Active string switching

[Lazlow]

I had a typo in my first post, it is the 5048GK not MK. The GE and GK are for the purposes of this discussion equivalent. My apologies for the time you wasted in exploring that. Just to be clear there will be three charge controllers/inverters (one per string) but they network together and act as one.

While this will be a new system, I have experience with both of these charge controllers and (to a much lesser extent) the other two charge controllers I mentioned. All four drop out at around 120V. I do not have any experience with the MK. At least one of the models (do not remember which) did continue outputting (at a dramatically lower level) after the mppt dropped out in a PWM manner. As a side note the Midnight Solar charge controllers also drop out, but at anything below 130% of battery voltage (not a specific number but the actual battery voltage at that instant).

Aside from that; you have a grasp of where I am headed.

 

[tictag]

Ahhh, OK, no problem. So, yes, it looks like the 5048GK is a little bit more modern than the 5048GE, with Bluetooth and USB etc, also supports up to 5kW PV. But the problem is defined - you are concerned that the array's Vmp will dip below 120V.

So here's where I'm struggling:



I appreciate that this is NOT your panel, I'm guessing your Voc to be around 49V, based on your Vmp. But that just means that the plots above just get shifted right along the x-axis.

An MPPT SCC will always try to find the Maximum Power Point (MPP), which can be visualised as the peak of each of the heavy lines above. For example:

At 1,000W/m² (i.e. STC), Pmax occurs at about Vmp = 31V, Imp = 8A (or 250W for this example panel)
At 600W/m² Pmp is achieved at about Vmp = 30V, Imp = 4.9A
At 200W/m², Pmp is achieved at about Vmp = 29V, Imp = 1.5A

Going from 1,000W/m² to 200W/m² represents a 400% decrease in solar irradiance but the panel only produces a 6% drop in voltage.

This performance chart exactly matches my own experience.

The voltage produced by my series-connected panels varies little during the day and, as mentioned in my previous post, my SCC remains switched on well after the sun goes to bed. OK, yes, I get bugger all charging current ... but that's not what we're talking about here.

I do not understand why a series-connected array of 10 x 49Voc = 490Voc would drop anywhere near, let alone below, 120V during the day - it should be able to produce more than 120V in moonlight!!

This is what is making my head hurt.

Edit: Added acronym clarifications