Renewables

SiC and GaN cut system costs

WBG components reduce losses when generating renewable energy and cut system costs.

Renewable energy is on the advance worldwide: In 2019 alone, 176 GW of new electricity generating capacity was installed - and according to the International Renewable Energy Agency (IRENA) three quarters of it was from renewables. The cost of electricity from renewable energy sources has also fallen sharply over the last 10 years, thanks to improved technologies, economies of scale, increasingly competitive supply chains, and the growing experience base of developers. Utility-scale photovoltaic energy has seen the biggest cost reduction (82%) since 2010, for example, while the cost of onshore wind energy has fallen by 39%, and that from offshore wind by 29%.

Minimise energy loss

That trend is set to continue, with WBG power electronics playing an important role. After all, gallium nitride (GaN) and silicon carbide (SiC) semiconductor materials produce smaller, faster, more reliable energy systems than conventional silicon-based semiconductor components, and also work more effectively. In fact, these semiconductors can eliminate about 90% of the energy loss during power conversion. In the medium voltage range from 600 to 900 V where photovoltaic inverters operate, the application areas of SiC and GaN overlap. At higher voltages of 1.7 kV and above, as are reached by wind turbines, SiC power semiconductors are mainly used.

Cut system costs

Photovoltaic inverters featuring SiC power electronics suffer much lower switching losses and improve system efficiency. Using SiC components in photovoltaic inverters improves power density, minimises heat dissipation, and can also reduce the size of passive components. An example of this is the Sunny Highpower PEAK3 inverter from SMA Solar Technology: The silicon carbide-based solar inverter converts the direct current generated by the solar cells into grid-compatible alternating current with over 99% efficiency. Rated for 1500 Volt direct current, each unit outputs 150 kW of power. By comparison, the silicon-based predecessor model is rated for only 1,000 V DC and - at the same size and weight - outputs only 75 kW of power. The SiC modules virtually double the specific power output from 0.97 to 1.76 kW/kg. Thanks to their compact design, the inverters are much easier to transport and much quicker to install. So whereas the installer previously had to transport and install two converters, with the SiC inverters only one unit is now needed. Though SiC-based power semiconductors are more expensive than silicon solutions, the cost is more than balanced out at system level: Higher switching speeds and efficiency mean that transformers, capacitors, heat sinks - and ultimately also housings - can be configured smaller, so saving on system costs.

More efficient energy storage

WBG semiconductors provide more efficient solutions not only for renewable energy generation, but also for energy storage. Home storage systems, in particular, are crucial to reducing carbon emissions and stabilising power grids. To achieve this, however, they must also be optimised in terms of efficiency, cost and resource consumption. GaN power transistors enable the development of simpler and more efficient energy storage devices with as much as 50% less power loss.

One of the major challenges of home storage systems is that the batteries are charged within a few hours in intense sunlight and then discharged over a long period of time (overnight) at very low power (partial load). Consequently, battery inverters need high conversion efficiency over as wide a power range as possible. The Fraunhofer Institute for Solar Energy Systems ISE has developed highly efficient battery chargers for the purpose, including the key innovative control engineering. A core element was the development of compact and modular battery controllers using GaN and SiC components. The transistor bridge circuits form the core of the battery chargers, making it possible to switch at ever increasing speeds with lower losses. This was combined with an efficiency-optimised operational management system adapted to the power range. Simulations have shown that with such a system households can expect to make annual savings of 150 to 250 euros when purchasing electricity.