Numerical - Compute the number of cells required if solar cells are utilized to charge the battery

If solar cells are utilized to charge the battery 15 V supplied to an earth satellite with a continuous current of about 2A then compute the number of cells required if each cell during exposure yields 1V at 60 mA. Illumination of Solar cells takes place by Sun for 12 hours in every duration of 24 hours with an assumption of solar voltage 16.5 V.


a. 540
b. 575
c. 590
d. 528

Correct Answer: d. 528


It is essential to connect the solar cells in series to obtain requisite amount of voltage.
At the same time, it is also crucial to connect such groups in parallel combination for the provision of essential current.

It is almost a prior condition that the charging voltage must be greater than battery voltage.

Number of solar cells connected in series combination
= Solar bank Voltage /Continuous Current

Assuming that the solar voltage to be 16.5 V, we can write

No. of solar cells in series connection = 16 /2 = 8

Charge of battery within 24 hour duration = 24 x 2 = 48 Ah

It is mandatory for solar cells to supply the charge of 48 Ah over the similar duration.

Conceptually, solar cells has an ability to supply the current only under the influence of illumination.

This implies that current can be delivered only for 12 hours in every 24 hours.
Thus, the required charging current from solar cells = 48 Ah / 12 h
= 4 A
Consequently, total no. of groups in parallel combination equals to the ratio of output current to the cell current.

Total No. of groups = 4 / (60 x 10-3)

= 66

As a result, the total number of solar cells necessary for an earth satellite

= No. of solar cells in series combination x total no. of groups of solar cells in parallel combination

= 8 x 66

= 528
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