How much electricity does a solar panel produce per day?

A 400W panel in a state with 5 peak sun hours per day produces about 2 kWh per day (400W × 5h × 0.80 efficiency factor). Annual production per panel is roughly 730 kWh. A 7kW system (17–18 panels) produces approximately 8,000–11,000 kWh annually depending on location.

Why does my solar production vary by season?

Solar production drops in winter because days are shorter and the sun is lower in the sky, reducing the angle of incidence and effective panel output. In northern states, winter production can be 40–50% of summer peak. NREL data shows this variation by location — the estimator uses annual averages.

How accurate are solar production estimates?

Production estimates using NREL data are typically accurate within ±15–20% for well-sited residential systems. Key variables that affect real-world output: roof angle and orientation, local shading, panel brand, and maintenance frequency. Estimates assume optimal or near-optimal siting.

Quick Tools

Solar Production Estimator

Estimate daily, monthly, and annual solar energy output by system size and state, using NREL peak sun hour data.

Input method

System size (kW)

State

8.00 kW system · 5.5 peak sun hours/day · 80% efficiency

Daily

35.2 kWh

Monthly

1,056.0 kWh

Annual

12,848.0 kWh

How we calculate solar production

Estimated output starts with NREL peak sun hours for your state, then applies a performance ratio to account for inverter losses, temperature derating, soiling, and wiring losses.

Daily kWh = System kW × Peak Sun Hours × 0.78

Monthly and annual totals are derived from the daily estimate — expect 30–40% less production in winter versus summer in northern states.

Frequently Asked Questions

How much electricity does a solar panel produce per day?: A 400W panel in a state with 5 peak sun hours per day produces about 2 kWh per day (400W × 5h × 0.80 efficiency factor). Annual production per panel is roughly 730 kWh. A 7kW system (17–18 panels) produces approximately 8,000–11,000 kWh annually depending on location.
Why does my solar production vary by season?: Solar production drops in winter because days are shorter and the sun is lower in the sky, reducing the angle of incidence and effective panel output. In northern states, winter production can be 40–50% of summer peak. NREL data shows this variation by location — the estimator uses annual averages.
How accurate are solar production estimates?: Production estimates using NREL data are typically accurate within ±15–20% for well-sited residential systems. Key variables that affect real-world output: roof angle and orientation, local shading, panel brand, and maintenance frequency. Estimates assume optimal or near-optimal siting.

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Solar Production Estimator

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Reviewed April 2026

Methodology and source note

PowerSizing calculators use shared formulas, documented assumptions, and current planning inputs that are summarized on the methodology page. Use these tools for first-pass planning, comparison, and sanity checks, then confirm local code, pricing, utility tariff, and installer specifics before you buy equipment.