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Andrew avatar image
Andrew asked

help mppt sizing strings?

I am trying to setup an offgrid system with left over panels from moving house (long story). This would be for garden use horticulture poly tunnel, pond pumps, lights charging power tools and whatever i can use.

I have the following, and have put 5 panels on a pagoda (ready to go) with 15 deg tilt south facing with no shading. The other 5 are more of a problem as was going to put them on the garage roof but shading problems due to house shadow. Can't use main roof. Considering right of pagola but rather not due to losing growing area and would need to go higher than the 5 as cant go more down the garden or we will not have a garden.

PANELS = JA SOLAR JM60S20 380/MR 380W
VOC 41.62 V 665.92V TOTAL VOC
VMP 34.77 V 556.32
ISC 11.47 A 183.52
IMP 10.93 A 173.28
CLASS II
MAX SYS 1000V
MAX AMP 20

Q is the single mppt enough to allow for some in paralel? Trying to use mppt calc sizing but mixed results and it seems 1 mppt = all 10 have to be in series. How many can i wire in series/parallel without adding another mppt, is anything else required eg rotary isolator,
The cost of another mppt to make 2 strings of 5 one parallel and other in series @ 700ukp am wondering what to do, use less panels or bite bullet and buy mppt, do i need same one as below

Victron Easysolar II GX 3000 48v with inbuilt mppt 35a
250/70
10 x JA Solar panels spec =
JA SOLAR JM60S20 380/MR



panel.jpggarage roof - pagola in background - right side of pagola is an option but physically problematic









solar sizing
panel.jpg (1.1 MiB)
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10 Answers
marekp avatar image
marekp answered ·

@Andrew

Those 10 JASolar panels can be connected to MPPT250/70 as 5s2p. (two 5 panel serial strings connected in parallel)

You will also need DC over-voltage and over-current protection between panels and MPPT.


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Andrew avatar image
Andrew answered ·

Thanks for advice Marekp, would that mean for time being i could use 5 on garage roof with shading issues, series wire, but parallel wire the string? My aim is to have them side by side but cant do this at present. Thought if i put the garage roof 5 on in series it will lower whole system but is that why wire panels in series strings in parallel ?


NOTE only 5 panels setup at the moment but going to mount inverter etc over weekend.

re protection for over / under voltage i take it the two fuses multibloc 160a (125a inside housing not sure why difference in amps on each fuse) are not going to do undervoltage,is there a specific all in one device? if so, what would you recommend and i take it i would add to each string before the inverter?

Am trying to locate a decent schematic for wiring the whole system. Have help of non solar knowledge electrician who will only check the consumer unit which is not much help as am nearly there by that stage. Would i better for now, (until i get the other 5 near to the pagola, to just use the existing one 5 panel string, or would you add the 5 on garage in situ for now?

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marekp avatar image
marekp answered ·

@Andrew

If you have shading on one string out of two in parallel you can try this setup.

screen-shot-2022-08-11-at-111435-am.png

Over voltage protection that I use:

screen-shot-2022-08-11-at-115128-am.png

Over current protection for 10-38 32A fuse:

screen-shot-2022-08-11-at-115414-am.png


screen-shot-2022-08-11-at-111435-am.png (14.1 KiB)
screen-shot-2022-08-11-at-115128-am.png (120.9 KiB)
screen-shot-2022-08-11-at-115414-am.png (118.6 KiB)
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Andrew avatar image
Andrew answered ·

perfect as did calc the other day it said 5 and 2 which i assumed 2 meant panels, so now clear.

thanks :-)

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Andrew avatar image
Andrew answered ·
  1. Thanks much more easy to understand now, so to the inverter symbol i take under/overvoltage protection would go before inverter - easysolar II gx (inbuilt mppt) to safeguard it? i suspect fuse for overvoltage but under? is it a specific device?
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marekp avatar image
marekp answered ·

@Andrew

Fuse is used as over-current not over-voltage protection.

On DC line from PV panels.

Under voltage protection is not used.

Over voltage protection goes before MPPT inside your inverter to eliminate surge from lightning strike.

Over current goes between panels and MPPT inside your inverter. This one from the picture can also be used as disconnect for PV panels.

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Andrew avatar image Andrew commented ·

Trying to adapt much of whats missing by looking at a hybrid system and can only see rotary isolators but suspect others hidden. Without any guidance from the fly2064715355.jpg -by-night seller of the system (except panels) i have 2 x fuses as pic, 6mm wire


You have helped fill in many blanks, i can look at others designs all day long but they differ.

I want to be sure it is properly protected at panel string end, inverter to battery and then battery to consumer and not concerned so much if it doesnt generate in winter months so much, it is what it is.

But to be sure nothing will short I was putting isolators/fuses on each string, Would you suggest any other components for protection as no installer would touch this as they wanted to sell it, but happy doing it just getting mixed guidance until now. But now happy i am doing it as learning how it works. Pity my electronics were above pat and computers.

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marekp avatar image
marekp answered ·

@Andrew I do not know that unit on the picture, but it for sure is for AC side not DC.

Maybe this will help

screen-shot-2022-08-11-at-15524-pm.png



screen-shot-2022-08-11-at-15524-pm.png (26.6 KiB)
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Marco Dressel avatar image
Marco Dressel answered · 
Was steckt hinter den Modulen? Dioden? Wenn ja, wie werden diese bestimmt und wo kann man sie kaufen?
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marekp avatar image marekp commented ·

@Marco Dressel

Ask your PV equipment supplier.
screen-shot-2022-08-12-at-12639-pm.png

screen-shot-2022-08-12-at-12822-pm.png

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screen-shot-2022-08-12-at-12822-pm.png (60.7 KiB)
Marco Dressel avatar image
Marco Dressel answered ·

Ist das die Regel? 4 Module in Reihe, davon 3 Strings. also sollte man die strings mit dioden schützen? Dort geht Energie verloren.

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marekp avatar image marekp commented ·
@Marco Dressel

If you have more than one parallel string and one gets shadows, diode prevents the other strings from feeding energy into the shadowed string.

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Juraj Nikolov avatar image Juraj Nikolov marekp commented ·

@MarekP

do the diodes make sense even with half cut panels ???

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klim8skeptic avatar image klim8skeptic ♦ Juraj Nikolov commented ·

You need to look at your panels specs, and understand the "series fuse rating"




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Andrew avatar image
Andrew answered ·

@MarekP Hi Marek, not sure how I send a message here. I posted recently and wondered if you are able to check if I have done the setup correct as followed much of your advice and it correlated with a company I purchased some equipment from. I mainly want to be sure of parallel - series wiring, can I merely join the two strings to single +/ feeds to fuses or use a 4 pole? I also have 2 reverse current protection diodes 20/1000v, a two pole surge protection for lightening 16a, and a 2 pole disconnect 16v/1000v. I bought before this a 4pole fuse which can be changed to various settings v and amps. Looking at you diagram where the

Battery to inverter fuse Multibloc 2 single pole NH00 fuse casing 120A for pylontech as per guidelines of manufacturer and advice before wiring up much appreciated.


Q title


1664791068061.png

3.8kw Offgrid: Victron EasySolar 2 48v.35 with mppt 250/70 3000w Design + Fuses



1664791068061.png (2.9 KiB)
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