Calculate usable demand
Daily load is divided by system efficiency, multiplied by autonomy days, then increased by the design reserve.
Off-grid storage planning
Solar Battery Bank Size Calculator
Size a LiFePO4, lithium-ion, AGM or flooded battery bank from daily energy use, backup days, system voltage, temperature, conversion losses and reserve—then calculate the 12 V battery count and supporting solar array.
Wh → Ah conversionChemistry-aware DoDSeries + parallel countSolar array sizing
What the calculator actually does
It separates the energy your loads need from the larger nameplate battery bank required after conversion losses, reserve, temperature and chemistry limits.
Adjust the battery bank
The usable demand is divided by depth of discharge and the remaining temperature capacity.
Build a real bank
Watt-hours become amp-hours at the selected voltage, then module count is split into series and parallel strings.
Bank Wh = ((Daily Wh ÷ system efficiency) × autonomy days × (1 + reserve)) ÷ (usable DoD × temperature factor)
Why chemistry changes battery size
Usable depth of discharge is not identical across chemistries. The presets use planning defaults—80% for LiFePO4, 85% for lithium-ion and 50% for lead-acid—but your manufacturer’s warranty limits take priority. For the complete method and a worked example, read how to size a solar battery bank.
For runtime from an existing battery rather than sizing a new bank, use the battery backup time calculator.
Series and parallel are not interchangeable
Batteries in series raise voltage while amp-hour capacity stays the same. Parallel strings raise amp-hours. The calculator validates that your module voltage divides cleanly into the selected bank voltage before giving a battery count.
Always have a qualified designer verify protection, cable sizing, balancing and battery-management requirements.
How the solar array estimate works
The array output covers the battery-side daily load plus your reserve within the entered peak-sun-hours window, adjusted for charge efficiency. Real production also depends on weather, shading, tilt, wiring and controller limits.
This is a planning estimate, not an electrical-system design. To estimate recharge duration for an existing bank, use the solar panel battery charging time calculator.
Measure loads before buying
Utility bills, inverter logs and plug-in meters are better than guessed appliance labels. Review typical starting values in the home appliance wattage chart, then replace them with measured daily energy.
Solar battery sizing questions
How many batteries do I need for a 5 kWh daily load?
It depends on autonomy, voltage, chemistry, efficiency, temperature and reserve. With the default two-day LiFePO4 example, the calculator recommends about an 18 kWh nameplate bank.
Is a 100 Ah battery always 1.2 kWh?
Only at 12 V: 12 V × 100 Ah = 1,200 Wh nameplate. At 24 V the same Ah rating is 2,400 Wh, and at 48 V it is 4,800 Wh.
Should I size from average or peak load?
Use daily energy for storage capacity, but separately confirm that the inverter handles continuous load and motor/compressor startup surge.
Why add a temperature derating?
Available capacity can fall outside the battery’s preferred temperature range. Enter the manufacturer’s stated derating for your expected conditions.