What This Calculator Does
This solar panel output calculator tells you how much electricity a set of panels will make in a year where you live.
You give it the number of panels, how strong each one is, your region and which way your roof faces. It gives back kilowatt-hours per day and per year. Then you can hold that up next to what your home uses.
How To Use This Calculator
- In Number of solar panels, type how many panels you have or plan to buy.
- In Power rating per panel, type the watts printed on the panel's datasheet. New home panels in 2026 are about 430 to 470 W. Not sure yet? Leave it at 435.
- In Your region, pick the country or area closest to you. This fills in the next box for you.
- Daily yield per kWp is now set for your region. Only change it if you looked up an exact value for your own address, for example in the free PVGIS tool linked under the calculator.
- In Roof direction and tilt, pick how your panels face. South at 35° is the best case.
- Read Yearly energy production in the result card. Below it you see the total size in kWp, the daily average and what one panel makes per day.
The Formula, In Plain Words
One panel's yearly output is its watts divided by 1,000, times the daily yield, times the roof factor, times 365. Multiply that by the number of panels to get the year.
The daily yield is what 1 kWp of panels delivers per day, averaged over a year. People also call it "effective sun hours". That's a fancy way of saying "how many hours of full-strength sunshine your panels get, once the whole day is squeezed together, after losses".
The region values come from PVGIS, the free solar tool of the European Commission. For one city per region, PVGIS worked out the yearly kWh of 1 kWp at the best angle, with its standard 14% losses for cables, dirt and the inverter. The calculator divides that by 365.
For the Netherlands, PVGIS gives 1,026 kWh per kWp in Utrecht, which is 2.81 a day.
The roof factor comes from PVGIS too. In the Netherlands, an east or west roof at 35° makes 79% of the best case, and a flat panel 83%.
A Worked Example
Say you have 6 panels of 435 W in the Netherlands, on a south roof. The region sets 2.81 kWh per kWp per day.
One panel makes 0.435 × 2.81 = 1.22 kWh a day, or 446 kWh a year. Six panels make 7.33 kWh a day.
Over a year that's about 2,677 kWh. Hold that next to your own yearly use from the energy use calculator.
On an east or west roof it drops to 2,677 × 0.79, or about 2,115 kWh.
What To Watch Out For
This is a yearly average. In December a Dutch roof makes about a third of its average day, and in June about 1.5 times as much.
So an off-grid home that must run all year needs to plan for the dark months, not the average.
The regions use one city each. Your own spot can differ by 10% or more, and shade from trees or chimneys can cost a lot. Read about roof angle and orientation to see how much direction matters.
PVGIS assumes no shade from nearby objects. Real Dutch homes average lower: Milieu Centraal works with about 870 kWh per kWp.
Hard Words
| Term | What it means |
|---|---|
| Kilowatt-hour (kWh) | An amount of energy. One kWh runs a 100 W lamp for 10 hours. |
| Panel rating (W) | How much power a panel makes in perfect test sunlight, printed on its datasheet. |
| Daily yield per kWp | What 1 kWp of panels delivers per day, averaged over a year, after normal losses. Also called effective sun hours. |
| kWp | Kilowatt-peak: the total watts of your panels in perfect test sunlight, divided by 1,000. |
| PVGIS | A free online solar tool from the European Commission that estimates panel output for any spot in Europe and beyond. |
| System losses | Energy lost to heat, dust, cables and the inverter before power reaches your sockets. |
Common Questions
How much electricity does a 435 W solar panel make per year?
It depends on where you live and how it faces. In the Netherlands, PVGIS gives 2.81 kWh per kWp per day for a south roof, so a 435 W panel makes about 1.22 kWh a day, or roughly 446 kWh a year. Southern Spain gives about 63% more. The calculator fills in a value for your region.
What are effective sun hours?
Effective sun hours are what 1 kWp of panels delivers per day, averaged over a year, after normal losses. They are much lower than the hours the sun is up. A Dutch summer day may be 16 hours long, but the yearly average works out to 2.81 hours.
Why is my result different from other solar calculators?
Many calculators use raw "peak sun hours" that ignore losses from heat, dirt, cables and the inverter. This calculator uses PVGIS yields that already include those losses. Others use real-world averages that include badly placed roofs. Check which kind of number each tool uses.
How do I get the exact value for my house?
Use the free PVGIS tool from the European Commission. Enter your address, roof angle and direction, and divide the yearly kWh per kWp by 365. Type that into the Daily yield per kWp box and set the roof direction to south, because your PVGIS number already includes your direction.
Does solar output change between summer and winter?
Yes, a lot. For a Dutch south roof PVGIS gives about 127 kWh per kWp in May and only 30 in December. This calculator gives a yearly total and an average day, so it is useful for comparing with yearly use. An off-grid home needs extra margin, or a backup, for the darkest months.