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| Fig. 1: Graph of planned ZEV sales as percentage of all light vehicle sales. [2] (Source: D. Wang) |
Since California passed its first Zero Emission Vehicles (ZEV) mandate in 1990, issued by the California Air Resources Board (CARB), mounting pressure to address climate change by reducing vehicle emissions has prompted many modifications to the original mandate. Most recently, California governor Gavin Newsom's executive order N-79-20 required all new passenger vehicle sales in California to be ZEVs by 2035. [1] In response, CARB proposed a new set of regulations: Advanced Clean Cars II. [2] Should it go into effect, this regulation creates a roadmap for the percentage of new car sales required to be ZEVs, which include battery electric, fuel cell, or plug-in hybrid vehicles (see Fig. 1). [2]
Despite the potential health benefits and reduction in greenhouse gas emissions promised by this law, it has also provoked significant criticism. In the face of historic droughts and record heat waves, California's electricity demands have only increased while its supply of hydroelectric power has decreased due to dwindling water reservoirs. [3] As such, it is natural to question the wisdom of bringing more consumption in the form of ZEVs onto the power grid when California appears to already be struggling to meet peak demand. The law could even have the opposite intended effect, by forcing California to become more reliant on fossil fuels to meet the power demand. In contrast, environmental activist groups have criticized ACCII for not being "nearly strong enough to aggressively advance the market for zero-emission vehicles" and meet California's climate goals, urging the governor to consider reaching 100% ZEV sales as early as 2030. [4]
Our method of estimating the additional power demand will be to calculate the number of ZEVs sold each year, assuming the ZEVs will require the same amount of energy per year as the average internal combustion engine vehicle (ICEV). In other words, after accounting for differences in energy efficiency, we expect ZEVs and combustion engine cars to drive the same amount, requiring the same energy. Using this, we can estimate the total amount of energy needed from the power grid each year.
According to CARBs own estimates, baseline light duty vehicle sales without enacting ACCII in 2035 should be roughly 1.99 × 106 vehicles. [2] If we assume all of these cars are ZEVs, that means an additional 1.99 × 106 ZEVs will be sold. To simplify our calculations, we will also assume that once a ZEV is sold, it will remain in use forever. This is clearly an overestimate since old cars are used less and less each year until they are no longer used at all. However, this is an appropriate assumption for estimating an upper bound, and allows us to just examine the year-over-year additional energy needed for the new cars while ignoring that some ZEVs no longer require power.
To estimate the differences in energy efficiency between ZEVs and ICEVs, we will assume all new ZEVs are battery electric vehicles. As of now, BEVs are by far the most common vehicle being sold, so we will assume all the additional cars are also BEVs. The energy efficiency of all ZEVs is about the same as that of battery electric vehicles. The energy efficiency of a typical combustion engine car tested with highway driving ranges between 20% - 30%, whereas for typical EVs such as the Chevrolet Volt or Nissan Leaf it ranges between 74% - 82%. [5] For both, we will pick the middle of the range to be the average energy efficiency, which is 25% and 78% respectively. Thus, the ratio of energy efficiency between combustion engine cars and ZEVs is
| 0.78 0.25 |
= | 3.12. |
As for the actual amount of energy consumed by a typical combustion engine car, the average fuel efficiency was 25.6 mpg in 2021 according to the Environmental Protection Agency (EPA). [6] Given that the average new light duty vehicle will be driven for 1.85 × 104 miles y-1, this means each car will consume [2]
| 1.85 × 104 miles y-1 25.6 miles gal-1 |
= | 723 gallons of gasoline per year |
With an approximate energy density of 1.2 × 108 J gal-1, this means that each car requires
| 723 gal y-1 | × | 1.2 × 108 J gal-1 | = | 8.67 × 1010 J y-1 |
Accounting for the aforementioned efficiency difference between ICEVs and ZEVs, the total amount of additional energy required from the entire power grid each year is
| 8.67 × 1010 J y-1
ZEV-1 3.12 |
× | 1.99 × 106 ZEV | = | 5.53 × 1016 J y-1 |
Converting this to gigawatt hours, we get that a total of
| 5.53 × 1016 J y-1 3.6 × 1012 J GWh-1 |
= | 1.54 × 104 GWh y-1 |
is needed to power all of the additional cars.
