Need Recommendation for Expandable 48v System

[chemikalguy]

I'm new to solar in general, but I'm looking at building a house in the next year, and want to have it either off-grid, or hybrid at a minimum. The property is in the country, so any power outage that happens to the grid could last for days if not weeks.

My questions stem from expandability. I'm looking at getting the largest parallel-capable inverter I can afford, and 3-6 48v server rack batteries. I already have access to an 'actual' server rack that can hold something like 10 batteries if I ever get to that point.

My concern is with respect to adding a second inverter and additional batteries. If I go with 3 batteries, that's fairly straightforward. I get the EG4 bus bar kit, attach all three to it, and wire that to the inverter. I'm not sure about if I go with more batteries, and how to wire that with respect to what gauge to use, what breaker and T-class fuse size to go with, etc.

Do I have to have the inverter chosen before I choose the fuse and breaker, and size them to the inverter, or do I size them to the max output of the batteries (300 or 600 amps)?

Then, to complicate things, I'm thinking about when the time comes to add a second parallel inverter and/or an additional set of batteries. Do I wire each inverter with it's own battery bank if, say, I ultimately get 6 or more batteries?

Example:

To start:
An EG4 Gridboss
An EG4 Flexboss21
3x EcoWorthy 48v server rack batteries
EG4 600A bus bar kit
included wires from batteries to bus bars
4/0 gauge wire from bus bars to inverter


Later:
A 2nd EG4 Flexboss21
3x Ecoworthy 48v server rack batteries

In this later case, would I be able to add a second connection from the existing bus bars to the second inverter, using the 4/0 cable, and add 3 more batteries to the bank?

Also, what if I went more than 6 batteries? Each battery is rated at 100A of output, so would I need to replace the bus bars with ones that are rated for higher current, or would it make more sense to split the 10 battery bank into 2 5 battery banks, each connected to a separate inverter?

Sorry for all the confusion, but I haven't seen much information on these questions out there, other than to say not to wire more than a couple of batteries in series, and to use bus bars.

 

[Redpineapple]

A few things for you here.

1. Where are you installing the FB21's.

If you're saying "indoor" my answer is a hard "no" due to heat and noise. Not even in an attached garage unless you have a mini split to cool the room.

Look at 2x FB18's please. Don't just shoot for the moon. I doubt you need 3x MPPT's per inverter.

2. If you can swing it, go with a wallmount 48v battery and avoid the server rack side of things. EG4's are UL rated and you can get indoor or outdoor versions if needed. You can also go with other brands that are indoor rated and put them in a detached structure.

3. The new EG4 batteries coming out soon include not only 4 quick connectors but a screw terminal for the bus bar.

Wallmount > Server Rack for flexability. Even the DIY build your own are great and can work with EG4 equipment if that is what you want to do.

 

[teal95]

Batteries are generally shared between all of the inverters. Batteries are all tied to a busbar (or perhaps multiple interconnected busbars) and all of the inverters connect to the same busbar.

I think you're seriously underestimating the amount of batteries you're going to need/want. I'm running a single SolArk 15k and I have 3 racks (so 18x 100 Ah) batteries.

 

[Rezin777]

I think you're seriously underestimating the amount of batteries you're going to need/want. I'm running a single SolArk 15k and I have 3 racks (so 18x 100 Ah) batteries.

Strong agree. Especially if you plan to use those FB21s to their potential.

 

[BrianVeg]

I do think you are under estimating your battery capacity. It will be your most expensive part of your system. I have 2 cabinets of RUIXU Server Rack batteries (9 total for 46 kWh) and really need more.

Wall mount batteries were just coming out when I built my system. While I'm happy with my configuration, if I had a do-over with today's technology I would seriously consider wall mount batteries.

 

[chemikalguy]

A few things for you here.

1. Where are you installing the FB21's.

If you're saying "indoor" my answer is a hard "no" due to heat and noise. Not even in an attached garage unless you have a mini split to cool the room.

Look at 2x FB18's please. Don't just shoot for the moon. I doubt you need 3x MPPT's per inverter.

