Home Resilience Hub

Backup power planning

Solar Power Calculator

Begin with essentials, use your own peak-sun-hours assumption, and verify final production in PVWatts.

Size essential backup power first

This tool sizes a conservative solar-and-battery starting point for essential loads, not a whole-home installation.

Essential loads

Select the loads you would keep on during an outage. Their listed hours are practical planning defaults that you can refine with appliance data.

Optional load not shown above.

Hours this custom load runs each day.

Sun and battery assumptions

Use a conservative annual average peak-sun-hours value. This calculator does not convert weather observations into solar production.

Choose 2-8. A lower value gives a more conservative plan.

1-7 days of essential-load use without meaningful recharge.

Open PVWatts

Enter this ZIP in PVWatts for a site-specific estimate. It is not sent anywhere by this calculator.

Whole-home comparison

Optional comparison only. Essential loads remain the sizing basis above.

Your utility-bill daily average, if you want to compare it with essentials.

Use the result well

Use the estimate as a design brief

Start with essential loads and a conservative solar assumption. The result helps frame questions for site-specific production modeling and professional electrical design.

  1. Step 1

    List essential appliances, their running watts, daily hours, and any motor or compressor startup load.

  2. Step 2

    Use a conservative peak-sun-hours value for the least favorable season you expect the system to cover.

  3. Step 3

    Check production in NREL PVWatts, confirm site constraints, and have final electrical work designed and permitted correctly.

Questions about this estimate

Does this tell me how many panels fit on my roof?

No. It estimates energy capacity and a rough area. A site assessment must account for shade, orientation, setbacks, structure, wind or snow loads, equipment clearances, and local codes.

Why is battery capacity larger than one day of use?

Storage planning includes the autonomy period and conversion or usable-capacity assumptions. Real performance also varies with temperature, age, discharge limits, and equipment settings.

Can I use this as a final electrical design?

No. Verify solar production with a tool such as NREL PVWatts, confirm surge loads, and use qualified professionals for final equipment, permitting, and electrical work.