How Many Solar Panels Do You Need (Solar Calculator)
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Most people approach solar panel sizing the wrong way.
They ask "how many panels should I get?" when the real question is "how much energy do I need to replace each day?"
Those are completely different questions. And only one of them leads to a setup that actually works.
Quick Answer
- Refrigerator only: around 200W to 250W of panels in typical conditions
- Refrigerator plus devices: around 200W to 300W of panels depending on total load
- Refrigerator plus freezer: typically 400W to 500W of panels for full daily recovery
- CPAP only without humidifier: around 100W panel in good sun conditions
These numbers come from a simple calculation. Use the free calculator below for your exact answer, then see our Top 5 solar-ready power stations for refrigerator backup for compatible models.
⚠️ The Sizing Mistake That Makes Systems Fail
Choosing a panel based on what comes bundled with a power station rather than calculating what your actual load requires. A bundle pairing a 2000Wh station with a 100W panel looks complete on the product page. In practice, a 100W panel recovers approximately 400Wh to 500Wh per day. A refrigerator running overnight consumes approximately 960Wh. The panel replaces less than half the nightly consumption. The battery depletes a little more each day until the system fails entirely.
Solar panel sizing has a reputation for being complicated. It is not. There is a simple calculation that takes about two minutes and tells you exactly what you need. The confusion comes from skipping that calculation and guessing instead. Too few panels means your battery never fully recharges and your system slowly depletes over multiple days. Too many panels means money spent on capacity you will never use. Neither outcome is ideal when you are counting on backup power during a real outage.
What Actually Determines How Many Panels You Need
Your Daily Energy Consumption
This is the starting point for every solar sizing decision. How many watt-hours do your appliances consume over a 24-hour period? A refrigerator averaging 120W across compressor cycles running for 8 hours overnight consumes 960Wh. Add a CPAP at 50W for 8 hours and that becomes 1360Wh per day. Every other calculation follows from this number. The compressor does not draw a constant wattage. It cycles on and off, and the startup surge when it kicks in is a separate concern from the average draw used in solar sizing.
Your Available Daily Sunlight
Solar panels only produce power during daylight hours, and output varies significantly with sun intensity. The standard planning figure for most of the continental United States is 4 to 5 peak sun hours per day. In high-sun regions like Arizona or Florida, the figure is higher. In the Pacific Northwest, it can be lower. Using 4 to 5 peak sun hours is the right conservative estimate for most households.
Panel Efficiency Losses
Real-world panel output is approximately 75% to 85% of the rated figure due to heat, wiring losses, and non-ideal sun angles. A 200W panel produces approximately 150W to 170W of effective charging power in good conditions. Always use 80% of rated output as your working figure when calculating daily recharge capacity.
The Simple Calculation
The formula has three steps and takes two minutes:
Solar Panel Sizing Formula
Calculate your daily watt-hour consumption
Multiply each appliance's wattage by the hours it runs per day. Add them together. This is your daily consumption figure.
Example: Refrigerator 120W x 8 hours = 960Wh. CPAP 50W x 8 hours = 400Wh. Total: 1360Wh per day.
Add 25% for system losses and safety margin
Multiply your daily consumption by 1.25 to account for inverter losses, battery protection cutoffs, and charging inefficiency.
Example: 1360Wh x 1.25 = 1700Wh of solar recharge needed per day.
Divide by your peak sun hours and panel efficiency
Divide the adjusted daily need by your available peak sun hours. Then divide by 0.80 to account for real-world panel output. This gives you the minimum rated panel wattage needed.
Example: 1700Wh divided by 5 hours = 340W. Divided by 0.80 = 425W of rated panel capacity needed.
Step 2 accounts for system losses and adds a safety margin. Step 3 adjusts for real-world solar panel output. These are two separate factors applied in sequence.
In this example, the household running a refrigerator and a CPAP overnight needs approximately 400W to 450W of rated solar panel capacity for a self-sustaining daily cycle in good sun conditions. That means two 200W panels or one large 400W panel. To check whether that panel wattage actually sustains your fridge day after day, use the solar runtime calculator.
Free Solar Panel Calculator
Enter your daily energy need and sun hours. The calculator gives you the minimum and recommended panel wattage for your specific load, along with compatible station and panel recommendations.
Solar Panel Size Calculator
Find the exact panel wattage your setup requires
1 Your total daily energy consumption
Add up all appliances: watts multiplied by hours of daily use. Refrigerator only overnight = roughly 960Wh. Fridge plus CPAP = roughly 1360Wh.
2 Peak sun hours per day in your area
Most U.S. locations: 4.5 to 5.5 hours. Arizona and Florida: 6 to 7 hours. Pacific Northwest: 3.5 to 4 hours.
