Voc and Vmpp in practice

[Nickel]

Sorry if this is a basic question that's been asked before, but I can't see the answer to my practical questions.

We have 16 panels with a Voc stated as 37.4 - so total array Voc 598.4. They have a Vmpp stated as 30.3 so total 484.8.

We have a SunnyBoy SMA3600TL and it displays the incoming voltage typically in a range from 450v to 503v [maximum seen]. On a sunny day when the roof orientation is pointing directly at the sun it will usually be showing 497 - 503v.

So my simple questions - Is the Inverter displaying Voc or Vmpp? Does the inverter constitute load on the panels, so that it is only Vmpp that is arriving at the inverter? Do these values look like all panels are working - I am a little puzzled that they are way below Voc but above Vmpp.

Many thanks for any help.

Regards

Nick

 

[BruceB]

The inverter is displaying the actual voltage measured at the inverter, which will be the total voltage generated by the panels less that lost in the dc cabling by virtue of the current flowing.

If no current was flowing then it would be Voc. If max power current was flowing then it will be a little under Vmpp (because of losses in the cable).

If you have somewhere in between then it is because the tracker in the inverter has decided that particular combination of current and voltage produces maximum power with that amount of sunlight.

I would trust the SMA inverter unless there is some good reason not to.

 

[SibertSolar]

Don't forget that the datasheet values are at STC and that the voltage has a negative temperature coefficient....other than that, what Bruce said!