Battery sizing starts with the energy you use in a day. From there, choose how many days the battery should support without useful charging, the system voltage, and how much of the battery’s rated capacity you plan to use.
SunPlanner’s calculator turns those choices into a planning estimate. It does not replace the battery manufacturer’s instructions or the electrical design for the system.
What numbers do I need before sizing the battery?
Start with total watt-hours per day. Add the daily energy for the refrigerator, cooking equipment, water system, electronics, lighting, heating, cooling, and anything else the battery needs to carry.
The Solar Sizing Planner can build that total from named appliances. Each starting value stays editable, so measured power or an equipment label can replace the estimate.
You also need the system voltage and the number of backup days you want to plan around. Voltage matters because the calculator reports the battery estimate in amp-hours.
What are battery backup days?
Battery backup days describe how long the battery should support the planned loads without useful charging. One day covers one day of energy use. Three days cover three days of the same planned use.
More backup days increase the battery estimate quickly. That does not mean everyone needs a large reserve. It means the calculator is carrying more days of the same load before solar input is counted again.
What does usable battery capacity mean?
The rated capacity on the battery and the portion you plan to use are separate numbers. The calculator calls the second number the usable-capacity planning assumption.
The current starting values are 50 percent for lead-acid and 80 percent for lithium iron phosphate. Both values are editable. Confirm the right number for the specific battery and system before buying equipment.
How does the calculator estimate amp-hours?
The calculation multiplies daily watt-hours by backup days, then divides by system voltage and the usable-capacity assumption.
For example, a 2,000 Wh daily load with two backup days, a 48 V system, and an 80 percent usable-capacity assumption produces an estimate of about 104 Ah.
That is a planning target. Cable size, protection, battery configuration, current limits, temperature, equipment compatibility, and installation rules still belong in the final electrical design.
Does a larger battery change the solar forecast?
No. Battery capacity changes how much energy the system can store. It does not make the panels produce more power and does not change SunPlanner’s predicted solar production.
SunPlanner keeps the two jobs separate. The solar forecast estimates what the configured panels may produce. The battery estimate translates planned energy use into a storage target.
What should I do next?
Build the appliance list first. Then compare the low, typical, and heavy-use results in the Solar Sizing Planner. Use the result as a clearer starting point for a system design, not as permission to skip the equipment instructions or an electrical review.