How Many Watt-Hours Do I Need for an Apartment Power Outage?

The Simple Formula: How to Calculate Your Watt-Hour Needs

Step 1: List Every Appliance You Need During an Outage

Start with your non-negotiables: the devices you genuinely can't go without for a safe and functional night or workday. Common apartment priorities: CPAP or BiPAP if you've sleep apnea, WiFi router if you work remotely, refrigerator to prevent food spoilage, phone and laptop for communication, and basic lighting.

Step 2: Find Each Appliance's Wattage

Check the label on the back or bottom of the device. Most electronics have a label showing voltage (V) and amperage (A) or watts (W) directly. If only V and A are shown, multiply them: Watts = Volts × Amps. If you can't find the label, use the reference table below.

Step 3: Estimate Hours of Use Per Day

Be realistic. Your refrigerator runs 24 hours but the compressor only cycles on for 20–40% of that time. Your laptop charges for 2–3 hours and runs for 8. Your microwave runs for 5 minutes but consumes 1,200W during those 5 minutes (= 100Wh for a 5-minute use).

Step 4: Multiply and Add 20% Buffer

The formula:
Total Wh needed = (W × hours for each device) summed, then × 1.20
The 20% buffer accounts for inverter conversion losses (typically 8–15% for quality pure sine wave inverters) and real-world battery capacity versus stated capacity (typically 92–96% on quality LFP units).

Apartment Appliance Wattage Reference Table

All wattages are typical ranges. Exact consumption varies by model, age, and usage pattern. For precise figures, check your device label or use a $15 plug-in watt meter (Kill A Watt is the most popular option).

5 Pre-Built Apartment Outage Scenarios

These scenarios are pre-calculated using the appliance table above. Each assumes a 20% buffer is already included in the final capacity recommendation.

Scenario A: Bare Essentials Overnight

Target: Phone, WiFi router, LED lights, one night only

Scenario B: CPAP User, One Night

Target: CPAP without humidifier, WiFi, lights, phone

Scenario C: Work From Home, Full Day

Target: Laptop, monitor, phone, router, LED lights, 8-hour workday

Scenario D: Comfort (Mini-Fridge + Devices), 24 Hours

Target: Mini-fridge, CPAP, laptop, WiFi, lights, phone, 24-hour outage

This scenario illustrates why the refrigerator is the dominant load. Without the mini-fridge, Scenario D drops to 1,280Wh, covered by a Delta 2 with room to spare.

Scenario E: Medical Priority (CPAP + Oxygen Concentrator)

Target: Medical devices first, plus basic communication

The Refrigerator Problem: Why It Dominates Your Calculation

Why Refrigerators Have High Surge Wattage

A refrigerator's compressor motor requires 2–3× its running wattage to start. This surge lasts only a fraction of a second but a power station must have sufficient peak output to handle it. A mini-fridge running at 100W average may surge to 300–400W at compressor start. A full-size refrigerator running at 150–200W may surge to 400–600W. Units with inadequate surge capacity will trip their protection circuit and fail to start the appliance.

Mini-Fridge vs. Full-Size: The Watt-Hour Cost Difference

A compact mini-fridge (under 4 cubic feet) consumes approximately 80–150W running, with a 300–400W surge. Over 24 hours, expect 640–1,200Wh of consumption. A full-size refrigerator (18–22 cubic feet) consumes 150–200W running, with a 400–600W surge. Over 24 hours: 1,200–1,600Wh. Running a full-size fridge 24 hours completely depletes a 1,024Wh EcoFlow Delta 2 before the day is done.

Which Power Stations Can Handle Refrigerator Surge

To safely run a full-size refrigerator, your power station needs: a pure sine wave inverter (all reviewed units qualify), at least 1,500W continuous output, and at least 400–600W surge capacity above the compressor start requirement. From our table: EcoFlow Delta 2 (1,800W/2,700W surge), Bluetti AC200L (2,200W/4,800W surge), EcoFlow Delta 2 Max (2,400W/5,000W surge), and Anker Solix C1000 (2,400W/3,000W surge) all qualify. The Bluetti AC70 (700W/1,400W) and Jackery 1000 v2 (1,000W/2,000W) can't reliably start a full-size refrigerator compressor.

How Solar Recharging Changes the Math

With 200W Balcony Solar: Sustain 600–900Wh Daily Draw Indefinitely

A 200W portable solar panel on a south-facing balcony generates approximately 600–900Wh per sunny day in most U.S. cities (based on 3–4.5 average peak sun hours). This is enough to run Scenario B (CPAP user, essential overnight) indefinitely, the panel recharges what you use each night. For Scenario C (work-from-home), you'd need either a 400W solar setup or a larger battery capacity to bridge the deficit.

Peak Sun Hours by City: Solar Harvest Reference

Estimates assume a south-facing panel at optimal tilt angle. Cloud cover, shading, and panel angle reduce actual harvest. Multiply your local peak sun hours × 200 × 0.85 (MPPT efficiency) for a real-world harvest estimate.

Sizing Recommendations by Apartment Type

Related Guides

• Best Portable Power Stations for Apartments, Top picks sized for the scenarios above
• Balcony Solar Kit Guide, Add solar recharging to sustain longer outages
• LFP vs NMC Battery Guide, Why chemistry affects real-world capacity delivery