LiFePO₄ loves long life
Many LFP packs retain 80% capacity after 6,000+ cycles when limited to ~80% DoD—over 16 years if cycled daily.
Cycle champ
Battery Storage Sizing — Estimate Needed kWh for Solar Systems
Loads, Autonomy & Assumptions
Power & Module Details (optional)
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
This battery storage sizing calculator helps you estimate how much battery capacity you need for a home, cabin, RV, or small business. It turns everyday energy use into a practical battery size so you can plan a solar battery bank, backup power system, or off-grid setup with confidence. The goal is simple: cover your typical energy needs for a chosen number of days, while accounting for real-world losses.
The calculation starts with usable energy. If you use a certain amount of electricity each day (kWh/day), and you want enough energy for a set number of days of autonomy, the calculator multiplies those values and adds a buffer. That buffer covers uncertainty, extra loads, or periods of lower solar production. Next, it adjusts for efficiency losses. Power passes through an inverter, and batteries are not 100% efficient when charging and discharging. Finally, it converts from usable energy to nameplate capacity by considering depth of discharge (DoD), because most batteries should not be cycled from 0 to 100% every day.
Use the calculator in a few steps:
- Enter your average daily energy use in kWh (often found on your utility bill or energy monitor).
- Choose your desired days of autonomy, like 1 to 3 days for backup or more for off-grid living.
- Set a buffer percentage for extra margin, then select inverter efficiency, battery round-trip efficiency, and depth of discharge.
- Click Calculate to see the recommended battery capacity in total kWh.
For example, a household using 10 kWh per day with 2 days of autonomy and a modest buffer may need a battery bank in the 25 to 35 kWh range, depending on inverter and battery efficiency. An RV with smaller loads might need far less, while a workshop with power tools may need more. This makes the tool useful for comparing battery storage options, estimating system cost, and deciding how many modules you need.
Formula (fractions): Required nameplate kWh ≈ Load × Days × (1+buffer) ÷ (InvEff × RTE × DoD).
5 Fun Facts about Battery Storage
Cold shrinks capacity
At 0 °C a lithium pack can deliver 10–15% less usable energy, so off-grid cabins often oversize by a “winter” buffer.
Temperature tax
Inverters are hungry
Converting DC→AC typically costs 5–8%, so sizing only from AC load without that loss can leave you short during storms.
Conversion cost
C-rate keeps packs happy
Pulling 2C from a lithium battery can trigger voltage sag and extra heat. Most home systems cruise at 0.5C or less for longevity.
Current sanity
Partial SOC is fine
Lithium chemistries prefer resting around 30–70% SOC; occasional full charges are for balancing, unlike lead-acid which needs regular full absorption.
SOC sweet spot
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.