What is a solar panel and how does it work?

A solar panel is an assembly of solar cells that can convert light directly into electricity. By combining the capacity of several solar panels, part of a family’s electricity needs can be covered.

At the moment, depending on the type of panel, 5 to 19 % of the light energy can be converted into electricity. This is known as the “output” of the panel. As the technology is constantly being improved, the output should increase further.

Using solar panels you can convert sunlight, which is free and inexhaustible, into electricity. This conversion is achieved thanks to the so-called “semiconductor” material from which each solar cell is made.

Two generations of solar panels

The material most often used for solar cells is silicon. This material can occur in three forms:

• monocrystalline silicon
• polycrystalline (or multicrystalline) silicon
• amorphous silicon

These various forms produce different types of solar panels with differing prices, useful lives and output:

• First-generation solar panels use monocrystalline or polycrystalline silicon (output of 12 to 19 %).
• Second-generation solar panels consist of solar cells made of amorphous silicon. This name also applies to solar panels based on other materials that have appeared on the market more recently:
  • CIS (copper-indium-selenium)
  • CIS (copper-indium-gallium-selenium)
  • CdTe (cadmium telluride)
    The particular feature of this second generation is that it uses thin semiconductor layers (“thin films”). This explains why these panels are less expensive and more aesthetic, but also have a lower output (from 5 to 11 %).

The convertor: the most important element in the installation

A solar panel generates direct current. To be able to use this current in the home or place the surplus on the grid, it has to be converted to alternating current of 230 V. This is done by the converter, which is integrated into the electrical circuit close to the solar panels.

What production level can we expect?

The capacity of a solar installation is expressed in watt peak (Wp). This is the maximum electrical capacity that a solar cell can yield under ideal circumstances: solar collector directed towards the sun in a cloudless sky.

The ideal orientation for solar panels is indeed south-facing. If the panels are installed between the south-east and the south-west, the loss of output amounts to 5 %. If the panels are installed outside these limits, the loss increases rapidly. In Belgium the ideal angle is 35°.

Here an installation of 1,000 Wp facing due south at an angle of 35° and without any shade generates approximately 850 kWh/year.
For a Brussels family, in practical terms that means:

• on the assumption that around 10 m² of panels (1,250 Wp) are needed to generate 1,000 kWh/year (depending on the technology chosen) …
• and given that a Brussels family of two to three people uses an average of 3,500 kWh/year …
• we can conclude that solar panels covering 10 m2 can provide just under one-third of the annual needs of a family.

In the city it is often difficult to use more room for solar panels. But as the output of the panels is increasing all the time, it will be possible to cover an ever bigger proportion of the needs with the same surface area!