using 2 different panel types?

[defed]

will this panel combination cause any noticeable issues? i think that they are close enough, but just want to be sure.

there would be (4) of each type, (2) sets of each in series pairs (4 series pair) paralleled in a combiner box to the mppt (60a) controller.

the main difference (besides the 5w rating difference) is "SET A" is multicrystalline and "SET B" is monocrystalline. i can't find "SET A" anymore. also want to be sure mixing mono and multi is ok....pretty sure it is as i've seen several ppl doing it.

"SET A" (multi)

Power (W) 175 Watts
Open Circuit Voltage (V) 43.60 Voc
Short Circuit Current (A) 5.30 Isc
Maximum Power Voltage (V) 36.10 Vmp
Maximum Power Current (A) 4.85 Imp
mV/C -160

"SET B" (mono)

Power (W) 170 Watts
Open Circuit Voltage (V) 43.80 Voc
Short Circuit Current (A) 5.14 Isc
Maximum Power Voltage (V) 35.20 Vmp
Maximum Power Current (A) 4.83 Imp
mV/C -149

i used the xantrex mppt string configuration tool on each panel, and the charging amps for them are nearly identical (22a vs 23a at PTC) though wattage does differ (17w PTC under proposed config).

thanks.

[defed]

here are 2 scenarios of hooking the panels in the same system:

panel A

36.10v
4.85a

panel B

35.20v
4.83a

scenario 1:

if i connect, in series, (1) panel A with (1) panel B, i would add voltage but each panel would be restricted by the lowest amp rating:

(36.10v + 35.20v) x 4.83a = 344.379w per series set.

1377.516w total array wattage of (4) series pairs.

scenario 2:

if i connect, in series, like panels ( (2) panel A or (2) panel B) and then parallel them, i would add amps, but be restricted by the lowest voltage rating:

35.20v x (4.85a + 4.83a) = 340.736w per series set.

1362.944w total array wattage of (4) series pairs.

am i doing this correct? if so, is there a problem putting a panel A in series w/ a panel B?

[ghurd]

Series one of A with one of B.

All 4 pairs would operate at the same Vmp (36.10 + 35.20).

The difference in Imp is only 20mA.  Less than half of a %.
The panel's sticker is nowhere near that close.

For calculating each pair, try Vmp is 71.3V, Imp is 4.835A.
G-

[defed]

there shouldn't be an issue w/ putting a mono and multi-chrystalline panel in series with each other?  i forgot to re-mention that in my 'scenarios' posting.

i was thinking that since the amp ratings were nearly identical, that putting one of each in series would be best...i should also repeat that i have a xantrex mppt, and wanted to be sure this combo wouldn't 'confuse' it.

not sure what you mean by this:  "The panel's sticker is nowhere near that close."

thanks for the advice.

[ghurd]

"The panel's sticker is nowhere near that close."
The sticker is sort of a guess at the minimum.  They just are not as close to the sticker as you think they are.

Test the exact same panels in the exact same conditions, and there will be a lot more variation than 20mA.  And the one with the higher amp output may be the one with a lower amp output if something changes (the temperature, humidity, angle the sun is hitting them)

It would not surprise me at all if one of panel A had a lower Vmp than one of panel B.
And another one of panel B had a higher Imp than one of panel A.

The panels are a current source. 
And each in the series pair (one of A, one of B) will operate at the same amount of current, just a little different Vmp voltage.  The controller has no way to know if one is 12V and the other is 48V, it only knows the combined Vmp.

[defed]

i used xantrex's mppt configuration tool with each panel.  it lists the STC and PTC, and had both panels in its database, so i at least have an idea of the 'rated ' power vs the 'actual' power that each generates.  if i recall, the amperages of series pairs (2 A's or 2 B's) were within 1 amp of each other.

this, of course, does not take into account differences amongst panels of even the same brand/model.

since their STC and PTC specs were fairly close, and the amperages were the same, i figured it would be easier on the mppt to series one of each, but just wanted to be sure it would work like i thought it would.
 

[Ungrounded Lightning Rod]

there would be (4) of each type, (2) sets of each in series pairs (4 series pair) paralleled in a combiner box to the mppt (60a) controller.

"SET A" (multi)

Maximum Power Voltage (V) 36.10 Vmp

"SET B" (mono)

Maximum Power Voltage (V) 35.20 Vmp

The maximum power curve is a hump, so it's pretty flat near the max and a nontrivial change in voltage will give you a small change in power.

I'd put them in series pairs of like types, parallel the pairs, and set the common max power controller to a voltage that splits the difference between the two types - 35.7V (plus the voltage drop of the wiring from the panels to the controller).  Also:  If the wiring lengths from different pairs to the controller is different I'd put the higher-voltage panels farther out, so they'll run closer to their max power due to the greater voltage drop in the wiring (and tweak up the controller setpoint accordingly.)

[defed]

there would be (4) of each type, (2) sets of each in series pairs (4 series pair) paralleled in a combiner box to the mppt (60a) controller.

"SET A" (multi)

Maximum Power Voltage (V) 36.10 Vmp

"SET B" (mono)

Maximum Power Voltage (V) 35.20 Vmp

The maximum power curve is a hump, so it's pretty flat near the max and a nontrivial change in voltage will give you a small change in power.

