Solar Panel Output Calculator
This calculator uses your panel count, wattage, and local peak sun hours to project yearly kilowatt-hour generation and the dollar savings on your electricity bill. Solar payback periods and environmental benefits depend heavily on these three variables, making accurate inputs essential for planning.
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Formula
Annual kWh = Panel Count × Panel Wattage × Sun Hours/Day × 365 ÷ 1,000
Panel count times wattage gives the total system capacity in watts. Multiplying by daily peak sun hours yields watt-hours per day. Scaling by 365 days and dividing by 1,000 converts to kilowatt-hours per year. Multiplying by your electricity rate converts energy production to dollar savings.
How to use the Solar Panel Output Calculator
- 1
Enter your number of solar panels
A typical home system uses 15–25 panels.
- 2
Enter your panel wattage
Most modern residential panels are 350–450 watts.
- 3
Enter your peak sun hours per day
US averages range from 3.5 (Pacific Northwest) to 6.5 (Southwest). Check NREL's PVWatts for your zip code.
- 4
Enter your electricity rate
Find this on your utility bill. US average is about $0.13/kWh.
- 5
Read your results instantly
Results update in real time as you type.
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How Solar Panels Generate Power
Photovoltaic (PV) solar panels convert sunlight directly into electricity using semiconductor cells, typically made of silicon. When photons from the sun strike the cells, they knock electrons loose, creating a flow of direct current (DC) electricity. An inverter then converts this DC power into the alternating current (AC) used by your home. The amount of power generated depends on panel efficiency, system size, and how many hours per day the panels receive direct sunlight — known as peak sun hours.
Understanding Peak Sun Hours
Peak sun hours are not simply the hours of daylight — they represent the number of hours per day that sunlight intensity averages 1,000 watts per square meter (the standard test condition for panels). The US Southwest averages 5.5–6.5 peak sun hours daily, while the Pacific Northwest averages 3–4. This single variable has an enormous impact on system output. A 20-panel, 8 kW system in Phoenix produces roughly 40% more electricity per year than the same system installed in Seattle.
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Return on Investment and Incentives
The federal Solar Investment Tax Credit (ITC) allows homeowners to deduct 30% of the total installation cost from federal taxes, significantly improving payback periods. Many states and utilities offer additional rebates or net metering programs that credit you for excess electricity sent back to the grid. With incentives, most residential systems pay for themselves in 6–10 years and last 25–30 years, delivering 15–20 years of essentially free electricity after payback.
Tips & Insights
Maximize Your Sun Hours
In the northern hemisphere, panels should face true south at an angle equal to your latitude for maximum annual output. Even a 10–15% shading loss from trees or neighboring structures can significantly reduce production — use a shading analysis tool before installation.
Right-Size Your System
Aim to generate 90–100% of your current electricity usage. An oversized system produces excess power you may not be compensated for, while an undersized system leaves savings on the table. Review 12 months of utility bills before selecting panel count.
Pair Solar With Battery Storage
Adding a home battery like the Tesla Powerwall lets you store excess daytime solar production for use at night or during outages. This increases self-consumption rates and protects against grid failures — a growing concern in areas prone to extreme weather.
Worked Examples
Suburban Southwest Home
21,024 kWh per year, saving approximately $2,523 annually on electricity bills.
Northeast Starter System
6,132 kWh per year, saving approximately $1,104 annually on electricity bills.
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Frequently Asked Questions
What is the average solar panel output per day?
A single 400-watt panel with 5 peak sun hours produces about 2 kWh per day. A typical 20-panel system generates roughly 40 kWh per day, though this varies significantly by location and weather.
How many solar panels does it take to power a home?
The average US home uses about 900 kWh per month, or 10,800 kWh per year. Depending on location and panel wattage, most homes need 15–25 panels to cover 100% of their electricity needs.
Does this calculator account for panel degradation?
No — this calculator shows peak theoretical output. In practice, panels degrade about 0.5% per year in efficiency, and system losses from inverters, wiring, and dust reduce output by 15–20% from the nameplate calculation.
What is net metering?
Net metering is a utility billing arrangement that credits solar panel owners for excess electricity fed back into the grid. When your panels produce more than you use, the meter runs backward and your bill is reduced by the credited amount.
How long do solar panels last?
Most modern solar panels carry a 25–30 year performance warranty and are expected to produce power for 30–40 years. After 25 years, most panels still operate at 80–85% of their original capacity.
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