Backup Hours
(Battery Ah x Battery V x DoD x Inverter Efficiency) / Load W
Use this for battery runtime on backup, off-grid, or hybrid systems.
Solar Calculator
Size backup runtime, charging, and full solar systems from one page.
Enter battery amp-hours, load watts, panel watts, and sun hours to estimate runtime, charge amps, array size, inverter size, and backup storage.
Battery AH to runtimeSolar watts to charge ampsOff-grid and on-grid sizing
What You Can Calculate
Battery Runtime
Solar Charging
System Design
Charge Current
(Solar W x Controller Efficiency) / Battery V
This estimates the bulk charging amps your array can send into the battery bank.
Array Sizing
Daily kWh / (Peak Sun Hours x System Derate)
Use this to estimate the array needed to cover daily energy use.
Battery Runtime
How long will this battery bank run my load?
Adjust AH, voltage, and usable depth to estimate true backup hours.
Stored battery energy
19.2 kWh
400Ah at 48V
Usable battery energy
15.9 kWh
90% DoD x 92% inverter efficiency
Estimated backup time
15.9 hr
At 1,000W continuous load
Battery needed for target time
301.9 Ah
14.5 kWh required for 12.0 hours
Solar Charge
How many amps will solar charge my battery with?
Estimate bulk charging amps and recharge time from panel wattage and sun hours.
Bulk charging current
47.5 A
From 2,400W into 48V battery
Amp-hours to replace
320.0 Ah
80% state-of-charge swing
Ideal bulk charge time
6.7 hr
Real finishing and balancing time may be longer.
Daily solar harvest
10.6 kWh
1.5 solar days from start to target
Charge rate
0.12C
Useful for checking whether charge current is conservative or aggressive for the battery.
Off-Grid Sizing
Size a full off-grid solar and battery system.
Translate daily load into battery bank, panel count, controller amps, and inverter size.
Daily energy use
9.6 kWh
1,200W x 8.0 hours
Battery bank required
23.2 kWh
483.1Ah at 48V for 2.0 day autonomy
Solar array required
2.2 kW
4 panels at 550W each
Charge controller size
56.8 A
Includes 25% controller headroom.
Recommended inverter
2.5 kW
Sized from continuous load and starting surge.
On-Grid + Hybrid
Size a grid-tied solar system and optional outage backup battery.
Use utility consumption for net-metering solar and add a battery for critical loads during outages.
Required solar array
11.4 kW
21 panels at 550W each
Expected monthly production
1,530 kWh
85% offset target
Expected annual production
18,360 kWh
Before local shading, snow, and utility export limits.
Estimated monthly savings
$245
At $0.16/kWh
Hybrid backup battery
18.1 kWh
377.4Ah at 48V for 10.0 hours
Hybrid inverter target
9.7 kW
Size the inverter for both backup loads and practical PV coupling.
Engineering Note
Use these numbers as a fast sizing estimate, then finalize with equipment and site specifics.
Need the actual equipment matched to these calculations?