Battery Capacity Calculator

The Science of Solar Energy Storage: How to Size Your Battery Bank

As net-metering policies shift and DISCOM peak-hour tariffs rise in 2026, residential solar is transitioning from "grid-tied" to "hybrid". Our Solar Battery Capacity Calculator helps you architect the perfect energy storage system to ensure critical load backup during outages while maximizing your solar self-consumption.

1. Understanding Battery Chemistry: LFP vs. NMC

When selecting a home solar battery in India, the two dominant lithium-ion chemistries are Lithium Iron Phosphate (LFP) and Nickel Manganese Cobalt (NMC).

• LFP (Recommended): Offers a longer cycle life (up to 6,000 cycles at 80% DoD), exceptional thermal stability (crucial for Indian summers), and contains no toxic cobalt. Most modern systems like Tesla Powerwall 3 and Luminous Li-ON series use LFP.
• NMC: Has a higher energy density (smaller physical footprint) but degrades faster and carries a slightly higher risk of thermal runaway under extreme heat.

2. Depth of Discharge (DoD) Explained

The DoD rating indicates how much of the battery's total capacity can be safely used without causing permanent chemical degradation.

Usable Capacity = Total Nameplate Capacity × DoD %

For example, if you purchase a 10 kWh lead-acid tubular battery with a 50% DoD, you only have 5 kWh of usable energy. However, modern Lithium LFP batteries boast a 95% to 100% DoD, meaning a 10 kWh LFP battery yields nearly 10 kWh of usable backup power. This is why our calculator asks for the DoD parameter.

3. Sizing for Critical Loads (Surge vs. Continuous Power)

Your battery bank must be sized not just for total energy capacity (kWh) but also for instant power output (kW), which is constrained by the hybrid inverter.

• Continuous Power: The steady stream of electricity required to run lights, fans, and televisions simultaneously.
• Surge (Peak) Power: The massive, instantaneous spike in current required to start inductive loads like Air Conditioners, water pumps, and refrigerator compressors. A 1.5-ton Inverter AC might run at 1500W continuously, but require a 3000W surge for 2 seconds to start.

Ensure your chosen hybrid inverter can handle the combined surge load of all appliances you intend to back up.

4. Battery Subsidies and Tax Economics

While the PM Surya Ghar CFA subsidy explicitly covers grid-tied solar components, it does not currently cover the cost of the lithium battery bank itself. However, for commercial installations, battery depreciation can be written off under standard corporate tax codes. As peak electricity tariffs continue to rise (Time-of-Use pricing), a properly sized battery system will naturally decrease your ROI payback period by shifting solar usage into expensive evening hours.