Fuel Cells vs Batteries In the Automotive Sector
Dr. Jeffrey Wishart Senior Project Engineer, Intertek Transportation Technologies
The following paper will provide an overview of pros and cons of both fuel cells and batteries and their place in the automotive landscape.
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Fuel Cells vs Batteries In the Automotive Sector
Contents Introduction ..........................................................................................................................3 The Benefits of Fuel Cell Vehicles ......................................................................................3 The BEV Advantage ............................................................................................................9 Competing or Complementary Technologies? ........................................................... 11 Fuel Cell Vehicles for the Masses .................................................................................... 13 A Place for FCHEVs and BEVs .......................................................................................... 15 Intertek Fuel Cell and Battery Testing Activities ............................................................ 17 Contact Us ......................................................................................................................... 18
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Fuel Cells vs Batteries In the Automotive Sector
Introduction If you follow the alternative fuel industry at all, you may have heard this little pearl of “wisdom”: Fuel cells are a technology of the future…and always will be. On the other hand, battery electric vehicle (BEV) supporters claim that are BEVs represent the automotive future and, by the way, can be bought today.
Fuel Cells are the technology of the future… -Or-
The EV forums are full of comments that fuel cells will never be a part of the transportation system, and that any money spent on fuel cell
…Any money spent on fuel cell development is good money thrown after bad.
development is good money thrown after bad. To be fair, fuel cells have seemed to be on the cusp of
Which one is right?
commercialization in vehicles several times in the past, only to famously fail to take hold - the last time being in the mid-2000s.
The Benefits of Fuel Cell Vehicles To be fair, fuel cells do have strengths that can’t be ignored. For one thing, unlike conventional batteries, the reactants (the chemicals that are needed for the electrochemical reaction that produces electricity) are external, meaning that as long as the reactants continue to be fed to the fuel cell, electricity can be produced. Moreover, refueling an empty reactant tank is also much faster than recharging a battery. There are several different types of fuel cells, including alkaline fuel cells (AFCs), direct methanol fuel cells (DMFCs), phosphoric acid fuel cells (PAFCs), molten
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Fuel Cells vs Batteries In the Automotive Sector
carbonate fuel cells (MCFCs), and solid oxide fuel cells (SOFCs). However, proton exchange membrane (also known as polymer electrolyte membrane, or PEM) fuel cells are seen as the most viable for vehicular applications for the following reasons (the other fuel cell types have some, but not all, of these characteristics): 1. The electrolyte is solid, and so leaking of corrosive fluids is not an issue and the fuel cell can operate in any orientation. 2. The operating temperature is relatively low (80-100°C, 176-212°F), meaning start-up times are short. 3. Relatively high power density (compared to other fuel cell types). 4. 99.999% H2 is required, but air can be used to supply the required O2. The PEM fuel cell (PEMFC) uses hydrogen and oxygen gases as its reactants. The oxygen gas is simply extracted from the surrounding air. Hydrogen gas serves as the “fuel” of a PEMFC, and when compressed, it is much more energy dense than even the most advanced batteries (in both a volumetric and gravimetric sense). This means that for a given volume and mass, more energy is contained - well beyond what batteries are expected to achieve for the foreseeable future. As shown in Figure 2, gasoline is a very efficient energy carrier and a lot of energy is concentrated in a low volume with low weight. Compressed hydrogen gas is much less efficient; however, it’s still more than an order of magnitude better than the specific energy and energy density of the Li-ion battery pack (or more accurately, energy storage system (ESS) of a representative BEV, the 2013 Nissan Leaf.
