Grid-connected Inverters for PV Systems

A grid-connected power inverter, or simply inverter, is the core of any photovoltaic (PV) system to produce solar power from sunlight. PV systems usually produce direct current. However, alternating current is required to feed into the public grid and to operate most electrical appliances. A power inverter converts direct current solar power from the photovoltaic system into alternating current.

For grid-connected photovoltaic systems, we have PV power inverters from the following brand manufacturers in our range: AEG Industrial Solar, Fronius, SMA, KOSTAL and SAJ. All the solar power inverters we offer have a maximum efficiency for long-term high yields. This applies to both single-phase and three-phase inverters, with and without transformers.

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What power inverters are used for

The DC voltage of the solar energy is characterized by a constant strength and direction. Alternating voltage, however, is sinusoidal. To convert the direct voltage of the PV into alternating voltage, a process called “pulse width modulation” is used. In this process, the direct voltage is “chopped up” and partially turned in its direction. The pulses resulting from the chopping are then averaged and filtered. This is done with the help of complex electronic circuits. As a result, you get alternating voltage at a frequency of 50 Hz.

What tasks does the device perform?

The PV inverter is not only used to produce alternating current from solar power. Another important component of the device is MPP tracking. MPP is the abbreviation for Maximum Power Point. The electrical properties of a PV system change with the strength and direction of solar radiation and temperature. MPP tracking ensures that the system always operates in optimum range. It is therefore essential for the efficiency of the PV system. The solar energy is never 100% converted into electricity. Today’s common efficiency of PV systems is between 98% and 99%.

What types of inverters are there?

These are the classifications for inverters:

  • Single-phase:

    In single-phase devices, the solar energy is converted into electricity through a single power line. Therefore, single-phase devices usually have a lower output. On the other hand, they require fewer components, which makes them more affordable.

  • Three-phase:

    In three-phase devices, electricity is transported via three lines. By that it is possible to reach higher outputs, without using expensive, ultra-high quality electronics that would be necessary to achieve the same output with a single-phase solution. For this reason, devices with power ratings above 5 kW typically use a three-phase approach.

  • Module inverter:

    For this approach, each module of the PV system has its own solar inverter. Compared to the other devices, it is rather expensive but offers some key advantages. With module inverters, each module of the PV system can be controlled individually. This is useful, for example, in case of a fault. Since module inverters generally do not produce any reactive power, they are only approved for systems with limited capacity.

  • String inverters:

    Groups of solar modules are connected by strings, which are connected to a single inverter. String inverters are used for larger photovoltaic systems. They can feed the current in one or three phases, as they produce both active and reactive power.

  • Central inverters:

    These are devices for large commercial photovoltaic systems. More than 12 strings can be connected to them.

  • Hybrid inverter:

    It is the combination of a PV inverter and a battery inverter. This results in a greater security of power supply.

  • Battery inverters:

    They are installed in AC-coupled systems to charge batteries.

What’s important when choosing an inverter?

If possible, a photovoltaic system should be installed with an inclination of 35° to the south. This ensures the best yield of solar power. However, the choice of the right solar inverter is also decisive for the performance of the system. The rated output of the solar system can be up to 10% higher than the rated output of the solar power inverter. For higher gaps, part of the solar energy cannot be converted and is therefore lost. It is also important that the maximum DC voltage of the PV system never exceeds the permissible input voltage of the solar rectifier.