Solar module

A solar module consists of several solar cells that convert sunlight into electricity. The main component of solar cells is a semiconductor material, usually silicon. Semiconductors are materials that cannot be assigned to the group of isolators or conductors and whose electrical properties can be altered by the deliberate, controlled introduction of impurities (doping). The solar cell consists of two adjacent semiconductor layers which feature separate metal contacts. These have each been doped in such a way, that an n-layer (n=negative) with an excess of electrons and an underlying p-layer (p=positive) with a shortage of electrons has emerged. Due to the concentration gradient, electrons diffuse from the n- to the p-layer. As a result, an electric field is formed inside this semiconductor structure, the so-called depletion zone.

In a solar cell, the upper n-layer is very thin. Therefore, the photons of the incident sunlight can penetrate the layer and transfer its charge to an electron in the depletion zone. The excited electron is mobile, follows the internal electric field and thus moves from the depletion zone to the metal contacts of the n-layer. When a consumer is connected, the circuit is closed: The electrons flow through the consumer to the back-side contact of the solar cell and finally to the depletion zone.

More than 95 percent of all solar cells produced worldwide are made of the semiconductor material silicon (Si). As the second most abundant element in the Earth’s crust, it is available in sufficient quantities. Moreover, the processing of the material can be environmentally friendly. Depending on the type of crystal, there are three different cell types: monocrystalline, polycrystalline and amorphous.

The different cell types differ in their manufacturing costs and efficiency. The efficiency of amorphous cells (thin-film cells) is lower than of the other two cell types; however, due to the less complex manufacturing process, they are less expensive.

Efficiency is generally defined as the ratio between output and input power. The output power can never exceed the input power. As a result, efficiency levels can never be higher than 1 (instead of performance, you can also calculate the ratio of energy absorbed and emitted). In solar power generation, one differentiates between cell, module and system efficiency. In commercial mass production, a cell efficiency of up to 20 percent is currently reached, depending on the technology used.

The module efficiency refers to the entire surface of a module and is therefore always slightly lower than the cell efficiency. This is due, among other things, to the non-useable gaps between the strung solar cells in the module. In addition, the inverter converts the direct current of the solar generator into alternating current with a certain efficiency. Two partial efficiencies play a role: the conversion and dynamic tracking efficiency, which reflects the precision and speed of the MPP tracking. High-end devices now reach a total efficiency of up to 99 percent.

The system efficiency refers to the complete photovoltaic system. In relation to the modules and inverter efficiency, a further drop is recorded here, which is due to transmission losses, e. g. by cable.

Monocrystalline as well as polycrystalline modules are made of silicon. In the case of polycrystalline modules, however, the silicon is less pure. As a result, the material takes on the typical bluish crystalline structure, as soon as it is cooled down. Due to the lower cost of the material and the production, polycrystalline modules are slightly cheaper than monocrystalline modules. By contrast, these have a higher power output and a better efficiency.

PV modules do not only use the direct sunlight, but also diffuse light irradiation when it is cloudy. The brighter it is outside, the higher is the performance of the modules. In Central Europe, the share of diffuse irradiation accounts for nearly 50 percent.

The reasons for a loss of power in a solar electric systems can be manifold: For example, the modules may be soiled, there may be a defect in one or more components or the modules may be shaded by a tree or neighboring buildings. A professional will identify the reason for the loss of power and find a solution.

Outdated modules can often be replaced by newer modules. However, technical and optical aspects should be taken into account. As far as electrical considerations are concerned, the system design with the inverter should be checked, in particular. We will be happy to help you with further questions.

It is not mandatory to ground modules. The mounting frame, like all metal structures and facilities of a building, is connected to the potential equalisation.

With proper and regular maintenance, photovoltaic modules have a very long lifespan. This becomes apparent when you have a look at the voluntary manufacturer warranties of up to 30 years.

The proper maintenance differs from one plant to another. Most importantly, plug connections, insulation and other exposed parts should be checked. In addition, a regular visual inspection for external damage as well as a cleaning of particularly soiled modules is recommended.