Zero-emission vehicles? Not without clean electricity 


Katherine Jordan  – Blog post for Skibo Energy

Large-scale electrification of vehicles, including passenger vehicles like sedans and SUVs as well as larger vehicles, such as commercial delivery vans, buses, and short-haul freight trucks, is a key element of Rapid Substitution. We can maximize emissions reduction during the switch to electric vehicles by simultaneously cleaning up the electric grid. In recent modeling work at Carnegie Mellon University, my colleagues and I explore the possible greenhouse gas emissions (GHG) reductions from widespread light- and heavy-duty EV adoption both with and without additional climate policy, such as a clean electricity standard.  

While greenhouse gas emissions are nearly always lower for an EV than a gasoline vehicle, the magnitude of the benefit of driving an EV depends on the fuel source used to generate the electricity that powers it, as shown in this analytic tool from the Union of Concerned Scientists. In places where the electric grid runs primarily on coal and natural gas, switching to electric vehicles (EVs) shifts transportation emissions from vehicle tailpipes to powerplant smokestacks.  

Regardless of the upstream electric generation, vehicle manufacturers and policymakers at state and federal levels have begun implementing internal targets or legislative mandates for Zero Emission Vehicle (ZEV) sales to reduce transportation emissions.  

For example, General Motors, VolvoFord, and Volkswagon all have aggressive electrification targets. In California, Governor Gavin Newsom issued an executive order setting zero-emission vehicle standards for vehicles sold in the state. Although it is not yet legally binding, it will require that all passenger vehicle sales and all off-road vehicles and equipment are zero-emission by 2035, and all medium- and heavy-duty vehicle operations are zero-emission by 2045. At the federal level, President Biden recently signed the Executive Order on Strengthening American Leadership in Clean Cars and Trucks, setting the goal that half of all new passenger cars and light trucks sold in the US will be battery electric, plug-in hybrid electric, or fuel cell electric vehicles by 2030. 

To explore GHG emissions in the US as a consequence of vehicle electrification, we modeled two zero-emission vehicle (ZEV) standards. We defined ZEVs as being battery electric vehicles, plug-in hybrid electric vehicles, and hydrogen fuel cell electric vehicles (in accordance with President Biden’s recent Executive Order).  

The first policy scenario applies only to passenger vehicles and light-duty commercial trucks. In the second, we model a policy that applies to all on-road vehicles, including those covered by the light-duty standard, but with the addition of transit buses, school buses, and medium- and heavy-duty trucks.  

In accordance with the Executive Order on Strengthening American Leadership in Clean Cars and Trucks, our simulated ZEV policies require that half of new vehicle sales are EVs by 2030. While the Executive Order does not address vehicles sold beyond 2030, we assume that the policy would be renewed and tightened as time progresses. We model ZEV standards that increase linearly from 50 percent of new vehicle sales in 2030 to 100 percent of sales in 2050. 

In our simulations, which agree with the broader literature, we find that transitioning to EVs will reduce GHG emissions even without additional policy mechanisms.  

The following graph tracks the anticipated reductions in emissions produced by the three modeled scenarios, Business As Usual (BAU), All Zero Emission Vehicles (All ZEVS), and All Zero Emission Vehicles and Clean Energy Standards (All ZEV CES) from 2020 to 2050.  The model differentiates between emissions produced by the transportation and generation of the electricity that powers those EVs.  It also considers substantial increases in wind and solar resources due to projected cost reductions, adding to the overall decarbonization process. 

Compared to the business-as-usual model (BAU), implementing a zero-emission vehicle (ALL ZEV) standard on passenger vehicles and commercial trucks reduces total GHG emissions from transportation and electricity generation from 2020 – 2050 by a modest 8 percent.  

When we include buses and trucks (All ZEV), cumulative emissions from 2020 to 2050 are 11 percent lower that the BAU bars.  

While achieving these reductions would be laudable, meeting deep decarbonization goals will require more drastic emissions reductions. The All ZEV CES bars show emissions with a zero-emission vehicle standard on all on-road vehicles plus a clean electricity standard. This standard requires 80 percent clean electricity by 2030, rising to 100 percent by 2050. The impact of the clean electricity standard is obvious in the graphic. In 2030, the first year the standard is binding, electricity generation emissions under the clean electricity standard are more than 50 percent lower than 2030 BAU emissions. 

The ‘All ZEV CES’ scenario achieves a 31-percent reduction in emissions from transportation and electric generation than the BAU model, more than double the reduction obtained from a standalone ZEV standard.  

Critically, when we model vehicle electrification without a clean electricity standard, meeting elevated electricity demand, natural gas generation actually increases compared to the BAU model, an outcome antithetical to decarbonization goals. 

Ultimately, our work shows that our collective climate goals can be best achieved by implementing the principles of Rapid Substitution across the entire energy economy. It is insufficient to focus only on introducing electric vehicles, decarbonizing the electrical grid, or electrifying individual economic sectors.  

Rather, we must transition entirely away from fossil fuels economy wide. While our recent work focuses on electric generation and transportation vehicles, deploying ZEVs and zero-carbon electricity generation are only parts of the solution.  

We can achieve even deeper emissions reductions with a range of solutions including electrifying residential and commercial heating and cooling, reducing overall energy demands, and implementing low-carbon industrial process solutions.  

Rather than a sector-by-sector approach, Rapid Substitution should be considered holistically to achieve climate targets, decrease our dependence on fossil fuels, and work towards a cleaner, brighter future.  

This blog is based on work presented at Carnegie Mellon’s Energy Week Poster Competition. “Zero-Emission Vehicles? Not Without Climate Policy” prepared by Katherine Jordan; Peter Adams, PhD;  Paulina Jaramillo, PhD; and Nicholas Muller, PhD. 

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