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Open Access Publications from the University of California

Scholarly Works (9 results)

  • Article
Working Papers (2015)
Natural gas vehicles have been favored by U.S. air quality agencies for the cleaner burning properties of natural gas. However, the climate consequences of a switch to natural gas vehicles for long distance, heavy-duty applications has been less clear. The radioactive forcings of short-lived methane leakage must be weighed against any long term benefits of emitting less CO2. The scientific literature reports a variety of results and conclusions, thus policy makers often find it hard to make science-based, sound decision-making. But there is inherent natural variability in the system and virtually any result can be justified based on a given choice of input values. Some scholars deal with this variability with probabilistic distributions of inputs to produce probabilistic distributions of results. But this treatment of uncertainty might not resound with decision makers, who might prefer the simplicity of one single estimate. In this study, we attempt to tackle and communicate uncertainty in a simplified way in which a transparent base case scenario is modified one input at a time to determine the distinct parameters that are critical to assessing the climate impact of natural gas as a transportation fuel. Instead of focusing on a specific number, this analysis shows what makes a natural gas fuel a better option versus a bad option, so policy makers and agencies can focus on promoting these best practices among the interested parties. We utilize Argonne’s GREET1 2014 model to test sensitivities for the life cycle carbon intensity of natural gas versus diesel fuel under a range of scenarios for upstream and in vehicle methane leakage, fueling and storage technologies, and operational performance of various kinds of class 8 engines. We evaluate the relative importance of engine technology, natural gas fuel storage choice, upstream methane leakage (i.e., well-to-tank), and vehicle methane slip (i.e., tank-to-wheel). We find that: 1) Upstream methane leakage contributes between 7 and 11% and vehicle methane leakage (i.e., methane slip) contributes between 5 and 9% to the total carbon intensity of natural gas in long haul trucks; 2) Variability factors include whether natural gas fuel is stored as compressed (CNG) or liquefied (LNG) and whether a natural gas vehicle uses spark ignition or compression ignition. Natural gas engines typically being spark ignition, which are around 10% less efficient than compression ignition diesel engines; 3) If no efficiency penalty is assumed (as in the case of the currently out of market HPDI model), NGVs offer a climate advantage compared to diesel only if well-to-tank methane leakage remains under 5%; and 4) CNG storage is more sensitive to leakage than LNG storage. This analysis allows us to identify the most important strategies to reduce the carbon intensity of NGVs.
    Cover page: The Carbon Intensity of NGV C8 Trucks
    • Article
    White Papers (2019)
    California has a range of existing and proposed targets toward a low carbon future. This paper summarizes an analytical review, focused on modeling approaches and what is known about their feasibility and cost. The findings in this paper are based on the Climate Change Policy Modeling (CCPM) forum, which included modelers, policy makers and stakeholders evaluating targets and pathways to low-carbon futures and identifying required policies to achieve goals. The third forum, CCPM-3, was on May 14th, 2018, at the University of California, Davis and provided critical discussion and a gathering of the key experts in this topic area This report builds on the findings of CCPM and integrates with other literature where possible. It includes a review of the CO2-relevant targets, discussion of studies and modeling efforts to assess meeting such targets, including feasibility and cost. This includes analysis in the transportation and energy sectors, as well as land use and carbon sequestration.
      Cover page: California Climate Change Target Setting: A Workshop Report and Recommendations to the State of California Based on the Third California Climate Policy Modeling Dialogue and Workshop
      • Article
      Research Reports (2019)

      This report makes an initial investigation into the potential for combining very high penetration levels of electric vehicles with similarly very high penetration of variable renewable electricity (VRE) in California. A literature review is performed regarding the potential for high levels of EV sales and VRE penetration at both the U.S. and California level. Such scenarios have been developed by a number of researchers, such as U.S. national laboratories for the White House (under the Obama Administration), and by Energy and Environmental Economics, Inc. (E3) for the California Energy Commission. Such studies indicate that both of these “extreme” futures are entirely plausible and have the potential to coexist. However, none of the reviewed studies has undertaken detailed analysis of how large numbers of EVs could interact with and support a VRE-dominated system, and how these might interact in a useful way. This could include grid-to-vehicle (G2V) and vehicle- to-grid (V2G) movement of electricity, with vehicle batteries providing large scale electricity storage.

