DID almost same as you, the BIGGIE is to make sure each string is < 450VDC (
you can go to 500) they prefer you don't
and watch the amperage. Each MPPT can take two strings, (there in parallel) On a Sunpower retrofit, where I removed the dead SMA sunnboys
(a pair) and replaced with a Sol-Ark 15k
Here is Mine.
MPPT 1:
#1 – 407VDC 3AMP
#2 – 407VDC 3AMP
MPPT2:
#3 – 291VDC 2.3AMP
#4 – 468VDC 3.4AMP
MPPT3:
#5 -- 420VDC 3.1AMP
#6 – 180VDC? 2.3AMP?
String 6 was we had to remove three panels from the old group and run a new string, I was over volting
electrician gave me the readings, but I never wrote them down
Jonathan
When you connect parallel strings into a single MPPT, the total output power is limited by the VOLTAGE of the lower-voltage string. The CURRENT adds together (from two or even 3 strings) with no loss.
But WITHIN each string (of panels wired in series), the current received by the MPPT is limited to the current of the lowest-performing panel. This is why some installations add 'optimizers' to each panel - the job of each 'optimizer' is to cut out the panel from the string when the panel's own current is seen to be much lower than the current value from the other running panels.
When active, its acts sort of like like a string of Chrsttmas lights - the low-perfoming light is made to go out completely, while the the others remain at ful brighness. Without optimizers, it would be like all panel becoming "dim" when only one or two have become shaded.
- - - -
In any case, you need to re-arrange your strings so that each MPPT is connected to strings with roughly the same VOLTAGE. On a Sol-Ark 15K, with each MMPT supporting current up to 26A (and safely protecting from even higher values), you have zero concerns with current - all six parallel strings could wired into a single MPPT. But in using only one MMPT, the widely varying VOLTAGE values would yield only 180 volts * 17.1 amps= 3078 watts of input power.
Strings #1 and 2 could be combined with string #5 on a single MPPT, degrading the voltage of string #5 from 420 volts to 407 volts. That's not a huge power loss. Your high-voltage string #4 exceeds the MPPT operating limit of the Sol-Ark units. It might work at 450 volts 3.4 amps, using "MPPT2 all by itself. And that is what I would do - alone on MMPT2
String #3 (2.3A @ 291 Volts = 669 watts input) should be isolated on MPPT3, because it's very low voltage would degrade the performance of any other "higher voltage" string on the same MPPT.
String #6 offers only 414 watts to begin with. The only possible combination (with string #3) would pull down the power of String #3 from 669 to 4141, a loss of 348 watts -- the net "gain" in the combination would be only around 60 watts, probably not worth the extra wiring hassles. So I would put string #3 on MMPT3 alone, not connecting string #6 at all.
- - -
In my scheme, your peak input power would be about 3700 watts from MPPT1 (Strings 1+2+5, with 5 degraded to 407 volts); 1530 watts from MPPT (String 4 alone, downgrade to 450 volts); and 700 watts from MPPT3 (String 3 alone). That's only 5300 watts total.
The 3 big MPPT units within the Sol-Ark 15K are EACH capable of far more, but your panel arrangement is weird - what sort of panels put out only 3 amps? Please diagram or describe the strings, and the individual panels they contain.
