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Wolfspeed, BPEI study uses ESOI analysis to show energy efficiency superiority of SiC in EVs

The Biophysical Economics Institute (BPEI), a non-profit organization dedicated to bringing the natural sciences into economic analysis and decision making, has partnered with Hedgerow Analysis to evaluate the implementation of SiC chips in electric vehicle usage on behalf of silicon carbide technology leader Wolfspeed, Inc.

Specifically, the study estimated the net energy return of silicon carbide (SiC) Metal Organic Semiconductor Field Effect Transistors (MOSFETs) as compared to silicon-based Insulated Gate Bi-Polar Transistors (IGBTs).

Silicon Carbide (SiC) microchips present an important test case of energy efficiency. Combining two crystal structures into a single compound produces unique properties relative to conventional chips and SiC promises increased energy efficiency across a multitude of potential applications. However, SiC chips are more energy-intensive to produce than silicon, leaving open the question of which promotes greater energy energy efficiency over the long run.


The study uses BPEI’s proprietary Energy Saved on Energy Invested (ESOI) metric, defined as the ratio of energy conserved over a product’s life cycle vs. the incremental energy required to produce that product. By quantifying the “lifecycle energy return on energy invested,” ESOI provides an apples-to-apples comparison of alternative energy-saving technologies.

ESOI can be maximized either by increasing the numerator (the energy saved via a product’s use) or by decreasing the denominator (the marginal energy required to make the product). The electric car study investigated both.

BPEI first estimated the energy required to manufacture silicon carbide vs. traditional silicon chips, and then evaluated EV energy consumption, using each type of chip, over a lifetime of use. The analysis, which utilized SimaPro software, quantified every significant energy input (and its associated CO2-equivalent emissions) in the production of each device.

Estimating the energy consumption of each EV type requires technical modeling of vehicle efficiency over selected test cycles, such as the Worldwide Harmonized Test Cycle (WLTC) for personal light-duty vehicles, and other models for different vehicle use cases. The modeling accounted for vehicle-specific parameters such as weight and drag.

The ESOI analysis quantified thousands of environmental and energy flows across entire lifecycles of silicon and silicon carbide chip-powered vehicles, involving dozens of energy production vs. consumption model iterations, and supporting statistical analysis. These analyses were buttressed by a survey of dozens of peer-reviewed articles, and hours of discussion with academic and industry experts.

The study estimated that, over a 200,000-mile estimated lifetime of personal EV use, the replacement of silicon insulated-gate bipolar transistors (IGBTs) with silicon carbide metal-oxide semiconductor field effect transistors (MOSFETs) produces energy savings that are many times greater than the incremental energy required to produce the silicon carbide devices.

The ESOI for a 400V SiC vehicle application is approximately 7:1 for a typical personal EV sedan (400V silicon carbide MOSFET vs. 400V silicon IGBT) and 13:1 for an 800V implementation (800V silicon carbide MOSFET vs. 400V silicon IGBT). That’s an 85% increase vs. the 400V silicon carbide MOSFET, due to reduced chip surface area and corresponding energy invested.

The ESOI gain is even greater for fleet vehicles, such as taxis and delivery vans, with higher duty cycles and 500,000 estimated lifetime miles.

The analysis also underscored the potential for large fuel savings based on intelligent location of manufacturing hubs. Wolfspeed’s operations in upstate New York, which offers ample clean energy via hydroelectric power, has the potential to increase the ESOI of SiC technology up to 28% by reducing the primary fossil energy (and CO2 emissions) needed to generate electricity.

We believe the next generation in power semiconductor technology will be driven by silicon carbide. These study results reinforce the superiority of silicon carbide and the direct impact a more energy-efficient technology has on the reduction of carbon emissions, which has a positive impact on the environment. As the world shifts to a more sustainable future, it will need efficient materials to power it.

—John Palmour, chief technology officer at Wolfspeed


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