Would Eight 48V LiFePO4 server rack batteries be appropriate for a Sol-Ark 15K?
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Ampster
Renewable Energy Hobbyist
Inverter size is not the criteria for sizing a battery. The criteria for sizing a battery is the loads that need to be served when solar is not producing and any extra capacity in case there is no solar for a day or two.
For example I have 45 kWhs of battery capacity and my inverter can put out 5kW. Simple math would say that is eight hours but I dont
use that overnight and during the day my solar can charge the battery pack to full by Noon. However if I have a grid outage I want the capacity to allow me to run some critical loads for a few days, and i do not want to take a chance if those few days are cloudy so i have excess battery capacity. It all depends on where you are standing and what risks you want to plan for.
Eight batteries would be a good start.
For example I have 45 kWhs of battery capacity and my inverter can put out 5kW. Simple math would say that is eight hours but I dont
use that overnight and during the day my solar can charge the battery pack to full by Noon. However if I have a grid outage I want the capacity to allow me to run some critical loads for a few days, and i do not want to take a chance if those few days are cloudy so i have excess battery capacity. It all depends on where you are standing and what risks you want to plan for.
Eight batteries would be a good start.
Last edited:
Hedges
I See Electromagnetic Fields!
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You would like to connect them such that each sees exactly the same wire resistance.
You can do pretty well with matched length wires to busbars.
It is also OK to have length of (+) plus length of (-) wire the same for all, even if in some cases (+) is a couple feet longer but (-) is a couple feet shorter.
Another approach, connect as 4 pairs with matched wires. Connect two of those pairs (by opposite corners on each pair) into groups of 4 (same for other two pairs.) Connect two groups of 4 by opposite corners as a group of 8. All batteries see same length to load, and matched wires carry same current.
Class T fuse per battery would be ideal. Or other fuse with AIC rating at least as high as short-circuit current of a battery. Time-current curve needs to be higher than any anticipated surge. (Would like any one battery to be able to carry inverter but that isn't feasible, need at least 3 batteries worth to supply 12kW inverter.)
With 8 batteries and cables fanning in to one inverter, would like wire gauges and fuses such that a short or overload anywhere blows a fuse before overheating wire. That may get complicated with the pairs of pairs of batteries. Simpler 8 cables through fuses to busbar, one fuse through cable to inverter; that starts to look more reasonable.
You can do pretty well with matched length wires to busbars.
It is also OK to have length of (+) plus length of (-) wire the same for all, even if in some cases (+) is a couple feet longer but (-) is a couple feet shorter.
Another approach, connect as 4 pairs with matched wires. Connect two of those pairs (by opposite corners on each pair) into groups of 4 (same for other two pairs.) Connect two groups of 4 by opposite corners as a group of 8. All batteries see same length to load, and matched wires carry same current.
Class T fuse per battery would be ideal. Or other fuse with AIC rating at least as high as short-circuit current of a battery. Time-current curve needs to be higher than any anticipated surge. (Would like any one battery to be able to carry inverter but that isn't feasible, need at least 3 batteries worth to supply 12kW inverter.)
With 8 batteries and cables fanning in to one inverter, would like wire gauges and fuses such that a short or overload anywhere blows a fuse before overheating wire. That may get complicated with the pairs of pairs of batteries. Simpler 8 cables through fuses to busbar, one fuse through cable to inverter; that starts to look more reasonable.
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