How Much Power Does a Solar Panel Produce? (kWh per Day)

A typical 400-watt solar panel produces about 1.6 kWh per day on an average US day with 5 peak sun hours. Depending on where you live, that ranges from about 1.1 to 1.9 kWh a day, or roughly 400 to 700 kWh a year.

This guide is about one panel’s output. If you want to size a whole system for your home, use our solar power calculator instead.

How do you calculate a solar panel’s daily output?

Use this formula: daily kWh = panel watts × peak sun hours × (1 − losses) ÷ 1,000.

A peak sun hour is one hour of sunlight at 1,000 watts per square meter. That is the same light level used to rate panels in the lab. Most of the US gets 4 to 6 peak sun hours a day, averaged over the year. Losses cover heat, wiring, inverter conversion, dirt and small mismatches between panels. We use 20%, a cautious rule of thumb. NREL’s PVWatts calculator uses a 14% default, so real output can be a little higher.

Here is the math for a 400 W panel with 5 peak sun hours:

1. Raw output: 400 W × 5 hours = 2,000 Wh.
2. After 20% losses: 2,000 Wh × 0.8 = 1,600 Wh.
3. Convert to kWh: 1,600 Wh ÷ 1,000 = 1.6 kWh per day.
4. Per month: 1.6 kWh × 30 = 48 kWh.
5. Per year: 1.6 kWh × 365 = 584 kWh.

You can cross-check with the yearly rule of thumb. The US average is about 1,350 kWh per kW of panels per year. A 400 W panel is 0.4 kW, so 0.4 kW × 1,350 kWh = 540 kWh a year. That is close to the 5-sun-hour estimate and works out to about 4.6 sun hours a day.

How much does a solar panel produce by wattage?

Most new home panels are 400 to 450 W and about 21 sq ft each. That works out to about 19 watts per square foot (400 W ÷ 21 sq ft). Smaller 100 W and 200 W panels are common in RV, shed and portable kits.

How much does a 400-watt solar panel produce in my state?

Sun hours vary a lot by location. Here is the same 400 W panel in sample states, using approximate yearly average peak sun hours:

Sun hours are only part of the story in each state. Rates, rebates and net metering rules matter just as much for savings. See our state guides for solar panels in Texas and solar panels in California.

How much power does a solar panel produce per hour?

A panel’s rating is its output under lab conditions: bright light and a cell temperature of 77°F. On a real roof, a 400 W panel usually peaks at around 75%–90% of its rating, or about 300–360 W, near midday on a clear day. So its best single hour yields about 0.3–0.36 kWh. Mornings and late afternoons produce much less, and output is zero after dark.

What affects how much power a solar panel produces?

• Season: winter output can be half of summer output or less in northern states. Our guide on whether solar panels work in winter explains why.
• Shade: even partial shade on a few cells can cut a panel’s output sharply.
• Heat: panels lose about 0.3%–0.4% of output for every 1.8°F (1°C) above 77°F. A cell at 131°F is 54°F (30°C) above that, so it loses about 30 × 0.35% ≈ 10.5%.
• Tilt and direction: in the US, south-facing panels tilted near your latitude do best. East- or west-facing roofs often produce about 10%–20% less.
• Dirt, pollen and snow: a dirty or snow-covered panel can lose a large share of its output until it is cleared.
• Age: panels lose about 0.5% of output a year. See how long solar panels last for the full degradation math.

What can one solar panel run?

One 400 W panel making 1.6 kWh a day can roughly cover any one of these, as long as you have a battery for the hours without sun:

• A modern refrigerator using about 1–1.5 kWh a day.
• A 10 W LED bulb for about 160 hours (1,600 Wh ÷ 10 W).
• A Wi-Fi router (about 10 W) for more than 6 days (240 Wh a day).
• A 1,500 W space heater for only about 1 hour.

For a whole home, you need many panels. A home using 30 kWh a day would need about 30 ÷ 1.6 ≈ 19 panels at 5 sun hours. For a full system size based on your bill and roof, see our guide to panels for a 1,500 sq ft house or the calculator linked above.

Frequently asked questions

How many kWh does a 100-watt solar panel produce per day?

About 0.4 kWh with 5 peak sun hours. Across most of the US, expect roughly 0.3 to 0.5 kWh a day.

How much does a 400-watt solar panel produce per month?

About 48 kWh a month at 5 sun hours. The range is roughly 34 kWh in low-sun areas to 58 kWh in the Southwest.

Do solar panels ever produce their full rated wattage?

Sometimes, briefly, on cold, very clear days. Most of the time real panels run hotter than lab conditions and see less intense light, so they produce less than their rating.

How much power does a solar panel produce on a cloudy day?

Often about 10%–25% of its normal output, depending on how thick the clouds are. Thin, high clouds cost less; heavy overcast costs more.

Sources

• NREL PVWatts Calculator
• NREL: Solar Resource Maps and Data
• US Department of Energy: Planning a Home Solar Electric System

Last updated: October 2026. Output figures are estimates; your panel’s real output depends on your site, equipment and weather. This article is for information only and is not electrical advice.