What is the use of an inverter

Inverters for photovoltaics - areas of application and selection criteria

In addition to the solar module in which the actual power generation takes place, a photovoltaic system also includes a so-called solar inverter. This converts the direct current generated in the solar module into alternating current and makes it usable in the first place. Solaranlage.de offers you extensive information on the subject of photovoltaic inverters.

Why is an inverter (photovoltaic) needed?

Inverters are also called inverters and, together with rectifiers and converters, belong to the group of power converters. These use electronic components such as transistors or diodes to convert one form of electrical current into another. In the case of inverters (photovoltaics), direct current is converted into alternating current. This is necessary in connection with photovoltaic systems insofar as direct current is generated in the solar modules, while the public power grid and devices connected to it use alternating current. In order to feed the self-generated solar power into the public grid or to use it in your own household, a conversion by an inverter is necessary. Solar inverters are already part of the photovoltaic system and have a DC power controller on the input side, which controls the maximum power point tracker by means of a microprocessor and feeds the intermediate circuit. On the output side, a one- to three-phase inverter feeds the generated electricity into the medium-voltage network. Depending on whether it is a closed island system or a connection to the public power grid, the feed-in must be self-controlled or externally controlled.

Are you looking for a photovoltaic system? Find a photovoltaic systemCompare several offers from specialist dealers

Types of inverters in the field of photovoltaics

In terms of control, a distinction is made between two types of inverters:

  • Self-commutated inverters (for stand-alone systems)
  • Third-party or grid-commutated inverters (for feeding into the public grid)

Self-commutated inverters work independently of an external power grid and are therefore suitable for stand-alone systems that are not integrated into the public power grid. In contrast to line-commutated inverters, they generate their own AC voltage with their own clock frequency and can therefore be equipped with self-deactivating valves such as transistors and IGBTs. In the case of photovoltaic systems that feed electricity into the public grid, however, the clock frequency must be synchronized. Externally controlled inverters are required for this, which draw what is known as a commutation reactive power and are dependent on a fixed alternating voltage in the grid. As a rule, they use valves that cannot be switched off automatically, such as diodes, thyristors or triacs.

When choosing the inverter, the type and size of the photovoltaic system also play a role in addition to the shape of the power grid. The following inverters are used in the field of photovoltaics:

  • Module inverter
  • String inverter
  • Central inverter
  • Hybrid inverter
Are you looking for a photovoltaic system? Find a photovoltaic systemCompare several offers from specialist dealers

With the modular inverter, each individual solar module has its own single-phase inverter. Since no direct current cabling of the modules is necessary, the use of module inverters is particularly useful for photovoltaic systems that consist of differently oriented or shaded subfields (e.g. cars or airplanes coated with solar modules). String inverters are used when the current of one or more strings of solar modules is to be fed into the grid. Depending on the number of strings, they have single or three-phase inverters. Central inverters are used for very large systems (outputs from 100 kWp). Hybrid inverters, on the other hand, are a combination of inverters and storage batteries. These enable an uninterruptible power supply and optimize self-consumption.

Criteria for choosing the right inverter

When choosing the right photovoltaic inverter, the shape and size of the system play a decisive role. With regard to the amount of electricity actually produced, it should also be ensured that the capacity of the inverter is optimally filled. Of course, quality also plays an important role. Efficiency is an important quality criterion. This relates to the loss that occurs during the conversion: the currently best inverters feed around 97% of the electricity produced into the power grid, worse versions correspondingly less.

Are you looking for a photovoltaic system? Find a photovoltaic systemCompare several offers from specialist dealers

Installation of a solar inverter

Photovoltaic inverters are usually installed near the solar modules in order to avoid losses due to long cables and additional interconnections. In the case of modular inverters, it is usually already integrated in the junction box. Otherwise, inverters are often installed in the basement or - in the case of roof systems - under the roof. Due to the noises during power conversion, care should be taken that the inverter is not too close to the living area.