Solar panel yield and return
How to estimate solar panel yield, what affects output over the year, and the difference between yield and return.
A rule of thumb in the Netherlands: a panel produces roughly 0.85 to 0.9 times its watt-peak rating in kilowatt-hours per year. A 400 Wp panel lands around 340 to 360 kWh a year.
How do you estimate yield?
A panel's power is rated in watt-peak (Wp). To estimate yearly yield, use a rule of thumb: multiply the total wattage by about 0.85 to 0.9. Ten 400 Wp panels are 4,000 Wp together, so around 3,400 to 3,600 kilowatt-hours per year.
It is an estimate, not a guarantee. Real output depends on your roof and the weather, but for a first read the rule works well.
Yield by season
In the Netherlands a solar installation produces most of its yearly yield between March and September. A summer month like June easily produces five to six times as much as December. Over a full year that averages out to the rule of thumb of 0.85 to 0.9 kWh per Wp.
The sun sits higher and longer in summer. Winter output is much lower, but across twelve months you land at the figure from the rule of thumb. KNMI data confirms that diffuse light in spring and autumn still generates output.
What determines your yield?
Four things weigh most: roof orientation (south gives the most, east-west a bit less but spread across the day), the tilt, shade from trees or chimneys, and the quality of panels and inverter.
Shade on part of your roof often costs more than you would expect. We look at this closely during the survey, because sometimes a different layout or an Enphase micro-inverter solves it.
Yield versus return
Yield is how much power you generate in kWh. Return is what your investment earns in euros against the cost. The faster you pay back the system, the higher the return. At SolarFast we typically calculate about five years payback for panels.
Because prices and schemes change, we leave hard payback figures off this page and prefer to calculate them for your situation in your quote.
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