Mixing Solar Panel Types

TheBatteries

TheBatteries

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I asked this a while ago and I remember Daniel telling me it's a bad idea, but I don't understand why and want some more information...

Right now I have 8pcs of 36V solar panels. The specs are 320W, 46.2Voc, 37.3Vmp. I cannot wire these in 3s on the PCM60X because on bright sunny cold winter days, the open circuit voltage exceeds what the PCM60X can handle and the unit shuts down. To prevent this from happening, I have the panels wired in 2s giving 92.4Voc and 74.6Vmp. The minimum MPPT voltage for the PCM60X is 60V, so I feel like I'm losing some power I could be harnessing in the early morning/late evening by running my strings at only 92.4Voc.

I also have 4pcs of 12V Renogy panels. The specs on these are 100W, 22.5Voc, 18.9Vmp.

I would like to wire them like this
320W-320W-100W||
320W-320W-100W||
320W-320W-100W||
320W-320W-100W||== Combined Output

Doing this would give me 114.9Voc and 93.5Vmp. I was told before this was a bad idea. If all the 320W are exactly the same and all the 100W are exactly the same, each 3-panel string is exactly the same. Why would this be bad an I lose efficiency?
 
mike said:
I asked this a while ago and I remember Daniel telling me it's a bad idea, but I don't understand why and want some more information...

Right now I have 8pcs of 36V solar panels. The specs are 320W, 46.2Voc, 37.3Vmp. I cannot wire these in 3s on the PCM60X because on bright sunny cold winter days, the open circuit voltage exceeds what the PCM60X can handle and the unit shuts down. To prevent this from happening, I have the panels wired in 2s giving 92.4Voc and 74.6Vmp. The minimum MPPT voltage for the PCM60X is 60V, so I feel like I'm losing some power I could be harnessing in the early morning/late evening by running my strings at only 92.4Voc.

I also have 4pcs of 12V Renogy panels. The specs on these are 100W, 22.5Voc, 18.9Vmp.

I would like to wire them like this
320W-320W-100W||
320W-320W-100W||
320W-320W-100W||
320W-320W-100W||== Combined Output

Doing this would give me 114.9Voc and 93.5Vmp. I was told before this was a bad idea. If all the 320W are exactly the same and all the 100W are exactly the same, each 3-panel string is exactly the same. Why would this be bad an I lose efficiency?
Click to expand...
Each string will push current at the rate of the lowest rated panel
 
mike said:
Ooooooh I see. So you're saying because the operating current of the 100w is 5.29A, the 320W panels will never exceed that? Meaning they operate at roughly 63%...
Click to expand...

Yep

Also make sure Voc doesnt exceed charge controller input voltage limit.
In the USA most controllers are 150v max due to NEC codes
 
It would be better to connect all 3 100W panels together and then tie them into the others. However, to get the best MPPT out of each set, you'd want an MPPT on each string, so you'd have 5 based on the above.
320W-320W||
320W-320W||
320W-320W||
320W-320W||
100W-100W-100W-100W||

But, you could do
320W-320W-320W-320W||
320W-320W-320W-320W||
100W-100W-100W-100W||

And have 3 MPPT controllers. You want to have each "zone" with it's own MPPT controller so you can maximize them. Some MPPT have more than 1 string capability.
I don't remember what you're panel layout is, but lets say you have a string on each side of the roof peak, then have a string below those. So that's 4 strings. But because they have different angles, you need different MPPT's for them. If you have (going over the roof) 100W, 320W (peak) 320W, 100W strings, because of difference in wattage on each level, you'd need 4 total.
I hope I got that explained right. My brain is a little foggy with the wording :p
 
It might work to put the 100 Watt panels in series. This woulkd give you about same voltage as the 320 Watt panels, an the consider the series connected 100 watt's an extra 320 watts.
 
If you going to parallel the 100w with 320w you need to have the exact same voltage. If not you will loose some wattage from the setup. The most optimal is to split them and not use 100W on same as the 320W panels because they are not optimal to hook together in any combination.
 
The PCM60X will still run the panels at their MP point even in the morning/evening, so you're not loosing any significant power early morning/late evening!

If you watch the voltage from the panels as the sun comes up at first light (hopefully from a data logger!) you'll see the voltage comes up quickly to the MP voltage (~74V for you?) & stays around there until the batteries are full, when the controller lets the voltage rise towards Voc (or maybe a bit less with house load). The actual power from the panels before they get to 60V is negligibly small. When the charger first switches on you can see the watts collected are pretty small & same as the sun drops in the evening.

Actually, 4x the 100W panels Vmp of 18.9V = ~75.6 which is very close to the 74.6V Vmp of 2x the 320W panels.
So you could just connect like Korisahn suggested & it would be a pretty good match:
320W-320W||
320W-320W||
320W-320W||
320W-320W||
100W-100W-100W-100W||

That should give you about 2960W into the PCM60X and (depending on the battery voltage at the time) be around 60A charger output ie maxed out!
 
I would say its more of 2850W if we compare and look at the voltages they give out. Its still very close to max. The panels behave different. :) (Its like combining different batteries in parallel.. )

Are all panels the same? Poly vs Mono? If not they can diff even more. Note that the Vmp is different based on the incoming sun as well.

But yeah Korishans suggestion will for sure work!
 
Ok, stop saying my suggestion is right (jk), my head will explode from all the ego boosts :p
 
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