      We undertake our own preliminary simulation for a 2030 and 2050 scenario for California, using an 8760 hours (full year) electricity demand profile and VRE generation example. We assume a ramp- up of VRE to 60% of all electricity generation by 2030 and 100% by 2050, with a similar increase in the EV share of new LDV sales, creating a significant stock (about 7 million) by 2030 and nearly complete transition (to over 20 million vehicles) by 2050. Using an “averages, peaks and valleys” analysis on the electric side, and a typical spare battery storage potential on the vehicle side, our simulation shows that by 2030 a large share of excess VRE electricity generation could be stored, and a large share of electricity shortfall from VRE could be provided, by electric vehicle batteries throughout the year, though there would be many cases where they cannot provide full coverage of these situations. However by 2050, if nearly 100% of the fleet were EVs, only about half of their available, spare capacity is needed to store the excess electricity from a full VRE system on the highest generation day and only about 40% would be needed to store and supply the shortage from lack of VRE generation on the highest shortfall day.

      While these results are encouraging, a deeper simulation is needed to provide a true hour-by-hour assessment of battery use and the incidence of storage need compared to driving need. Management of charging times that could not be assessed here may also play a critical role. In addition, our initial assessment only covers a single day shortfall. Shortfalls could occur for longer periods, particularly if the VRE electricity system were sized to take better advantage of seasonal storage options. Vehicle batteries are best suited to very short duration storage and may not be adequate to keep the electricity reliable for many consecutive days of shortfall. Hydrogen (H2) has the potential to be a longer-term energy storage option and could be stored in fuel cell vehicle tanks (and the H2 system associated with generating, storing and distributing H2 to those tanks). The next stage of our research will involve running a full simulation using our (ITS-Davis) California ZEV power model (“CALZEV”), a version of the larger Message model, applied to consider both electricity and hydrogen (with large numbers of both of these types of vehicles) in order to: 1) gauge the relative storage potential and cost over a range of time frames and VRE scenarios, and 2) estimate the relative value and possible synergies in a system with both types of vehicles and fuels.

      • 1 supplemental PDF
      Cover page: Analysis and Projections of BEVs, Renewable Electricity, and GHG Reductions through 2050
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2015)
      This paper documents the stock market's reaction to a 2009 paper in the Nature journal of science, which concluded that only a fraction of the world's existing oil, gas, and coal reserves could be emitted if global warming by 2050 were not to exceed 2 °C above pre-industrial levels. This Nature article is now one of the most cited environmental science studies in recent years. Our analysis indicates that this publication prompted an average stock price drop of 1.5% to 2% for our sample of the 63 largest U.S. oil and gas firms. Later, in 2012-2013, the press "discovered" this article, writing hundreds of stories on the grim consequences of unburnable carbon for fossil fuel companies. We show only a small negative reaction to these later stories, mostly in the two weeks following their publication. This limited market response contrasts with the predictions of some analysts and commentators of a substantial decline in the shareholder value of fossil fuel companies from a carbon bubble. Our paper discusses possible reasons for this discrepancy.
        Cover page: Science and the stock market: Investors' recognition of unburnable carbon
        • Article
        White Papers (2019)
        The recent emergence of natural gas as an abundant, inexpensive fuel in the United States could prompt a momentous shift in the level of natural gas utilized in the transportation sector. The cost advantage of natural gas vis-à-vis diesel fuel is particularly appealing for vehicles with a high intensity of travel and thus fuel use. Natural gas is already a popular fuel for municipal and fleet vehicles such as transit buses and taxis. In this paper, we investigate the possibility that natural gas could be utilized to provide fuel cost savings, geographic supply diversity and environmental benefits for the heavy-duty trucking sector and whether it can enable a transition to lower carbon transport fuels. We find that a small, cost-effective intervention in markets could support a transition to a commercially sustainable natural gas heavyduty fueling system in the state of California and that this could also advance some of the state’s air quality goals. Our research shows that an initial advanced natural gas fueling system in California could facilitate the expansion to other U.S. states. Such a network would enable a faster transition to renewable natural gas or biogas and waste-to-energy pathways. Stricter efficiency standards for natural gas Class 8 trucks and regulation of methane leakage along the natural gas supply chain would be necessary for natural gas to contribute substantially to California’s climate goals as a trucking fuel. To date, industry has favored less expensive technologies that do not offer the highest level of environmental performance.
          Cover page: Exploring the Role of Natural Gas in U.S. Trucking (Revised Version)
          • Article
          Research Reports (2016)

