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Fraunhofer claims 99.3% efficiency inverters for solar PV systems

Fraunhofer Institute for Solar Energy Systems (ISE) claims a record 99.3% efficiency for inverters used in solar photovoltaic (PV) systems.

“We now use junction field-effect transistors (JTEFs) made of silicon carbide (SiC) manufactured by SemiSouth Laboratories Inc. This is the main reason for the improvement,” says Professor Bruno Burger, leader of the Power Electronics Group at Fraunhofer ISE. “In addition, we have optimised the gate units and many other details of the circuit.”

The record was measured for a complete solar PV inverter including its internal power supply, a digital signal processor (DSP) for controls, an LCL grid filter and a relay for connection to the grid.

“I see enormous potential for the new silicon carbide transistors. They are constantly becoming better and less expensive, whereas the costs for passive components which contain significant amounts of copper and other metals are rising continuously,” Burger adds.

Fraunhofer ISE says it will do further tests of the solar PV inverter's components and adaptation of the circuits and switching frequencies to the new specifications.

Furthermore, the solar energy research institute says SiC transistors are “significantly better than the conventional IGBTs of silicon (Si) used commonly today, particularly for higher reverse voltages.” The main reason why SiC are better, is because of the breakdown field strength – it is 10 times higher for SiC than Si. The band gap is three times larger for SiC than for Si.

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Photovoltaics (PV)