Solar Panel System Sizing
Proper solar system sizing depends on your energy consumption, available roof space, local sunlight, and budget. Most homes need 5-10kW systems to offset electricity bills.
Solar Panel Calculator
Our solar panel calculator helps homeowners and installers plan photovoltaic systems. Estimate how many panels you need based on energy consumption, calculate expected output based on location and panel specifications, and see potential cost savings over time.
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Updated: November 2025
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Solar Panel Calculator calculator
kW
kWh/day
m²
hrs
W
%
$
/kWh
Results
18
kWh/day
Monthly Output
540 kWh
Yearly Output
6570 kWh
Panels Needed
13 panels
Roof Area
22.1 m²
Yearly Savings
$985.50
CO₂ Avoided
2628 kg/year
wb_sunny Peak Sun Hours (US)
Southwest
5.5-6.5 hrs
Southeast
4.5-5.5 hrs
Midwest
4.0-5.0 hrs
Northeast
3.5-4.5 hrs
solar_power System Losses
- 🔌 Inverter: 3-5% loss
- 🌡️ Temperature: 5-15% loss
- 📊 Total efficiency: ~80%
How to Use the Solar Panel Calculator
1
Select Mode
Choose to calculate output, required system size, or panel count
2
Enter System Specs
Input system size or energy usage, panel wattage
3
Set Location Factor
Enter peak sun hours for your area
4
View Results
See energy production, savings, and panel requirements
The Formula
Solar output depends on panel wattage, sunlight hours in your location, and system efficiency losses (inverter, wiring, temperature, shading).
Daily Output (kWh) = Panel Watts × Peak Sun Hours × Efficiency
lightbulb Variables Explained
- kWh Kilowatt-hours of energy produced
- W Panel wattage (nameplate rating)
- PSH Peak Sun Hours (varies by location)
- η System efficiency (typically 75-85%)
tips_and_updates Pro Tips
1
Peak sun hours vary by location: 3-4 in cloudy areas, 5-6 in sunny regions
2
Account for 15-25% system losses (inverter, wiring, temperature)
3
South-facing panels (in Northern Hemisphere) produce most energy
4
Optimal tilt angle roughly equals your latitude
5
Panel output decreases ~0.5% per degree above 25°C
6
Shading from trees or buildings significantly reduces output
7
Most residential panels are 350-450W each
Residential solar installations have grown exponentially, with the US adding over 6 GW of residential capacity in 2024 alone, driven by falling panel costs (now averaging $0.25-$0.35 per watt for panels) and federal tax incentives like the 30% Investment Tax Credit extended through 2032. The key to a successful solar installation is accurate system sizing — installing too few panels leaves you paying utility bills, while oversizing wastes capital. System output depends on three primary factors: panel wattage (modern residential panels range from 370W to 430W), peak sun hours at your location (ranging from 3.5 hours in the Pacific Northwest to 6.5+ hours in the Desert Southwest), and system efficiency losses from inverter conversion, wiring, shading, and temperature (typically reducing output by 15-25%). A typical US household consuming 10,500 kWh annually in a location receiving 5 peak sun hours would need approximately 20 panels rated at 400W each. Beyond sizing, financial viability depends on local electricity rates, net metering policies, and available incentives. Most residential systems achieve payback in 6-10 years and continue generating free electricity for 25-30 years beyond that.
Maximizing Solar Output
Optimize output by choosing south-facing orientation, proper tilt angle (roughly equal to latitude), minimizing shading, and keeping panels clean.
Frequently Asked Questions
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Data sourced from trusted institutions
All formulas verified against official standards.