"Power electronics is the key technology that connects everything."

Expert Interview – April 26, 2024

Dr. Sönke Rogalla, , Head of the Power Electronics and Grid Integration Department at Fraunhofer ISE

With the expansion of renewable energies, power electronics is increasingly taking center stage. Power converters efficiently connect virtually all energy transition technologies.

They are increasingly taking on grid-forming functions and thus ensuring the stability of our electricity grids. The market for grid-forming inverters and other new applications will therefore grow dynamically in the coming years.

Dr. Sönke Rogalla, Head of the Power Electronics and Grid Integration Department at Fraunhofer ISE in Freiburg, explains the exciting trends in technology development and application.

What role do power electronics currently play in the energy transition?

Power electronics is the key technology for all energy transition technologies, from wind and PV generation to energy storage in batteries and hydrogen, heat pumps and charging infrastructure. In the decarbonized energy system of the future, we will need much more power electronics at all system levels than we do today.

What are the new functionalities and tasks of power electronics?

It will increasingly fulfill intelligent functions: While inverters had to convert DC into AC as efficiently as possible in the past, they are increasingly becoming a system-controlling element. We have been seeing this in the residential sector for several years now.

PV hybrid inverters control and optimize the energy flow between PV generation and battery storage. Charging options for electric cars are also increasingly being integrated and heat pumps will certainly also be integrated in the future.

On a small scale, we can clearly observe the trend towards electrification. Power electronics enable us to use locally generated energy locally. This only works with efficient, multifunctional power converters.

What developments on the technology side were necessary for power electronics to be able to fulfill this role at all?

Over the past ten years, wide-bandgap semiconductor switches based on silicon carbide and gallium nitride have been developed and are now increasingly being used in commercially available devices. These allow significantly faster and more efficient switching and therefore smaller filter components, which in turn leads to savings in resources and costs.

I would like to illustrate the enormous improvement in power density with an example: A casing that was needed 15 years ago to house a 30 kW inverter can now house a 300 kW inverter. The power density has increased tenfold in this time.

Where do you currently see the most important technology trends in terms of applications?

More and more solutions are being integrated and electrified, whether this is the charging infrastructure or the heat pump. This hybridization, which we are already experiencing at residential level - as just described - is continuing in the commercial & industrial sector.

The aim is to supply a wide range of industrial processes with as much of their own electricity as possible while at the same time being as grid-friendly as possible. Controllable loads have even greater potential. Converters are required between all these elements. Finally, we will also see a strong hybridization of so-called utility-scale systems, e.g. large-scale PV power plants.

We are still at the beginning here. But grid connection points will become increasingly rare. That is why we will try to operate PV, wind, storage, electrolysis, fast charging infrastructure, etc. at shared grid connection points wherever possible. And you guessed it: everything will be connected by power electronics.

To what extent will power electronics then also influence the electricity grids?

That's a very exciting topic. Over the next ten years, we will see a fundamental change in technology thanks to grid-forming inverters. Until now, inverters have been programmed to feed the available current into the grid. T

o do this, they must first synchronize with the grid frequency. However, grid voltage and grid frequency are still regulated by the rotating generators of large power plants. But what happens when conventional power plants are no longer connected to the grid for long periods of the year?

This is where grid-forming inverters come into play. They are controlled in such a way that they can regulate the grid voltage and frequency in a similar way to synchronous generators.

Research has made very good progress in this area in recent years. We have been able to prove in large-scale laboratory tests that it is possible to operate a stable interconnected grid using only inverters. The time is now ripe for the technology roll-out of grid-forming converters. We will see exciting markets for this in the near future.

In particular, there will be additional revenue models for large-scale battery storage systems in the short term. In the medium term, grid-forming will also become an issue for other technologies, as around half of all inverters will have to be grid-forming over the next decade in order to ensure stable grid operation.

How will the power electronics market develop in the context of the energy transition?

The energy transition technologies like wind power, photovoltaics, battery storage, electrolysis, heat pumps, electromobility and converters for grid applications are all enormous growth markets.

None of these technologies work without power electronics. By 2045, we will have around 1 terawatt of power electronics connected to the grid in Germany. If we look at the global demand, we are talking about enormous quantities.

What kind of challenges does this bring with it in terms of resources?

For me, two things are crucial in view of the huge demand. Firstly, the need for materials: We can no longer afford to think in linear terms but must manage to use the materials in a cycle.

Design for repairability and recyclability will become a much more important part of the power electronics design process.

The second point is the increase in system voltages according to the simple formula: Higher voltage - lower current - smaller cable cross-sections - less copper!

The time seems ripe for power electronics to move into the medium-voltage range above 1,500 V, particularly for high-performance applications such as PV battery power plants or fast-charging infrastructure for heavy-duty vehicles.

This will save costs and materials in the future. It is no coincidence that we at Fraunhofer ISE will soon be launching the key topic "Medium Voltage" in order to highlight research and development activities in this future field.

Event information:

The seminar Power Electronics for PV, Batteries and EVs is taking place for the 17th time. It is aimed at developers of power electronics, but also at people who want to better understand current power electronics trends.

The intensive course will take place on June 17 – 18 in the run-up to Intersolar Europa at the Novotel Messe München.

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