MPPT Online calculator different result to spreadsheet?

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chrisgla asked Feb 15, '20

MPPT Online calculator different result to spreadsheet?

I'm looking for MPPT (either separate or Easysolar II GX 250/70) to use with 6 off JA Solar JAM60S10 -340/PR. I have an existing 6mm cable limiting me to 39 amps.

The online calculator gives me a result of MPPT 250/60 for 6 in series, or MPPT 150/35 for 3S2P.

But spreadsheet I added a custom module which is then not accepted and neither the Max PV V or current makes sense to me unless temperature is the impact (I'd expect 248.16V and 10.46A for serial?):-

Are 6 off these panels ok in series and any idea why spreadsheet fails?

Thanks!

MPPT Controllers

mppt1.jpg (86.2 KiB)

mppt2.jpg (86.3 KiB)

mppt3.jpg (60.9 KiB)

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Matthias Lange - DE answered · Feb 15, 2020 at 08:44 PM

The value for V temp coeff. must be negative and with only 2 decimal digits.

If I enter a value higher 0 or with more than 2 decimal digits I get this (with Firefox):

mppt-calc-1.png (42.1 KiB)

mppt-calc-2.png (155.6 KiB)

mppt-calc-red.png (4.9 KiB)

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Attachments: Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Modifications Space

Node Red Space

Answer 1 · 2020-02-15T20:11:36Z

klim8skeptic answered · Feb 15, 2020 at 08:11 PM

The spreadsheet is correct! 273.226v @ -10c.

The online tool is broken.

mppt-calc.jpg (62.6 KiB)

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Answer 2 · 2020-02-17T10:11:57Z

Lasse answered · Feb 17, 2020 at 10:11 AM

@M.Lange is correct, the system should have given an error when you tried to add a positive value to the V. temp. coeff. [%/C] apparently this is was not the case. It is a problem that occurs with Chrome, not with Firefox, this will be fixed in the next release.

5

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JohnC ♦ commented · Feb 17, 2020 at 10:30 AM

It happens with FF too. I tested this earlier, but by the time I nailed it down the question was already answered.

A little thin red line around that box under certain circumstances, but it happily shows the incorrect result.

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klim8skeptic ♦ commented · Feb 17, 2020 at 10:53 AM

"the system should have given an error when you tried to add a positive value to the V. temp. coeff. [%/C] "

To further this, temps below STC will have a positive temp coefficient effect on the Voc. It should not matter if you add a - #, or a number greater than zero.

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Bob (Victron Energy Staff) ♦♦ klim8skeptic ♦ commented · Feb 18, 2020 at 07:57 AM

Dear klim8skeptic,

the temperature coeff. of the voltage of a solar panel should be a negative value, mr. Lange answered this already. This will affect the voltage automatically and increases the solar panel voltage when the cell temp. is going down.

The problem would be if you insert a positive coeff. in the calculator, it would calculate a lower solar panel voltage @ lower temperatures. Which is in real life not the case.

Regards,

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klim8skeptic ♦ Bob (Victron Energy Staff) ♦♦ commented · Feb 18, 2020 at 09:26 AM

"the temperature coeff. of the voltage of a solar panel should be a negative value"

Unfortunately the app has not been set up to apply those rules, at least in this instance.

Just a green tick.

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Lasse ♦♦ klim8skeptic ♦ commented · Feb 18, 2020 at 06:18 PM

Dear @klim8skeptic the field validation did know that the value was incorrect but due to the different browser implementations of showing errors, this was not visible. Yesterday this has been fixed and pushed to production.

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Answer 3 · 2020-02-19T22:09:31Z

chrisgla answered · Feb 19, 2020 at 10:09 PM

Thank you for fixing this, both the online and spreadsheet tools are really useful tools!

Looking forward to receiving my Multiplus ii 5k, Cerberus and CAN MPPT. I work in Smart Grid and the Modbus functionality with Victron quality and support will let me try a few innovative ideas....

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Answer 4 · 2020-07-22T16:20:51Z

Warwick Bruce Chapman answered · Jul 22, 2020 at 04:20 PM

I have been able to reproduce this.

For Canadian 365's, web suggests a 150/60 is fine but Excel says current will be limited:

Another example for Canadian 415's, web suggests 150/45 is fine but Excel says current will be limited:

screenshot-2020-07-22-at-181210.png (2.3 MiB)

screenshot-2020-07-22-at-181148.png (361.2 KiB)

screenshot-2020-07-22-at-180509.png (313.6 KiB)

1595434838858.png (2.3 MiB)

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