How the Solar Battery Backup Time Calculator Works
The calculator starts with the battery bank's nominal stored energy. It then applies the usable depth of discharge, any reserve you choose to keep unused, and the estimated inverter/system efficiency. The remaining energy is divided by the average AC load to estimate backup duration.
How to Use It
Select whether your battery is specified in kilowatt-hours or by voltage and amp-hour capacity. Enter the total number of identical battery units, the average load you expect to run, the usable DoD recommended for your battery/system and an appropriate efficiency assumption. Click Calculate backup time to see the estimated runtime.
Understanding Your Result
The result is an energy-based planning estimate. For example, a nominal battery bank cannot normally deliver every nameplate kilowatt-hour to AC appliances: some capacity may intentionally remain unused, while conversion losses reduce energy delivered through the inverter. Real appliance loads also fluctuate, so actual runtime can be shorter or longer than a calculation based on one average wattage.
Factors That Can Change Battery Backup Time
Important factors include battery chemistry, battery age and condition, temperature, discharge rate, inverter efficiency, BMS settings, depth-of-discharge limits and the way appliances cycle. Motors and compressors also introduce high startup power even though their energy consumption over time may be lower.
Using This Calculator in Nigeria
Homes and businesses in Nigeria can use the calculator for solar and inverter backup planning without assuming a particular battery brand or technology. Equipment specifications should come from the actual battery and inverter being considered. Current equipment costs belong in Finelib Prices, while supplier and installer enquiries can move into Finelib Match.
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Frequently Asked Questions
How do I calculate battery backup time?
Estimate the usable battery energy after depth-of-discharge limits, reserve and conversion losses, then divide the estimated delivered energy by the average electrical load in kilowatts.
Is battery kWh the same as backup time?
No. kWh measures stored energy. Backup time depends on how much of that energy is usable and how much power the connected appliances consume.
How does depth of discharge affect backup time?
A higher usable depth of discharge makes more of the battery's nominal energy available and therefore increases calculated runtime. The appropriate limit should follow the battery/BMS manufacturer's requirements.
Why is inverter efficiency included?
Battery energy is stored on the DC side while most household and business loads use AC power. Conversion is not perfectly efficient, so delivered AC energy is generally less than the usable DC energy.
Can I calculate backup time from battery voltage and Ah?
Yes. Nominal watt-hours can be estimated from volts × amp-hours × number of appropriately configured battery units, then converted to kWh before applying usable-capacity and efficiency assumptions.
Will a calculated battery runtime be exact?
No. It is a planning estimate. Actual runtime changes with real load patterns, battery condition, temperature, discharge rate, inverter losses and equipment control limits.
Does this calculator size my inverter too?
No. Inverter sizing must account for continuous power and startup/surge requirements. Use the separate Finelib Inverter Size Calculator for that task.