Design the battery for an industrial application that requires 20-kWh energy in 2 h for a dc load at 240 V four times daily for 300 days every year. The battery must be completely recharged in 2.5 h after each discharge.

Use NiMH cells with the following cell parameters: average discharge voltage 1.2 V, average charge voltage 1.45 V, c/d ratio 1.15, trickle charge rate C/80, and average life 1500 cycles at 100% DoD. For the purpose of reliability, design the battery with two strings in parallel. To avoid one string charging the other, place an isolation diode with 1-V drop in the discharge path of each string. Assume that each cell has 15-mΩ internal resistance at the operating temperature. If the battery must last 7 calendar years before replacement, determine for each parallel string: 

(1) The number of cells in series, 

(2) The discharge current, 

(3) The ampere-hour ratings of each cell,

(4) The charge current, 

(5) The charge voltage, and

(6) The trickle charges current.