Flexible grid-based electrolysis hydrogen production for fuel cell vehicles reduces costs and greenhouse gas emissions
Introduction
Transportation is a major global consumer of energy (28% of total energy demand) and source of CO2 emissions (24% of energy-related emissions), growing to as much as 10.3 GtCO2/yr globally in 2040 assuming minimal shifting away from petroleum-based fuels [1]. There were approximately 1.2 billion vehicles on the world’s roads in 2014, with 95% of those being light-duty passenger vehicles; by 2035, this number may increase to 2 billion, and reach 2.5 billion by 2050 [2]. Therefore, transportation systems emitting less CO2 and pollutants will rapidly be needed as the total number of vehicles continues to grow.
According to previous literature [3], [4], [5], [6], the transportation sector will be among the most difficult to decarbonize, due to a combination of urban infrastructure built around vehicle dependency, rapid adoption of vehicles in the developing world, mature and inexpensive combustion-based engine technologies, low petroleum costs, and limited alternatives to petroleum-derived fuels for many non-highway modes like aviation and marine transport. One way to decarbonize the sector is through electric vehicles (EVs), whose sales have grown rapidly since 2010, stimulated in part by falling battery costs and strong government policies in several countries. EVs recently surpassed 5 million cumulative sales at the end of 2018, up 62% from the previous year [7]. Most projections of future transportation vehicles assume accelerating growth of battery and plug-in hybrid EVs, with optimistic forecasts indicating >250 million EVs by 2030 and >550 million by 2040 [8].
However, hydrogen can also play an important role in our future transportation system [9], [10]. Currently, three light-duty hydrogen fuel cell electric vehicles (FCEVs) are commercially available in some parts of the U.S. [11]: the Toyota Mirai [12], Hyundai Nexo [13] and Honda Clarity [14]. Outside the U.S., China is starting to embrace a hydrogen future, with a vision of 1 million FCEVs on the road by 2029 [15]. The country is home to many established companies as well as new startups pursuing hydrogen, and its government is investing tens of millions of U.S. dollars in R&D and purchase subsidies [16]. Smaller FCEVs, such as motorcycles and scooters, are also being developed for global markets by companies such as Intelligent Energy [17], Suzuki [18], Honda in collaboration with Nissan and Toyota, as well as Volkswagen, Hyundai and General Motors [19].
Meanwhile, heavy-duty FCEVs are being developed around the world. FCEV buses are being evaluated in many locations in the U.S. [20]; the California Fuel Cell Partnership maintains a growing map of FCEV bus activities globally [21]. Hyundai, Kenworth, Nikola, Toyota, TransPower, UPS and US Hybrid are also developing FCEV trucks [22], [23], [24], [25], [26], [27]. In 2017, China Railway Rolling Corporation Tangshan Co. began demonstrating the world's first FCEV tramcar in Tangshan, China; the company also plans to introduce the technology in Quanzhou, Taizhou and Tianjin, China, as well as Toronto [27]. In Germany, Alstom has introduced the Coradia iLint, a first-of-its-kind FCEV train that was placed into service in 2018 and has since expanded to six German states. Starting in 2021, the Landesnahverkehrsgesellschaft Niedersachsen (LNVG) will begin transporting regular passengers on 14 such trains in Saxony, Germany [28]. In the U.K., the HydroFLEX train began tests in June 2019 [29]. There is also interest in hydrogen-powered ships [30] and airplanes [31].
The production of hydrogen without substantial CO2 emissions will be key to lowering emissions from the transportation sector. Pavlos and Andreas provide a comprehensive review of typical hydrogen production processes [32]. Hydrogen can be generated from many energy sources, but most hydrogen produced today is made from steam reforming of methane from natural gas, which is inexpensive and 85% efficient, but emits significant amounts of CO2 (and can leak methane, a potent greenhouse gas). While hydrogen could be made from biomass [33], fossil fuels with CO2 capture and sequestration [34], or even fossil resources that remain in the ground along with produced CO2 [35], water electrolysis provides a scalable, flexible and distributed approach to hydrogen production. The level of CO2 emissions associated with water electrolysis depends on the electricity generation mix. Electricity with a high fraction of low-carbon sources can lower CO2 emissions relative to conventional vehicles, while reliance on electricity generated from fossil fuels can raise CO2 emissions.
