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Solar panel efficiency

In this article we will analyze the efficiency of solar panels, that is, what are the causes that affect this efficiency.

Solar panel efficiency

It can be worth investing in solar panels, especially in the long term and with rising energy prices. The efficiency of solar panels is an important factor in the decision about installing solar panels. The higher the return, the faster you can recoup your investment. The efficiency of solar panels depends on several factors. Find out everything in this article.

Solar panel efficiency – what does that mean?

The efficiency of the solar panel (efficiency solar panels) is approximately between 15% and 22%. This means that a solar panel can convert between 15% and 22% of the available sunlight into electricity.

For example: in a 1.5m² solar panel with a capacity of 250 Wp, the sun radiates with a capacity of 1300 Wp. The efficiency of that solar panel, or the amount of sunlight that the panel can convert into electricity, is then 19.2% (250/1300).

Performance – area – maximum power ratio

There is a relationship between efficiency, surface area and peak power (Wp) of solar panels. For example, a solar panel with a certain surface area and higher efficiency will achieve a higher peak power than a solar panel with the same surface area but with lower efficiency. In the case of solar panels with the same surface area, the more efficient solar panel will therefore convert more sunlight into electricity.

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In other words, more efficient solar panels need less surface area to produce certain energy. That doesn’t make them better than lower-efficiency solar panels, but especially more interesting when you don’t have as much space available on your roof. Thanks to the most powerful solar panels (high-efficiency solar panels), you can still generate the desired energy on a limited area.

” Example

Suppose you have a roof area of ​​20m² and you want to generate 3500 kWh of electricity per year with your solar panels (average amount for a family of 3 people).


Option 1: 2m² solar panels with a maximum power of 300 Wp

⇒ Solar panel efficiency = Peak power (Watt) / (Area (m²) * 1000)
15% = 300 / (2 * 1,000)

⇒ Required number of solar panels: 3500 kWh / 300 Wp = ± 12 solar panels

⇒ Area: 12 solar panels * 2m² = 24m² (too large for the available roof area)


Option 2: 1.24m² solar panels with a maximum power of 245 Wp

⇒ Efficiency solar panels = Maximum power (Watt) / (Area (m²) * 1000)
19.75% = 245 / (1.24 * 1000)

⇒ Required number of solar panels: 3500 kWh / 245 Wp = ± 14 solar panels

⇒ Area: 14 solar panels * 1.24m² = 17.36m² (suitable for available roof area)


 Recovery period of solar panels

We have already mentioned that efficiency has an important influence on the  recovery time of solar panels  . To calculate the payback period, you must also know the performance of the solar panels.

To calculate the performance of a solar panel, you need to know what the power of the panel is. Power is expressed in Watts Peak (WP)  . However, a solar panel does not consistently supply the same amount of power and only provides maximum power under ideal conditions. In Belgium and the Netherlands, where roughly the same weather conditions apply, you can assume that a solar panel can run at full power for 850 to 900 hours per year. Therefore, the expected power of a solar panel is expressed in kWh (kilowatt hours)  .


Suppose you want to generate 4,500 kWh per year (a family of four), then you need 4,500 / 0.85 = 5,300 Wp. Suppose you use solar panels with a capacity of 250 Wp, then you need 5300/250 = 21 solar panels to generate enough power.

With 21 solar panels of 250Wp you can generate 4,462.5 kWh (5,250 * 0.85) per year. At an energy price of € 0.25, this represents a saving of € 1,115.62 (4,462.5 * 0.25) per year.

If we assume an installation with a price of € 10,800, we can conclude based on the previous calculation that it has recovered the investment for solar panels in approximately 9 years (10,800 / 1,115.62).

The payback period for solar panels depends on the investment amount, expected maintenance costs, and the price of electricity. On average, you should take into account a payback period of 8 to 13 years. On average, solar panels last 25 years. So you can enjoy savings on your energy bill all these years. 

Some other examples:


Number of people Annual electricity consumption Required power (kWh / 85%) Number of solar panels Indicative price (VAT included, installation, inverter) Savings / year (electricity price € 0.25 / kWh)
1 2500 kWh 3000 Wp 12 € 6,200 € 630
two 3000 kWh 3500 Wp 14 € 7,400 € 750
3 3500 kWh 4.100 Wp sixteen € 8,900 € 870
4 4000 kWh 4.700 Wp 18 € 10,000 € 1,000
5 4.500 kWh 5.300 Wp twenty-one € 10,800 € 1120
6 5,000 kWh 5.900 Wp 2. 3 € 11,900 € 1,250



Factors affecting performance

Since solar panels are powered by  solar energy  , it goes without saying that there are several external factors that have a great influence on efficiency. These are certainly not unimportant to keep in mind:


1. Type of solar panel

Generally, you can generate the most energy with monocrystalline or polycrystalline solar panels. Monocrystalline panels are more expensive to buy   (read more about the price of solar panels)  , but they offer a higher yield per square meter than polycrystalline solar panels. With a small ceiling area, it can be attractive to opt for a high-efficiency solution. Read more about the different types of solar panels


2. Location

The number of hours of sunshine and the degree of insolation differ depending on the location. For example, the insolation in the west is higher than in the east, so you will generate relatively more energy on the coast than in the middle or east of the country.


3. Temperature

At higher temperatures, a solar panel performs worse than at low temperatures. This has to do with the conductivity of solar cells. The ideal temperature is 25 ° C. At this temperature, a solar panel can generate electricity more efficiently.

Therefore, you may generate more power on a sunny spring day than on a hot summer day. It also depends on the panel installation method. Roof mounted panels are naturally cooled by the wind. This is not the case with the integrated ceiling panels.


4. Shadows

The efficiency of a solar panel can be adversely affected by shadows from nearby objects such as street lamps, trees, other houses, a fireplace, or the presence of a dormer. When installing solar panels, therefore, you must take into account the presence of such objects that disturb the incidence of light.


5. Angle of inclination of solar panels

High efficiency of solar panels is achieved at an angle of inclination of 30 to 40 degrees. Many pitched roofs have a 35 ° pitch angle, which makes them suitable for installing solar panels. If the roof slope is less than 30 degrees or greater than 40 degrees, an energy efficiency of less than an average of 10% must be taken into account. With  solar panels on flat roofs  , the angle of inclination is never a problem because the solar panels are placed in a frame whose angle of inclination can be optimally adjusted.


6. Orientation of a solar panel

With a south facing solar panel, you will achieve maximum efficiency. Solar panels facing southwest or southeast can produce 10% less. However, this does not mean that this orientation is not profitable. The payback period is only longer and may require a few more panels. The least good orientation is an east or west orientation. The yield is then on average 20% lower than with an ideal orientation towards the south.

TIP: Proper placement of solar panels is important to get the most out of them and enjoy optimal performance and fast payback time. Therefore, it is recommended to leave the installation to a professional. He has the knowledge and experience necessary to bring the job to a successful conclusion and assure you of quality. 


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