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Old 15-03-2017, 19:37   #1
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Adding another solar panel

I.have 3 275watt panels installed. I wish to add a 4th. Does it matter if I use a panel from another manufacturer as long as the specifications are similar?
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Old 15-03-2017, 21:06   #2
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Re: Adding another solar panel

No as long as the voltages are same
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Old 15-03-2017, 23:54   #3
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Re: Adding another solar panel

If you are using a MTTP controller the Vmp needs to be the same.
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Old 16-03-2017, 01:56   #4
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Re: Adding another solar panel

Correction:

If you are using a MPPT controller the Vmp needs to be the same.
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Old 16-03-2017, 04:49   #5
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Re: Adding another solar panel

I believe controllers like the Victron give more flexibility than others?

panels in series, match Amps (I think Imp)

in parallel (incl series strings in parallel) match Volts (Vmp?)

on both "pretty close" is OK
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Old 16-03-2017, 11:32   #6
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Re: Adding another solar panel

I am going to run four panels in two strings so both in series and parallel. I have an Outback mppt controller does the new panel need to be exactly the same voltage as the old ones or can it be within a couple of volts?
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Old 16-03-2017, 11:47   #7
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Re: Adding another solar panel

I had a similar issue not long ago. Where I landed was that if the Vmp isn't within a few percentage of each other, then there will be measurable efficiency loss. Thinking in the range of low tenths of a volt. Otherwise, the MPPT will try to hit the average Vmp, which won't be optimal for any panel. If you're average Vmp drops by 5% (about a 1 volt drop), then you, more or less, lose 5% of the panel's rated output.

For whatever reason, my original panels have a rather odd Vmp, which I couldn't come close to matching. I sold my big solar controller and replaced it with two smaller ones, with no outlay of additional cash. If I had to spend $100+ on a new controller, I might have went down a different path. Maybe.
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Old 16-03-2017, 12:08   #8
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Re: Adding another solar panel

Quote:
Originally Posted by newhaul View Post
No as long as the voltages are same
This has me thinking, I have four 250W panels in Parallel, when one is shaded it often falls to 24 VDC or so while the other three are 35 VDC.
Is the low volt one just not contributing anything in that instance? Cause when its cloudy the output for the whole array will fall to 24 VDC of so, yet it still charges the bank at 20 amps or so.
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Old 16-03-2017, 12:12   #9
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Re: Adding another solar panel

In theory, a perfect match is best. How else can the controller optimize the conversion?

However, with shading, and differences in wire length, temperature, sun angle, and aging, unless each panel has a dedicated controller, there will be always be some mismatch.

The truth is that you should be able to find something very close.
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Old 16-03-2017, 18:47   #10
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Re: Adding another solar panel

Ok so I've been searching online and cannot find a panel with similar voltages. Here's what I'm looking for if anybody knows of a brand that matches
275 watts. Mpv 35.82 mpc 7.86 ocv 46.98. Short circuit current 8.18
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Old 17-03-2017, 15:15   #11
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Re: Adding another solar panel

The company that made my solar panels in Spain as went out of business. Anybody that can just a 275 watt panel with similar voltage as I posted it would be greatly appreciated
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