Our estimate above was a fairly loose upper bound on the total amount of energy needed since we overestimated the demand whenever possible. As a reminder, we assumed that all new cars sold were ZEVs. Moreover, we also assumed that the power demand from the new ZEVs would only add to the existing demand, neglecting the fact that older cars are used less or even phased out entirely. With this worst-case estimate, we can see that the extra demand is 15.4 TWh/211 TWh = 7.30% of California's current supply. [3] In comparison with the growth of wind and solar power in California between 2020 and 2021, the additional demand of 15.4 TWh is somewhat more than the increase in supply of less than 10 TWh. [2]
As an additional sanity check, we will also calculate the total energy consumption of the current fleet of internal combustion cars. According to some sources, a total of 15 billion gallons of gas will be burned in 2022. [7] This means that if California's entire fleet of cars were to be replaced by ZEVs, they would need a total of
| 1.5 × 1010 gal y-1
× 1.2 × 108 J gal-1 3.6 × 1012 J GWh-1 |
× | 1 3.12 |
= | 1.6 × 105 GWh y-1 |
Converting this number to a percentage of California's total energy supply, 1.6 × 105 GWh / 2.11 × 105 GWh = 76%. However, if we assume the entire fleet of cars is replaced by ZEVs over the same 13 year time period, this corresponds to a modest 5.8% increase per year, which is on par with our earlier estimate.
In conclusion, from a purely numbers perspective it seems that ACCII sets an ambitious yet achievable timeline. If the growth of renewable energy industries continues at the current rate, California may be able to keep pace with the additional demand, even without additional fossil fuel for power generation. However due to the limitations of the above analysis, this in itself is not sufficient evidence that the regulations will work as expected. There are both important economic and political considerations which must also be taken into account but are beyond the scope of this report.
For one, this analysis does not consider any supply side issues. It may not even be possible for manufacturers to produce enough ZEVs to meet the amount of demand estimated above. Additionally, charging infrastructure for the ZEVs could be another bottleneck. Even if California is capable of providing the necessary power, without much more charging infrastructure consumers may find it extremely inconvenient if not impossible to use ZEVs. On the other hand, having so much additional energy storage in the grid in the form of ZEV batteries could also be used to help supply power when there is excess demand and drain power when there is excess supply, thus giving the power grid as a whole more reliability.
Finally, for political reasons, it is unclear if CARB's regulations will even be enforceable. The authority to set emissions standards comes from the Clean Air Act, which allows the EPA to grant California special waivers to set their own standards, independent of federal emission standards. However, this could fail for two reasons:
Other states could sue the EPA for improperly granting the special waiver without sufficient cause (and have expressed the intent to do so), and could even try to have this part of the Clean Air Act removed entirely.
It is possible that future administrations beyond the current Biden administration will not be as sympathetic to California's latest regulations, and could revoke the waiver, as the Trump administration did for a similar waiver granted in 2013.
Ultimately, these political challenges could also prove to be far more difficult to overcome than the basic issue of power supply matching demand.
© David Wang. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] G. Newsom, "Executive Order N-79-20," State of California, September 2020.
[2] "Advanced Clean Cars II: Proposed Amendments to the Low Emission, Zero Emission, and Associated Vehicle Regulations," California Air Resources Board, January 2022.
[3] "2021 Annual Report on Market Issues and Performance", California Independent System Operator, July 2022.
[4] D. Shepardson, "Environmental Groups Press California on Electric Car Rules," Reuters, 7 Mar 22.
[5] J. Thomas, "Drive Cycle Powertrain Efficiencies and Trends Derived from EPA Vehicle Dynamometer Results," SAE Int. J. Passeng. Cars Mech. Syst. 7, 1384 (2014).
[6] "The 2021 EPA Automotive Trends Report", U.S. Environmental Protection Agency, EPA-420-R-21-023, November 2021.
[7] R. Mitchell, "Prepare For More Gas Price Hikes. Here's Why - and Who's to Blame," Los Angeles Times, 4 Dec 22.