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diy solar

Shopping for the missing parts for a 24 or 48v

lokmer

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Sep 24, 2021
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Okie dokie, here's what I've got:
9x340v solar panels (72in long)
10x365v solar panels (60in long)
One all-in-one inverter charge controller which'll handle the 9 panel array
2x24v 100ah LiFePO batteries

I need to fill holes in this and come up with a design to power a cabin in northern Washington. I have an unobstructed southern slope to erect a ground mount rack on, but unsure how to control for possible wind loads in the design. Not sure which cables and fittings to buy, or how to fuse the system. Fire risk must be minimal, because I'm in an area prone to wildfires and I'd rather not burn down the forest.

I've got the tools on Will Prowse's "tools" page as well as a bunch of tools for standard household AC and for vehicle wiring--I've done a lot of both. What I don't have is a full conceptual picture of how to put the system together safely, how to decide cable gauge, etc.

I know I'm gonna need another charge controller/inverter unit for the second array. Gonna want extra batteries, as many as I can afford, to get through the cloudy days. I have a 7kw supplemental generator which I'll want to wire in to charge on the cloudy days (haven't yet figured out how). Beyond that...I'm muddling, but currently at a bit of a loss.

Household usage will be 4kw/h/day when being careful, about 9 kw/h/day when being profligate.

Any advice would be greatly appreciated!
 
Will this be a 24 volt build or a 48 volt build?

For the panels going into the new SCC, what are the voltages and amps?

I’m a fan of Victron For the SCC. The same model of an SCC will handle half the total wattage as on a 48 volt system, so the voltage of the battery system along with panel voltages will drive the size of the SCC,

For your power requirements, your 4800 wh of batteries seems really underpowered, unless nearly your entire 4 - 9 kWh of daily consumption is only when the sun is shining. The battery bank you mentioned does not leave room to get through the first cloudy day, never mind several. You did say you had the generator.
 
As batteries are the most expensive part, I'm planning to build out on the installment plan. This first round of equipment buy will include 2 more 100ah/24w batteries, to double the size. By this time next year I hope to do another 4 rounds of buys of that size, or build my own out of prizmatics once I have a better handle on it.

I have not yet decided on whether to do 24v vs 48v system. Currently I seem to have the latitude to go either way, but am unsure what the trade-offs are.

Bank one (the 9-panel array) has the following specs:
Nominal Max. Power (Pmax): 340 W
Opt. Operating Voltage (Vmp): 37.9V
Opt. Operating Current (Imp): 8.97A
Open Circuit Voltage (Voc): 46.2V
Short Circuit Current (Isc): 9.48A

Bank 2 (the 10-panel array) has the following specs:
Pmax: 315Wp
Vmp: 33.2V
Imp: 9.49A
Voc: 40.7V
Isc: 10.04A

This is the inverter/charge controller unit that I have right now (still in the box):

MPP SOLAR 5000w 48vdc 120v 208V 240V Split Phase Solar Inverter 80A 2X Dual MPPT Charger max PV input 145V (amazon link:https://www.amazon.com/dp/B07R18ZTKC



 
I am working on a 12 volt to 24 volt upgrade. I had wanted to do a 48 volt upgrade, but the 12 volt system had some parts that were not rated for a 48 volt system that I’d have to replace:

-Three Victron SCCs that could only charge a 12 volt or 24 volt, NOT 48 volt system.
-Maxi Fuse not rated for 48 volts
-Busbars rated at 48 volts, not the mid 50 volts for charging
-Battery switch rated at the same thing

For the up to 48 volt parts, I don’tknow what happens if I go to 55 volts, but there’s a huge jump in price and its Slightly harder to find parts for a 48 volt system.

If your MPP is 48 volts, seems like you will have a 48 volt system. I think you’re planning on doing a 3S3P set up which at a quick glance is well under voltage. I’m just not sure as this voltage rises in the winter if it will exceed the MPP rating.

I mentioned a Victron SCC earlier, but saw you may want a second MPP. For your MPP, can you parallel multiple units?

If not I think that means your just have to have a completely separate AC circuit For the second one.

Honestly though, for a 5000 watt inverter, really need to go 48 volts, especially if you’re going to add on later.
 
Makes sense. Okay, so, 48w. Second 5000w or bigger inverter to run in parallel or as separate circuits (I can make either configuration work).
The next obvious question:
I gotta connect all this stuff together. How to I size the wires, figure out what kind of fusing do I need, etc.?

(this is obviously a general question to anyone with 48v experience, not just the gracious Pohton Sorcerer Chrisski :) )
 
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