Solar batteries: what to know before you buy
Lithium vs lead-acid, how to size a battery, and what backup you can expect.
A battery lets your solar system keep essential loads running during power cuts and in the evening. Here is how to choose one.
Lithium-ion vs lead-acid
Lithium (usually LFP, lithium iron phosphate) batteries last many more charge cycles, can be discharged more deeply, need no topping up and take less space. Lead-acid batteries cost less upfront but wear out sooner and need ventilation and maintenance. For new systems we generally recommend lithium.
How to size a battery
- List the appliances you want during an outage: lights, fans, Wi-Fi, fridge, a computer.
- Add up their power in watts and multiply by the hours of backup you need.
- Add a margin for inverter losses and the battery's usable depth of discharge.
Example: lights and fans totalling 600 W for 4 hours need about 2.4 kWh, so a battery of around 3-3.5 kWh usable capacity is a sensible starting point.
What a battery won't do
A home battery is sized for essential loads, not for running several air conditioners through the night. Heavy loads need a much larger, costlier system.
Subsidy
The PM Surya Ghar subsidy is calculated on panel capacity only; battery cost is not subsidised.
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