Enter your daily energy use and backup days below, then choose a battery chemistry and voltage. Formula: Battery Capacity = (Daily Use × Backup Days) ÷ Depth of Discharge ÷ Round-Trip Efficiency ÷ Cold-Weather Capacity Factor.
Your Energy & Backup Needs
Not sure what a field means? Tap the ⓘ next to its label.
Battery Chemistry & Voltage
Choose a chemistry to auto-fill a typical Depth of Discharge and round-trip efficiency, or edit either field yourself.
The most common lithium chemistry for home solar storage. Long cycle life, stable, and safe, with a high usable Depth of Discharge.
A lithium chemistry common in electric vehicles and some home batteries. Slightly higher energy density than LFP, with a somewhat shorter cycle life.
A premium lithium chemistry with an exceptionally long cycle life and strong cold-weather performance, at a higher cost than LFP or NMC.
An emerging, cobalt-free chemistry with lower energy density than lithium options but good cold-weather tolerance and lower raw material cost.
The traditional, lowest-upfront-cost option. Limited to a much shallower Depth of Discharge and shorter cycle life than lithium chemistries. Choose a subtype below.
Cold-Weather Adjustment
Battery capacity drops as temperature drops. Enter the coldest temperature your batteries will actually sit in.
Your Results
This chart shows the nominal battery capacity your same daily use and backup days would require under each chemistry's typical Depth of Discharge and efficiency, holding your entered temperature constant. Your currently selected chemistry is highlighted — useful for weighing upfront battery size against cost and cycle life before you shop.
Results are for reference and estimation only. Verify all values before use in any solar system design or purchase. See full disclaimer below.
How to Use the Solar Battery Storage Calculator
Solar Battery Storage Guide
A deeper look at what goes into correctly sizing a battery bank, and how to choose between chemistries — written for first-time buyers and job-site reference alike.
Depth of Discharge for a Home Battery
On a house that stays on the grid, the battery is usually covering evening peak, a short outage, or time-of-use shifting — not days of cloudy-weather autonomy. Depth of Discharge is still the number that sets how large the wall unit must be. A home lithium pack that can use about 90% of nameplate needs far less purchased kilowatt-hours than a lead-acid bank limited to about 50% for the same usable kilowatt-hours. That is why a garage wall unit can look small next to a lead-acid rack that delivers the same evening backup.
Round-Trip Efficiency on Daily Home Cycling
A grid-tied home battery that charges from solar at midday and discharges after dinner does that round trip every sunny day. Losses show up on the utility bill, not just on a spec sheet. Lithium chemistries typically return about 95–98% of the energy put in; lead-acid typically returns about 75–85%. For a house that cycles daily, the lower efficiency is not a one-time tax — it is a tax on every cycle, which is why this calculator applies round-trip efficiency before it reports the bank you should buy.
Garage, Utility Room, and Winter Capacity
Home batteries are often mounted in a garage that is colder than the living space. Capacity is rated near 77°F (25°C). Lithium Iron Phosphate commonly keeps roughly 90% of rated capacity at freezing and around 65% at -20°F; lead-acid can fall to roughly 80% at freezing and 40% at -20°F. If the pack will sit in an unheated garage, size it for that room's coldest expected temperature, not the regional average outdoor temperature.
Home Storage Chemistries — What This Page Is For
Most packaged home solar batteries sold today are Lithium Iron Phosphate: long cycle life, a stable chemistry, and a deep usable Depth of Discharge. Nickel Manganese Cobalt appears in some electric-vehicle packs and a smaller set of home products. Lithium Titanate and sodium-ion are listed here so you can compare a premium or emerging option against LFP, not because they are the default wall unit. Lead-acid — Flooded, Absorbent Glass Mat, or Gel — is still the lowest upfront cost for a DIY rack, with a shallower Depth of Discharge, shorter cycle life, and, for Flooded, a ventilation requirement. Off-grid autonomy, generator backup, and array-plus-bank sizing together live on the Off-Grid System Sizing calculator, not on this page.
Common Sizing Mistakes
The most frequent errors are: using a single generic Depth of Discharge number for every chemistry instead of the chemistry actually being purchased, ignoring cold-weather capacity loss for a bank that will sit in an unheated space, and sizing the battery bank without checking that the paired solar array can actually recharge it within a single sunny day. Always size the array and the battery bank together — use the Solar Panel Size Calculator alongside this tool to confirm both numbers are compatible.
This guide is provided for educational and reference purposes. Always confirm system specifications with a licensed solar installer or electrician before purchasing or installing equipment.
Battery Capacity Quick Reference Table
Common daily energy-use levels mapped to an approximate battery bank size, assuming Lithium Iron Phosphate chemistry (90% Depth of Discharge, 96% round-trip efficiency), 1 day of backup, and 77°F installation temperature — the standard battery rating temperature, with no cold-weather capacity loss. Use this to sanity-check a calculated result at a glance — your own inputs above will differ from these defaults.
| Daily Use (kWh) | Battery Capacity | Modules (5 kWh) | Typical Household |
|---|---|---|---|
| 10 | 11.6 kWh | 3 | Small apartment, minimal AC |
| 15 | 17.4 kWh | 4 | Small home, gas heat |
| 20 | 23.1 kWh | 5 | Average home, moderate AC |
| 25 | 28.9 kWh | 6 | Larger home, central AC |
| 30 | 34.7 kWh | 7 | Home with EV charging |
| 40 | 46.3 kWh | 10 | Large home, electric heat |
| 50 | 57.9 kWh | 12 | Large home, pool, EV charging |
Calculate a battery bank size above to enable this section.
Solar arrays and batteries are often purchased and tracked separately. Enter what you're paying for batteries, plus your electric rates, to estimate total investment and a simple Time-of-Use payback. For a full whole-system cost and incentive analysis including your solar array, use the Solar Savings Calculator.
Time-of-Use savings assume one full daily charge/discharge cycle at your entered rates and do not include incentives, demand charges, or battery degradation. For a full analysis including your solar array and available incentives, use the Solar Savings Calculator. Estimates only — verify with your utility's actual rate schedule.