Thoughts on three panel system

[regult51]

Hello - looking to install three panels on my Sprinter van. Space constraints dictate panel choice. Two thin ones sandwiching fan and rectangular in front topping them. I'm thinking series connections is best to maximize voltage to charge lithium battery bank (3x100ah). This is what I'm considering:

2x thin panels:
Solarland SLP080S-12M mono 80w
Vmp: 18.46
Imp: 4.33
Voc: 22.52
Isc: 4.56
**OR**
Solarland SLP080-12M multi 80w
Vmp: 17.2
Imp: 4.65
Voc: 21.6
Isc: 5.17

top panel:
Solarland SLP075-12 multi 75w
Vmp: 18.4
Imp: 4.08
Voc: 22.0
Isc: 4.51
**OR**
Renogy mono 100w (compact)
Vmp: 17.9
Imp: 5.72
Voc: 21.6
Isc: 6.24

I was going to pair it with a Victron 100/20 charge controller:

Questions:
- the SLP080S and SLP075 have very similar electrical stats. Perhaps best to use those panels and wire parallel?
- perhaps best to wire parallel the SLP080S and the higher wattage Renogy? My calcs seem to indicate higher wattage vs series.
- wiring order: if I go series, is the order of wiring relevant i.e. higher voltage first?

Thanks!

-r51

 

[MisterSandals]

Putting all 3 in series will add the voltages and clip amps to the lowest of the series. You can take the voltage of each panel and multiply that by the lowest amp panel. Sum wattage from that to get string output in watts.

For parallel, it will add the amps and clip the volts to the lowest of the parallel set. Do the same math but using the lowest voltage and each panels' amps to get the parallel string watts.

It looks like 3 of any of those panels will stay within the 100/20 input voltage so that's not an issue. Similarly, 3 of any of those in parallel will only be roughly 15 amps so not an issue.

Looking them over, my best guess would be:
2x Solarland SLP080-12M multi 80w (Imp: 4.65) in series with

1x Renogy mono 100w (compact) (Imp: 5.72 clipped to 4.65) 100w x (4.65/5.72) = 80.9w (19w loss)

 

[regult51]

Thanks! Should the Renogy (Vmp 17.9) be wired first in the series string, to allow the higher voltage to flow through to the SLP080 (Vmp 17.2)?

 

[MisterSandals]

Thanks! Should the Renogy (Vmp 17.9) be wired first in the series string, to allow the higher voltage to flow through to the SLP080 (Vmp 17.2)?

Good question, i never thought about it in that much detail. If you get a chance to try it both ways, I'd be interested to hear the results. I <now> wonder if its the location of the lower/higher amp panel (since in series (Edit: was parallel) it would be clipping amps) that matters as opposed to the voltage (though they are very intertwined).

 

[Whinny]

IMHO it would make zero difference, which way does current flow??

 

[orangeminnie]

Thanks! Should the Renogy (Vmp 17.9) be wired first in the series string, to allow the higher voltage to flow through to the SLP080 (Vmp 17.2)?

Series circuits don't care what order the devices are in.

 

[regult51]

Thanks for all the comments.
Since the panels are mismatched, better to go with:
A) match panels as closely as possible electrically, with lower overall production - 2x80w, 1x75w)?
B) go with the greater mismatch but higher production (2x80w, 1x100w)?

 

[MisterSandals]

A) match panels as closely as possible electrically, with lower overall production - 2x80w, 1x75w)?

Why are you saying this is closer “electrically”? Based on watts?
I chose the other setup because the panel amps were closer (electrically). And this combination had the least amount of loss because the amps are closer which also helps greater production.

 

[regult51]

Why are you saying this is closer “electrically”? Based on watts?

I'm assuming that for solar arrays, ideally all the panels would be identical. I can't due to space constraints, so two panel types that are closely spec'd, should be most efficient.

I should just run the calcs:

Series:
1)
2x slp080s + 1 slp075 (235w array)
(18.46v x2 + 18.4v) * 4.08a = 225w

2)
2x slp080s + 1 renogy (260w array)
(18.46v x2 + 17.9v) * 4.33a = 237w

3)
2x slp080 + 1 slp075 (235w array)
(17.2v x2 + 18.4v) * 4.08a = 215w

4)
2x slp080 + 1 renogy (260w array)
(17.2v x2 + 17.9v) * 4.65a = 243w

If I run the panel "electrically closest" in parallel, I'll get:
5)
2x slp080s + 1 slp075 (235w array)
18.4v (4.33a x2 + 4.08a) = 234w

So it looks like my best choice for absolute power output would be the #4, which is what you called for - great!

Alternatively, I could run #5 for a very efficient system, considering I'm using two panel types. However, reviewing the numbers and especially desiring to run the array in series, I think #4 is the winner.

Thanks for humoring me as much of this was me thinking out loud!