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

Thanks — we’ve logged this for review.

About the Battery Storage Calculator

### Why Use the Battery Storage Calculator Calculator?
The Battery Storage Calculator is a valuable tool for homeowners who want to invest in a battery storage system to backup their home during power outages or to optimize their solar panel system's performance. This calculator helps users determine the required battery capacity to meet their specific needs, taking into account their daily home electricity use, target backup duration, and what they want to power during the backup. By using this calculator, users can avoid oversizing or undersizing their battery storage system, which can lead to wasted money or insufficient backup power. The calculator provides users with a clear understanding of their battery capacity needs, the number of Tesla Powerwall units required, and an estimated cost of the battery system.

### History of the Battery Storage Calculator
The concept of battery storage calculators has its roots in the early days of renewable energy systems. As solar and wind power became more popular, the need for energy storage solutions grew. In the 1990s, researchers and engineers began developing models and tools to size battery banks for off-grid solar systems. One of the key figures in this development was the National Renewable Energy Laboratory (NREL), which published guidelines and software tools for designing and sizing battery-based renewable energy systems. Over time, these tools evolved to incorporate new technologies, such as lithium-ion batteries, and to address the specific needs of grid-tied solar systems with battery backup. Today, online calculators like the Battery Storage Calculator provide users with easy-to-use tools to determine their battery storage needs.

### The Science Behind the Calculations
The Battery Storage Calculator uses a set of formulas to determine the required battery capacity. The calculation starts with the user's daily home electricity use, which is typically measured in kilowatt-hours (kWh). The calculator then applies a factor to account for the user's target backup duration and what they want to power during the backup. This factor is based on the user's selection of "What to Power During Backup," which ranges from 25% to 100% of their normal electricity use. The calculator also takes into account the battery's usable depth of discharge (DoD), which is the percentage of the battery's capacity that can be safely used without damaging the battery. The formula for calculating the required battery capacity is:
Needed Capacity (kWh) = Daily Electricity Use (kWh) x Target Backup Duration (hours) x Load Factor / Usable DoD.
Where Load Factor is the factor applied based on the user's selection of "What to Power During Backup." The calculator then uses this required capacity to determine the number of Tesla Powerwall units needed and estimates the total cost of the battery system.

### Real-Life Application and Examples
Let's consider a real-world scenario where a homeowner, John, wants to install a battery storage system to backup his home during power outages. John's daily home electricity use is 30 kWh, and he wants to be able to power his critical loads, such as lights, fridge, and outlets, for 24 hours during a backup. He selects "Critical loads only (25% of normal)" as his "What to Power During Backup" option. John also selects a battery usable depth of discharge of 90%, which is typical for lithium-ion batteries like the Tesla Powerwall. Using the Battery Storage Calculator, John enters his daily electricity use, target backup duration, and selections for "What to Power During Backup" and "Battery Usable Depth (DoD)". The calculator returns the following results:
Battery Capacity Needed: 18.0 kWh
Tesla Powerwall 3 Units: 2 units
Estimated Battery System Cost: $14,000
Confirmed Backup Duration: 23.9 hours
Based on these results, John can determine that he needs a battery storage system with a capacity of at least 18 kWh to meet his backup needs. He can also see that he would need 2 Tesla Powerwall units to achieve this capacity, and the estimated cost of the system would be around $14,000. With this information, John can make an informed decision about his battery storage system and ensure that he has a reliable backup power source for his home.

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