Questions regarding Solar Panel Requirements to charge LIFEPO4 batteries.

[Redemption]

Hi All,

I am new to the forum and a novice. Five years ago, I installed a system in my parent's home. Since then, they have outgrown the system, and now I am considering an upgrade.

The current system consists of;

16 x 100 Watt Mono pannels
1 x Outback Flexmax 80 FM80 MPPT
1 x AIMS Power PICOGLF20W24V120VR
4 x 220 AH 6v batteries wired in Series for 24 volts.

They use the system daily. They have a Manual disconnect box to switch from grid to off-grid. I am considering purchasing an EG4-LifePower4 Lithium Battery, 48V. 100AH. That battery would be comparable to what they currently have with the added benefit of being able to draw them down to 20 percent as opposed to the 50 percent of the Lead-acid batteries they currently have. It would also mean less maintenance than the Lead Acid batteries.

I was told a few things yesterday that did not sound right, and I want to separate facts from fiction.

1- One 48v 100AH battery will be horrible; as they discharge, they will not be able to hold a load the same as having multiple batteries.
2- My 1600-watt solar panels will not be able to charge one 48v 100AH battery effectively. LIFEPO4 needs more panels than traditional LEAD acid batteries to achieve the same level of charging.

Currently, my parents do not use a lot of power. As I understand it, this is the math for their current system.


1600w x 4 hours of peak sun will give them up to 6400 watts every day on sunny days. "They probably generate more, but this formula I used to size their needs."

They have 24v x 200ah, giving them a total of 4800-watt hours. They can only use a max of 50% of that power, giving them 2400 watts to play with. During the day, the excess energy can be used to power most of their loads, consisting primarily of a tv, fan, and refrigerator. TV draws 70 watts, the fan draws 100 watts, and the fridge is pretty new and draws less than 100 watts. Fan TV is used sparingly in the evening and the fridge is on 24/7. Fidge consumes about 70 percent of the power, give or take 5 percent.

If I got them a 48v 100 AH battery, that would give them 5.12 KWH or 5400 watts. The battery would give them an extra day or two of energy on cloudy days. Drawing them down to 20 percent max would provide them with a total of 4320 watts, which is more than they currently use.

With all that In mind, here are my following few questions.

1- If I purchased Two G4 batteries, how many watts worth of panels should I shoot for to be able to charge the two banks in one typical day to 100%? Why two batteries? They recently purchased a mini-split AC unit. They do not use it on solar, but it would be nice if they could use it at least at night.

2- How many watts worth of panels to charge just one bank in one day to 100%?

For purposes of my use case, let's assume that I will Buy the all-in-one EG4 inverter/Charge controller unit. Also, the panels are located in Puerto Rico, with a fair bit of sun except on rainy days.

Thanks for the help in advance.

 

[Rocketman]

Do you want to replace the inverter? And go to 48v or do you want to stay at 24v?

The solar panels will charge lithium the same as lead-acid. (Actually lithium is easier - because you don’t need a long time in absorbing mode). I looked up your SCC (solar charge controller) and I believe it will work for 48v (if you want to go to there - and I think it is fully adjustable so you can give it a lithium profile (if you have a password). Depending on how you wired-up the solar panels you may (or may not) need to change the wiring to run with 48v. How are they wired series and parallel?

If you want to stay at 24v you can find 200ah 24v batteries EG4-LL batteries. That way you don’t replace the inverter.

One big difference with lithium vs lead - is lead can handle a massive current load at once - the bms in lithium batteries usually limits the current to about 100 amps per battery. So if your inverter has a large draw - you may need more batteries. But everything you talked about is low draw stuff- so one battery may be sufficient.

Being in Puerto Rico you won’t have to worry about charging the batteries below 32F or 0 degrees C.

What are the details on the mini-split unit - 120v or 240v - how many amps? You probably do not want to put that on the solar system. Bigger inverter needed, more batteries and another solar array (with a another Solar Charge Controller)…. But it could be done.

Good Luck with your project!!!

 

[Rocketman]

Also, do you have a battery monitor on the system so they know how full the batteries are? Something like a Victron Smartshunt or BMV712? (There are other ones too.)

 

[Redemption]

Rocketman,

Thank you for the reply and all the information. Am I considering switching to 48 volts, as I understand it will allow me to put more panels down the road?

I am currently using an ECO LLC 6 String PV Combiner Box. If I remember correctly, they are wired in four serial banks of 4 x 100-watt panels. Would that make it four serial and four parallel? I do have the password for the Charge controller. I did install a cheaper shunt, but in hindsight, I should have gotten a Victron. The one they have does not seem to be all that accurate; it works well if you go by the voltage to calculate available energy, but my parents are having a hard time figuring things out that way.

The mini split is 120volts, but I am unsure how many amps it draws. All the loads in the house are 120.

I am leaning towards getting an EG4 6.5kW inverter; among other reasons, my current inverter has limited options for when to shut down. I want more control over that functionality. The one negative of the EG4 is the 100-plus watts it draws. Do you have a recommendation for a different charge controller/ inverter? I am also considering two EG4-LL batteries. I would like to have at least a 4000-watt inverter; that way, they can run other appliances, like a coffee maker here and there.

I was thinking 2500 watts worth of panel to charge, two EG4-LL batteries; what are your thoughts there?

 

[Bvillebob]

To answer the question you didn't explicitly ask, don't ever discuss solar with whoever gave you the information you described, it's complete BS. It's clear you know far more than them, they're just misleading you, probably for profit.

 

[Rocketman]

I liked Bvillebob reply and totally agree with it!

On the panels- can you get the same exact panels? they need to be the same specs on the label to add them to your current array.

Larger panels have dropped more in price than the 100w panels. It may be cheaper to setup a second array with 3 or 4 330w panels and another Solar Charge controller (look at Victron mppt 150/45 - for example). (Edit… for 48v system - put your Outback on the new array - put your old array on a mppt 150/35. - that will be cheaper).

On the inverter- look at a Victron Multiplus. They have a integrated transfer switch. That means you wire up the local grid power to it - run everything you want to power out of it. When you want to run on the grid and recharge the batteries set it to “on” when you just want to run off battery (and solar), set it to “inverter only”. If the power goes out when it is on and charging the battery- you won’t even notice it - except the battery stops charging.

 

[Redemption]

Awesome, thank you both for the solid advice!