I have 2, 310w panels with Voc of 40.15. I would like to connect in series. When Voc is doubled then 25% safety factor is added it comes to 100.375 volts. I have a 100/30 smart controller. The nifty Mppt sizing tool says all I need is the 100/20. Does the sizing tool not take into account the 25% safety factor? I could just connect them in parallel, but I think it maybe more efficient connected in series. It is a 24 volt system. Temps here range between 6 deg c and about 35 deg c
If the nifty MPPT sizing tool says that it’s ok, and you are certain of the panel and temp specifications you entered, then you are good to go.
https://mppt.victronenergy.com/?locale=en
The 100V limit is firm.
Hi Frankie. Fascination drives me, so please forgive. Where do you get this '25% safety factor' from?
I'd series-connect the panels, and you can check your panel V from the smart app in the coldest of weather to see. That won't be Voc, more likely Vmp under solar production, but they're related. If you suspect that 100Voc might be exceeded, pull a solar wire & check it with a multimeter.
Thankyou for your replies. JohnC, I have been advised, and have read that it is prudent to add a 25% safety factor into any Voc or Isc formula regarding Controller sizing. I believe it is actually a complience code in some areas. Personally I always thought it extreamly high, but the promised doom and gloom if I didn't has made me factor this in. Maybe a subject for another thread?
If your going to add in a 25% safety factor, you would be good down to -20c. How cold does it get? What model panels?
Interesting. But as soon as you mention 'compliance code', I think - Aahh, perhaps related to cowboy domestic installers working with ac-coupled LV of 600V or more, who don't bother with the calcs - or can't anyway. Klim does it in his stride, hey.
You're in the range of what's called ELV in my country (120V?), and whilst there are some regs, they're much more relaxed.
At least that fudge-factor didn't come from Victron. I would have found that most strange, hence my asking.
You should be fine.
Cheers klim8skeptic. It goes down to about 6 deg c here in the winter. The panals I have are:
Somewhere tropical :).
Temp coefficient of .28%, Voc 40.05 @ 25c.
Voc 42.85 @ 0c
Plenty safe 2 in series.
Thanks again for the answers guys. Ha ha NZ is hardly tropical, getting close I suppose :) I shall go forth and Install.