About 4% of global hydrogen is produced by electrolysis today [36]. Previous literature has examined the cost of various electrolysis technologies, including proton exchange membrane, alkaline, and solid oxide [37], [38], [39], [40]. Ursua et al. projects that water electrolysis will be deployed in the future because both hydrogen and electricity can be produced flexibly and transported over long distances [41]. Also, hydrogen production can be integrated with the electricity grid to support electricity generation, and at high penetrations of renewable generation, the CO2 emissions associated with hydrogen production can become quite low. Moreover, the ability to generate hydrogen flexibly using water electrolysis can support grid operations by helping to maintain grid stability and reducing operational costs. While dispensed hydrogen costs between $12 and $16 per kg today [42], many expect that hydrogen retail prices could drop significantly in the future [43]. In the current study, the average hydrogen production cost from electrolysis is assumed to be reduced to ~$4/kg (excluding distribution and dispensing costs), consistent with U.S. Department of Energy (DOE) targets [44]. However, the average electrolytic hydrogen production cost is affected by both capital and operating costs, and thus is expected to vary with electrolyzer size and utilization.
Renewable electricity installed capacity continues to increase rapidly in many parts of the world, with about 100 GW of solar PV, 50 GW of wind, and 30 GW of other renewable generation (excluding large hydropower) installed in 2018, bringing the total global renewable electricity capacity to 2400 GW [45]. As renewables become a greater contributor to electricity generation they will create operational challenges, such as balancing instantaneous power demand with fluctuating and intermittent power output from an increasing share of generators [46]. While flexible grid resources that address these issues exist today, they are mostly fossil-based, such as ramping natural gas or coal power plants. To minimize electricity-sector CO2 emissions, a combination of more widespread load flexibility, dedicated energy storage, and flexible low-carbon generation technologies (including hydro, biomass-fired plants, geothermal and concentrating solar power) must be developed. Grid-connected EVs have been identified as a growing flexible load resource that could play an increasingly important role in renewables integration [47], but hydrogen generation via electrolysis can also act as a buffer to help match electricity supply to demand [48].
In this study, we simulate hydrogen production via electrolysis in the U.S. Western Interconnection (WI) power system. While this region encompasses the entire U.S. (and parts of Canada and Mexico) west of approximately 105°W, the 5.3 million FCEVs we simulate are assigned to California, with no FCEVs outside the state. These forecasts, while aggressive for 2030, are consistent with some long-term forecasts of 20% FCEV penetrations for cars and trucks [49]. For example, the IEA has developed FCEV scenarios assuming that 12–25% of passenger light duty vehicle stock and 5–10% of freight vehicle stock (light commercial, medium-duty and heavy-duty trucks) are hydrogen-powered by 2050 [50]. Our purpose is to investigate the time-dependent influence (and cost in particular) of hydrogen refueling on grid operations under different assumptions of electrolysis sizing and flexibility, using a large-scale power system model implemented in PLEXOS. The methods of this study, while limited to one specific year and region, can be readily generalized to other electricity grids and FCEV penetration levels, providing potentially useful results applicable to other cases.
Section snippets
Methodology
The model methodology can be divided into three steps. The first step estimates time-resolved energy consumption of FCEVs by class (light-duty, medium-duty, etc.). For different kinds of vehicles, a detailed vehicle model is used to calculate the energy consumption, which is converted to hydrogen dispensing profiles according to refueling behavior assumptions specific to each vehicle class. Second, hydrogen refueling demand is aggregated geographically, and converted to an electricity demand
Results
Fig. 2 shows a two-day representative snapshot in January of hourly hydrogen consumption, production, and storage for two electrolyzer capacity factor cases (CF = 50% and 100%), as well as the total electricity production cost. The hydrogen consumption (withdrawal) rate is the same for both cases. Hydrogen is expressed in terms of equivalent GW (production and consumption) or GWh (storage). We see in the CF = 100% case that hydrogen production is by definition constant, whereas for the CF = 50%
Conclusion
Hydrogen production via electrolysis can be regarded as a flexible load added to the electricity grid. This flexible load can provide support to the grid in a variety of ways including shifting load demand profiles and mitigating generator startups and shutdowns. In the scenarios explored in the paper, hydrogen electrolysis loads constituted ~3% of overall grid load. Compared to inflexible (100% CF) electrolyzer operation, greater flexibility can reduce these grid operational costs by more than
CRediT authorship contribution statement
Cong Zhang: Data curation, Investigation, Methodology, Software, Visualization, Writing - original draft, Writing - review & editing. Jeffery B. Greenblatt: Conceptualization, Data curation, Formal analysis, Validation, Methodology, Project administration, Software, Supervision, Visualization, Writing - original draft, Writing - review & editing. Max Wei: Conceptualization, Methodology, Project administration, Supervision, Writing - original draft, Writing - review & editing. Josh Eichman:
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research was funded by the Fuel Cell Technologies Office of U.S. Department of Energy. The Contract No. is DE-AC02- 05CH1123 (with the Lawrence Berkeley National Laboratory) and DE-AC36-08GO28308 (with the National Renewable Energy Laboratory). It was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal
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