2. If you can swing it, go with a wallmount 48v battery and avoid the server rack side of things. EG4's are UL rated and you can get indoor or outdoor versions if needed. You can also go with other brands that are indoor rated and put them in a detached structure.

3. The new EG4 batteries coming out soon include not only 4 quick connectors but a screw terminal for the bus bar.

Wallmount > Server Rack for flexability. Even the DIY build your own are great and can work with EG4 equipment if that is what you want to do.

Definitely something to think about. I was focusing mainly on the rackmount batteries because I have a rack already, and the Ecoworthy batteries are very cost effective, and could add a battery here and there as funds become available.

I have been focusing on the Flexboss21 because of the high output it's capable of, and the fact that 3x of them (potentially) in parallel would cover the equivalent of a code-compliant 200A 240v residential service (based on my quick research is 48000 watts) when using both battery and solar simultaneously. Obviously, that would be a very long term goal.

I was planning on putting them in a detached garage, but can put them outside if I went with outdoor-rated gear.

I'll have to do some more thinking. Thanks!

 

[chemikalguy]

Batteries are generally shared between all of the inverters. Batteries are all tied to a busbar (or perhaps multiple interconnected busbars) and all of the inverters connect to the same busbar.

I think you're seriously underestimating the amount of batteries you're going to need/want. I'm running a single SolArk 15k and I have 3 racks (so 18x 100 Ah) batteries.

Wow. 90KWh? How long would that last you in a cloudy situation with minimal solar? Are you totally off grid?

 

[chemikalguy]

I do think you are under estimating your battery capacity. It will be your most expensive part of your system. I have 2 cabinets of RUIXU Server Rack batteries (9 total for 46 kWh) and really need more.

Wall mount batteries were just coming out when I built my system. While I'm happy with my configuration, if I had a do-over with today's technology I would seriously consider wall mount batteries.

One thing I failed to mention is that I have a gas generator that I can use to supplement solar when there are cloudy/stormy days, but I definitely want to max out the battery capacity over time.

 

[BrianVeg]

One thing I failed to mention is that I have a gas generator that I can use to supplement solar when there are cloudy/stormy days, but I definitely want to max out the battery capacity over time.

With a gas generator I would plan on adding an EG4 Chargeverter into your configuration. They work great and clean-up generator power and augments solar by charging your batteries. I call it my backup of last resort.

 

[chemikalguy]

With a gas generator I would plan on adding an EG4 Chargeverter into your configuration. They work great and clean-up generator power and augments solar by charging your batteries. I call it my backup of last resort.

Yep, that's a definite must!

 

[teal95]

In the summer and winter I use up to 100 kWh/day. Not off grid. Can't make nearly enough November through January. At high loads times I make it through the night, but without much to spare. When I had only 2 racks I was draining the batteries every night.

 

[LoganV]

I'll have to do some more thinking. Thanks!

Smartest thing any of us can say. Never stop thinking n learning. Never!

 

[chemikalguy]

In the summer and winter I use up to 100 kWh/day. Not off grid. Can't make nearly enough November through January. At high loads times I make it through the night, but without much to spare. When I had only 2 racks I was draining the batteries every night.

Wow, that's crazy. Where do you live? My consumption, if I'm reading my historical power usage from my current utility correctly is between 30kwh and 40kwh, and that's with my wife working from home, running computers, lights, etc.

 

[Redpineapple]

I average 20kwh a day

Your 5 times my average.

What in tarnarion are you doing with all that usage.

Look at reducing consumption- it’s the cheapest solution

 

[LoganV]

We're in E TN, on the Cumberland Plateau, ZIP 37726. Just me n my bride in 1900 sq ft of very well insulated house. Propane and wood heat.

My first recommendation is to use an online tool called PVWatts. Enter your ZIP code and some array details and it will tell you how much production to expect. You can even get an hourly output over an entire year if you're an obsessed engineer like me and want to model solar output vs use. PVWatts includes overcast data and a Monte Carlo type model to simulate sunny and cloudy days.

