Have you asked yourself how electricity is generated from the sun and what exactly is going on in photovoltaic (PV) solar cells? The solar cells are responsible for this – we will explain how they are constructed and how they work! The structure and function of the solar cell are based on elementary physics. However, you don’t have to be a physicist to understand the operating principle. We try to explain to you in an understandable way with the help of a graphic representation of the structure of a solar PV cell, what takes place in it, and how ultimately electricity is generated from the sun!
- 1 What is a solar cell?
- 2 Who invented the solar cell?
- 3 How is a solar cell constructed?
- 4 What types of solar cells are there?
- 5 What does a solar cell cost?
What is a solar cell?
Photovoltaic solar (pv) cell systems are often also referred to as solar systems, which is, however, a rather unspecific name. Because the group of solar systems includes both photovoltaic and solar thermal systems. Both types of systems collect the sun’s energy. The difference between solar thermal and photovoltaic systems lies mainly in whether the solar energy is converted into electricity or heat. Photovoltaics describes the direct conversion of solar radiation, so-called photons, into electricity. The solar cells, which form the smallest component of a system, are responsible for the conversion. Most common solar cells are made of the semiconductor material silicon (quartz sand). One property of semiconductors is that they have improved conductivity through the addition of energy – in photovoltaics, this energy supply is light.
How can you easily explain how a solar cell works?
The solar (pv) cell works relatively simply: When sunlight hits the solar cell, the electrons in the cell are excited so that they move. Inside the cell there is an interaction between the irradiating sunlight and the doped semiconductor of the solar cell. This releases electrical charge carriers, so-called electrons. This causes current to flow, which is dissipated through metal contacts on both sides of the cell. The electricity generated in this way is then transported further into the house via a power cable.
Who invented the solar cell?
The French scientist Alexandre Edmond Becquerel discovered in the 19th century that batteries last longer and produce more power under sunlight. In 1893, based on his research, the first solar (pv) cell was built that generated electricity with the help of the sun.
How is a solar cell constructed?
The structure of a silicon photovoltaic solar cell consists of three layers. The main component is made up of two differently doped silicon layers:
- n-doped layer: some phosphorus is mixed in with this layer, which makes it negative (free electrons)
- p-doped layer: some boron is mixed in with this layer, which makes it positive (missing electrons)
There is a boundary layer between the two layers through which released charges can only pass by means of sunlight. In this core of the solar cell, the movement of electrons creates an electric field, which is also known as the pn junction.
What happens in the solar cell?
The sun’s rays contain microscopic energy carriers, so-called photons, which hit the surface of the cell. The semiconductor silicon used reacts to the sun’s rays by detaching electrons. Positively charged holes remain at these points. Depending on their charges, the electrons move to the negative or positive electrode. As the electrons move to the top of the silicon, the holes move to the bottom. The charges flow upwards through the conductive metal layers and thus reach the consumer where the energy is needed, such as a light bulb, PC or power grid. The electrical circuit is then closed by the electrons migrating back to the layer with the missing electrons.
In order to be able to use the electricity generated, it is necessary to apply metallic contacts to the front and rear and to connect them to one another via a cable. For this purpose, a holistic contact layer is applied to the back. These divert the electrons and cause them to flow via a cable, creating an electrical circuit. On the other hand, the contacts are applied in the form of a thin grid on the front so that the light can fall on the surface.
What types of solar cells are there?
Solar (pv) cells are one of the most important components of a photovoltaic system. They largely determine how high the acquisition costs of the PV system are and how much electricity can be generated. There are currently three different types of solar cells that are of interest to private users. Each type has different properties as well as advantages and disadvantages – here you have to decide for yourself which one suits you and your requirements best.
1.) Monocrystalline solar cell
This type of solar (pv) cell consists of monocrystalline silicon. During production, monocrystalline rods are drawn from liquid silicon and then sawn into thin rods, which are also called “wafers”. Compared to polycrystalline cells, this cell type has a very high silicon content and is therefore the most effective solar cell with an efficiency of approx. 20 percent in direct sunlight. However, due to the complex production, monocrystalline modules are comparatively expensive.
2.) Polycrystalline solar cell
Like monocrystalline solar cells, this cell type is made of silicon, although the silicon is not as pure. A silicon block is first cast, which is then cooled so that the liquid silicon solidifies. This creates crystal structures of different sizes. Thin panes are cut from this – each pane is a polycrystalline solar cell.
The module production is less complex and there is little waste due to the square shape of the cell. For this reason, polycrystalline cells are cheaper and also better for the environmental balance of the photovoltaic system, since not as much energy is required for production. This is why these solar cells are often considered to be the ones with the best price-performance ratio. However, at around 15 percent, the efficiency is lower because less pure silicon is used.
3) Thin-film cells
This type is one of the amorphous, i.e. non-crystalline solar cells. The thin-film cells are also made of silicon, which is mixed with other materials and evaporated in a very thin layer onto a carrier material such as glass. The efficiency is only five to seven percent and must therefore be compensated for by a larger module area. Depending on the carrier material, the cells are very flexible and can even be rolled and folded. This means that in principle any shape can be realized. The production process is relatively straightforward, which means that large quantities can be produced on an industrial scale. This makes these cells cheaper than crystalline cells (thick-film cells).
The development of using crystalline organic semiconductors instead of crystalline semiconductors is relatively new. These are thin-film modules made from organic plastics. The term “organic” means that the molecules only contain carbon. The advantage is that they are cheap and easy to process and can be made in any shape. The efficiency of an organic solar (pv) cell is still low, but further research into the material can be further improved. The disadvantages associated with the low level of efficiency can be compensated for by the fact that the usable area is significantly larger than for crystalline solar cells. Because they can easily be glued to any wall, window, roof or even to any parasol.
What does a solar cell cost?
The cost of a solar (pv) cell always depends on the type and area chosen. Whichever type of solar cell and thus also the photovoltaic system you choose, the purchase is always associated with an investment. However, you can benefit from various funding programs such as a feed-in tariff or a cheap loan from banks.