Outage Planning · Watt-Hour Calculator

Plan Your Backup With a Power Station Runtime Calculator

Work out how much battery capacity your appliances need during an outage. Edit your loads and solar harvest below, then compare power stations using the current price ledger.

Choose Your Appliances

Check the appliances you plan to run. All values are editable; hours are equivalent running hours per day.

Appliance checklist and editable running watts, hours per day and startup surge watts
ApplianceRunning WHours/DaySurge W
24 h cycling ≈ 8 h running
24 h cycling ≈ 8 h running
Humidifier preset: 300 W
Enter the device’s rated watts and startup draw
Set Your Outage Plan

Enter energy actually harvested into the battery after controller and charging losses, rather than the panel’s watt rating. Winter sun is lower; daylight timing and storage limits can reduce the energy you can use.

Your Outage Energy Estimate

Appliance Energy per Day
1,880 Wh
Appliance Energy for the Outage
3,760 Wh
Rated Battery Capacity Needed
4,915.03 Wh
Peak Continuous Power
205 W
Single-Start Surge Power
655 W

Capacity includes inverter losses and the usable discharge limit, then credits your solar harvest. This energy balance assumes the entered solar is available when needed; even a zero net capacity result needs storage for night and cloudy periods.

No Single Station Covers This Plan

The largest ledger units are shown below with their capacity gaps.

Ledger checked 2026-10-23. Prices are the latest recorded brand-store prices; each card shows when its price was verified. View the ledger and sources.

A match is an energy and output estimate. Verify startup duration, output voltage and device requirements with the manufacturer; missing surge ratings remain unverified.

These are brand-store source links; this site has no approved affiliate programs yet. Link disclosure.

EcoFlow

EcoFlow DELTA Pro 3

$2,799.00 · $0.68/Wh

Capacity
4,096 Wh
Continuous
4,000 W
Surge
Unlisted

Price verified 2026-10-23.

Startup surge is unverified: check the manufacturer before choosing this unit.

Capacity gap: 819.03 Wh. Add 1 expansion batteries only if each provides 4,096 Wh; actual pack size and compatibility are not listed. Ledger expansion ceiling: 48,000 Wh. Alternatively, harvest 368.56 additional solar Wh/day during the outage. Enter solar Wh/day to estimate extra charging days.

Anker SOLIX

Anker SOLIX F3800 Plus

$2,399.99 · $0.62/Wh

Capacity
3,840 Wh
Continuous
6,000 W
Surge
Unlisted

Price verified 2026-10-23.

Startup surge is unverified: check the manufacturer before choosing this unit.

Capacity gap: 1,075.03 Wh. Add 1 expansion batteries only if each provides 3,840 Wh; actual pack size and compatibility are not listed. Ledger expansion ceiling: 53,800 Wh. Alternatively, harvest 483.76 additional solar Wh/day during the outage. Enter solar Wh/day to estimate extra charging days.

Bluetti

Bluetti Elite 200 V2

$899.00 · $0.43/Wh

Capacity
2,073.6 Wh
Continuous
2,600 W
Surge
Unlisted

Price verified 2026-10-23.

Startup surge is unverified: check the manufacturer before choosing this unit.

Capacity gap: 2,841.43 Wh. Add 2 expansion batteries only if each provides 2,073.6 Wh; actual pack size and compatibility are not listed. Alternatively, harvest 1,278.64 additional solar Wh/day during the outage. Enter solar Wh/day to estimate extra charging days.

How the Math Works

For each checked appliance, multiply running watts by equivalent running hours per day, then add those watt-hours together. Multiply that daily total by outage days to get the appliance energy for the outage. Divide appliance energy by inverter efficiency as a fraction, subtract harvested solar watt-hours across the outage, clamp the result at zero, then divide by usable depth of discharge as a fraction to get rated battery capacity needed. Peak continuous watts are the sum of running watts, while single-start surge adds the largest difference between surge and running watts. A station must cover the calculated capacity and continuous output, and any listed surge rating must also cover the surge estimate. For example, the default refrigerator, CPAP and router need 1,880 Wh per day and 4,915.03 Wh of rated capacity for the default outage plan.

Runtime Questions

Can a 1,000 Wh Station Run a Fridge Overnight?

At the default efficiency and discharge settings, usable appliance energy is 1,000 Wh × 85% × 90% = 765 Wh. Dividing by the table’s 150 W fridge load gives 5.1 equivalent running hours; compare that with how long your fridge’s compressor actually runs overnight. The station must also supply the table’s 600 W startup surge.

How Many Watt-Hours Do I Need for a CPAP?

The table’s 40 W CPAP for 8 hours uses 320 Wh. With no solar, divide by 85% efficiency and 90% usable discharge to get 418.3 Wh of rated capacity for that night. The 300 W humidifier preset changes the same calculation to 3,137.25 Wh; edit the preset to match your equipment.

How Does Solar Change the Capacity Estimate?

Subtract harvested battery-side solar energy from appliance energy divided by inverter efficiency, before applying the discharge limit. For the default loads, 2 days with 500 Wh/day harvested reduce rated capacity needed from 4,915.03 Wh to 3,803.92 Wh. This assumes all that harvest is usable during the outage; it does not model overnight storage or cloudy-day timing.