Quick Answer
The average US home uses 30 kWh/day and needs 15-20 solar panels (at 400-550W each) to offset their electric bill. The exact number depends on your energy usage, location's sun hours, and panel wattage. Use our free sizing calculator for a personalized answer in 30 seconds.
In This Guide
The Formula
Every solar sizing calculation comes down to one formula:
Number of Panels = Daily kWh / (Sun Hours x Panel kW x 0.80)
The 0.80 factor accounts for real-world system losses (inverter efficiency, wiring, temperature, soiling). Some systems lose more, some less — 20% is a conservative industry standard.
Let's break down each variable so you can plug in your own numbers.
Step 1: Find Your Daily Energy Usage
Check your electricity bill for your monthly kWh consumption, then divide by 30 to get daily usage. Most utilities show a 12-month history so you can find your average.
| Home Type | Monthly kWh | Daily kWh |
|---|---|---|
| Small apartment / efficient home | 500-700 | 17-23 |
| Average US home (2,000 sq ft) | 800-1,000 | 27-33 |
| Large home (3,000+ sq ft) | 1,200-1,800 | 40-60 |
| Home with EV charging | 1,500-2,500 | 50-83 |
| Off-grid cabin | 150-400 | 5-13 |
Don't have your bill handy? Our off-grid load calculator lets you add individual appliances to estimate daily usage.
Step 2: Look Up Your Peak Sun Hours
"Peak sun hours" is the number of hours per day when sunlight intensity averages 1,000 W/m2. This isn't daylight hours — it's the equivalent full-power hours your panels actually produce at rated output.
| Region | Peak Sun Hours |
|---|---|
| Southwest (AZ, NV, NM) | 6.0-7.0 |
| California, Mountain States | 5.0-6.0 |
| Southeast (FL, GA, TX) | 4.5-5.5 |
| Mid-Atlantic (NC, VA, MD) | 4.0-5.0 |
| Northeast (NY, MA, PA) | 3.5-4.5 |
| Pacific Northwest (WA, OR) | 3.0-4.0 |
For your exact location, check NREL's PVWatts Calculator.
Step 3: Account for System Losses
No solar system produces its full rated output in the real world. Standard system losses include:
- Inverter efficiency: 3-5% loss converting DC to AC
- Wiring losses: 1-3% depending on wire gauge and run lengths
- Temperature derating: 5-10% in hot climates (panels lose efficiency above 77F)
- Soiling/dust: 1-5% depending on environment and cleaning frequency
- Shading: 0-20%+ depending on obstructions
Using 80% system efficiency (20% total losses) is a safe standard assumption. If you have significant shading, use 70-75%.
Step 4: Choose Your Panel Wattage
Modern solar panels range from 100W (portable/RV) to 600W+ (commercial). For residential rooftops, 400-550W panels are the current sweet spot — they offer the best combination of output, physical size, and cost per watt.
| Panel Size | Best For | Physical Size |
|---|---|---|
| 100-200W | RVs, boats, small off-grid | 2' x 3'-4' |
| 300-400W | Residential rooftops, limited space | 3.5' x 5.5' |
| 400-550W | Residential & small commercial (best value) | 3.5' x 7' |
| 550-620W | Ground mounts, commercial | 3.8' x 7.5' |
Browse our solar panels to compare specs and pricing across wattages.
Real Examples by Home Size
Average Home in Massachusetts (30 kWh/day)
Daily usage: 30 kWh
Peak sun hours: 4.0 (Northeast)
System efficiency: 80%
Panel wattage: 500W
30 / (4.0 x 0.50 x 0.80) = 19 panels (9.5 kW system)
Large Home in Arizona (50 kWh/day)
Daily usage: 50 kWh
Peak sun hours: 6.5 (Southwest)
System efficiency: 80%
Panel wattage: 550W
50 / (6.5 x 0.55 x 0.80) = 18 panels (9.9 kW system)
Off-Grid Cabin in Colorado (10 kWh/day)
Daily usage: 10 kWh
Peak sun hours: 5.5 (Mountain)
System efficiency: 75% (off-grid has battery charging losses)
Panel wattage: 400W
10 / (5.5 x 0.40 x 0.75) = 7 panels (2.8 kW system)
Get Your Exact Number
Plug in your specific kWh usage and location for a personalized calculation with product recommendations.
Open Solar Panel CalculatorOff-Grid vs Grid-Tied Sizing
The calculation above works for grid-tied systems where the grid acts as your backup. Off-grid systems need extra consideration:
Grid-Tied
- Size to 100-110% of annual usage
- Net metering credits excess production
- Grid covers cloudy days
- No battery required (but recommended)
- Use 80% efficiency factor
Off-Grid
- Size to 120-130% of daily needs
- Must recharge batteries fully each day
- Oversize for cloudy-day reserves
- Battery bank is required
- Use 70-75% efficiency (battery charging losses)
Planning an off-grid system? Start with our off-grid load calculator, then size your battery bank.
Frequently Asked Questions
How many solar panels do I need for a 2,000 sq ft house?
A typical 2,000 sq ft home uses about 30 kWh/day. In the northeast US (4 peak sun hours), you'd need roughly 9.4 kW of panels, or about 17-19 panels at 500W each. In the southwest (6.5 sun hours), you'd only need about 5.8 kW, or 11-12 panels.
How many solar panels do I need for 1,000 kWh per month?
1,000 kWh/month equals about 33 kWh/day. Divide by your peak sun hours and multiply by 1.25 for system losses. In a 5-sun-hour region, that's about 8.3 kW, or 15-17 panels at 500W each.
Can I install solar panels myself?
Yes, DIY solar installation is legal in most US states for your own property. You'll still need electrical permits and inspections. Ground-mounted systems are easier for DIY; roof-mounted systems require more expertise for waterproofing and structural considerations. Browse our mounting kits designed for DIY installers.
How many solar panels for off-grid living?
Off-grid systems need to be oversized by 20-30% compared to grid-tied because you can't draw from the grid on cloudy days. Start by calculating your daily Wh needs with our load calculator, then size panels to fully recharge your battery bank in one sunny day.