Three MPPTs??

[Marvin]

Thanks to the help from posters in my last post I understand about how different voltage/amperage panels on the same string can cause loss of power.

 

I have an existing 6KW Grid tied system with 2 MPPTs. I think I will need three or 4 MPPTs to be able to add different panels (old ones no longer available) to the system. Is there an economical way I can change my system?

 

Any ideas?

 

Marvin

 

 

[MikeSharp01]

Get a 4 mppt inverter 

 

[sharpener]

In short, get a second inverter to suit the new panels (?higher voltage rating). The interface to yr existing system will then be at 230V AC so the exact rating of the panels themselves is not important, only that they are matched to one another.

 

It is clear from yr table reproduced below that the old and new panel voltages are almost identical. From this we can deduce

(i) they probably both have the same number of cells as the volts per cell is pretty much a constant

(ii) it is the current capability that is different in order to account for the different nominal power

(iii) so you will not be able to mix old and new in a series string.

 

I don't see a way of connecting the new panels to your existing inverter to make use of its spare capacity, so you will have to replace it or, cheaper, add a second one. There is a company somewhere in the SW that advertises second hand ones on ebay.

 

If you have a battery system you could alternatively - depending on the capabilties of yr existing inverter - add the new panels on the DC side (I have 16 x 230W panels installed in 2011 on a grid-tied inverter and 8 x 405W installed in 2022 on the 48V DC bus via a Victron DC-DC MPPT).

 

320Watts panels				435Watt panels
	STC	NOCT			STC	NOCT
Power	320	237.1		Power	435	325
Voc\V	40.9	38.2		Voc\V	39.33	36.93
Vmp\V	33.9	31.3		Vmp\V	33.04	30.15

[Dillsue]

Going down the second inverter route likely means another G99 application so a tad more involved.

 

Are all the panels going to be facing the same direction as that has a big bearing on peak generation and hence what you can have on each of the existing MPPTs. How many new panels do you want to add?