For the yearly yield of your solar panels, we first calculate the total power of your solar panels from Watt-peak to kilowatt hour. Let's say the total power of your solar roof is 4000Wp. On average, 1Wp generates about 0.83kWh in the Netherlands. Multiply 4000Wp by 0.83kWh. Your solar roof then generates about 3320kWh per year. When you multiply this number by the current energy price, you get the amount you save on your energy bill. For example: 3320kWh x € 0.34 = € 1129.

The yield per month and season can vary a lot. The sun shines more in June than in November. Do you want to know what your solar panels generate in a month? You need the following formula: annual yield x percentage of the monthly yield. For example, in May the yield is about 13%. Your 4000Wp solar roof then generates 432kWh (3320 x 0.13) That's about € 147.

Want to know how many kilowatt hours a solar panel produces per day? Divide the 432kWh by the number of days in the month. Divide 432 by 31 days for May, which is 14 kilowatt hours per day. That's about € 5. How much your solar roof yields per day, depends on the weather. A warm spring day is better for generating than a cloudy or rainy day.

How much your solar panels actually generate depends on more:

• The amount of Watt-peak of your solar panels. The higher the Watt-peak, the more energy your solar panels generate.
• What your solar roof is like. Think of the amount of panels on your roof, the incline, and how often it's in the shade.
• The season. Your solar roof yields the most when the sun shines often, but it's not too warm yet.
• The age of your solar panels. The yield of your solar panels slowly decreases every year. After 25 years, solar panels yield about 89% of their total power.