Minimum Rated Panel Wattage
for a self-sustaining daily cycle in your conditions
Adjusted Daily Need
Minimum Panel
Recommended Panel
Your sizing summary
Compatible stations for your solar setup
Real Examples by Household Type
| Household Load | Daily Consumption | Adjusted Need | Panel Recommendation |
|---|---|---|---|
| CPAP only, no humidifier | 400Wh | 500Wh | 100W panel |
| CPAP with heated humidifier | 1040Wh | 1300Wh | 200W to 300W panel |
| Refrigerator only | 960Wh | 1200Wh | 200W to 250W panel |
| Refrigerator plus devices | 1200Wh | 1500Wh | 250W to 300W panel |
| Refrigerator plus freezer | 1900Wh | 2375Wh | 400W to 500W panels |
| Fridge, freezer, CPAP, devices | 2400Wh | 3000Wh | 600W panels (2 x 300W) |
All estimates use 5 peak sun hours per day and 80% real-world panel efficiency. Refrigerator assumes 120W average draw over 8 hours. Freezer assumes 100W average draw over 8 hours. CPAP assumes 50W without humidifier and 130W with heated humidifier.
For a detailed breakdown of how long each station runs a refrigerator on battery alone, see our guide on how long a power station will run your refrigerator.
Quick Sizing Shortcut
Panel sizing by load type
The Most Common Sizing Mistakes
Using the Panel's Rated Wattage as the Actual Daily Output
A 200W panel does not produce 200W continuously for however many hours the sun is up. It produces approximately 200W at peak midday conditions for a fraction of each day. The daily energy output of a 200W panel in 5 hours of peak sun is approximately 800Wh to 1000Wh, not 200W multiplied by 12 hours of daylight. Using the wrong figure makes your system appear twice as capable as it actually is.
Ignoring the Station's Maximum Solar Input Rating
Every power station has a maximum solar input rating measured in watts. The EcoFlow Delta 2 accepts up to 500W of solar input. The Bluetti AC180 accepts up to 500W. There is no benefit to pairing a 600W panel array with a station rated for 500W maximum input. Match the panel total to the station's maximum input rating. The calculator above filters compatible stations based on your total panel requirement automatically. For help choosing the right station capacity, see our guide on what size power station you need for a refrigerator.
Not Accounting for Cloudy Days
The sizing calculation assumes average conditions. If your outage occurs during a weather event with heavy cloud cover, panel output drops to 10% to 30% of the calculated figure. This is why having adequate battery capacity as a buffer matters. For areas with frequent overcast, sizing panels one level above the calculated minimum provides meaningful additional resilience.
⚡ Modern Energy Tip
When in doubt between two panel sizes, choose the larger one. The cost difference between a 200W panel and a 300W panel is typically $50 to $100. The difference in daily recharge capacity is approximately 400Wh. Oversizing panels slightly provides buffer for cloudy days, higher loads, and future needs without meaningful additional cost.
What You Actually Need for Each Common Scenario
Single overnight appliance, refrigerator or CPAP without humidifier. A 200W to 250W panel paired with a 1000Wh to 1200Wh station creates a potentially self-sustaining daily cycle in most U.S. locations. This is the most common and most cost-effective home backup solar setup.
Multiple appliances overnight, refrigerator plus CPAP or refrigerator plus devices. A 300W panel paired with a 1500Wh to 2000Wh station handles combined loads without daily battery depletion in good sun conditions. This is the setup that most serious outage-preparedness households should target.
Full household essentials, refrigerator plus freezer plus devices. A 400W to 500W panel array paired with a 2000Wh station is the minimum for a self-sustaining cycle in typical conditions. Two 200W panels connected in parallel provide this capacity at a lower cost than a single large panel in most cases. For a complete guide to solar-compatible stations and solar backup strategy, read our solar generator for refrigerator complete guide.
Solar Panel Sizing Checklist: Before You Buy
- Calculate your total daily watt-hour consumption (watts x hours for each appliance)
- Add 25% safety margin for system losses and inefficiency
- Divide by your peak sun hours and by 0.80 for real-world panel output
- Verify your station's maximum solar input rating matches or exceeds your panel wattage
- Check connector compatibility between panel and station (MC4, XT60, or Anderson)
- In cloudy regions, size up one level above the calculated minimum
- When in doubt between two sizes, choose the larger panel
Final Verdict
Match Your Energy Usage to Your Recharge Capacity. Do Not Guess.
The calculation takes two minutes. Or use the free calculator above to skip the math entirely. A correctly sized system can sustain itself day after day in good sun conditions. A system sized by guessing depletes a little more each day until it fails when you need it most.
Every station in our verified Top 5 lineup is solar-compatible with clearly published maximum solar input ratings so you can match them to the panel size your calculation requires.
If this guide helped you, consider saving Modern Energy Guide in your bookmarks so you can quickly find the right information during your next power outage.