batt. question

Re: batt. question

You're saying:

1). battery bank is 360 Amp hours @ 24 Volts
2). load is 10 Amps @ 24 Volts

From that we can deduce that the batteries will supply the loads for up to (0.5 * 360 / 10) 18 hours.

To offset the 10 Amp @ 24 Volt (240 Watt) load use you need panel output that would average that amount during the sun hours. This would usually require about 312 Watts and an MPPT type controller. Such would only keep up with the loads for as long as the insolation was sufficient to maintain output.

If you want to completely offset 240 Watts for 12 hours you need to make up (240 * 12) 2880 Watt hours of power. This then becomes a matter of how many hours of equivalent good sun you get. If it is 4, then the array size would need to be at least (2880 / 4) 720 Watts factored by the derating or typically 935 Watts total.

Don't ignore the losses; they are important. How and when the loads are used plays a big factor in the over-all efficiency. That's why the end-to-end derating of a battery-based system is a dismal 52%. As such the 2880 Watt hours AC would probably need (2880 / 0.52 / 4) 1385 Watts of array. That's nearly double what the "plain, without losses" calculation would indicate.

Re: batt. question

erne wrote: »

how many watts are in these 4 batteries that is usable to 50% capacity. erne

Watt hours. The "hours" part of the label is essential. Watt is just a rate of power use; Watt hours is a quantity used.

360 Amp hours discharged 50% is 180 Amps hours * 24 Volts = 4,320 Watt hours stored.

Now here's the disclaimer portion:
A battery's actual capacity will vary according to the rate of current draw (higher current = lower capacity) and temperature.
Battery Voltage is not steady @ nominal: it has a varying range. Usually nominal is the minimum Voltage used (although some systems allow dipping below that) so it is a fairly safe number to use for approximating available power.
Batteries lose capacity with age, no matter how well cared for.
DC Watt hours stored in a battery are not the same as AC Watt hours available for use due to inverter power consumption and conversion efficiency.

Leaving out these little inefficiency losses is how many people get in trouble with system design: using all nominal numbers and expecting the best. It is better to err on the side of caution. People who try to run on the edge usually fall off it.