New transformerless solar inverters achieve 98 percent efficiency

This performance enables the plant operator to make a higher profit during infeed into the medium-voltage system. In addition, system costs can also be reduced with the option of a voltage window increased from 900 to 1000 volts.

In this case, for example, a number of photovoltaic (PV) modules are linked together as in a chain and fewer generator terminal boxes and smaller conductor areas are needed. The new inverter series also includes units with graduated ratings of 500, 1000 and 1500 kilowatts and also 2 megawatts, which is the most powerful transformerless inverter currently on the market. The new Sinvert inverters are suitable for applications in medium and large-scale PV power plants.

The new central inverter units satisfy the currently effective medium-voltage regulations and can be used either as a stand-alone solution or in combination. The master-slave principle with “rotating master”—introduced on the market by Siemens over ten years ago—is above all an advantage in the event of changing intensities of solar radiation in the course of the day or in case of cloudiness. Depending on the degree of radiation, the necessary inverters are energized or de-energized by means of an ingenious process.

This increases the efficiency of the PV plant, especially in partial-load operation. Only the required number of inverters is operated subject to light intensity. The connection of as many as four inverters in the form of a master-slave system enables the plant to start already at low levels of solar radiation and to achieve very high efficiencies even in the low output range.

The rotating master contributes to the long useful life of the system, for the inverter unit with the lowest operating hours is always controlled as master and therefore the operating time distributed uniformly among the inverters.