          The University of California, Davis and the California Energy Commission held a series of three Emerging Technologies Workshops in late 2015 and early 2016. The goal of these workshops was to identify environmentally and economically promising alternative fuel and vehicle emerging technologies, and to identify and evaluate the critical business and policy barriers blocking their widespread adoption in the State and develop solutions for those barriers. Additionally, the workshops were to analyze the broad range of commercial barriers and identify strategies to increase the adoption and rapid scale-up of emerging technologies, fuels and fueling infrastructure that will help the state achieve its goals for air quality and greenhouse gas emissions. Each of these workshops convened groups of over 100 stakeholders engaged in the commercialization of emerging technologies for the light-, medium- and heavy-duty transportation sectors. Participants included manufacturers of incumbent and emerging alternative vehicle technologies, manufacturers of traditional and alternative fueling infrastructure, traditional and alternative fuel (including electricity) producers and supplies, financial institutions and investors, and public agencies concerned with energy, the environment, transportation, and the California economy.

          View the NCST Project Webpage

            Cover page: Assessment of Critical Barriers to Alternative and Renewable Fuel and Vehicle Deployment – Workshop Series
            • Article
            • Peer Reviewed
            2017 Publications (2017)
              Cover page: The Potential to Build Current Natural Gas Infrastructure to Accommodate the Future Conversion to Near-Zero Transportation Technology
              • Article
              Research Reports (2017)

              The emergence of natural gas as an abundant, inexpensive fuel in the United States has highlighted the possibility that natural gas could play a significant role in the transition to low carbon fuels. Natural gas is often cited as a “bridge” to low carbon fuels in the transportation sector. Major corporations are already investing billions of dollars to build infrastructure to feed natural gas into the U.S. trucking industry and expand the use of natural gas in fleets. In the state of California, natural gas fueling infrastructure is expanding, especially in and around the ports of Los Angeles and Long Beach. The use of natural gas fueled medium and heavy duty fleets is currently on an upswing. The authors examine the precise natural gas infrastructure that is economically and technologically synergistic for both natural gas and renewable natural gas in the near-term, and alternative fuels like renewable natural gas (RNG) and hydrogen in the long term. In particular, the authors examine optimum paths for developing infrastructure in the near-term that will accommodate alternative fuels once they become available at the commercial scale. The original design of the Low Carbon Fuel Standard (LCFS) provides time for the development of advanced, near zero technologies. The authors consider the credits from the LCFS in our analysis.

              View the NCST Project Webpage

                Cover page: The Potential to Build Current Natural Gas Infrastructure to Accommodate the Future Conversion to Near-Zero Transportation Technology
                • Article
                • Peer Reviewed
                UC Davis Previously Published Works (2021)
                Despite increased awareness of the lack of gender equity in academia and a growing number of initiatives to address issues of diversity, change is slow, and inequalities remain. A major source of inequity is gender bias, which has a substantial negative impact on the careers, work-life balance, and mental health of underrepresented groups in science. Here, we argue that gender bias is not a single problem but manifests as a collection of distinct issues that impact researchers' lives. We disentangle these facets and propose concrete solutions that can be adopted by individuals, academic institutions, and society.
                  Cover page: Gender bias in academia: A lifetime problem that needs solutions
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