Battery Sizing for Inverter

[taiyoken]

I have a 24V SOK 100aH lithium battery, and recently purchased a 24V Growatt 3000TL LVM. The Growatt hasn’t arrived yet, but upon looking through the manual (and reading a bit more about inverter sizing), I’m realizing that at least 200 aH battery capacity is recommended. Am I totally out of luck (and need either a small inverter or another battery), or will I just be unable to run the inverter at full capacity for long (or at all)? I’m really not expecting a lot of heavy AC usage (at least initially), and think my normal loads will fall under 2000W, so I’m hoping it will still work and I can perhaps add another battery down the line.

 

[Mattb4]

I have been running on a 24v 80ah lithium battery for little over a month now with my EAsun 3k-U. (Voltronic made just like the Growatt is). Works good. Just got a second one in today and will be adding it to my system. You do have to watch max charging amperage and keep it within battery recommendations.

Your battery is 100ah at 24v that equals 2400wh. Which would run a 2000w load for just under an hour.

 

[Charleswgibbs]

It looks like the sok has a discharge limit of 100a, you should just barely be able to squeeze 2000w out of a single battery. Less as it discharges.

 

[taiyoken]

Thank you both, that definitely makes me feel better!

@Mattb4 , can you tell me a little more about watching the max charging amperage? Is that when I'm charging from AC, or when I'm discharging the battery under load?

One other question... would I be totally unable to hit 3000W, given the battery specs? I don't plan on it, but I'm curious whether I could run that high and it would discharge very quickly (much less than an hour), or if I'm hard limited to 2000-ish W (which is the max I'm expecting anyway).

 

[Mattb4]

Batteries will often have listed max charge amperage. My 80ah ones show 20a. Charging amperage is from all sources whether solar or Utility.

LiFePO4 battery BMS have max amp draw current (many are 100a). thus if you have a ~24v battery your with max draw of 100a you can supply at max a load of 2400w. (Reality is the battery is slightly higher voltage and the inverter and other losses will limit the max but 2000w load max is about right) Watts = Volts X Amps

 

[Mattb4]

I think I should mention that if you are running on your inverter from both battery and solar power you can set your max amperage to reflect both your loads and your battery charging needs. In my case I have a 30a limit set. This works out good with my 900w solar panels since at best they max out at 720w. (30a X 24v) So 20a to battery and 10a to loads. My continuous loads most often run about 4-8a.

 

[sunshine_eggo]

I have a 24V SOK 100aH lithium battery, and recently purchased a 24V Growatt 3000TL LVM. The Growatt hasn’t arrived yet, but upon looking through the manual (and reading a bit more about inverter sizing), I’m realizing that at least 200 aH battery capacity is recommended. Am I totally out of luck (and need either a small inverter or another battery), or will I just be unable to run the inverter at full capacity for long (or at all)? I’m really not expecting a lot of heavy AC usage (at least initially), and think my normal loads will fall under 2000W, so I’m hoping it will still work and I can perhaps add another battery down the line.

Part of the 200Ah recommendation is that growatt has a high idle consumption. It will burn about 45W 24/7 even if you have no loads attached. That's 1080Wh of daily capacity consumed. Your battery has 25.6*100 = 2560Wh. This means 1080/2560 = 42% of your battery capacity will be consumed by the inverter and the first 200-300W of your array will be dedicated to replenishing this consumption.

 

[taiyoken]

@sunshine_eggo that’s a really good call out, I hadn’t considered it! I’d heard these all-in-one units have a high idle consumption, but I hadn’t put pen to paper to do the math. That makes sense!