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Over supply(kW) from PV


Deon Zeelie
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I need some guidance.  I am using an RCT iii with 16x 365 panels, connected in two strings of 8 each. When I started the system I had 6 panels(1 string) and best output was around 2.3 kW. Based on this I installed the above configuration on the final structure. Now I am getting 2.8 kW per string. Doubling it would give me 5.6 kW. Will this damage my RCT VM iii, which is an 5 kW inverter when running into Overload situations. 

Answers on forums seems to swing both ways.

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10 hours ago, Deon Zeelie said:

I need some guidance.  I am using an RCT iii with 16x 365 panels, connected in two strings of 8 each. When I started the system I had 6 panels(1 string) and best output was around 2.3 kW. Based on this I installed the above configuration on the final structure. Now I am getting 2.8 kW per string. Doubling it would give me 5.6 kW. Will this damage my RCT VM iii ...

The specs say maximum PV array power 5 kW, so you're well over that figure.

These high voltage solar charge controllers seem to have a strict 18 A limit to PV current (though the Axpert VM III manual I just looked at doesn't mention the 18 A figure). So it depends on the Imp of your panels (you didn't give the panel model). It would be close; guesstimating the Vmp at 38 V, 2.8 kW / 38 V / 8 panels = 9.2 A per string, so two strings would be over the magic 18 A limit. There have been burned SCCs with 20 A of panels.

So: I would not do it.

Edit: it's a real shame that inverter hardware doesn't keep up with the increase in specifications of PV panels. 18 A was probably a sensible limit back when this inverter was designed.

Edited by Coulomb
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 A: 5.6kW array for a 5kW array  inverter is not that bad considering that in hot weather the efficiency is reduced and you can get say 80% of your array size.

B: I think its not advisable to run these high frequency inverters at more than 75% of their rated capacity. Under full throttle, they tend to get quet hot which ia not good for electronics. It reduces the lifespan of the electrical equipment

 

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5 hours ago, phoenix752 said:

 A: 5.6kW array for a 5kW array  inverter is not that bad considering that in hot weather the efficiency is reduced and you can get say 80% of your array size.

B: I think its not advisable to run these high frequency inverters at more than 75% of their rated capacity. Under full throttle, they tend to get quet hot which ia not good for electronics. It reduces the lifespan of the electrical equipment

 

I just did the test to max out the system, normally I am in the 3 kW range. 

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On 2021/01/02 at 1:41 AM, phoenix752 said:

 A: 5.6kW array for a 5kW array  inverter is not that bad considering ...

While the inverter's output is rated at 5 kW, the solar charge controller is rated at 4 kW (80 A at 50 V). So 5.6 kW is 56/40 = 1.4x rated. Generally, 1.25x (the 5 kW maximum array power mentioned in the specifications) is all that is allowed.

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