What inputs do I need?

Enter daily load (kWh/day), days of autonomy, chemistry (or set depth of discharge and round-trip efficiency), and inverter efficiency. Optionally enter peak load (kW), system DC voltage, and your preferred module size (kWh) to get a module count.

We estimate usable energy needed, adjust for inverter and round-trip losses, then divide by depth of discharge to get nameplate kWh. We also estimate a module count and check peak DC current at your battery voltage.

No. This tool runs locally in your browser. Nothing is sent to a server.

Battery Storage Sizing — Estimate Needed kWh for Solar Systems

Friendly estimates for planning and awareness. Private by design — runs locally in your browser.

Loads, Autonomy & Assumptions

Daily load (kWh/day) Days of autonomy (days) Weather buffer (%)

Chemistry preset Depth of discharge, DoD (%) Battery round-trip efficiency (%) Inverter efficiency (%)

Power & Module Details (optional)

Peak load (kW) System DC voltage (V) Module size (kWh each) Recommended max discharge (C-rate)

C-rate sanity check compares the pack’s nameplate energy and peak power at your DC voltage.

Awareness-level estimate. Real designs also consider temperature, charge limits, min/ max SOC windows, surge power, code, and specific product data sheets.

Results

How This Battery Sizing Works

We first compute the usable energy you want to cover: kWh/day × days of autonomy × (1 + buffer). Then we account for losses so the pack can actually deliver that energy through the system:

Through inverter: divide by inverter efficiency.
Through battery round-trip: divide by battery round-trip efficiency.
Nameplate (total) kWh: divide by DoD (you don’t cycle 0→100% each day).

Formula (fractions): Required nameplate kWh ≈ Load × Days × (1+buffer) ÷ (InvEff × RTE × DoD).

Tips

Chemistry presets: LFP is friendly to daily cycling (typical DoD 80–90%, RTE ~92%); NMC/NCA similar RTE but sometimes narrower daily SOC; lead-acid prefers shallow cycles (DoD ~50%).
Peak power: Check that your inverter’s continuous/surge ratings match loads. This tool gives a quick DC current check at your battery voltage.
Module counts: Enter a module size (kWh) to get a whole-module recommendation with a small rounding buffer.