Study finds EV use-phase fuel savings exceed marginal increase in energy demand for WBG semiconductor manufacturing by 2 orders of magnitude
Power electronics semiconductors, which manage voltage and current, are a key technology for enabling improvements in “fuel economy” in electric vehicles. While conventional silicon-based semiconductor technology currently owns the plug-in vehicle power electronics market, emerging wide band gap (WBG) semiconductors offer significantly greater energy efficiency potential than silicon.
A team from Oak Ridge National Laboratory, Argonne National Laboratory, Northwestern University and the US Department of Energy (DOE) has now estimated the potential energy benefits in electric vehicles for two leading WBG semiconductor architectures—silicon carbide (SiC) and gallium nitride (GaN)—and compared those with conventional silicon. Their paper is published in the ACS journal Environmental Science & Technology.
Numerous life cycle studies indicate that well-to-wheel (WTW) greenhouse gas (GHG) emissions of electric vehicles would depend on the fossil content of the electricity mix. Compared to conventional internal combustion engine vehicles, WTW GHG emissions could decrease by 80% if electric vehicles use renewable electricity. It has been estimated that an 80% domestic GHG reduction could only be achieved at a relatively high rate of electrification (40% of miles and 26% by fuel), with significant quantities of low-carbon liquid fuel in cases with low or moderate travel demand growth. However, a widespread adoption of EVs is found to be an unwise strategy given the existing and near-future marginal electricity generation mix in several US states.
The use of WBG semiconductors in electric vehicles rather focuses on the fuel economy improvements, resulting in additional benefits during the vehicle life cycle use stage. In terms of WBG life cycle energy, most studies to date have focused on use phase savings potential over incumbent technologies. … A data gap exists in that relatively few studies have investigated the energy impacts of the raw material acquisition and part production life cycle stages of WBG semiconductors, even with conventional Si semiconductors.
… In this paper, materials and manufacturing energy estimates for SiC and GaN are developed and compared with use phase savings potential in electric vehicles versus conventional Si. Results are interpreted within the context of the market substitution potential of these WBG semiconductors in place of conventional Si over time in the United States light-duty vehicle fleet.—Warren et al.
The team developed a cumulative energy demand (CED) estimate of the materials and manufacturing life cycle stages for two WBG architectures: SiC device on SiC substrate (SiC/SiC) and GaN device on silicon substrate (GaN/Si). The former is the most mature WBG technology, while the latter has significant low cost potential and can be used at relatively higher frequencies of 0.5−3 MHz.
In addition to the cradle-to-gate CED analysis of WBG devices, the team developed use-phase deployment scenarios of WBG devices within the US light-duty vehicle (LDV) fleet to estimate the potential use-phase impacts from WBG semiconductors. One market cases was derived from the DOE-EIA Annual Energy Outlook (AEO) with modest penetration of alternative vehicles; the second was derived from the DOE’s Transportation Energy Futures (TEF) study with aggressive penetration of alternative vehicles.
Among their findings were:
Compared with Si/Si, SiC/SiC is more than 2.5 times as energy intensive in the materials and manufacturing phase on a per cm2 basis. The magnitude of vehicle use phase fuel savings potential is comparatively several orders of magnitude higher than the marginal increase in cradle-to-gate energy.
GaN/Si is nearly equivalent with Si/Si in the materials and manufacturing phase, with use phase savings potential similar to or exceeding that of silicon carbide.
The energy savings achievable in the use phase will be dependent on the market adoption of both alternative vehicles (i.e., HEV, PHEV, and BEV) and WBG power electronics in them. Cumulative energy savings associated with the technical potential of WBG were estimated to be 0.3% (2 billion GJ) for the AEO case and 4.2% (20 billion GJ) for the TEF case.
Adoption of WBG power electronics may be constrained by their cost and reliability. For cost-sensitive scenarios in which WBG power electronics reach cost parity with Si counterparts in 2020 and 2030, the cumulative energy savings for the TEF vehicle market case decline to 13 billion GJ and 5 billion GJ, respectively.
[An] important implication of this finding is that, for SiC/SiC, an increase of energy use in the semiconductor manufacturing industry will be required for power electronics in order to save many times more energy in the transportation sector. As industries continuously seek to reduce their energy use, the WBG example presented here underscores the need to consider a life cycle perspective when evaluating new manufacturing technologies so that innovations saving energy elsewhere are not discouraged.—Warren et al.
Joshua A. Warren, Matthew E. Riddle, Diane J. Graziano, Sujit Das, Venkata K. K. Upadhyayula, Eric Masanet, and Joe Cresko (2015) “Energy Impacts of Wide Band Gap Semiconductors in US Light-Duty Electric Vehicle Fleet” Environmental Science & Technology doi: 10.1021/acs.est.5b01627