What are peak sun hours?

Peak sun hours represent the number of hours per day when sunlight intensity averages 1,000 W/m². This varies by location — desert areas may get 6–7 hours while northern climates average 3–4 hours. You can find your local value from solar irradiance maps or weather databases.

What is system efficiency loss?

No solar system is 100% efficient. Losses come from the inverter (typically 4–8%), wiring resistance, panel temperature, shading, and soiling. A standard derate factor of 80% (20% loss) is a conservative real-world estimate for most residential installations.

Does this account for battery storage?

This calculator sizes for grid-tied systems based on daily production vs. consumption. For off-grid battery systems, you would also need to factor in battery capacity, depth of discharge, and days of autonomy — those calculations are more complex and site-specific.

How accurate is the annual savings estimate?

The estimate assumes you consume all the solar energy you produce (net metering or self-consumption). Actual savings depend on your utility's net metering policy, time-of-use rates, seasonal variation, and shading. Use this as a planning baseline, not a financial guarantee.

What panel wattage should I use?

Modern residential panels typically range from 300W to 450W. A 400W panel is a good midpoint for estimation. Higher wattage panels produce more power per panel but cost more individually; the total system size in watts is what matters most.

Solar Panel Calculator

Name: Solar Panel Calculator
Availability: InStock
Author: Nham Vu

Enter your daily energy usage, peak sun hours, panel wattage, and electricity rate to estimate your solar system size and annual savings.

System Inputs

Daily Energy Usage (kWh/day)

Average US home: 28–33 kWh/day

Peak Sun Hours (hours/day)

Phoenix: ~6.5 • New York: ~4.7 • Seattle: ~3.5

Panel Wattage (W per panel)

Typical residential panel: 300–450 W

Electricity Rate (cents/kWh)

US average: ~16 cents/kWh

System Efficiency (%)

80%

Accounts for inverter, wiring, and temperature losses

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Panels Needed

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System Size (kW)

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Daily Output (kWh)

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Annual Savings (USD)

Full Breakdown

Required system output —

Gross solar output needed —

Required system size —

Number of panels (rounded up) —

Actual daily production —

Annual production —

Monthly savings (est.) —

Energy Coverage —

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Summary

Enter your daily energy usage, peak sun hours, panel wattage, and electricity rate to estimate your solar system size and annual savings.

How it works

Enter your average daily electricity usage in kilowatt-hours (kWh).
Set the peak sun hours for your location (typically 3–6 hours per day).
Choose your panel wattage (standard residential panels range from 300W to 450W).
Enter your local electricity rate in cents per kWh.
Optionally adjust system efficiency loss to account for inverter, wiring, and temperature losses.
The calculator instantly shows the number of panels, total system wattage, daily output, and annual savings.

Use cases

Homeowners evaluating whether rooftop solar makes financial sense.
Engineers sizing off-grid solar systems for cabins or remote sites.
Students learning about photovoltaic system design.
Real estate investors estimating solar ROI on rental properties.
DIY solar installers planning panel counts before purchasing equipment.
Businesses calculating potential savings from commercial solar installations.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu