A solar inverter has the important task of converting the direct current generated in the solar modules into alternating current and making it usable for the public power grid. It is, therefore, an indispensable part of the photovoltaic system: the operation of electronic devices with solar energy is only possible by means of current conversion.

Inverters have an input side (for direct current, abbreviation: DC), which has one or more DC controllers with MPP tracker that are controlled by a microprocessor. In the next stage, the actual transformation of the energy takes place in the form of alternating current (abbreviation: AC), which is subsequently passed on to the output side. From there, it is stored in the power grid. Inverters are available in various versions. Nowadays, there are models with or without a transformer. However, modern inverters often have no transformer and thus have higher efficiency. In addition, a distinction is made between three different inverters for photovoltaic plants. These are briefly described and explained below in more detail.

Solar inverters: models and versions

Inverters for photovoltaic plants must meet a number of requirements in order to profit economically in the long term. Modern models are quickly and flexibly adapted to the amount of solar energy generated, e.g. variations in cloud cover and weather changes. The solar inverter should achieve its highest efficiency both at high and low input voltages. Depending on the size and location of the photovoltaic system, the respective inverters, therefore, have different characteristics. The inverter should always be matched to the photovoltaic system in a manner appropriate to the needs of the customer.

Module inverters

This type of solar inverter is connected directly to the respective solar module. Each solar module thus has its own inverter. Module inverters are used mainly for small solar systems or for solar systems with different orientations of the solar modules.

String inverters

Several solar modules are interconnected in series and form a strand (or string). A string inverter thus connects a whole series of connected photovoltaic modules to the public power grid. This form is now widely used as it offers a wide range of applications and a good price/performance ratio. String inverters are suitable for small household systems as well as for large free-standing systems.

Central inverters

As a rule, a central inverter is only used for large and very large photovoltaic plants. A large number of solar modules can be connected to it. Central inverters have high efficiency and are therefore particularly efficient. The disadvantage: if a fault occurs, the operation of all solar modules is affected and large losses of output occur.

Solar inverters and MPP tracking

If you are looking for a powerful solar inverter, do not miss out on the MPP tracking. MPP stands for "Maximum PowerPoint" and indicates the point at which a solar module performs its highest performance. This depends on the solar radiation, the temperature and the individual properties of the solar module. MPP tracking is, therefore, a matter of continually recording the performance of the photovoltaic module and adapting it to the respective circumstances. The MPP Tracker ensures that the maximum amount of energy is always produced. It is controlled by a microcontroller, in which a certain setpoint is pre-determined. Due to the importance of MPP tracking for photovoltaic systems, modern solar inverters often have more than one MPP tracker.

The solar inverter and its efficiency

The efficiency of the solar inverter is of central importance for a photovoltaic system. It provides information about the maximum energy conversion of the entire plant and decides decisively on its yield and the associated profitability. The level of efficiency is dependent upon many factors, e.g. the solar radiation, and the location of the PV system and the system configuration. The solar inverter, therefore, does not always provide its full power and the same device can have a different efficiency at different locations. In order to make the equipment comparable, the "European Efficiency" was introduced some years ago. This represents an average of the efficiencies at different partial capacities (5, 10, 20, 30, 50 and 100 per cent of the maximum power). The weighting of this value takes place taking into account average European temperature and weather fluctuations.

Where should the solar inverter be connected?

Several factors play a role in the choice of the correct placement of the solar inverter. In principle, it should be protected from wind and weather, which is why installation is in the interior of the home, e.g. in the basement or the garage. And even then there are further specifications: Among other things, the ambient temperature is crucial for the installation of the solar inverter. In the case of the conversion from direct current to alternating current, losses occur which are emitted in the form of heat to the environment. In warm rooms, the heat cannot be dissipated correctly through the air. The high temperatures influence the life of the device and its electrical components. Close proximity to the ceiling or other inverters can also limit heat dissipation. Fixed minimum distances should ensure safe operation of the equipment. Another factor that should be taken into account during assembly is the noise level generated during the transformation. Although modern solar inverters usually operate very quietly, there may be occasional buzzing or clicking noises at high power. For this reason, it is advisable not to install the unit in the immediate vicinity of the living rooms. Last but not least, the distance to the feed-in counter is of particular importance in the case of string inverters. In principle, the installation of an inverter should only be carried out by people with professional knowledge.

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