A solar cell is an electrical component that converts light into electrical energy. The physical principle behind this is the photovoltaic effect. Several solar cells can be electrically connected to form a solar panel. The type of connection that is selected allows the electrical operating range (power and voltage) to be specifically tailored to the respective application of the solar panel.

Solar cells are made of various semiconductor materials. Semiconductors are substances that can conduct electricity when heat or light is added, and they also act as electrical insulation at low temperatures.



To produce a solar cell, the semiconductor material needs to be “doped”, i.e. chemical substances are specially inserted into the semiconductor; these then ensure either a positive (p-type semiconductor) or negative (n-type semiconductor) excess charge carrier. A so-called p-n-junction is created on the barrier layer. The special feature of this barrier layer is that a strong electrical field is created locally.

If light falls onto the semiconductor free positive and negative charge carriers are created due to the photoelectrical effect. If this process takes place close to the p-n-junction, the local electrical field ensures that the positive and negative charge carriers are separated from each other. These move toward the outer electrodes (contact fingers or reverse side contact) and generate current; the solar cell therefore works similar to a battery. If the electrodes are then connected to an electrical consumer, current flows.

The level of efficiency of a solar cell or solar panel is the ratio of the produced electrical energy to the irradiated light energy. Due to their inherent bandgap semiconductors can only absorb a part of the light spectrum and thus only a part of the sunlight. Its maximum theoretical level of efficiency is approx. 30 % compared to approx. 85% for multi band systems that make use of the whole light spectrum. The level of efficiency of a solar cell however is not a fixed number, it can change depending on the irradiation of the sun, the temperature and the electrical connection conditions of a solar cell. Due to the aging process, the level of efficiency will decrease slightly over time; manufacturers for example will provide warranties for at least 80 % of the initial energy yields after 20 years of use.

A further interesting factor is the energy payback which states how often a solar panel can recover the energy spent on its production during its service life. Assuming the service life is 30 years. The energy payback for mono-crystalline silicium panels is 5 to 8, for poly-crystalline silicium panels 7 to 14 and for thin-layer panel 9 to 21. Accordingly, an energy payback period can also be stated. This is the time which the solar panel requires to generate the energy spent on its own production.

The individual properties of a solar panel are described by characteristics. You can read here about how these characteristics can be interpreted.