Questions about over paneling and derating

[merckmaverickz]

I have a question about the BluePower SP6548 Inverters, but it could apply to a general over paneling/derating question. If the unit is rated for 8000 watts of PV input on 2 strings 4000watts max each. Can the panels total watts be higher than that for example 10 panels (5S2P, 5 panels in series, in parallel with 2 rows) of 445w = 4450 watts per string. Two PV inputs would take that to 8900 (typo corrected) watts, which is higher than the rated 8000 watts, but will the derating keep that under 8000w, or should the panel array be reduced? The unit can only generate 6500 watts AC, so I'm not sure if it even makes sense to over panel anyway? Let me know what you think.

 

[Groscout]

I’m pretty sure you mean 8900 watts. 900 watts over shouldn’t be an issue. But you should check with the manufacturer or wait until someone chimes in with a “I did that and it worked for years”.

 

[rmaddy]

Nothing about this is related to derating. This is all about over paneling. You should have no trouble putting 4450W on each MPPT input. If your panels happen to be able to produce more than 4000W in the current solar conditions then the MPPT will only make use of 4000W and the extra potential will simply go unused.

Keep in mind that the max PV wattage has nothing to do with the inverter's AC output so don't worry about the 6500W AC output when thinking about the PV input wattage.

One thing I'm confused by with this unit is that is claims a max 120A charge current. 120A x 48V = 5760W. Is that 120A for each of the 2 MPPTs? 5760W is well over 4000W but well under the 8000W total. Not sure what that means.

 

[merckmaverickz]

I’m pretty sure you mean 8900 watts. 900 watts over shouldn’t be an issue. But you should check with the manufacturer or wait until someone chimes in with a “I did that and it worked for years”.

yes typo, thanks I corrected it

 

[merckmaverickz]

Nothing about this is related to derating. This is all about over paneling. You should have no trouble putting 4450W on each MPPT input. If your panels happen to be able to produce more than 4000W in the current solar conditions then the MPPT will only make use of 4000W and the extra potential will simply go unused.

Keep in mind that the max PV wattage has nothing to do with the inverter's AC output so don't worry about the 6500W AC output when thinking about the PV input wattage.

One thing I'm confused by with this unit is that is claims a max 120A charge current. 120A x 48V = 5760W. Is that 120A for each of the 2 MPPTs? 5760W is well over 4000W but well under the 8000W total. Not sure what that means.

but if they produce more than the 4000W wouldn't that damage the MPPT module/inverter? The manufacturer simply recommends staying under 4000 watts per string: Here was my question and their response:

"QUESTION: how many of these panels can I connect safely to each of your inverter units? (445watt panels at Voc of 49, we could only have 5 connected?)

ANSWER: As long as the PV array MPPT voltage is 90-230VDC and less than 8000w(4000*2) that would be ok, there are two PV array ports in this SP6548 unit"

I was referring to derating as the panels would never produce their maximum rated value, Isn't that referred to as derating? Let me know, and thanks for answering

 

[rmaddy]

but if they produce more than the 4000W wouldn't that damage the MPPT module/inverter?

Panels don't push power into a solar charge controller. The controller takes what it needs, limited by the max the panels can produce at the moment.

It's no different than an electrical plug in your home. Let's say you have a 120V 15A outlet. That means the outlet can provide up to 1800W. You can plug in a 60W light. When the light is on the light will only take 60W from the outlet. When off it doesn't take any watts. The outlet isn't pushing 1800W to the light.

It's no different with the SCC and solar panels. When your battery is full and there are no loads, the SCC doesn't need any power. Even if your panels are out in the sun in midday in the summer and capable of producing 4400W, the SCC doesn't take anything and it's all happy. Now if you turn on lots of loads for the inverter, say 6500W of loads, then the SCC will take everything it can get from the panels. But it can only take 4000W per MPPT so that is all it will take, even if the panels could be producing more at that moment.

This is how most SCCs work. They have a max charge current and that is the most it will ever pull from the panels. But the specs on your all-in-one are confusing. It has two MPPTs that state 4000W each for a total of 8000W. But it also states a max charge current of 120A. When charging a 48V LiFePO₄ battery, for example, that's a charge voltage of about 57V. 57V at 120A is 6840W. So what does that actually mean with this all-in-one? Is it actually only 60A per MPPT or something else? Why is this number so different from the 8000W maximum? Is their claim of 8000W maximum their attempt to assume some over paneling?