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green-techie asked

SmartSolar MPPT 450/100 Online Sizing "undersized" calculation

Apologies if I'm missing something obvious. However, using the below configuration the online sizing calculator suggests that this panel configuration is "70% (undersized)". But 8 * 405W panels, per tracker, is 6480Wp total and the datasheet gives the maximum charge power as 5.8kWp. So shouldn't this be 11% oversized?

https://mppt.victronenergy.com#djE7Y3VzdG9tLDgsMSw1MSwtNDAsODUsNDgsMTEuNywwLjA0LDEyLjQsNDA1LDM0LjY0LC0wLjI1LDQxLjYsMzAsNjtjdXN0b20sOCwxLDUxLC00MCw4NSw0OCwxMS43LDAuMDQsMTIuNCw0MDUsMzQuNjQsLTAuMjUsNDEuNiwzMCw2

The Excel sizing utility gives the "Total PV Power @STC" as 6480Wp and if I increase the panel wattage in the "Modules" section from 405W to 472W (just over 130%) I get the "more than 30% oversize" warning.

Any insight appreciated,
Jamie

mppt rssolar sizing
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Alexandra answered ·

@green-techie

The online calculator and the spreadsheet approach things a little differently.

The online one does not really size where your peak production is then capped by the max output of the mppt. Where the spreadsheet does allow max current limit cap and over panel setups.

Float x 8 = 408voc

You have 41.6VOC. 408 ÷ 41.6 is 9.8 modules max number at 25°C

So your proposed 8 in a string x2 slightly under the max VOC it can take for the float.

But with 6480W your system at 48V will be charging at 135A (if the mppt was able to) hence over 30% over size. Meaning 35A of yelid will be capped or lost.

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green-techie avatar image green-techie commented ·
Thanks for the explanation. I also found that with 9 panels I am in danger of exceeding the 409voc maximum at low temperatures, so there doesn't seem to be a combination that meets all my goals. Hopefully the larger array size will still be a benefit in the winter and with lower light levels in the morning/evening. I also see I can use DVCC to at least make some use of the excess charging current.
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Alexandra avatar image Alexandra ♦ green-techie commented ·

Look for panels with lower Voc but higher isc Like these jinkos for example

Jkm 405m 54hl4 v. It has a voc of 30.5v but isc 13.4A.

Tried uploading a photo but i guess the internet is on the fritz again.


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green-techie avatar image green-techie Alexandra ♦ commented ·
Thanks again, you've been very helpful. I see that even the Jinko 420W panels would still comfortably allow me strings of 9, as would the JA Solar 405W. Unfortunately my installer has indicated his supplies of available panels are limited and said these were what he knew he could get, but I'll see if there may be another option.
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