Different amperage strings tied in parallel - why not?

[67King]

So everything you read everywhere says that an input has to have panels all getting equal sun, blah blah blah. Looking at putting panels on a covered boat slip/dock, and I can run 2 strings, but I'd be beyond the nominal voltage. Why would I have a problem putting a 3rd input with an E facing 6 panel series string wired in parallel to a W facing 6 panel series string? How would the inverter "know" that the 17 Amps it sees is from one string making 11 amps and the other making 6, as opposed to each one 8.5? I know I could run optimizers or microinverters, but I don't understand why I'd need to spend that money?

Maybe everything I am reading only applies to series connected strings, and either I just miss that disclaimer, or it isn't made. But I don't see how it would matter if the parallel strings have different current.

 

[efficientPV]

The strings have to have close to equal nameplate voltage. No blocking diodes are needed. I run six strings of of panels in parallel. Usually about 60-70% of them are shaded at any time. Panels will not absorb power if shaded.

 

[SamDeleted]

You can mix panels of different watts, volts and amps , in series and parallel .

You just pay a price for the privilege

Try this calculator

Solar Panel Series & Parallel Calculator - Footprint Hero

Use our solar panel series and parallel calculator to easily find the wiring configuration that maximizes the power output of your solar panels.

footprinthero.com

 

[SamDeleted]

It can actually work out really well if you're careful

 

[efficientPV]

There is no price to pay if you aren't stupid.

 

[SamDeleted]

There is no price to pay if you aren't stupid.

like a lot of things in life

 

[chrisski]

I think it would be OK, but I’d really want to review carefully the specs on the inverter and not exceed any of them.

I feed my solar into SCCs not inverters. On one smaller setup I have 300 watts each in an East, South and West facing strings to provide a couple hundred watts shortly after sunrise throughout the day. My SCC does not care what each individual string is outputting, only the amperage that can be supplied total. This is not a grid tied setup so, the SCC only draws what it needs from the panels, not the max amount it can push.

 

[67King]

Looking at BlueSun 460W panels, 50.8V, 11.22A. Sol-Ark 15K, 3 MPPT's, nominal voltage 175-425V. Max current 25Amps. I'm well within all of that. From the replies, there appears to be no reason I can't do that. Since they are facing E-W and opposing each other, each series wired string will be producing a different output (current) for all but a brief period around high noon. At high noon, I should be 304.8V@22.44A.

 

[Vigo]

The amps dont matter as long as the max that will actually be simultaneuously produced is not WAY over what the solar controller is rated for. The voltage matters a lot because if the arrays are at wildly different voltages, the highest voltage string will act more or less normally and the lower voltage strings will contribute very little. In terms of ‘maximum power point’ unless the strings are acting basically the same you will never be hitting the maximum power point of each array other than by coincidence. You will just be getting the maximum power point of the whole mess, which could be close to ideal or VERY far from it depending on how different the strings are.

If youre paralleling strings that due to orientation or shading are never really producing at the same time anyway, then its pretty much completetely fine, dont overthink it, and just go ahead. ?

 

[Tomthumb62]

You can mix panels of different watts, volts and amps , in series and parallel .

You just pay a price for the privilege

Try this calculator

Solar Panel Series & Parallel Calculator - Footprint Hero

Use our solar panel series and parallel calculator to easily find the wiring configuration that maximizes the power output of your solar panels.

footprinthero.com

Thank you. THAT is an awesome calculator. I have three sets of different panels, two of each kind. Any way they're configured there is a 3 to 3.6% loss due to the slightly different voltage/amps of each type of panel. Which is really nice to know that it really doesn't make that much of a difference how they're wired (in my case) other than if all 6 are in parallel, that will require thicker wiring to handle the amps. Which is how I wired it up, so if I ever switch to 2s3p the wiring will be just fine if not overkill and switching back to 6p will be dandy as well.

 

[chrisski]

Thank you. THAT is an awesome calculator.

I noticed this calculator does not determine wire losses for parallel wiring or check for max ampacity of wires.

I went 2s3p versus 6p for wires losses and ampacity.