# Calculation of battery capacity in home energy storage system

No introduction

This article describes how the battery capacity and solar panel data in the solar system are calculated. Based on this, you can refer to the establishment of a solar home energy storage system.Specific examples are given below.

60w load solar power generation system design

1.Battery capacity calculation

The current consumed by the solar power generation system with a load of 60w is (24v power supply):

I=60÷24=2.5A

24-24v power supply by battery

The capacity of the battery can meet 24h work a day and work continuously for 15 days, then the minimum capacity of the battery is:

capacity=2.5×24×15=900(A.h)

2.5-current

24-24h

15-15 days

2.Selection of solar cell arrays

The charging circuit that a standard rigid solar module can provide to the battery pack is 4A. In most areas, in the case of the sun, the maximum charging current that the rigid  solar module can provide to the battery pack is 3A, and the charging time with 3A current is only 4 hours/day, the charging current available at other times is less than 3A.

On cloudy days, the charging current that a standard rigid solar module can provide is only about 0.7A/block.

Assuming that in relatively bad weather, within 15 days, 4 sunny days, 6 cloudy days, and 5 rainy days (without charging), the charging current that each rigid solar module can provide to the battery pack is as follows:

4 sunny days:

3A×4h+(3A+0.7)÷2×4h=19.4(A.h/day)

(3A+0.7)÷2-Take the average of the highest current and the lowest current

19.4×4=77.6(A.h)

6 cloudy days:

0.7A×8h=5.6(A.h/day)

5.6×6=33.6(A.h)

Total: 4 sunny days+6 cloudy days

77.6+33.6=111.2(A.h)

Assuming that 18 rigid solar  modules with an input voltage of 12V/4A are used, the total charge that can be provided to the battery pack within 15 days is:

18÷2×111.2=1008（A.h）＞900A.h

Therefore, the parameters set above meet the needs of system power supply.

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