Georgia Tech study suggests unlinking EVs from CAFE and coordinating with power sector for low-cost benefits
8 September 2013
A team from Georgia Tech suggests, based on their modeling of electric vehicle (EV) adoption scenarios in each of six regions of the Eastern Interconnection (containing 70% of the US population), that coordinating EV adoption with the adoption of controlled EV charging, unlinking EVs from consideration in the CAFE fuel economy regulations; and implementing renewable electricity standards would deliver low-cost reductions in emissions and gasoline usage. (For the study, they define EVs as including both battery-electric (BEV) and plug-in hybrid electric (PHEV) vehicles.
Only in the case of high EV market share and a high renewable electricity standard (RES) do EVs make a material contribution to greenhouse gas (GHG) reductions, they found. However, managed EV adoption can reduce the cost of achieving GHG reductions through a RES, they concluded in their paper published in the ACS journal Environmental Science & Technology.
Specifically, they found that a scenario combining 100% EV new vehicle market share by 2025; a 33% renewable electricity standard (RES); controlled charging for EVs; and unlinking EVs from fuel economy requirements would reduce in 2030 combined electric- and vehicle-sector CO2 emissions by 27% and reduce gasoline consumption by 59% at a cost as low as $40/vehicle-year more than the reference case.
The controlled charging of EVs can reduce electricity costs and improve the integration of wind energy. The benefit per average vehicle is small at low to moderate EV adoption levels because EVs are a small fraction of the fleet. However, the cost benefit of controllability is significant at all EV adoption levels on a per EV basis. The main cost saving is from reduced electric system capacity requirements rather than switching to generation with lower marginal costs.
EV adoption links the electricity system with the transportation system. Understanding these linkages provides a basis for developing energy strategies with consideration of cost, technology, and policy goals.—Choi et al.
In their study, they considered the aggregate implications of EV adoption, fuel economy policy, EV charging methods, and renewable electricity standards (RESs). They simultaneously considered all factors that have been explored singly or in limited combinations in earlier work.
They used data from the 2009 National Household Travel Survey 19 to model the charging demand for cars, vans, and sport utility vehicles.
They validated capacity expansion decisions through simulation of the day-ahead unit commitment and hour-ahead economic dispatch processes using data for hourly wind availability in each region and with sensitivity testing for lowest wind and highest demand weeks for each of the six electric system regions.
They evaluated the required fuel economy of conventional vehicles (CVs) endogenously, assuming either linked EV and CV fuel economies as in the current policy, or unlinked fuel economies.
The CAFE standard is calculated using a harmonic mean; given the high fuel economy assigned to EVs by the EPA, scenarios with higher EV market share result in a lower required conventional vehicle (CV) fuel economy. Taken to the extreme, this would lead to falling CV fuel economy as EV adoption increases.
In other words, the researchers note, under the current policy, there is an inverse relationship between EV adoption levels and CV fuel economy required to comply with the fuel economy standard.
They considered two ways of managing the charging of EVs: (i) uncontrolled charging where the driver plugs in the vehicle after completion of the last trip of the day and charging commences immediately and (ii) controlled charging. Under controlled charging, the driver plugs in the vehicle after completion of the last trip of the day, and charging is scheduled to minimize the cost of electricity and ensure that the vehicle is fully charged at the beginning of the first journey of the next day. Uncontrolled charging is the current norm.
They considered three scenarios for EV adoption: (i) that EV sales reach 10% of LDV fleet sales by MY 2025, which is the US EPA and NHTSA projection; (ii) that EV sales reach 20% market share by 2025; and (iii) that EV sales reach 100% market share by 2025. At these market share levels, EVs comprise 8.4%, 16.8%, and 80.7% of the LDV fleet, respectively, in 2030. They assumed a gasoline price of $4/gallon (2009 $).
They considered two RES levels: the current state-level standards with a weighted average of 10% and a 33% level. They considered biomass, wind, solar, and municipal waste resources within the Eastern Interconnection eligible to meet RESs. They developed region-level renewable resource potentials, assumed biomass and solar resources added in a region supply demand in that region, and assumed all inter-regional transfer of wind energy required construction of dedicated transmission. They then apply the models and assumptions to analyze implications for the 36 states of the Eastern Interconnection region from 2010 to 2030.
Among their findings were:
Adoption of EVs at the 10%, 20% and 100% levels results in a 1.7%, 3.3%, or 15.8% increase in overall electric demand in 2030 relative to the reference case with no EVs.
Based on the current Corporate Average Fuel Efficiency (CAFE) regulations (linkage), the reduction in gasoline demand for the 10%, 20% and 100% EV scenarios in 2030 is 2.9%, 4.4%, and 44.9% respectively relative to the reference case with no EVs. With unlinked EV and CV fuel economies, the 2030 gasoline demand is reduced by 6.2%, 12.4%, and 59.3% for the 10%, 20%, and 100% scenarios respectively compared to the reference case with no EVs.
Unlinking fuel economies results in more gasoline savings at the 10% EV adoption level than linking fuel economies does at the 20% level.
With no EVs, total GHG emissions from the transportation and electricity sectors are projected to be 12% lower in 2030 than in 2010 due to the fuel efficiency standards, a projected partial shift from coal to natural gas, and the current RES.
With linking at the 10% RES level, total GHG emissions are about the same with EVs as without. With unlinking, all cases with EVs have lower GHG emissions than the reference case.
The case with 100% EVs, CAFE unlinking, controlled charging, and a 33% RES, results in 27% less emissions than the reference case.
With the current 10% RES, all of the unlinked cases have a negative ΔTCE (total consumer expenditure)—i.e., the average consumer spends less for electricity and transportation in a system with EVs than without. Given the relative attractiveness of EVs compared to CVs, the lower lifetime cost of EVs results in lower average consumer expenditure as EV adoption increases.
The ΔTCE for the case with 0% EVs and a 33% RES is $193/vehicle-year. In contrast, the ΔTCE for the case with 100% EVs, unlinked fuel economies, controlled charging, and a 33% RES is $40/vehicle-year. The ΔTCE of $40/vehicle- year with 100% EVs assumes 90% of EVs are BEVs. Alternatively if PHEVs comprise 90% of EVs, the ΔTCE increases to $111/vehicle-year.
Our results show that EV adoption can reduce the cost of RES compliance, gasoline consumption, and energy system costs, including the costs of GHG reductions. The potential to achieve these benefits can be strongly affected by linkage of CV fuel efficiency, EV adoption levels, and by how EVs are charged.
The linking of CV fuel efficiency standards with EV adoption rates does provide flexibility in meeting the standard and may also support development and adoption of EV technologies. However, due to the energy system linkages considered here, the linkage has negative consequences for gasoline consumption and consumer expenditure.—Choi et al.
Dong Gu Choi, Frank Kreikebaum, Valerie M. Thomas, and Deepak Divan (2013) Coordinated EV Adoption: Double-Digit Reductions in Emissions and Fuel Use for $40/Vehicle-Year. Environmental Science & Technology doi: 10.1021/es4016926
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