Enter daily energy use
Enter measured daily consumption in watt-hours or kilowatt-hours.
Solar Storage Planning Tool
Solar Battery Size Calculator
Calculate the battery-bank capacity required for a solar, hybrid, off-grid, or backup power system. Get results in kilowatt-hours, amp-hours, series batteries, parallel strings, and total battery quantity.
Battery capacity in kWh and Ah
Lead-acid and lithium presets
Series and parallel bank layout
Battery sizing inputs
Calculate your battery bank
Enter your daily energy use, required backup period, battery characteristics, and system voltage.
Solar focused
Daily energy sizing
Battery aware
DoD and efficiency
Bank arrangement
Series and parallel
Practical reserve
Ageing and load growth
How it works
Calculate solar battery size in four steps
The calculator converts daily electrical energy consumption into a practical nominal battery-bank recommendation.
Select backup days
Choose how long the batteries should operate without sufficient solar charging.
Apply battery factors
Add depth of discharge, efficiency, performance, and a reserve margin.
Review bank arrangement
View recommended kWh, Ah, series batteries, parallel strings, and total quantity.
How solar battery-bank sizing works
A solar battery bank must contain enough usable energy to operate the selected loads for the required backup period. The calculation begins with the total electrical energy used each day.
Daily energy consumption is multiplied by the selected number of autonomy days. A reserve margin is then added for load growth, uncertain usage, battery ageing, and changing environmental conditions.
Because batteries should not normally be completely discharged, and because real systems lose energy, the design energy is divided by the depth of discharge, battery efficiency, and performance factor.
Solar battery sizing formulas
Required load energy
Daily energy × backup days
Design energy
Required energy × (1 + reserve margin)
Nominal battery-bank energy
Design energy ÷
(DoD × efficiency × performance)
Required amp-hours
Nominal watt-hours ÷ system voltage
Why battery chemistry matters
Lead-acid batteries normally use a shallower depth of discharge to protect service life. Lithium iron phosphate batteries generally support deeper discharge and higher efficiency. Always replace preset values with the limits stated by the battery manufacturer.
Practical applications
When this solar calculator is useful
Use the calculator for early planning of common solar and battery-storage systems.
Home backup system
Size storage for lighting, refrigeration, internet, fans, and selected electrical outlets.
Off-grid property
Estimate battery storage where grid electricity is not available.
Small business
Plan backup energy for communications, security, refrigeration, and essential equipment.
Remote equipment
Size storage for cameras, routers, radios, sensors, and telemetry equipment.
Solar pumping system
Estimate storage while separately checking motor surge and inverter requirements.
Commercial backup
Estimate battery requirements for selected critical commercial loads.
Frequently asked questions
Solar Battery Size Calculator FAQs
Answers to common questions about battery capacity, autonomy, discharge limits, and battery-bank wiring.
How do I calculate solar battery size?
Multiply your daily energy consumption by the required backup days. Add the design reserve, then divide the result by the battery depth of discharge, efficiency, and performance factor. Divide the resulting watt-hours by the battery-bank voltage to calculate amp-hours.
Should battery capacity be calculated in kWh or Ah?
Both are useful. Kilowatt-hours show the total stored energy, while amp-hours show battery charge capacity at a particular voltage. The calculator provides both values.
What depth of discharge should I use?
Many lead-acid batteries are commonly planned around 50 percent depth of discharge. Lithium iron phosphate batteries may allow 80 to 90 percent. Always use the value recommended by the battery manufacturer.
How many backup days should I select?
One day may be suitable when grid power or generator backup is available. Off-grid systems may require two or more days depending on local weather, solar production, and the importance of the connected loads.
Why is battery efficiency included?
A battery system loses some energy during charging, discharging, cabling, battery management, and inverter conversion. Including efficiency produces a more realistic battery-bank recommendation.
What is the battery performance factor?
The performance factor allows for battery ageing, temperature, discharge rate, manufacturing variation, and other real-world conditions. A lower factor increases the recommended battery capacity.
How are series and parallel batteries calculated?
Batteries connected in series increase voltage. Parallel battery strings increase amp-hour capacity. The calculator determines the batteries required in each series string and the number of parallel strings.
Is this calculator suitable for final installation design?
This tool provides a planning estimate. Final installation should also verify inverter limits, charge-controller capacity, cable size, battery current limits, protection devices, ventilation, local conditions, and manufacturer requirements.
Important system-design notice
This calculator provides a planning estimate. Final
system design should verify battery current limits,
inverter and charge-controller specifications, cable
size, overcurrent protection, temperature, ventilation,
manufacturer requirements, and applicable electrical
regulations.