Short answer: a typical 400 W solar panel produces about 1.4 kWh a day with 4.5 peak sun hours, or about 525 kWh a year. In a cloudier climate with 3 sun hours, it makes about 1 kWh a day; in the desert Southwest with 6, about 1.9 kWh. In the UK, expect about 0.9 kWh a day averaged over the year.
To see how many panels your home needs from this, use the solar panel calculator.
The formula
kWh per day = panel watts × peak sun hours × 0.8 ÷ 1,000
A panel's wattage is measured in lab conditions: 1,000 W of sunlight per m² at 25°C. On a roof, heat, dust, wiring and the inverter typically cost around 20%, so the 0.8 performance factor gives a realistic figure. Peak sun hours convert a day's changing sunshine into the equivalent hours of full sun.
kWh per day by panel size and sunshine
| Panel | 2.5 sun hours | 3 | 4 | 4.5 | 5 | 6 |
|---|---|---|---|---|---|---|
| 100 W | 0.20 | 0.24 | 0.32 | 0.36 | 0.40 | 0.48 |
| 300 W | 0.60 | 0.72 | 0.96 | 1.08 | 1.20 | 1.44 |
| 400 W | 0.80 | 0.96 | 1.28 | 1.44 | 1.60 | 1.92 |
| 450 W | 0.90 | 1.08 | 1.44 | 1.62 | 1.80 | 2.16 |
Figures are yearly averages. Summer days produce much more and winter days much less, especially at high latitudes: in the UK a panel can make five times as much in June as in December.
Per month and per year
A 400 W panel at 4.5 sun hours makes about 44 kWh a month and 525 kWh a year. At UK sunshine (about 2.8 hours on average) it makes about 27 kWh a month and 327 kWh a year. At the US average electricity price of 18.2¢, a 400 W panel's yearly output is worth about $96 if you use it all yourself.
Rough peak sun hours
| Region | Peak sun hours (yearly average) |
|---|---|
| US Pacific Northwest, Northeast | 3–3.5 |
| US Midwest | 3.5–4.2 |
| US Southeast, California coast | 4.5–5 |
| US desert Southwest | 5.5–6.5 |
| United Kingdom | 2.5–3 |
| Canada (populated south) | 3.2–4.2 |
| Australia (Melbourne to Brisbane) | 3.8–5.5 |
For your exact address, NREL's PVWatts (US and worldwide) or the PVGIS tool (Europe and UK) gives a monthly estimate.
What makes a panel produce less
- Orientation: panels facing east or west make about 10% to 20% less than south-facing ones (north-facing in the Southern Hemisphere).
- Shade: even partial shade on one panel can pull down a whole string unless you have optimisers or microinverters.
- Heat: output falls by roughly 0.3% to 0.4% for every °C above 25°C cell temperature.
- Age: quality panels lose about 0.5% a year.
Frequently asked questions
How many kWh does a 100 W solar panel produce per day?
About 0.3 to 0.4 kWh with 4 to 5 sun hours; enough to charge phones and run LED lights, or top up a camping battery.
Can one solar panel power a house?
No. The average US home uses about 28 kWh a day, roughly 20 times what one 400 W panel produces. See how many solar panels to power a house.
How much power does a solar panel produce per hour?
At most its rated wattage in full midday sun, usually 70% to 85% of that in practice. A 400 W panel might produce 300 W at noon on a clear summer day.
Sources
- NREL, PVWatts calculator (solar resource and default system losses of about 14% plus inverter losses).
- European Commission, PVGIS (UK and Europe solar resource).
- Panel temperature coefficients and degradation rates from manufacturer datasheets.
Checked October 22, 2026.
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