Solar Panel Output Calculator
Estimate daily solar energy production based on panel wattage, number of panels, peak sun hours, and system efficiency.
Calculate solar output
Enter your panel wattage, number of panels, average peak sun hours, and an optional efficiency factor to estimate daily energy production.
5.76 kWh/day
Based on 4 panels at 400 W, 4.5 peak sun hours, and 80% system efficiency.
How to use this calculator
Enter the wattage of one panel, the number of panels, your average peak sun hours per day, and an efficiency percentage. The calculator estimates total daily and monthly energy production.
Tips for success
- Real output depends on season, tilt, shade, temperature, and equipment losses.
- An 80% efficiency factor is a reasonable planning estimate for many systems.
- Winter output is often much lower than summer output in northern climates.
- Use local peak sun hour data for better estimates.
- This is best used as a planning tool, not a guaranteed production forecast.
Practical note
This is useful for backup power planning, off-grid setups, cabin systems, battery charging estimates, and household resilience projects.
Common mistakes
- Using panel nameplate wattage as if it were constant real output.
- Ignoring system losses from inverters, wiring, and heat.
- Using summer sun hours for a winter planning scenario.
- Forgetting shade impacts.
- Confusing watts with watt-hours or kilowatt-hours.
FAQ
What are peak sun hours?
Peak sun hours are the equivalent number of hours per day when solar irradiance averages 1,000 watts per square metre.
Why is system efficiency important?
Real systems lose energy through inverter conversion, wiring, temperature effects, and other inefficiencies, so usable output is lower than simple panel math suggests.
Is monthly output just daily output times 30?
In this tool, yes. It is a simple estimate. Real monthly production varies with weather and season.
Can I use this for off-grid solar?
Yes. It is useful for off-grid and backup planning, especially when paired with battery runtime estimates.
How much power does one solar panel make?
Most modern residential solar panels are rated 350 to 450 watts. Under standard test conditions (1,000 W/m² irradiance, 25 °C cell temperature) a 400-watt panel produces 400 watts of instantaneous power. In real-world use, that same panel typically delivers 1.5 to 2 kWh per day in temperate climates with about 4 to 5 peak sun hours, dropping to under 1 kWh per day in winter or heavily shaded conditions. Total energy depends on location, tilt, season, and how many usable sunlight hours your roof or array sees.
How many solar panels do I need?
It depends on your daily energy use and your location's peak sun hours. The typical US home uses about 30 kWh per day. Divide that by your peak sun hours (4 to 5 in most regions) and an 80% efficiency factor, then divide by panel wattage. For 400-watt panels in a 4.5 sun-hour climate, 30 kWh / 4.5 / 0.8 / 400 W comes out to roughly 21 panels for full grid-tie offset. For backup or partial loads, scale down based on which appliances you want to cover.
Can solar power run my fridge?
Yes, but you need to size for it. A typical full-size fridge consumes 1.0 to 1.5 kWh per day. To cover that with solar alone, you need an array producing at least that much daily output plus enough battery storage for nights and cloudy days. A 400-watt panel in 4.5 peak sun hours produces about 1.4 kWh per day at 80% efficiency, so a single panel can roughly cover one fridge if everything aligns. Most off-grid setups use 2 to 4 panels per fridge to handle weather variability and to power additional small loads at the same time.
Pair with backup power planning
Solar arrays usually share the backup-power role with batteries and a generator for cloudy days or extended outages. Plan the full system together.