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Estimating battery requirements
41
Battery sizing example
This battery sizing example illustrates a typical calculation,
assuming an opportunity to charge the batteries every three
days.
This example illustrates how quickly your battery needs can
escalate. To reduce the required battery size, you can
recharge more frequently or conserve energy by eliminating
or reducing the use of some loads.
When sizing your battery, resist the temptation to skip the last
step of this calculation (multiplying by 2). More capacity is
better since you will have more reserve capacity, be better
able to handle large loads and surge loads, and your battery
won't be discharged as deeply. Battery life is directly
dependent on how deeply the battery is discharged. The
deeper the discharge, the shorter the battery life. Most battery
manufacturers recommend limiting the “depth of discharge”
to 50% of the battery capacity.
Appliance
(A) Power
consumption
(B) Operating
time per day
Daily watt-
hours needed
for this
appliance
(= A x B)
19” Color TV 100 W 2 hours 200 Wh
Power drill 400 W 1 hours 400 Wh
Computer system 300 W 2 hours 600 Wh
Total daily watt-hours of AC load 1200 Wh
x Number of days between charges 3
= Total watt-hours of AC load between charges 3600 Wh
Battery Ah used between charges (divide by 10) 360 Ah
Recommended Battery Bank Size in Ah (multiply by 2) 720 Ah