10kw in panels - should I go 24v or 48v? A few other thoughts.

[dudeinthewoods]

Hi, thanks in advance. You guys are awesome. I've been reading a while but finally jumped in bigger.

I've got 40 x 250w 24v panels. I've also got 16 LiFePo4 cells. So I was originally just thinking 24v battery x2 and panels in parallel and good.
Now I'm thinking with this much wattage maybe 48v makes sense? 2 panels in series x 20 and one 48v pack?

Obviously smaller wire requirements. One BMS vs two. Any reason I shouldn't go 48v over 24? Inverters etc?

I'm about to line it all up and I'm stuck on the 24 vs 48 part as it changes everything.

Edit: forgot to add for BMS I was planning on the chargery 8 or 16 obviously if its 24v or 48v.
I figure I'll commit to one, spec it out and let you guys tell me what I've done wrong =)

 

[kernel]

There is no reason to not adopt 48V, based on what you offered unless you are going to adopt 400V!

Theres always a bigger badder version.... 48V will be more appropriate for your power flows vs cost. Meaning if you dont need lower voltage dont use it.

 

[dudeinthewoods]

Haha great. That was the conclusion I came to but it seemed too simple. at the length I'm running (20'~) I don't think going up in voltage would make sense beyond 48v since thats where the batteries are. Wiring more panels in series would be easy but then I'd have to step it down anyways.

 

[kernel]

At 24V you would have 350A worth of charge to control. That is 3x 100A chargers or an expensiverer integrated unit. 175A to absorb voltage at 48V nominal. Better.

This assumes you could even allow this much current to the battery, but 48V is your friend.

 

[dudeinthewoods]

Right. I'm thinking 3x60 charge controllers but I haven't settled on those yet. Lot of choices to make here. Tons of power though. I've been living off 400w for a while not sure what I'll do with it all haha.

 

[kernel]

Love it. Hope your energy keeps being converted onsite!

 

[dudeinthewoods]

So thinking through wiring..

2-24v panels in series should be able to use the same wire correct? The voltage increases but amps remain constant so if say copper 12awg works for a single panel it would work for 2 in series? I'm thinking 12awg for 250w(x2) on a run to the bus which is the most at 20ft unless that's too little and I should use 10awg.

A group of panels is going to be 50amps if I go for 4 groups of 10 panels. 50 or 60 amp controllers are probably a sweet spot and it's a nice even number. So running to the controllers and controllers to battery 6awg should be plenty right? I could do 4awg but its a bigger expense and unnecessary right?

Now from the battery to inverter etc we're talking about the biggest loads. I'm thinking 4/0awg. It shouldn't push the limit at all on that but it's a few feet of cable why not oversize it I guess. It's TBD but I'm thinking to run either two 4k inverters or 3x3k or similar. 2/0awg or even 2awg seems ok if I want to save money.

I'll also put a step down to 12v but that's tbd and easy to figure out.


Summary or TL;DR if you prefer:

Chargery 16t for MBS
10kw in 40 total 24v 250w panels
Single panel or pair in series 250w/24v (500w/48v) = 10.5a = 12awg?
Cluster of 10x24v wired in pairs = 52.5a = 6awg?
Battery to inverters 4000w/48v = 83.3a = very short runs could use more expensive cable = 2/0awg or 2awg? Any advantage to 4/0awg?

This is exciting I'll get pics and video and try to write up a guide to help future cases in the same range.
I've still got a bit of work to do. I need to pick out a lot of parts. Off the top of my head:
controllers
Connectors
Fuse blocks
Bus bars
inverters
Anything else I should be looking for?

 

[dudeinthewoods]

Minor update. Too slow on the edit.

Maybe it makes more sense to do clusters of 12, or 12,14,14. It would be easier to maintain 3 than 4. I should still be able to use a 60amp controller for 12 and maybe for 14 upgrade to a 70am controller. I'm leaning towards 12's and sell 4 panels. 36 panels is 9kw which is more than I need.

 

[kernel]

Minor update. Too slow on the edit.

Maybe it makes more sense to do clusters of 12, or 12,14,14. It would be easier to maintain 3 than 4. I should still be able to use a 60amp controller for 12 and maybe for 14 upgrade to a 70am controller. I'm leaning towards 12's and sell 4 panels. 36 panels is 9kw which is more than I need.

It will come out on paper. Eventually the constellation of components will align and starlight will pour into them!

Myself i usually supply 2 to 4 extra modules for large systems. They are almost tough as nails, but stuff happens. Almost impossible to get the same panel 15 years later.

Then again, how many controllers did you say you need?

Twin 100s could do.

 

[dudeinthewoods]

Haha. Good idea I may just put those 4 away for backups.

I went ahead and got 3 60a makeskyblue controllers. I had heard good things about them and the price seemed right.

Now I'm just diagraming it up. There's a few things to consider like if I should (can?) run the power supplies and inverters in parallel or just independently if that makes sense? I feel like I can't have all the panels go to a bus bar and 3 chargers tap in then all the inverters tap in to their output busbar. It seems too easy. Even if it did work if you lost a charger you'd be in a bad spot with all those panels on two I guess.

I'm going to look at a few examples and dig in and figure it out.