Battery Storage Calculator

Battery Storage is evaluated from Daily Home Electricity Use, Target Backup Duration and What to Power During Backup. The calculation reports Battery Capacity Needed, Tesla Powerwall 3 Units and Estimated Battery System Cost.

Results

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About the Battery Storage Calculator

Battery Storage is treated here as a quantitative relation between Daily Home Electricity Use, Target Backup Duration, What to Power During Backup and Battery Usable Depth and Battery Capacity Needed, Tesla Powerwall 3 Units, Estimated Battery System Cost and Confirmed Backup Duration.

The calculator uses a multi formula configuration. Each reported value is read as a direct evaluation of the stored rules with the declared field formats and units.

Formula basis:
Required kWh = (daily usage x load fraction x backup hours / 24) / depth of discharge
Powerwall units = ceiling(needed kWh / 13.5 kWh)
Cost estimated at $1,000/kWh installed (mid-range 2024)

Interpret the outputs in the order shown by the result fields. Optional inputs affect only the outputs that depend on those variables.

Formula & How It Works

The calculation applies the following relations exactly as recorded in the metadata:

Required kWh = (daily usage x load fraction x backup hours / 24) / depth of discharge
Powerwall units = ceiling(needed kWh / 13.5 kWh)
Cost estimated at $1,000/kWh installed (mid-range 2024)

Each output field is produced by substituting the supplied inputs into the relevant relation and then applying the declared rounding or text format.

Worked Examples

Example 1: 24-hour backup, 30 kWh/day home, critical loads only, LFP battery

Inputs

daily_kwh: 30 backup_hours: 24 critical_only: 0.25 usable_depth: 0.90
Battery Capacity Needed: 8.3 kWh. Tesla Powerwall 3 Units: 1 units. Estimated Battery System Cost: $8,333. Confirmed Backup Duration: 38.9 hours

With Daily Home Electricity Use = 30, Target Backup Duration = 24, What to Power During Backup = 0.25 and Battery Usable Depth = 0.9 as the stated inputs, the result is Battery Capacity Needed = 8.3 kWh, Tesla Powerwall 3 Units = 1 units and Estimated Battery System Cost = $8,333. Each value corresponds to the declared output fields.

Example 2: 48-hour hurricane backup, 40 kWh/day home, 50% essential loads, LFP

Inputs

daily_kwh: 40 backup_hours: 48 critical_only: 0.50 usable_depth: 0.90
Battery Capacity Needed: 44.4 kWh. Tesla Powerwall 3 Units: 4 units. Estimated Battery System Cost: $44,444. Confirmed Backup Duration: 58.3 hours

With Daily Home Electricity Use = 40, Target Backup Duration = 48, What to Power During Backup = 0.5 and Battery Usable Depth = 0.9 as the stated inputs, the result is Battery Capacity Needed = 44.4 kWh, Tesla Powerwall 3 Units = 4 units and Estimated Battery System Cost = $44,444. Each value corresponds to the declared output fields.

Example 3: Solar self-consumption: 10 kWh/day needed at night, LFP battery, 12 hours backup

Inputs

daily_kwh: 20 backup_hours: 12 critical_only: 1.00 usable_depth: 0.90
Battery Capacity Needed: 11.1 kWh. Tesla Powerwall 3 Units: 1 units. Estimated Battery System Cost: $11,111. Confirmed Backup Duration: 14.6 hours

With Daily Home Electricity Use = 20, Target Backup Duration = 12, What to Power During Backup = 1 and Battery Usable Depth = 0.9 as the stated inputs, the result is Battery Capacity Needed = 11.1 kWh, Tesla Powerwall 3 Units = 1 units and Estimated Battery System Cost = $11,111. Each value corresponds to the declared output fields.

Example 4: Off-grid cabin: 8 kWh/day, 72 hours cloudy backup, full power, LFP

Inputs

daily_kwh: 8 backup_hours: 72 critical_only: 1.00 usable_depth: 0.90
Battery Capacity Needed: 26.7 kWh. Tesla Powerwall 3 Units: 2 units. Estimated Battery System Cost: $26,667. Confirmed Backup Duration: 72.9 hours

With Daily Home Electricity Use = 8, Target Backup Duration = 72, What to Power During Backup = 1 and Battery Usable Depth = 0.9 as the stated inputs, the result is Battery Capacity Needed = 26.7 kWh, Tesla Powerwall 3 Units = 2 units and Estimated Battery System Cost = $26,667. Each value corresponds to the declared output fields.

Common Use Cases

  • Calculate battery storage capacity for home backup
  • Size battery storage for solar self-consumption
  • Estimate battery backup duration for home loads