What are solar modules?
Solar modules also referred to as solar panels or PV modules are an elementary component of photovoltaic systems. They have the task to transform incident solar rays into electrical energy. In order to achieve this, solar modules are made up of several layers. Inside the panel are the solar cells. In each solar cell is a semiconductor, which is responsible for the conversion of sunlight into usable energy. Semiconductors have substances that develop electrical conductivity in light and heat, whilst having an insulating effect during cold weather. The semiconductors used in solar cells are doped differently. That is, various chemical elements have been added to them so that they are either positively or negatively charged. One speaks of p-type semiconductor layers and n-type semiconductor layers. If two differently charged semiconductor layers meet, a so-called p-n junction is formed at the interface. Here an inner electric field is formed. In the case of solar radiation, an electrical voltage is produced and delivered to connected consumer devices.
On the cell, the layer is a layer of EVA (ethylene vinyl acetate) or cast resin. It protects the sensitive semiconductor against weathering, moisture and corrosion. There is also a protective layer below the solar module. This stabilizes the module structure and prevents stored heat loss. In order for the solar energy to be efficiently used, at least one of these layers must be slightly-permeable. A special solar glass plate is installed on top of the EVA layer. In order to achieve efficient energy production, these special requirements must be met: The glass must be thick enough to withstand wind and weather effects, and at the same time the incident light must not be absorbed and stored by the panel itself.
How are solar modules manufactured?
The production of solar modules and solar cells are based on the synthesis of silicon. Silicon is a component of sand or quartz and is, therefore, one of the most abundant substances on earth. With a degree of purity of well over 90 per cent, silicon is considered a particularly pure substance. There are basically three types of solar modules: monocrystalline solar modules, polycrystalline solar modules and amorphous solar modules. These are different cell types and their differences can be traced back to the respective production methods.
Monocrystalline solar modules
In order to produce monocrystalline solar cells, the silicon oxide, which naturally occurs in the sand, is chemically reduced by the addition of carbon. This process takes place in a so-called arc furnace at a temperature of about 1.410 degrees Celsius. The result of this melt is a thin crystal rod, which is also referred to as a single crystal or monocrystal. The monocrystal is cut into very thin slices: with a thickness of 0.4 micrometres, the square slices are thinner than a human hair. The cut plate is called a "Wafer". After the wafer has been chemically cleaned, the doping takes place: At temperatures of 800 to 1,000 degrees Celsius, silicon atoms are replaced by atoms with a different valence. This increases the conductivity and thus the efficiency of the wafer.
Monocrystals are easily recognizable due to their dark appearance and rounded corners and have a particularly high efficiency due to their purity. Under ideal conditions, this can be about 20 per cent. Critics criticize the high energy expenditure required by the production of monocrystalline solar cells. Only after several years, such photovoltaic modules have a positive energy balance.
Polycrystalline solar modules
Polycrystalline solar cells are an alternative to monocrystals that are associated with a less complex production. In this method, liquid silicon is poured into prefabricated blocks and then sawn into individual wafers. Here, they lose their single crystal structure, which is why they are significantly brighter than monocrystalline. Their efficiency is slightly lower at about 15 per cent, but the simplified production process improves the energy balance and costs of manufacture.
Amorphous solar modules
Amorphous solar cells are the most favourable variant. For their production, liquid silicon is evaporated onto a carrier material (e.g. glass). As a result, hardly any material is lost, and production and energy costs are comparatively low. The cells have an efficiency of about seven per cent and are often found in pocket calculators and clocks.
From cell to solar module
For manufacturing a PV module, up to ten wafers are soldered with a copper ribbon. A so-called "string" is created. In order to achieve high performance, the individual solar cells should have the same properties. After the assembly, the cells receive the protective layer and the characteristic blue antireflection layer. At around 900 degrees Celsius, the cells are provided with contact strips from above and from below. These later ensure that electricity can flow. Once the solar module has been provided with an aluminium frame, a power test is carried out. On the basis of the results, the performance of the solar panel can then be classified before it is sold.
Which solar module is suitable for my roof?
There are several factors to consider when choosing a photovoltaic module. In principle, it should be checked before the installation whether the roof is sufficiently load-bearing. A solar module weighs up to 20 kilograms, whereas monocrystalline and polycrystalline solar modules are generally heavier than amorphous cells. The different efficiencies of the respective modules have already been addressed. With their high efficiency, monocrystalline solar modules are particularly suitable for installations in which a large amount of electricity needs to be generated or for small roof surfaces. This should at best be oriented towards the south, in order to ensure ideal exposure to the sun. If this is not the case, there is a loss of power generation, H. Sun energy is lost. This risk is greater for monocrystalline solar modules than for polycrystals, which also function fully in the case of diffused solar radiation. In addition, polycrystalline solar modules are more cost-effective and have a high life expectancy of up to 30 years. They are therefore particularly suitable for the long-term production of solar power.