A few days ago, I noted that I have made a tiny misstake when sizing the mppts, and that there is the highly unlikely case that my 150/70 mppt would encounter a open-circuit-voltage of 160V on a sunny winter day at -10° .
Most likely this would never have happened, however I replaced that guy with a 250/70, just to have everything “in line” with specifications (and eventually add another set of panels as well)
So, I’m now running two mppts, with the following arrays:
250/85 with 2x6 SOLARWATT 405W-31V SOLARWATT Panel vision AM 4.0 (405 Wp) black
250/70 with 2x4 SOLARWATT 405W-31V SOLARWATT Panel vision AM 4.0 (405 Wp) black
This currently results in Operation-Voltages of ~ 120V and 180V.
Now, surprisingly the 250 running at 120V shows an about 10% higher efficency than the 250 running at 180V, at least during the first 3h of the day so far. (Panels have same orientation ofc.)
Are there official efficency / mppt curves somewhere? Just wondering if this is explainable with regular efficency behaviour / mpp selection, or if my “larger” array is encountering some sort of current limitation due to “whatever”?
Cant say much about the MPPTs themselves, but it would be interesting to see the strings connected vice versa, to rule out if the difference is due to the panels
Nvm i guess, didnt notice that one has six and the other has four panels
I haven’t seen any. Doesn’t mean they don’t exist.
Orientation will play a part. Also is cable distance the same?
Is there a difference in charger temperature?
10% isn’t huge.
And probably it would be better to switch them to a 2x 2x5 layout, so both will operate at ~150V (if lower voltage is causing a higher efficency by default)
Uneven distribution was due to the 250/150 selection made earlier to match the “physical clustering” of the panels.
With better “angle”, the difference starts to vanish, or at least comes down to neglectable values:
Whatsoever, I will flip the strings in a couple of days, to see if this makes a difference, especially for the MPPT-Temperatures. (Values are measured on the central backside)
You charge a 48V battery, right?
A possible reason could be the MPPT with a smaller difference to 48V will work more efficiently, probably because the switching will be in a more efficient area of the buck FETs functioning. The other MPPT could switch in a marginal side of the efficiency curve of the FETs.
Yeah, Read that as well and makes sence that the difference towards 48 (or 52V) has an impact on DC-DC conversion efficency. Just wouldn’t have expected it to be that large.
Meanwhile, they are now talking with each other, it seems
PV-Currents are now about the same, which is what I would “expect” from the similiar layouts:
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