diy solar

diy solar

What batteries should I buy?

What in the name of all that is holy takes 40A @ 240VAC? Are you charging an EV at night? That's pretty insane. You realize it's likely buying an EV to charge another EV while you charge the EV that did the charging during the day.
I think he meant 40Ah @ 240V - or I hope so.
 
I think he meant 40Ah @ 240V - or I hope so.

No, I think he meant an unholy load:

"large off grid system, that will need a major current draw over night."

While I like my AGM (I'm one of those overpaid Silicon Valley types, who's time is worth too much to bother with the care and feeding of a small battery bank), he might be better off with FLA. Your forklift batteries got you twice as many Wh of storage for the same dollars. Trojan golf-cart type batteries would be fewer dollars, shorter lifespan if that better fits his needs.
 
No, I think he meant an unholy load:

"large off grid system, that will need a major current draw over night."

While I like my AGM (I'm one of those overpaid Silicon Valley types, who's time is worth too much to bother with the care and feeding of a small battery bank), he might be better off with FLA. Your forklift batteries got you twice as many Wh of storage for the same dollars. Trojan golf-cart type batteries would be fewer dollars, shorter lifespan if that better fits his needs.
Then for sure skip 12V, and 24V!

I had 32 Trojan T-105a and they sucked, didn't last two years - and don't even get me started on the resistance of all that cabling, and the hours of going back and retightening the connection bolts every 6 weeks or so. And watering 96 cells was a SERIOUS pain in the ass. I'm a HUGE fan of Industrial/forklift type batteries - the cheapest Ah you can get in the long run.
 
So far it seems most people (myself included) royally screw up their first lead-acid battery bank of any size so it might behoove you to go with a cheap one for your first with an eye towards upgrading to lithium iron phosphate at a later date.
Probably the best bang for the buck in lead acid is the 6V golf car batteries you can get at Costco or other retailers. They'll work but you'll be replacing them in 4-5 years at the latest.
 
32 Trojan T-105 6V 225AH arranged into 4 banks of batteries gave me 900Ah@48V at $180 ea cost $5760 plus another $75 in cabling, so $5835.
1 Monterrey Industrial 'Big Sur' 24-125-11 battery is 986Ah@48V is guaranteed for 10 years and costs $4995.
Your math may vary, but to me, the Trojans were a big pain in the ass and a waste of money.

$5835 for 3 or 4 years if you are lucky 900Ah lots of cables and 96 cells to water
$4995 for a guaranteed 10 years 986Ah no cables and only 24 cells to water

PS the Trojans were nowhere near their claimed rated capacity, but my Monterrey battery seems to exceed it's claimed capacity.
 
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