When the grid goes down—due to storms, wildfires, or infrastructure failures—solar power can provide a clean, quiet, and reliable source of backup electricity. But if you’re considering solar as your emergency power solution, one of the biggest questions you may have is: How much solar power (in watts or kilowatt-hours) do I need to run my home during an outage?
The answer depends on your home’s energy usage, the length of the outage, and whether you want to power essential appliances or your entire house. In this guide, we’ll break down how to estimate your solar power needs in both watt-hours (Wh) and kilowatt-hours (kWh), what size battery bank and solar array you need, and how to plan a system that keeps your household running when the lights go out.
Solar Power Basics: Watts vs. Watt-Hours vs. Kilowatt-Hours
Before we dive into system sizing, let’s clear up the difference between three key terms:
- Watts (W): The rate of power consumption or generation at a given moment. For example, a fridge might use 150 watts while running.
- Watt-hours (Wh): The total energy consumed or stored over time. A 150W fridge running for 10 hours uses 1,500Wh.
- Kilowatt-hours (kWh): 1 kWh = 1,000Wh. This is the unit your utility company uses to bill your electricity usage.
In short: Watts tell you how much power something uses right now. Watt-hours or kilowatt-hours tell you how much energy it uses over time.
Step 1: Identify Your Backup Power Goals
Start by deciding what you want to power during an outage. Do you want to run your entire home? Or just the essentials?
🔌 Common Emergency Power Loads:
| Appliance/System | Wattage (Avg) | Usage Time (Hrs) | Daily Consumption (Wh) |
|---|---|---|---|
| Refrigerator | 150W | 8 hrs | 1,200 Wh |
| LED Lights (6 bulbs) | 60W | 6 hrs | 360 Wh |
| Wi-Fi Router | 15W | 12 hrs | 180 Wh |
| Phone Charging (2 phones) | 10W | 4 hrs | 40 Wh |
| TV | 100W | 3 hrs | 300 Wh |
| Furnace Fan or Space Heater | 1,000W | 2 hrs | 2,000 Wh |
| CPAP Machine | 50W | 8 hrs | 400 Wh |
| Total (Essentials) | — | — | 4,480 Wh or ~4.5 kWh/day |
Pro Tip: Make a list of your essential loads and estimate their runtime. Add a 20% buffer for safety and inverter inefficiency.
Step 2: How Many kWh Per Day Does Your Home Use?
If you want to power your entire home, check your electric bill to see your daily average kWh usage. U.S. homes average about 25–30 kWh/day, but this varies by region and season.
If you’re only backing up critical loads, plan for 3–10 kWh per day depending on how many appliances you include.
Example scenarios:
- Basic essentials (fridge, lights, phones, Wi-Fi): ~2–3 kWh/day
- Expanded essentials (add microwave, TV, CPAP, fans): ~5–7 kWh/day
- Whole-house backup (A/C, well pump, laundry): 20–30+ kWh/day
Your solar power system must generate and store enough energy to meet these needs during an outage.
Step 3: Size Your Battery Bank
To run your home during an outage, you need energy storage—usually a solar battery or power station. Battery capacity is measured in watt-hours (Wh) or kilowatt-hours (kWh).
Formula:
Battery Size Needed (Wh) = Daily Energy Use (Wh) × Number of Backup Days
Examples:
- 3 kWh/day × 1 day = 3,000Wh (for basic needs)
- 6 kWh/day × 2 days = 12,000Wh (expanded essentials)
- 25 kWh/day × 3 days = 75,000Wh (whole-home backup)
Popular battery sizes:
- Portable power stations: 500Wh – 3,000Wh
- Expandable solar generators: 5,000Wh – 10,000Wh+
- Whole-home batteries (Tesla Powerwall, LG Chem): 10–15 kWh per unit, stackable for more capacity
Step 4: Size Your Solar Panel Array
Solar panels recharge your battery bank during the day. The number of panels you need depends on:
- How much energy you use daily (kWh)
- Peak sun hours in your area (avg. 3–6 hrs/day)
- Panel wattage (typically 100W – 400W per panel)
Formula:
Solar Panel Array Size (Watts) = Daily Energy Need (Wh) ÷ Sun Hours
Example:
- 6,000 Wh/day ÷ 5 sun hours = 1,200W solar array
- You could use 4 × 300W panels or 6 × 200W panels
If your system is portable or uses foldable panels, you may need to recharge over multiple days—or supplement with AC charging when available.
Real-World Backup Scenarios
🔋 Scenario 1: Basic Emergency Power (1–2 days)
- Daily use: ~3 kWh
- Battery: 3,000–6,000Wh
- Solar: 400W – 1,200W portable panel kit
⚡ Scenario 2: Critical Circuits Only (2–3 days)
- Daily use: ~5–7 kWh
- Battery: 10,000Wh+
- Solar: 1,500–2,000W rooftop system or high-capacity foldable panels
🏠 Scenario 3: Whole-House Backup
- Daily use: 20–30 kWh
- Battery: 30–90 kWh (multiple Powerwalls or similar)
- Solar: 6,000 – 10,000W+ rooftop solar array
Whole-home solar backup requires a hybrid inverter, critical load panel, and professional installation. It’s the most robust option but also the most expensive.
Top Solar Backup Systems for Home Use
🌞 EcoFlow Delta Pro + Smart Home Panel
- 3.6kWh base capacity, expandable to 25kWh+
- 240V output—can run HVAC, dryer, and well pump
- Smart integration for automatic switchover
🔋 Bluetti AC300 + B300 Expansion
- 3,072Wh per B300 battery—stackable to 12kWh+
- 3,000W AC output with solar and grid charging
- Ideal for running appliances and off-grid cabins
🏡 Tesla Powerwall 2
- 13.5 kWh usable capacity per unit
- AC-coupled for grid-tied or off-grid setups
- Requires professional installation
FAQs About Solar Power for Emergency Backup
Q: How much solar power do I need for a 24-hour outage?
Plan for at least your daily kWh usage (typically 3–10 kWh for essentials) plus a safety buffer. Match your battery and solar input accordingly.
Q: Can a solar generator power my refrigerator?
Yes. Most modern fridges use 100–800W. A solar generator with at least 1,000Wh capacity can run it for several hours.
Q: What happens if there’s no sun during the outage?
That’s why batteries are essential. Your system should store enough power to get through a night or cloudy day. Consider AC charging before outages if possible.
Q: Can I install my own solar backup system?
Yes—for portable setups. But whole-house systems with critical load panels require professional installation and permits.
Q: How many solar panels do I need to run my home?
It depends on your energy use and sun hours. For full-home backup, expect to install 15–30+ panels rated at 300–400W each.
Conclusion: Know Your Power Needs Before an Outage Hits
Understanding how many watts or kilowatt-hours you need to run your home during an outage is the first step to building a solar backup system that works. Whether you’re powering just the essentials or your whole house, the right combination of battery storage and solar generation can keep your family safe, connected, and comfortable—off-grid or on.
Take the time to calculate your energy needs, explore solar generator options, and prepare before the next power outage leaves you in the dark.
Want Help Choosing the Right System?
Start with our guide: What Size Generator Do I Need for My Home? to explore solar vs fuel options and find the ideal backup power solution for your household.