question

mfred68 avatar image
mfred68 asked

Adding another pv panel to the string

I guess I may have played it a bit too safe by under panelling my system for my mppt.

I have 415w Trina panels that are rated 50v oc, and the mppt is RS 450/100

I installed 7 panels per string (there was room on the roof for 8) and now since commissioning the system I'm getting a maximum system voltage per string of only 290v that's 160v less that the mppt is rated for. I understand it varies with temperature, but at the moment it's not that warm, and uk winters especially in Wales are never that cold. So would it be beneficial to add that 8th panel to the string, adding another 50voc to the system? I used the mppt calculator and it said to use 7 panels, but now I'm wondering if I was too conservative.

Solar Panelmppt rsmppt calculator
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2 Answers
1234enough avatar image
1234enough answered ·

PV VOC is only allowed 8 x battery float!! If you only float at say 52V, 8 panels are a no go - unless min temp is -3c, but if you float at say 60V it is OK to -20c.



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mfred68 avatar image mfred68 commented ·
My float charge voltage is 56v according to the battery specs. So would sn extra panel be ok, or better not to risk it?
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1234enough answered ·

With 56v float and -20c as a min temp the mppt calculator says yes to me, what figures did you put into calculator and it said no? Try the calculator again.

So I'd say yes 8 x Trina Vertex-S TSM-415 DE09R.05

is OK down to -20c

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MPPT RS Product Page

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