Understanding how many kWh a solar panel produces per day is the foundation of every solar sizing decision. It determines how many panels you need, how much battery capacity to install, and whether solar can realistically cover your energy use. The answer varies by panel wattage, your location’s sunlight, and real-world system losses — but the formula is simple once you know the inputs.
The Solar Panel Output Formula
Daily output in kWh = Panel wattage × Peak sun hours × (1 – System loss) ÷ 1,000
Peak sun hours is not the same as daylight hours. It measures the equivalent number of hours at full 1,000 watts per square meter intensity. A location might have 12 hours of daylight but only 5 peak sun hours because morning, evening, and cloudy periods produce less than full intensity. System loss accounts for wiring resistance, heat, dust, inverter conversion, and panel degradation — typically 15 to 20 percent total.
Solar Panel Output by Wattage (at 5 Peak Sun Hours)
Using 5 peak sun hours (a moderate-sun region like the US South, Australia, or South Asia) and a 20 percent system loss, here is what each panel wattage produces per day. A 330-watt panel produces 1.32 kWh. A 450-watt panel produces 1.80 kWh. A 550-watt panel produces 2.20 kWh. A 585-watt panel produces 2.34 kWh. A 610-watt panel produces 2.44 kWh. A 670-watt panel produces 2.68 kWh. And a 795-watt commercial panel produces 3.18 kWh per day.
Over a month (30 days), a single 585-watt panel in this region generates about 70 kWh — enough to run a refrigerator for a month. A 10-panel array of 585-watt panels would produce roughly 700 kWh per month.
How Location Changes Output
The same 585-watt panel produces very different daily output depending on where it is installed. In the US Southwest or Middle East with 6 peak sun hours: 2.81 kWh per day. In the US South or Mediterranean with 5 hours: 2.34 kWh. In the US Midwest or Central Europe with 4.5 hours: 2.11 kWh. In the UK lowlands with 4 hours: 1.87 kWh. And in Northern Europe or cloudy climates with 3 hours: 1.40 kWh.
The difference between 6 and 3 sun hours is exactly double — a homeowner in Arizona gets twice the daily energy per panel as one in Scotland. This is why panel count recommendations vary so much by region and why using a calculator with your specific location matters.
Annual Output and Seasonal Variation
Daily output is an average. In reality, summer days produce significantly more than winter days. A 585-watt panel in the US Midwest might produce 3.2 kWh per day in June but only 1.4 kWh in December. Annual output is a more reliable planning number: that same panel produces roughly 850 kWh per year in the Midwest, 1,050 kWh per year in the US South, and 630 kWh per year in the UK.
When sizing a system, conservative designers use winter output or annual averages rather than peak summer figures. This ensures the system performs adequately year-round rather than excelling in summer and falling short in winter.
Factors That Reduce Real-World Output
Several factors push real output below the calculated figure. Temperature is the biggest — panels lose about 0.3 to 0.5 percent efficiency per degree Celsius above 25 degrees. On a 40-degree day, a panel’s output drops by 5 to 7 percent. Shading from trees, chimneys, or other buildings can reduce a panel’s output significantly, and even partial shading on one cell can affect the entire string. Dust, pollen, and bird droppings accumulate over time — cleaning panels once or twice a year can recover 3 to 5 percent of lost output. And panels degrade by about 0.5 percent per year, so a panel producing 2.34 kWh today will produce about 2.22 kWh in 5 years.
From Daily Output to System Size
Once you know how much one panel produces per day, sizing your system is simple division. If your home uses 30 kWh per day and each 585-watt panel produces 2.34 kWh, you need 30 ÷ 2.34 = 13 panels (rounded up). Our calculator shows this figure as “Units generated per panel/day” and “Whole array/day” directly on the panel sizing step, along with monthly production — so you can see at a glance whether your array covers your consumption.
Units Generated: What 1 kWh Actually Powers
It helps to think of daily panel output in terms of what 1 kWh actually runs. One kWh powers a 150-watt refrigerator for about 6.5 hours, a 75-watt ceiling fan for 13 hours, a 1,200-watt air conditioner for 50 minutes, or a 10-watt LED bulb for 100 hours. When you see that a 585-watt panel produces 2.34 kWh per day, that means each panel generates enough to run your refrigerator for about 15 hours or your ceiling fan for an entire day. Framing output in appliance-hours makes it much easier to judge whether your array covers your real needs.
Check Your Panel’s Output Now
The Solar System Calculator shows real-time daily output for any panel wattage (100W to 795W or custom) at your region’s sun hours, with losses applied. The inline “Units generated” readout updates as you adjust settings — per panel, per array, and per month. No spreadsheet needed.