Battery Sizing

Northwest Power Co.

http://www.nwpwr.com

1. Total average amp hours per day from the system Load Calculation Worksheet

2. Maximum number of continuous cloudy days expected in your area

3. Multiply line 1by line 2.

4. Divide line 3 by ( maximum) 0.8 to maintain a 20% reserve after deep discharge period

to prevent less than a maximum 80% discharge divide by a lessor

Reserve wanted =

Special Condition #1: HEAVY ELECTRICAL LOAD

5. Maximum amperage that will be drawn by loads 10 minutes or more

6. Discharge rate of battery. If known, check with Battery supplier

7. Multiply line 5 by line 6

Special Condition #2: High Charge Current.

8. Maximum output amperage of PV array or other battery charger

9. Multiply line 8 by 10 hours

x

10

10. Amp Hours from line 4, 7, or 9 whichever is largest.

11. If you are using a lead-acid battery select the multiplier below which corresponds

to the batteries wintertime average ambient temperature:

Battery Temperature Multiplier

Multiplier

80F/26.7C

1.00

70F/21.2C

1.04

60F/15.6C

1.11

50F/10.0C

1.19

40F/4.4C

1.30

30F/-1.1C

1.40

20F/-6.7C

1.59

12. Multiply line 11 by line 10. This your optimum battery size in amp hours.

13. Amp Hours of battery chosen . (L16 is 360, T-105 is 225 etc. )

14. Divide line 12 by line 13. This is the total number of 12v batteries in series required

15. This is the number of total batteries to make up a 24v system

x

15. Round off to the next highest whole number.