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24v System Design and Feedback Request

Kartox

New Member
Joined
Oct 25, 2021
Messages
3
Hey folks,
First off, thanks to this great community for the excellent assistance and knowledge; it has been immensely helpful in learning and designing a system.

Secondly, After a few dozen/hundred hours of videos and internet reading, I think my design is at a stage where feedback is needed and I have a few questions.

Location: Southern California. Lack of sunny days is not an issue.

General Load and Use Cases for the System:
Backup for Home (refrigerator, freezer, other necessities) when the power is out
and
My commute is ~40 miles each day and the power generated can top off my Nissan Leaf each night via the 120V Level 1 Charger (speed of charge is not an issue for me) from the Battery Bank, and then finish with any grid power as needed.



Summary of Questions Below:

Question 1:
Solar Panel Math Check:
6 Used San San Solar Panels
https://store.santansolar.com/product/santan-solar-t-series-250w/
Or
https://store.santansolar.com/product/santan-solar-t-series-250w/

250W
VOC (Open Circuit Voltage): 37.6
VMP (Max Power Voltage): 30.3
Max Power Current: 8.27
Fuse: 15A

Wired: (Amounts rounded up)
3s2p
1500W
VOC: 115
Total Amps: 25
QUESTION: IS THIS MATH CORRECT? I just want to make sure I’m not going to blow out the Growatt/cause fire, etc.

Question 2: Do I need a breaker/disconnect between the solar combiner box and the Growatt?

Low Priority Question 3: Can I use this Victron Charger only hooked to the Negative to also use the monitoring software?
https://www.amazon.com/Victron-Blue-Smart-Charger-Waterproof/dp/B07DWJD84N
Answered: Need the shunt.

If possible, this would give me a charger and a monitor in 1 unit instead of purchasing 2 different pieces of hardware and I would just eliminate the shunt and replace it with a fuse instead.


System Build Details for Reference - Feedback, Critique and Suggestions welcome.
Thanks in advance for any comments or feedback to help improve this first attempt at a plan.

Inverter: Growatt SPF 3000TL LVM
https://watts247.com/product/spf-3000tl-lvm-24p/

Mounted to Hardibacker:
https://www.homedepot.com/p/James-H...-x-1-4-in-Cement-Backerboard-220022/100183556



INPUTS:

PV:
6 Used San San Solar Panels
https://store.santansolar.com/product/santan-solar-t-series-250w/
Or
https://store.santansolar.com/product/santan-solar-t-series-250w/


250W
VOC (Open Circuit Voltage): 37.6
VMP (Max Power Voltage): 30.3
Max Power Current: 8.27
Fuse: 15A

Wired: (Amounts rounded up)
3s2p
1500W
VOC: 115
Total Amps: 25

Into a 4-1 Solar Panel Combiner Box
https://watts247.com/product/solar-panel-combiner-box-4-circuits-to-1/


From Combiner Box -> Growatt

AC In:
Cut and Spliced AC Extension Cord to closest outlet
Planning to use:
https://www.amazon.com/Foot-Lighted-Outdoor-Extension-Cord/dp/B019P9ZGGO/




Batteries:
Two 12v 206AH LiFePOP4 (already on hand)
https://www.currentconnected.com/product/sok/

Wired in Series to get 24v
Specs:
Recommended Charge: 40A
Max Charge: 50A
Recommended Charge Voltage: 14.6v
Wire: 4 AWG
https://www.amazon.com/dp/B01F32MM46/


Battery Negative to Victron Shunt 500A:
https://www.altestore.com/store/met...s/victron-energy-smart-battery-shunts-p41526/


Shunt to Growatt

Positive to Disconnect Device: Blue Sea Systems 300A Battery Switch
https://www.amazon.com/Blue-Sea-Systems-Battery-Switch/dp/B00445KFZ2/

Disconnect to Growatt

OUTPUTS:
AC Out:
Wired to QO Breaker Box:
https://www.homedepot.com/p/Square-...c-Enclosure-and-Neutral-QO24L60NRNM/100174454
20A GFCI Breaker:
https://www.homedepot.com/p/Square-...le-GFCI-Circuit-Breaker-HOM120GFICP/100002959

To 4x4 Outlet Box
Outlets: https://www.homedepot.com/p/Leviton...t-Duplex-Outlet-White-R52-T5825-00W/203245679

Outlets power the load
 
Last edited:
Question 2: Do I need a breaker/disconnect between the solar combiner box and the Growatt?
If you have three or more panels in parallel you need a some current interrupt, whether circuit breaker or fuse. Two or less you don't need it; Hoever, building code may dictate. Whether or not you need one, I use circuti breakers and it makes turning on and off to troubleshoot a string so much easier.
Low Priority Question 3: Can I use this Victron Charger only hooked to the Negative to also use the monitoring software?
I'm not sure you linked the correct thing. You linked a charger, 12 volts. You have a 24 volt system. Is the intent to charge or monitor?
250W
VOC (Open Circuit Voltage): 37.6
VMP (Max Power Voltage): 30.3
Max Power Current: 8.27
Fuse: 15A

Wired: (Amounts rounded up)
3s2p
1500W
VOC: 115
Total Amps: 25
QUESTION: IS THIS MATH CORRECT? I just want to make sure I’m not going to blow out the Growatt/cause fire, etc.
-There is some form of temperature compensation. .2% to ,.5% raise n voltage per degree C cooler.

-2 P would get you a little less than 17 amps into the controller, but somewhere around 50 +/10 amps to charge the batteries.
 
If you have three or more panels in parallel you need a some current interrupt, whether circuit breaker or fuse. Two or less you don't need it; Hoever, building code may dictate. Whether or not you need one, I use circuti breakers and it makes turning on and off to troubleshoot a string so much easier.
Good point, I think the combiner box has a switch, just not sure if that counts as a breaker, as it seems the inputs are fused at 15a, not the whole output...if that makes sense.

I'm not sure you linked the correct thing. You linked a charger, 12 volts. You have a 24 volt system. Is the intent to charge or monitor?
Another great point and something I quickly overlooked when checking this charger. Looks like I'll need the shunt for monitoring. Was kind of hoping to save a few hundred and use the charger monitoring app in place of the shunt, but as you point out, it's 12v and not 24v.

Thanks for the quick response and any other feedback or confirmation of the math is appreciated.
 
There is an Aili Battery Monitor on Amazon for around $40, and is half price if purchased on alibaba. Victron's smart shunt is around$140 and can be monitored on Blue Tooth.
 
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