Can you solve this newbie battery bank question?

[Tularosa]

Hi all - with a 1.46kw 24v based solar array, what's the max 24v battleborn-based battery bank I can charge assuming 6hrs of sunlight if I draw an average of 5kw per day from the bank? what's the algorithm to figure out that max amp hour battery bank size given these params? BTW theh battleborn batteries are 12v 100ah.

Edit: i think i got it half way there. I found this post: https://www.diysolarforum.com/index...nd-inverter-is-needed-to-charge-a-battery.73/

So If i need 5kw/6hrs/.8=1.041kw array. (Great I have 1.46kw!) AND if I need 5kw, I will in theory need on average 5kw/24v = 208Amp hours (i.e., 2x12v 100ah batteries should suffice to start). NOW what I don't know is how many more pairs of 12v battleborns could I conceivably charge to maximize the size of my array given those params.

 

[Craig]

well you produce 1.46 kw per hour * 6 hours so that's 9kw per day (round numbers) each set of battleborns hold 2.4kw so you can fill 3.75 24v batteries at 100ah so 4 sets. but you would be theoretically using some of the power during charge times so you wouldn't necessarily be able to store all of it so you would have less to be able to save

 

[Supervstech]

The way I look at it is this.

1.46KW array.

5KWh of daily usage.

the more batteries you have, the less each one will be depleted each day, allowing as much of the array to trickle juice into it, and the longer you can operate when solar days are cloudy...

A rated 1.46kw array is NOT 1.46 kw... unless you can track the sun, and have ideal gain. More like 1.0 max, and .2 often. So be as redundant as possible, and have generator backup.

 

[svetz]

WOOT! Someone used the FAQ and got the right answer! I'm so jazzed!

Remaining Question: how many more pairs of 12v battleborns could I conceivably charge to maximize the size of my array given those params

Not 100% sure I understand the question.

I suspect you know that if you doubled the battery bank and fully consumed it each day you'd need twice the minimum array size to fully recharge them every day (2 x 1.041 = 2.082 kW) and that having extra watts in the array gives you some breathing space for cloudy days.

If you stay with the same draw rate and add extra batteries then you wouldn't need more panels because you current array covers it. Also, having another pair would halve the power draw and for lithium that seems to greatly extend their lives (see this post).

If you want to know how much power the panels generate, that 1.46 * 6 *.8 (array size * insolation hours * efficiency) = 7kw/d

 

[Tularosa]

well you produce 1.46 kw per hour * 6 hours so that's 9kw per day (round numbers) each set of battleborns hold 2.4kw so you can fill 3.75 24v batteries at 100ah so 4 sets. but you would be theoretically using some of the power during charge times so you wouldn't necessarily be able to store all of it so you would have less to be able to save

Thanks! So it’s that simple, i.e., take daily kw generated by the of array and divide by 24v battery set (2.4kw) to get theoretical amount of set you could charge. Nice. Of course I need to account for my usage/draw vs charging and times when I’d generate more or less than 9kw. Thank you!

 

[Craig]

Just remember what Supervstech said though. plan for extra. Honestly if I needed X kilowatts of storage and things were mission critical I would have 2 X Kw in storage and 4X kw in panels due to inefficiencies and to have some redundancy. that may be overkill but in the end panels are cheap. My situation also requires I generate as much power as fast as possible in the winter due to short charging days. Thats just me though Improbably not necessary. Svets point is well advised as well the less you draw as a percentage of batteries C rate the longer they will last. Same with charging.

 

[Tularosa]

Just remember what Supervstech said though. plan for extra. Honestly if I needed X kilowatts of storage and things were mission critical I would have 2 X Kw in storage and 4X kw in panels due to inefficiencies and to have some redundancy. that may be overkill but in the end panels are cheap. My situation also requires I generate as much power as fast as possible in the winter due to short charging days. Thats just me though Improbably not necessary. Svets point is well advised as well the less you draw as a percentage of batteries C rate the longer they will last. Same with charging.

Thanks Craig. I'm curious, would you mind sending the components in your setup. I was noticing your profile write up and pic and curious to learn what you have in your installation and how it's working for you. I'm now on the hunt for a pure sine wave inverter charger (thinking 4kw continuous to allow for expansion...Aims or samlex) and a charge controller (80A per Will's sage advice). I'll be using my trusty champion 3.5kw generator for backup.

 

[Supervstech]

Thanks! So it’s that simple, i.e., take daily kw generated by the of array and divide by 24v battery set (2.4kw) to get theoretical amount of set you could charge. Nice. Of course I need to account for my usage/draw vs charging and times when I’d generate more or less than 9kw. Thank you!

well, it isn’t about how many batteries you could charge. It is about how much usage you have, and how much array you need to stay ahead of it to replace what is used in the solar hours you get.

see? Batteries are reserve for the usage. The more you have, the less EACH battery will dip, and the longer with low solar production you can continue your energy demands.
As long as you have enough solar input to cover your usage, 2 cells or 200 cells... will still be replenished. The more batteries you have, the easier a time the batteries will have. Both with charging them, and with discharging them.

so, don’t worry about how many batteries your solar can handle.

worry about how much daily consumption the solar can replenish, and limit the usage during weak or short solar days.

 

[Supervstech]

Oh, and add as many batteries as you can afford... the more the better. Keep your usage below your TOTAL solar production, and you are fine.

 

[Tularosa]

Oh, and add as many batteries as you can afford... the more the better. Keep your usage below your TOTAL solar production, and you are fine.

Thanks. Going to start with a pair of 12v battleborns and then add up to 2 maybe 3 more pairs over time as needed. It's a weekend cabin so I'll play it by ear.

 

[Supervstech]

Weekend cabin.
So, it could charge when temps are below charging limits.

be CERTAIN you have temp management on the cells, or have the batteries in a conditioned space, or buried below the frost line.

 

[Tularosa]

All - Life distracted me from this project. I now have all these components except for fuses and wires. 1) do i need to ground the panels? 2) do i need a lighntning arrestor on panel combiner box? 3) any critique on my design? Installing memorial day weekend. So pumped.