World’s ‘1st’ Medium-Voltage String Inverter

• Fraunhofer ISE has launched what it terms is the world's first medium-voltage string inverter 
• It promises an output voltage of 1,500 V at 250 kVA using silicon carbide semiconductors 
• The team claims it can significantly bring down the use of copper by reducing the length of cables required compared to existing modern PV string inverters 
• It is now seeking solar developers and grid operators to test the same in the field 

German solar PV research institute Fraunhofer Institute for Solar Energy Systems ISE has commissioned an in-house developed medium-voltage string inverter for large-scale power plants, calling it the world's 1st. It can be used for solar PV as well as wind energy projects, electric mobility and industrial applications. 

Currently, modern PV string inverters have an output voltage between 400 VAC and 800 VAC; however, their voltage hasn't yet increased in keeping with the output of power plants that has been steadily going up, explains Fraunhofer ISE. 

It attributes this to the challenge of building an efficient and compact silicon semiconductor-based inverter. Additionally, it says there are no PV-specific standards that cover only the low voltage range (max. 1,500 VDC/ 1,000 VAC). 

Developed under the MS-LeiKra project, Fraunhofer ISE's medium-voltage inverter enables the output voltage to be increased to the medium-voltage range of 1,500 V at 250 kVA, using silicon carbide semiconductors with a higher blocking voltage.  

By increasing the voltage to 1,500 VAC, the cable cross-section can be reduced to 35 mm², thus reducing copper consumption by around 700 kilograms/km. of cable. 

In comparison, an average photovoltaic power plant requires dozens of kilometers of copper cables. For an output voltage of 800 VAC, a 250 kVA string inverter requires cables with a minimum cross-section of 120 mm². Hence, increasing the voltage generates significant savings potential. 

"Our resource analyses show that in the medium term, the electrification of the energy system will lead to copper becoming scarce. Increasing the voltage allows us to save valuable resources," added Director of Fraunhofer ISE Prof. Dr. Andreas Bett.  

Developed in collaboration with Siemens and Sumida, the product also uses a cooling concept using heat pipes, thus reducing the amount of aluminum. This makes it more efficient, it adds.  

Since there are currently no PV standards for this range, the team said it is also working on the standards that would result from increasing the voltage. 

Fraunhofer ISE is now looking for solar farm developers and grid operators to test the inverter concept in the field.