A battery specification sheet is written for a laboratory at 25 °C. A rooftop utility room in June is not that. The chemistry that survives the difference is the one worth paying for.
Lithium iron phosphate cells give up some energy density against nickel-manganese-cobalt, and in exchange they hold their capacity far better at sustained high temperature and tolerate abuse without thermal runaway. On an Indian rooftop that trade is not close.
45 °C
Sustained ambient LFP handles without accelerated fade
6,000+
Cycles at 80% depth of discharge
10–15 yrs
Realistic service life in North Indian conditions
Sizing against the evening, not the array
The common error is to size storage as a fraction of the solar array. Storage exists to move energy in time, so it should be sized against the load you want carried after sunset: the fans, the lights, the fridge, one air conditioner if you insist. Work out those watt-hours and you have your battery. Everything above that number is capital sitting idle.
Backup is not the same as off-grid
A right-sized residential pack carries essential loads through an evening outage comfortably. Running the whole house, including every air conditioner, through the night is a different specification and a very different price.
Buy the battery that carries your evening. The one that carries your imagination costs three times as much and cycles half as often.
What to take away
Meera Iyer
Systems engineering
Specifies panels, inverters and battery blocks for RePrime systems, and tests what the datasheets do not mention.
Run these numbers against your own bill
The calculator uses state-wise generation data and the current subsidy slabs. Two inputs, one estimate, no call required.
