450/200 start up voltage - datasheet does not match MPPT calculator ?

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bladerunnervf asked Feb 14, '24

450/200 start up voltage - datasheet does not match MPPT calculator ?

Hello, I used the MPPT calculator to work out the response for 4 panels in series for the RS 450/200

Result for one tracker

The green line shows Voc Start min, which I presume is the startup voltage, and according to this limit of about 170V it would only be achieved (String Voc > Voc START min) when temperature is below zero! And so basically will never work with 4 panels ?

But this datasheet states 120V startup voltage

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-MPPT-RS-EN.pdf

Q) Is this the correct datasheet ?

Q) Which is the correct start voltage ?

Thanks

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Answer 1 · 2024-02-15T06:02:43Z

Alexandra answered · Feb 15 at 06:02 AM

@bladerunnervf

Is it close to the total of your VOC start voltage at min. It is referring to that not the mppt capability.

You can check by adding another panel to the calculator and see the voltage change.

The graphs are there to show roughly what to expect from your panels in the config you have chosen.

The start voltage of the 450/200 is 120voc. Then it can track lower than that down to 80v before switching off again.

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bladerunnervf commented · Feb 15 at 12:22 PM

@Alexandra

Hi Alexandra, thanks for this

The comparable graph for 5panels is this

String Voc increases from 159.53 to 199.42V at 20degC as I would anticipate by adding a panel of nearly 40V.

Sorry, I don't quite understand your question "Is it close to the total of your VOC start voltage at min"

Does that cover your point ?

[Edit I appreciate Vmpp will track down to 80V and still provide usable energy until then]

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Answer 2 · 2024-02-15T06:37:36Z

Guy Stewart (Victron Community Manager) answered · Feb 15 at 06:37 AM

Hi @bladerunnervf,

It's a bug with the calculator.

The datasheet is correct. Start up voltage is 120V.

BUT

That said, 4 panels really aren't enough to make efficient use of the MPPT. It is the absolute minimum, and really should be higher for best performance.

See this example system where there were 4 panels on the 4 different trackers of an MPPT RS 450/200.

Changing that configuration to two 8 panel strings using only 2 of the MPPT trackers increased PV yield from 6000W to 7500W.

Worth having that extra voltage in the MPPT range.

I have an open ticket for the calculator to be fixed, and have just reminded the developers to escalate it :)

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bladerunnervf commented · Feb 15 at 01:11 PM

@Guy Stewart (Victron Community Manager)

Thanks very much for this Guy, solves the puzzle!

Also thanks very much for the illustration showing the comparison between 4panels on 4xMPPT and 8panels on 2xMPPT, rather interesting!

My reason for looking at four panels was to see if it makes sense as a solution splitting 10 panels on one roof into two groups, physically they would be 6 in top row and 4 in lower row. Looks like 10 panels on one MPPT is too much, the MPPT calculator warns of power limiting. I have a second roof with two rows of five panels also. Probably a topic for another thread? I'm about to get some quotes done and was trying to be at least a semi-intelligent customer!

Out of curiosity do you happen to know the orientation of the panels? By the look of the PV voltage I'd guess the panels for trackers 1&2 are in one direction and the panels for trackers 3&4 are in another.

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Guy Stewart (Victron Community Manager) ♦♦ bladerunnervf commented · Feb 16 at 03:03 AM

I don't know the details of the arrangement, but the overall power was still increased with the higher string voltage (even though there were other limits then).

If it was me, I would bring the panel wiring down in such a way that if I wanted too I could easily rewire the panels on the ground into a single string to test to see which provided better yield.

Remember the main and most important limitation is the 450 V on the input. I think 10 panels should still be under that, but double check. Current and power limits are soft and it's ok to exceed them a bit, the unit will just limit itself, and possibly still provide more power than a low voltage string.

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