The yield of solar panels
Calculating solar panel yield
The yield of solar panels is not the same every year. This is due to the weather and, in addition, over the years the yield of solar panels deteriorates slightly. It is important to take this into account when calculating the yield and the number of solar panels.
The yield of solar panels is indicated in kWh (kilowatt hours). In the Netherlands, due to weather conditions (solar radiation), we assume that the solar energy system yields 90% of its capacity in watt peak.
Yield of solar panels per month
The yield of solar panels varies not only from year to year, but also from month to month. This is because solar panels yield less in the winter than in the summer. Nevertheless, it is not true that solar panels do not yield anything at all in winter. About 30% of the annual yield of solar panels is generated between October and March. Less than in summer, but certainly not nothing. Even indirect sunlight on cloudy days, so-called diffuse light, provides yield.
The average yield of solar panels per month is calculated by dividing the example above by twelve months. The actual yield of solar panels per month is therefore very different per period and depending on the weather.
Deze factoren bepalen de opbrengst van zonnepanelen
Er zijn een aantal factoren die invloed hebben op de opbrengst van zonnepanelen:
Watt peak power tells you how much sunlight the panel converts to electricity under standard test conditions. A high Wp output does not always mean that the panel also produces the most. What matters is the effective output of the solar panels: the ratio of power to energy output. This depends on several factors, such as the location and quality of the solar panels. Keep in mind that the watt-peak power of standard glass-film solar panels decreases twice as fast as that of glass-glass panels. Also look carefully at the size of the panel. Sometimes large solar panels have high watt-peak capacity, but large panels are not always the best solution. What matters is efficiency, or Wp power per m2.
kWh is the abbreviation for kilowatt hour. Wh stands for watt-hour: the unit we use for amount of energy. The k stands for kilo, or 1000. 1000 Wh is 1 kWh. With solar panels, the number of kWh means how much electricity the panel produces. The power determines the energy yield, but quality, the technology used and environmental factors also play a role.
Solar panels yield the most when the energy output is matched as closely as possible to your energy consumption.
As with all other devices, the quality of the solar panels determines the yield and lifetime. So quality also plays a vital role in calculating your yield and return. Solar panels with a long life and high quality, produce much more energy during their lifetime than solar panels of inferior quality.
The area of your roof, and the amount of solar panels you install, affects the yield. As mentioned earlier, you achieve the highest yield by matching the number of solar panels as closely as possible to your current and future energy consumption.
The size of the solar panel affects the number of solar panels that will fit on the roof. A larger solar panel is not always better because then a larger part of the roof area often remains unused. There is then less power on your roof in total.
The environment of the solar panels is also very important for the yield. Consider the location and pitch of the roof. These affect the amount of sunlight that reaches the panels. Shadow on the roof from a dormer, chimney or tree, for example, can also reduce the yield.
The alignment of the various components of the solar power system in relation to each other is important for the output of your solar panels. Consider, for example, the string distribution of the solar panels and the power of the inverter. The knowledge and skill of the installer plays an important role in this.
The difference between yield and return
When we talk about the yield of solar panels, the terms yield and return are often used interchangeably. The yield of solar panels tells you what you save annually, in kWh or in euros. The return is the positive result on your investment. The return is the ratio of the cost to the average annual yield. This is often indicated in a certain percentage. For solar panels, the average return is between 10% and 25%.
Example calculating returns
To determine the average annual energy yield, we assume a depreciation period of 20 years.
- System composition: 10 x solar panels 360 Wp
- Total power: 3,600 Wp
- Expected energy yield first year: 3,240 kWh (0.9 * 3,600)
- Total investment: € 5,785
- Average yield per year*: € 1,527
- Return on investment of solar panels: 1.527/5.785 = 26,4%.
* Based on current energy price (price level May 2022): € 0.48 & annual energy price increase: 0%.