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ciacula avatar image
ciacula asked

Smartsolar 100/20 or 150/35?

I'm buying 4 solar panels (in STC there are: Wp 370 - Voc 41,3 - Isc 11,37 - Vmpp 34,2 - Impp 10,82. In NOCT: Wp 279 - Voc 38,9 - Isc 9,16 - Vmpp 32 - Impp 8,71), and I will wire the panels into 2 arrays. Of course I need to add to my 48V Victron setup the suitable solar charger. The MPPT Victron Online Calculator says that the charger will be the 150/35, but if I decrases a little the Impp from the STC nominal value, from 10,82 to 10, I get the 100/20 as suitable solar charger. Since I know the STC values are theoretical, I would like to ask if someone can help me in a good choice. Thanks. Alessandro

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snoobler answered ·

4 * 370W = 1480W

1480W/48V = 31A

100/20:

100Voc and 20A Isc maximum PV input.

A 2S2P array would meet the 100V limit, but your 22.74A Isc is over the input limit.

While NOCT may represent "real world" performance, arrays can exceed their rated output in ideal conditions. I routinely see my array exceed rated by just a bit, but I have very favorable solar conditions.

While the risk associated with 22.74A vs. 20A is low, personally, I would go for the 150/35 to ensure I could capture the full output of the array rather than potentially leave 50% on the table.




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JohnC avatar image JohnC ♦ commented ·
@Ciacula

Also, 2x of those panels in each string may struggle to reach enough Voltage to charge a 48V bank in less than optimum conditions. I'd use 3x (so either 3 or 6 panels), justifying the 150/ anyway. Do it properly..

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snoobler avatar image snoobler JohnC ♦ commented ·

I don't completely disagree, but those appear to be higher than typical 60 cell panels.

Don't NOCT ratings reflect elevated cell temperatures in the 40-50°C range?

32V * 2 = 64V = more than enough to charge even a Rolls Surrette.

If the ambient temperatures are 50°C, then I would definitely agree.

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JohnC avatar image JohnC ♦ snoobler commented ·

@snoobler

I wasn't talking STC, or even NOCT conditions. See this example of my own system from a few days ago, cloud, even rain drizzle (so not hot panels). 48V batts, similar panel specs, strung 3x..

1681787223795.png

Spent half the day hovering between 60-70Vmp. Take a third off that for 2x strings and it wouldn't have produced anything at those times. Sure it's a bad day, but the same thing happens near dawn and dusk every day.

So why design 2x strings into a new system when you'd do better with 3x and a 150/ mppt? And, IMO, the 100/20 (48V) is really a specialty item, perhaps introduced for cases of selective shade like on yachts. There's a really good reason why 150V is common with all the respected makers of 48V mppts..

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