Homeowner planning tool
Solar Battery Backup Calculator
Size home battery storage the way an installer does — from the appliances you actually need during an outage, not from your monthly bill divided by a battery's nameplate. Built for U.S. homeowners, with Texas summer loads in mind.
- Usable kWh you truly need
- Battery count for energy and for power
- Runtime and surge checks
- What longer backup would cost
Your electricity use
Give us whichever number you have. We calculate the others from it.
Monthly use
1200kWh
Daily use
39.5kWh/day
These figures are an estimate from your bill and electricity price. Enter kWh from a utility statement for a more accurate result.
This calculator provides an estimate for educational and planning purposes. Actual battery requirements depend on appliance loads, inverter specifications, battery specifications, weather, solar production, wiring losses, installation configuration, local requirements, and other factors. Final system sizing should be confirmed by a qualified solar/battery professional.
Battery backup questions
Will my solar panels power the house during an outage?
Usually not. A standard grid-tied system shuts down when the grid goes down. Panels only keep producing during an outage if the system includes backup/islanding equipment — typically a hybrid inverter paired with a battery.
Why does the calculator sometimes ask for more batteries than my energy needs suggest?
Because energy (kWh) and power (kW) are separate limits. You may store enough energy for 24 hours yet still be unable to start an air conditioner, since the inverter caps how much power flows at one instant. The tool shows both counts and recommends the greater.
How much battery do Texas homes usually need?
Essential-load backup for a fridge, lights, Wi-Fi, fans, and phones often lands near 5-10 kWh usable for a day. Adding central air conditioning in a Texas summer can multiply that several times over, which is why the appliance builder matters more than any rule of thumb.
What is depth of discharge and why does it matter?
Depth of discharge is how much of the pack you can safely drain. A 10 kWh lithium battery at 95% depth of discharge gives about 9.5 kWh usable; a 10 kWh lead-acid bank at 50% gives about 5 kWh. Nameplate kWh alone is misleading.
Keep researching
Solar battery cost
What storage adds to a project
Learn: solar batteries
Chemistry, lifespan, warranties
Learn: solar inverters
Why the inverter sets your power limit
Texas solar calculator
Full system size and savings
System size calculator
How many panels you need
Federal solar tax credit
How storage qualifies