are running at full efficiency wired in parallel, you are not going to get any more power out of them running in series. Along with that you will have some efficiency losses in the MPPT controller converting the higher voltage down to what your batteries need.
Many will argue this point but I believe that MPPT only beats out PWM when your panels are not running at 100%.

One thing you may try is running the two 80's in series and the two 155's in series and then run those pairs in parallel. That way you should get the max current out of each pair, but like you mentioned, mixing the pairs may be a problem for the controller.
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Old 10-14-2016, 08:40 AM   #4
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When you wire panels in series, the maximum current flow will be limited by the panel with the lowest rating.

WayneG's suggestion will work. You can also try wiring your two 80 W panels in parallel, and then add these to your two 155 W panels in series. Combining the two 80 W panels in parallel comes very close to acting like one of your 155 W panels. So when you add the other two 155 W panels in series, the MPPT controller effectively sees three 155 W panels in series.

I think the latter configuration will work better if one of the panels happens to be completely shaded since the bypass diodes will ensure that at least (2) 155 W panels are producing energy. Your mileage may vary.
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Old 10-14-2016, 03:11 PM   #5
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Thanks guys - I plan to wire at least 2 80w panels in parallel, if not all 4. Performance right now is absolutely horrible. I had to break out my generator yesterday for the first time this year.
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Old 10-14-2016, 03:41 PM   #6
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Thanks guys - I plan to wire at least 2 80w panels in parallel, if not all 4. Performance right now is absolutely horrible. I had to break out my generator yesterday for the first time this year.
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Old 10-15-2016, 02:17 PM   #7
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Assuming you're using the #10 AWG solar pre-wiring, your voltage losses due to the wires themselves will come close to 10% (Let's assume you have 60 ft total wiring, the resistance of the copper is 1 milliohm/ft, for a total resistance of 60 milliohms, the max current is 3*155W / 17V = 27A, and the voltage drop is 27A * .06 ohms = 1.62V, or 1.62/17 = 9.5% loss).

Wiring is series will certainly cut the voltage losses to less than 1% due to the pre-wiring. There's much debate about how well series vs parallel panels perform in shaded conditions. I'm always disappointed at how poorly most of these side-by-side tests were controlled, what type of MPPT controller was used, how little information there is available about how quickly their algorithms readjust to new operating conditions, which panels were used and what was the configuration for the bypass diodes. For this reason I choose to wire my panels in a series/parallel arrangement using the existing pre-wiring and I'm quite pleased with the results. Let us know what progress you make.
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Old 10-16-2016, 03:53 PM   #8
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I have 6ga wire...

I've gone back to gopower to determine the actual voltage the 155w and 80w panels generate.

I plan to go back to parallel wiring since 6ga can handle it. Also avoids issues with shading when running in series and allows me to take full advantage of the different current outputs from the 155 vs 80 watt panels...

Apparently victron mppt controllers want panels to haves matched voltages for best performance (maximum 0.3volts difference in panel output). So my fingers are crossed that the Panels have the same voltage output so that the mppt controller can maximize juice from the system.... more to come...
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Old 10-22-2016, 12:24 PM   #9
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I thought I was being clever :(

Well I've connected with a number of experts including Lew, go power and victron. Based on all my learnings I now have a good plan to maximize output from my mix 'n match panels.

A few things I learned:

Wiring in parallel will allow amperage to be additive, but voltage will be capped at that of the lowest value in the array.

Wiring in series will allow voltage to be additive, but the amperage will be limited to the lowest value in the chain.

My 80w panels are actually rated at 18.4volts and 4.35 amps

My 155watt panels are 17.5 volts and 8.6 amps.

The victron mppt controller needs a minimum of 5v difference between the PV array voltage and battery voltage in order to kick off the charging process

The victron mppt controller struggles to find the max power point when the voltage between panels in a PV array differ by more than 0.3 volts... but... it will still work.

Even a small amount of shading can dramatically reduce amperage output on a given panel... and if wired in series will drag down the output of the entire array.

So my plan... the best I can do with what I've got...

(1)wire the 2 80w panels in parallel. This will essentially create a 160watt "panel" rated at 18.4 volts and 8.7amps.

(2) wire the 160watt group to the 2 155 watt panels in series to boost voltage in order to ensure a large delta between the PV array and the battery to ensure charging kicks off sooner rather than later.

This will deliver a system that provides 17.5+17.5+18.4=53.4 volts @ 8.6 amps = 459watts to the controller.

This does not protect me from partial shading inefficiencies but if I wired everything in parallel I'd be capped at 17.5volts and that would not be enough for the victron controller to kickoff the charging process in many cases.

Today I am only seeing 160watts to the controller with everything in series because I'm capped at 4.35amps under ideal conditions... so this should be dramatically better and I am hopeful the result still outperforms my old pwm controller.

Plan to re-wire next weekend I'll post back the before / after input / output from the victron controller...
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Old 10-22-2016, 04:34 PM   #10
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Your plan sounds fine. If you have the time and it's not too difficult, I would suggest wiring everything in parallel and doing a comparison. Even though the Victron may struggle to find the best operating point, it's certainly not stressing the controller and the results would be interesting to compare to the series configuration.
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Old 10-22-2016, 04:43 PM   #11
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I thought I was being clever :(

The problem with everything in parallel (which would normally be my preference) is that I am capped at 17.5volts in ideal conditions. With a pwm based controller that is not a problem, however with a victron mppt it's another story....

The victron 100/50 mppt controller MUST see a minimum 5v delta between PV and battery voltage in order to begin its charging cycle.

So if my panels are kicking out 17.5v (again in ideal conditions) my battery would need to be no more than 12.5 volts before the victron would start its charging process, and that is in ideal sunlight.

So the issue is that the victron will simply not start charging if the battery has more than 12.5 volts and /or sunlight is not perfect and the panels kick out less than 17.5 volts.

A pwm charger does not have this issue (5v delta required before charging starts) but the victron does.

So higher voltage panels and/or wireing in series to deliver a higher voltage to the victron is required for it to work properly.

Hopefully that makes sense... I didn't know about the 5v delta requirement until after I purchased the unit. Nevertheless I am still optimistic that the mppt controller will will produce more amps to the battery with my panels as compared to my old pwm controller... we'll see here shortly....
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Old 10-26-2016, 11:30 PM   #12
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I thought I was being clever :(

Re-wired today in series / parallel.

100% increase in amps to the battery now that I'm not limiting the array to a measly max 4.35amps in ideal conditions no less...

I'm going to perform some more tests tomorrow to determine max output as measured by the victron system.

Also installed a victron 702 monitor today which makes a word of difference in evaluating SOC, charging and draw currents....

4 panels in series:
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2 panels in parallel and then connected in series to the remaining 2:
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Old 10-27-2016, 12:32 AM   #13
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Not an accurate comparison. Need the first config to be tested in bulk charge. Mine will drop to 1-2 amps going in in full sunlight with a full battery in float. I have the same Victron 702, same Victron 50 amp controller and 3x135 watt 24v panels. I would drain your batts a bit and test again
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Old 10-27-2016, 09:11 AM   #14
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yup, running some more tests today. In the past I was only able to get a max of 10-11Amps to the battery in Bulk mode (mid summer, clear sky at noon)...
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