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Old 05-24-2018, 06:01 PM   #1
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using two more different solar panel models

a friend is giving me his solar panels as he no longer needs them
they are a different make/model than what i have,10,20,581,729

i have a victron BlueSolar MPPT 100/30 MPPT controller

the max voltage & power output from the panels is differnat

can i place the two in parallel and still get good efficiency?
what happens to the voltage?
does the panel with higher voltage drop down to the lower voltage but send out a higher current

i do NOT want to put then in series , as the shading issue cause huge performance issues

can someone please advise

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Old 05-24-2018, 06:41 PM   #2
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If you have two panels with significantly different voltages, you have "huge efficiency issues". The stack can either take power efficiently from one *or* from the other one. There is no way to find a rational "max power point" for the combo. The controller will do it's best, but the result is not going to be pretty.

Simple math:

Panel one puts out 37 V at zero current.

Panel two puts out 27 V at zero current.

If the operating point is above 27V, nothing is coming out of panel two.

If the operating point is down around 23V ( so panel two is contributing ) you get current out of panel one. It's at 10V less than it should be. You just lost 1/3 of the output.

Consider that in series with diodes on the panels, your worst case is that you loose the output of the panel that is in the shade ( it has no light so ... no power ). That's it. Any other case will be more efficient than the "one out of commission" case.

So let's say that these things are equal power panels, but different voltages. That's a bit more fun. The higher voltage panel puts out about 1/3 less current than the lower voltage panel. Now pretty much no matter what you do ... yikes.

Simple answer: Grab a controller that does not mind being paralleled. Wire that up to the second set of panels.


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Old 05-24-2018, 06:51 PM   #3
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If they all are in parallel, they will average voltage. As such, arguably, if the Voc is within 1 volt of each other, the advantage of the added panels will outweigh the spec difference.

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Old 05-24-2018, 07:47 PM   #4
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Or you could series wire one old panel with one new one, then parallel a second set? If you have two old panels, and controller can handle voltage...
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Old 05-24-2018, 07:50 PM   #5
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ill see it i can get a less expensive MPPT controller to mage the 2nd panel

then each will mange their own type
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Old 05-25-2018, 12:31 PM   #6
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Originally Posted by waninae39 View Post
can i place the two in parallel and still get good efficiency? what happens to the voltage? does the panel with higher voltage drop down to the lower voltage but send out a higher current
You said "his solar panels", meaning you are adding more than one additional panel. However, I do not recommend mixing if the string voltage differences are greater than 5%.

Without knowing your panels' detail, especially given aging, you should expect some efficiency decrease. In general, the string with the lowest voltage limits the entire group on a single MPPT channel.

Please consider these as you upgrade:
1. Operate within the string sizing conditions for your Victron 100/30, using the Victron MPPT spreadsheet.
2. Make sure you have space in your combiner box for the additional fuses. Otherwise, you will need a new combiner. Properly size the fuses for the different string.
3. Properly size the conductors, combiner, disconnect switch, and over current protection for the additional panels.
4. Ensure you've implemented ground fault protection for the all panels. As stated in the Victron manual "The USA National Electrical Code (NEC) requires the use of an external ground fault protection device (GFPD). These MPPT chargers do not have internal ground fault protection. The system electrical negative should be bonded through a GFPD to earth ground at one (and only one) location.
5. Maintain the required single ground point, as the Victron manual requires: "The charger must not be connected with grounded PV arrays (one ground connection only)."

Should you choose to add a second MPPT charger, combiner, wiring, etc., use this opportunity to properly install your new system, and upgrade your older system, following the NEC.

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Old 05-25-2018, 01:31 PM   #7
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With the lack of info [ details of panels - models ] .
There can be no answer .
there are ways of mixing almost any panel , but it gets to be more than - working in the dark - no info on panels .
The link is general - not the model of panels your working with .
This may be a case where you need to find someone that knows solar electronics .
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Old 05-26-2018, 02:54 PM   #8
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I bought a Chinese mppt programmable controller as an experiment and it specifically says it can find the best point between 2x different panels on the input. I'm not using mixed panels but thought it was interesting that it supposedly can do that.
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Old 05-26-2018, 03:02 PM   #9
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using two more different solar panel models

Iíve done it. If you connect all panels in parallel the voltage of the lowest voltage rated panel will be what you see at the controller. Amperage is additive.

So you will loose some watts off the higher voltage rated panels but not that big a deal if they are all 12v nominal panels.

If you are using an MPPT controller their algorithms typically donít like a variance of more than 0.3v between panels... but it will work, just less efficient than a set of matching panels.

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