Hello,
I think that the MPPT algorithm to find the global power maximum is not working correctly.
When there is a cloudless sky and shading begins (hard shadow, caused by e.g. a wall, roof etc.) the algorithm of the shadow management gets stuck in a local maximum.
Example figure taken from Wikipedia - MPPT
My AC500 has two strings, each of them with three PV modules. The first string has one module which gets a (hard) shadow from a wall, beginning at ca. 15:00 (UTC + 2h). This is annoying because the highest sun position is at ca. 13:30 and therefore, there is a considerable loss.
(Shade on module 1 of string 1 at 15:45, 2024/09/30)
As the modules have bypass diodes, a good working MPPT should reduce the loss.
But what happens? See the next figure.
(Power production of string 1 and 2 at 15:47-15:48, 2024/09/30).
String 1 produces only 53 W. Then I switched off this string, waited a few seconds and switched it on again. And - what a surprise - the bypass is working and I will get 634 W.
The next day (1st october) I disconnected the two unshaded modules of string 1;
only the shaded one remained. Data were registered nearly at the same time, 15:51-15:52.
(Power production of string 1 with only the shaded module and 2 at 15:51-15:52, 2024/10/01).
The effect was the same: Before switching off string 1 it produces 22 W and after turning on again 154 W.
Well, maybe I’m wrong, I’m neither a PV expert nor an electrician but as far as I have read the past fortnight about shading and bypassing and power point tracking etc. I think it’s the AC500 MPPT algorithm that is caught in a local minimum.
I hope that the Bluetti tecnicians will improve the algorithm because disconnecting and connecting the string when the sun shines is no good idea. At the moment the best is an almost clear sky with some little clouds - which will break down the voltage for some time and thus help to find the global maximum.