We have 8 years of daily average use data at our house in kWh/day : Jan - 14.7 Feb - 14.4 Mar - 14.2 Apr - 13.2 May - 12.6 Jun - 14.8
Jul - 20.7 Aug - 20.5 Sep - 18.7 Oct - 13.7 Nov - 12.3 Dec - 12.7
I'm growing to a 50 kWh bank and may get bigger. Your plans sound like 30 kWh, so I'd recommend you plan real hard to grow bigger.

I can't address the noise issues with the inverter you've chosen like a reply above, but be sure with LFP batteries to keep 'em from freezing. Bad Juju!. Friends have had good results from a well-insulated cabinet around the batteries which they remove in warm weather to avoid heat issues. Apparently the small inefficiencies in charge/discharge cycles keep the batteries within a usable temp range.

Please continue to post here so we share what you learn.

 

[wepuckett]

I live in Western NC along the I40 coridor and during the current weather use between 40 and 50 Kwy a day, during the summer I can get to 120 KWh a day so a 100 plus KWH battery bank and being able to expand it is a great idea. By building a house you will be able to make it more energy efficient so that will help but nevery thinnk a battery bank is too large just look at last year and huricane Helene

 

[teal95]

I'm in Michigan with a wife and kids. ~3000 sq ft house, hot tub that eats electric in the summer and livestock tank heaters that eat power in the winter. 100 kWh is my high, this time of year I'm running around 50 kWh.

 

[Brucey]

With a gas generator I would plan on adding an EG4 Chargeverter into your configuration. They work great and clean-up generator power and augments solar by charging your batteries. I call it my backup of last resort.

I think the gridboss has a gen input. Assuming he isn't using some contractor grade unit that doesnt qualify to the fb21s requirements.

 

[Brucey]

In this later case, would I be able to add a second connection from the existing bus bars to the second inverter, using the 4/0 cable, and add 3 more batteries to the bank?

Also, what if I went more than 6 batteries? Each battery is rated at 100A of output, so would I need to replace the bus bars with ones that are rated for higher current, or would it make more sense to split the 10 battery bank into 2 5 battery banks, each connected to a separate inverter?

You need to calculate the maximum load. Which could end up being three fb21s.

Let's assume bank is nearly empty at 48V. 12kW from inverter from each fb21, 250A each, 750A for three of them at full output of 36kW.

 

[Rezin777]

I think the gridboss has a gen input. Assuming he isn't using some contractor grade unit that doesnt qualify to the fb21s requirements.

The gridboss does have a generator input and it has it's own requirements for the generator as well.

 

[BrianVeg]

Here in Lansing, MI my consumption runs between 50 and 80kWh per day. That consumption includes my daughter’s RV AC which is not on my system (ugh). Solar and battery cover almost 60% of it. My issue right now is that I don’t have enough solar to fully charge my 46kWh of battery to 100% so that I can run AC or Heat Pump at night without switching to grid. I’m adding 50% solar capacity (bringing it to 14kW to correct this.

My point is that it’s best to start with an approach that is adaptable. Which usually means adding . Just keep learning is the way to go.

I’m about 18 mos into my journey and learn more everyday.

 

[SplitUniverse]

Pretty much any inverter that can be paralleled will do, preferably in the 10-15KW range.
Think about how you want your batteries connected, one bank controlled by voltage? CAN bus comms? Split banks for each inverter? etc?
Your planned batteries will cover your basic loads in a Grid down situation but not for very long, depending on what you actually need / what you can compromise on, you can get away with that.

From what I've seen around here some FB/GB owners are not very happy with the units, you should do your due diligence on that.
Other options include Solis, SRNE, Solark (I got a 15K, not happy with it or the support they offer) and quite a few others, a lot of manufacturers / relabelers offer units that can be paralleled. Yet another option are the Scheider XW Pro that were on sale at NAZ, hard to imagine anyone needing more than 3 of those in parallel and they were pretty cheap n liquidation sale (they don't have an integrated SCC / MPPT).
Keep in mind that different generations / models of inverters even from the same manufacturer usually can't be paralleled.

If you can get an interconnect agreement with something like "net metering" you can use the Grid as your "battery" and rely on the in house batteries just in Outage cases.