I'd put them in series pairs of like types, parallel the pairs, and set the common max power controller to a voltage that splits the difference between the two types - 35.7V (plus the voltage drop of the wiring from the panels to the controller).  Also:  If the wiring lengths from different pairs to the controller is different I'd put the higher-voltage panels farther out, so they'll run closer to their max power due to the greater voltage drop in the wiring (and tweak up the controller setpoint accordingly.)

ok, i do see that the xantrex mppt has a parameter for setting a manual 'reference voltage' for the input.  i had forgotten about that, since i currently don't need it w/ all the same panels, it is set to 'auto'.  in fact, i never quite understood what it was for until now.

i guess the only concern w/ doing it as you suggest is the difference in the thermal coefficients.  at something like 95F, i believe the output voltages will be equal, and as temps drop, they will get further apart.  i live in an area where we rarely see 95F.  summer usually peaks in the 80's, fall and spring highs are 60's and winters can go down to 0F.

[Ungrounded Lightning Rod]

there would be (4) of each type, (2) sets of each in series pairs (4 series pair) paralleled in a combiner box to the mppt (60a) controller.

"SET A" (multi)

Maximum Power Voltage (V) 36.10 Vmp

"SET B" (mono)

Maximum Power Voltage (V) 35.20 Vmp

The maximum power curve is a hump, so it's pretty flat near the max and a nontrivial change in voltage will give you a small change in power.

I'd put them in series pairs of like types, parallel the pairs, and set the common max power controller to a voltage that splits the difference between the two types - 35.7V (plus the voltage drop of the wiring from the panels to the controller).  Also:  If the wiring lengths from different pairs to the controller is different I'd put the higher-voltage panels farther out, so they'll run closer to their max power due to the greater voltage drop in the wiring (and tweak up the controller setpoint accordingly.)

ok, i do see that the xantrex mppt has a parameter for setting a manual 'reference voltage' for the input.  i had forgotten about that, since i currently don't need it w/ all the same panels, it is set to 'auto'.  in fact, i never quite understood what it was for until now.

i guess the only concern w/ doing it as you suggest is the difference in the thermal coefficients.  at something like 95F, i believe the output voltages will be equal, and as temps drop, they will get further apart.  i live in an area where we rarely see 95F.  summer usually peaks in the 80's, fall and spring highs are 60's and winters can go down to 0F.

If the controller has an "auto" setting it may hunt for the actual max power point by cycling around it and measuring the result.  If this is the case it will find the max power point of the combined array.  In that case the auto setting may do better than any fixed setpoint voltage.

The fact that the max power voltages of the panels are close means that the combined array should have a max power point that produces a power level close to that of the sums of the outputs of the panels if they were operating at their individual optima.

[ghurd]

I think we are all saying the same thing.  'Mostly'.

I would be a hair more concerned with the rated Vmp since the Imp are nearly identical.
The concern comes from some experiments regarding a tracker concept for another member I did a few years ago, though I won't mention her by name.
The experiment involved various silicon structures, from various manufacturers, shipped in the same factory packaged skids/boxes (so presumably from the same production lots).
The results showed I remained relatively stable, but when I was the same (within 1~5mA?), E varied wildly under slightly differing conditions.

All that leads me back to ULR's "a nontrivial change in voltage will give you a small change in power",
and my "will operate at the same amount of current, just a little different Vmp voltage".

Back to 'mostly'.
No matter the configuration, they will each do about 4.84A Imp.
In like series pairs, 72.2V and 70.4V Vmp.  That is far more than the Imp percentage.
I would be more concerned with the Vmp under these circumstances.

The numbers are so close, I doubt it will make any difference at sunset.


ULR said "If the controller has an "auto" setting it may hunt for the actual max power point by cycling around it and measuring the result.  If this is the case it will find the max power point of the combined array.  In that case the auto setting may do better than any fixed setpoint voltage."
I agree.  A lot.
Vmp varies, and it can be the opposite of what is expected.
G-

[rossw]

If this is the case it will find the max power point of the combined array.  In that case the auto setting may do better than any fixed setpoint voltage."
I agree.  A lot.
Vmp varies, and it can be the opposite of what is expected.

I'd just like to add here that I agree completely from observed facts.

I have 6 arrays. 5 have similar modules (6 in series for around 100V DC output), the remaining one is totally different cell type (poly, not mono, 80 not 100W, different brands etc).

Of the 5 "similar" arrays, 3 are tracking, 2 are seasonal-only adjustment.
All experience different weather conditions (wind and therefore cell temperatures) etc.

All 6 arrays are parallelled (but each has a large schottky diode in series) and the output of that goes to a FlexMax 80 MPPT. It is abundantly clear from its performance that it hunts for the best power point across *ALL* the modules at any given time, and it does it quite well.

[defed]

so, from the sounds of it, i'll should be ok running (2) pairs of like panels (4 pairs total 2 of A and 2 of B), running them to the combiner box, then to the mppt.  and i may be ok just letting the mppt find the curve or i could set it to the average of the 2 arrays if i have to.