OutBack Power FXR2012A Installation Manual page 13

To Calculate Minimum Battery Bank Size (refer to previous page for letter designations):
1. The load size, item A, is measured in watts. Compensate this figure for efficiency loss. Multiply the
conductor efficiency by the inverter efficiency (E x F). (These items are represented as percentages, but
may be displayed as decimals for calculation.) Divide item A by the result.
2. Convert the compensated load into amperes (Adc). Divide the step 1 result by the system voltage (G).
3. Determine the best battery capacity (I) by dividing each rated capacity by the time in hours (as shown in
Table 3). This is the estimated discharge rate at that battery capacity. The number is usable if the step 2
result (the actual load rate) does not exceed it. Choose the closest (or smaller) rated amp-hour capacity.
4. Determine the daily load consumption in ampere-hours (Ah). Multiply the step 2 result by the daily usage
hours (item B).
5. Adjust the total for required days of autonomy (the days the system must operate without recharging) and
the maximum DoD. Multiply the step 4 result by C and divide by J.
The result is the total amp-hour capacity required for the battery bank.
6. Determine the number of parallel battery strings required. Divide the Ah figure from step 5 by the
individual battery capacity (I) determined in step 3. Round the result to the next highest whole number.
7. Determine the total number of batteries required. Divide the system voltage by the battery voltage
(G ÷ H). Multiply the result by the step 6 result.
The result is the total required quantity of the chosen battery model.
EXAMPLE #1
A . Backup loads: 1.0 kW (1000 W)
B . Hours of use: 8
C . Days of autonomy: 1
D . Grid-interactive system
(FXR3048A inverter)
E . Conductor efficiency: 98% (0.98)
F .
Inverter efficiency: 93% (0.93)
G . System voltage: 48 Vdc
H . Batteries: OutBack EnergyCell
220GH (12 Vdc)
I .
Capacity determined at 8-hour rate: 184.8 Ahr
J .
Maximum DoD: 80% (0.8)
EXAMPLE #2
A . Backup loads: 720 W
B . Hours of use: 2.5
C . Days of autonomy: 2
D . Off-grid system (VFXR3524A inverter)
E . Conductor efficiency: 97% (0.97)
F .
Inverter efficiency: 92% (0.9)
G . System voltage: 24 Vdc
H . Batteries: OutBack EnergyCell
200RE (12 Vdc)
I .
Capacity determined at 3-hour rate: 119.1 Ahr
J .
Maximum DoD: 50% (0.5)
900-0166-01-01 Rev A
1. A ÷ [E × F]
1000 ÷ (0.98 × 0.93) = 1097.2 W
2. 1 ÷ G
1097.2 ÷ 48 = 22.9 Adc
3. I = Ah ÷ hours
184.8 ÷ 8 = 23.1 Adc (larger than 22.9;
Compare to 2
this means 184.8 Ah is acceptable)
4. 2 × B
22.9 × 8 = 182.9 Ah
5. [4 × C] ÷ J
[182.9 × 1] ÷ 0.8 = 228.6 Ah
6. 5 ÷ I
228.6 ÷ 184.8 = 1.24 (rounded to 2)
7. [G ÷ H] × 6
[48 ÷ 12] × 2 strings = 8 batteries
1. A ÷ [E × F]
720 ÷ (0.97 × 0.9) = 824.7 W
2. 1 ÷ G
824.7 ÷ 24 = 34.4 Adc
3. I = Ah ÷ hours
119.1 ÷ 3 = 39.7 Adc (larger than 34.4;
Compare to 2
this means 119.1 Ah is acceptable)
4. 2 × B
34.4 × 2.5 = 85.9 Ahr
5. [4 × C] ÷ J
[85.9 × 2] ÷ 0.5 = 343.6 Ahr
6. 5 ÷ I
343.6 ÷ 119.1 = 2.9 (rounded to 3)
7. [G ÷ H] × 6
[24 ÷ 12] × 3 strings = 6 batteries
Planning
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