Upgrading Solar System

[Beeb1]

Hi all, I have a school bus conversion (skoolie) with an existing solar/electrical setup that I'm wanting to upgrade so we can run our window AC units.

My current system:

• 12V, 375Ah VMaxTanks AGM Batteries (3 batteries, connected in paralell)
• Roughly 1500W solar panels (I can't remember the exact size off the top of my head, but it's something around there)
• 1 100|50 Victron MPPT Charge Controller
• 1 100|50 MakeSkyBlue MPPT Charge Controller
• 600W Inverter (Samlex Power)
• Victron BMV-712 Battery Monitor
• 2 Window AC units, each draws roughly 600W continuous
• Various other 12V items (LED lights, 12v fridge, laptops, phone chargers, etc)

What I want:

1. I want to switch to LiFePo4 batteries (I was looking at these batteries recommended by Will). I want to have enough battery capacity to run my window AC units for a few hours after the sun goes down. Most of our time is spent in the desert, so we get a lot of sun, but that also means a lot of heat.
2. I want to have Victron products that all talk to each other so I don't overcharge my batteries. I nearly had my home burn down last year because I used a Renogy inverter/charger that just kept pumping power into my batteries even after they were fully charged. I don't want that to happen again. However - I want to have the Victron items hardwired together, not relying on bluetooth. I don't know if it's because we live in a metal box, or what, but nothing wireless works well inside our bus. I'd like to have the peace of mind knowing that they're connected physically and not wirelessly.
3. I'm going to get more solar panels. I want enough solar to be able to run the AC units during the day, as well as my various other appliances, and also get my batteries charged up. Most of my time will be spent parked on my property, so I can have ground-mounted solar panels if necessary.

I built out my current system myself, but that was years ago and I feel like I'm re-learning everything from scratch again. Plus, I've never worked with LiFePo4 batteries before. Right now I'm thinking maybe getting 4 of those batteries Will recommended (totaling 920Ah) - with a recommended charge rate of 46A each, that should (I think) mean I can have 2200W of solar. 920Ah of batteries would give me way more than I would need to run my window units for a few hours after sunset, plus room to spare for days when I don't get full charge.

What should my other considerations be? Do I need a CSL with these batteries? What's the best way to make sure my Victron devices all talk to each other without relying on wireless? Should I try to go to 24V or 48V? And if so, that's a whole new ballgame for me, so what should I be aware of in that setup that's different than 12V?

Basically - I'm feeling a bit overwhelmed (once again) as I try to relearn all this, so some pointers to get me started in the right direction would be awesome. I'd also honestly consider paying someone to plan out a full system for me, just for the peace of mind. But I'm not sure if I'm there yet.

 

[Dinobot248]

A few unorganized comments


Only option is 48v

General guidelines are
12v system should have max 2,000w
24v is 4,000w
48v is > 4,000w and future proofing



You need to get a handle on how much electricity you use now and what you will use in the future.


A general rule I follow is a usuable
Battery bank is about 60% of capacity. For example using simple math, a 100 kWh (51.2v x 2000 ah) battery bank will have 60 kWh of useable capacity. 20% is simply reserved to minimize drawing a battery to empty and reducing its life. The other 20% is efficiency loss which vary based on your inverter efficiency curve .



Victron is the only choice in my opinion. Your wallet may feel a bit lighter but your mind will be at ease. Those who goes blue tend to be happier and experience much less stress. Goto current connected websites and look at their kits. It has what you need to start your system.

My approach is to buy in key groups or categories
—solar panels
—batteries
—key hardware (inverter, SCC, cerbo gx, shunt, etc)
Do what you feel comfortable and what your wallet allows

 

[Beeb1]

Only option is 48v

General guidelines are
12v system should have max 2,000w
24v is 4,000w
48v is > 4,000w and future proofing

As in, 2,000W/4,000W of solar? Or something else? If I'm aiming for 2200W of solar, wouldn't that mean 24v is an option?

 

[Dinobot248]

it’s just a a guideline and it’s a free country. You can bend or break the guidelines as you chose.

Here 2000w refers to your electric load that is being used.

12v systems should be used to operate and support < 2000w of load from your house (or bus, rv, etc)

2000w / 12v = 167A
You need a thick copper wire to safely transfer 167A. Now imagine if you ran 5000w on a 12v system. You would run 417A which is well beyond the largest load supported with a 4/0 wire.



Incoming Solar is independent but closely related to your battery bank and daily usage. Incoming Solar needs to be consistently more than how much electricity you use each day and have extra to charge your batteries bank to get through however many days of low/no Solar days. Important considerations are not upsetting your spouse, letting the fridge / freezer go dead, keeping kids warm or cook, etc.


in terms of solar panels, 12v is really wasteful. If you had a 48v system, you would need 1 charge controller. That same system configured as a 12v system would need 4 of the same charge controllers.

Charge controllers are generally rated by how much they can charge a battery eg 20A, 60A

So 20A CC x 12v = 240W for 12v system
20A CC x 48v = 960w for 48v system.