How much electricity does a solar panel produce per day?

A standard 400W solar panel produces about 1.2–2.0 kWh per day depending on your location's peak sun hours (4–6 hours for most of the US). A 10-panel, 4,000W system produces roughly 12–20 kWh/day, or 440–600 kWh/month. NREL's PVWatts tool can give precise production estimates by zip code.

How do I calculate solar panel output?

Solar energy production = panel wattage × peak sun hours × system efficiency factor. A 400W panel in a location with 5 peak sun hours produces: 400W × 5h × 0.85 (efficiency) = 1.7 kWh/day. Multiply by your number of panels for total daily production. Annual production typically ranges from 1,100–1,800 kWh per installed kW.

How much electricity does a solar panel produce per day?

A standard 400W solar panel in average US conditions (4–5 peak sun hours) produces 1.4–2.0 kWh per day. A 20-panel, 8 kW system produces 28–40 kWh/day. Annual production is typically 1,200–1,600 kWh per kW of installed capacity depending on location, with Hawaii and the Southwest at the high end and the Northeast/Pacific Northwest at the lower end.

What reduces solar panel output?

Key production reducers: shading (even partial shading can reduce output by 20–50% with string inverters), panel soiling (dust, leaves, bird droppings can cut 5–15%), high temperatures (panels lose roughly 0.35–0.5% efficiency per degree Celsius above 25°C), incorrect tilt angle, and panel aging/degradation over time.

Solar Energy Production Calculator

Estimate how much electricity your solar system will generate — daily, monthly, annually, and over its full lifetime. Accounts for real-world efficiency losses and long-term panel degradation.

System Size (kW)

Peak Sun (hrs/day)

Years (yrs)

Electricity Rate (¢/kWh)

About This Calculator

The Solar Energy Production Calculator estimates the actual electricity output of a solar system over time, accounting for the real-world factors that reduce production below nameplate capacity. A perfectly efficient 8 kW system in full sun would produce 8 kWh per hour, but real systems lose 15–25% to inverter conversion, wiring resistance, heat, dust, and panel mismatch. This calculator applies your system efficiency factor to give a realistic production number you can compare against your actual electricity consumption.

Degradation rate is a critical but often overlooked factor in long-term production estimates. Most tier-1 solar panels degrade at 0.3–0.7% per year, meaning a system producing 10,000 kWh in year one will produce roughly 8,800 kWh by year 25 at a 0.5% degradation rate. Over a 25-year lifetime this means total cumulative production is about 11% less than if the panels never degraded. Premium panels from manufacturers like LG, Panasonic, and SunPower typically carry 0.25–0.4% annual degradation guarantees — worth asking about when comparing quotes.

To find your local peak sun hours, use NREL's PVWatts Calculator (pvwatts.nrel.gov) — enter your address and look for the "Solar Resource" value in kWh/m²/day. The Southwest U.S. averages 5.5–7.0 peak sun hours; the Northeast averages 3.5–4.5. System efficiency depends on your roof orientation and tilt: a south-facing roof at 30° tilt in a mild climate might achieve 85% efficiency, while a shaded or east/west-facing roof might only reach 70%. Your installer's simulation software accounts for these specifics more precisely.

Knowing your expected production allows you to cross-check installer proposals, verify utility net metering credits, and plan battery storage sizing. It is also the input that drives every financial calculation — savings, ROI, and payback all depend on an accurate production estimate as their foundation.

Calculations based on NREL solar modeling data and industry-standard assumptions, built and maintained by the independent SolarToolsOnline research team.

Estimates only — not financial, tax, or legal advice. Verify important results with a licensed solar installer or financial professional before making decisions.