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Fuel Cells vs Batteries In the Automotive Sector
Figure 1. Typical specific energy and energy density of gasoline, an H2 storage tank, and a Li-ion ESS Sources: Gasoline: Based on Shell Plus 89 at 15 degrees C: 42,900 kJ/kg, 0.74616 kg/L from Shell Ecomarathon rules, 2014: http://s01.static-shell.com/content/dam/shellnew/local/corporate/ecomarathon/downloads/pdf/sem-global-official-rules-chapter-1-2014.pdf Hydrogen Tank: Based on values from Table 6.21, page 220 of A. Godula-Jopek, W. Jehle, and J. Wellnitz (2012). Hydrogen Storage Technologies, New Materials, Transport and Infrastructure, John Wiley & Sons. Li-ion ESS: Based on 2013 Nissan Leaf ESS, 24 kWh, 275 kg and 485 L, from "First Responder's Guide" from Nissan website: (https://owners.nissanusa.com/nowners/navigation/manualsGuide?model=Nissan+LEAF&year=20 11)
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Fuel Cells vs Batteries In the Automotive Sector
One of the main drawbacks of a BEV is that the limited energy capacity of batteries means that the vehicle range is less than that of a conventional vehicle. With the ability to carry more energy on-board the vehicle, the advantages of a fuel cell vehicle (FCV) start to become apparent. The FCV can achieve a much longer range with an on-board hydrogen gas tank, making the FCV range competitive with conventional and hybrid vehicles. For example, the Hyundai Tucson Fuel Cell was recently driven for 435 miles in a mix of city and highway driving (at an average speed of 47 mph) though three Scandinavian countries. This real-world range approaches that of incumbent internal
The real-world range of FCVs approach that of incumbent internal combustion engine (ICE) vehicles, making a FCV potentially more palatable to the mass-market vehicle consumer.
combustion engine (ICE) vehicles, making a FCV potentially more palatable to the mass-market vehicle consumer. A comparison of sport utility vehicles (SUV) with a spark ignition (SI), compression ignition (CI, or diesel), SI hybrid electric vehicle (HEV), FCV, and BEV powertrains, respectively, is shown below in Figure 3. While the range of the FCV is clearly less than that of the conventional vehicles or even that of the HEV, it is more than twice that of the BEV.
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Fuel Cells vs Batteries In the Automotive Sector
* Estimate Figure 2. EPA ranges of an SI vehicle, CI vehicle, SI HEV, FCV, and BEV Source: Fueleconomy.gov Powertrain Specifications: Tucson: 2.4 L, 4 cyl, Auto GLK250: 2.1 L, 4 cyl, Auto, Turbo Highlander: 3.5 L, 6 cyl, Auto Fuel Cell: 100 kW Induction Motor, 24 kW ESS, 100 kW PEMFC RAV4: 115 kW Induction Motor, 41.8 kWh ESS
Another drawback of a BEV is the time needed for recharging. Using the fastest EV charging available, the Tesla Supercharger network (boasting a rate of 120 kW), means that a Model S with the largest battery pack (an industry-leading 85 kWh) would require at least 40 minutes for a full charge from full depletion. Meanwhile, the FCV can be refueled in about the same time as a conventional vehicle -
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Fuel Cells vs Batteries In the Automotive Sector
approximately five minutes. As shown in Figure 4, the refueling times of an FCV are comparable to the incumbent conventional vehicle, while BEV recharging is significantly (and some might say unacceptably) longer. The time required to recharge a BEV on a DC fast charger (DCFC) with a power rating of 60 kW (the rate of most DCFCs outside of the Supercharger) is provided to the 80% state of charge (SOC) mark. The reason is that since the charging rate of most BEVs slows considerably at the 80% mark, and further, the vehicle often ends the charge event at this mark and a second, top-off charge must be completed to obtain an SOC of 100%.
Figure 3. Approximate time to refuel/recharge a conventional vehicle, an FCV, and a BEV with a 24 kWh pack and 6.6 kW on-board charger (at an AC L2 rate and a DC fast charging rate to 80% SOC) www.Intertek.com/Automotive
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Fuel Cells vs Batteries In the Automotive Sector
The fuel cell and hydrogen community around the world has agreed upon a refueling standard, SAE J2601. Unlike the BEV industry, where there is one AC charging standard and two official DC fast charging standards plus Tesla’s proprietary technology in the US - not to mention the different standards in China and Europe - refueling will be the same everywhere. The “VHS vs. Betamax” standards wars that are currently plaguing the BEV industry can be avoided altogether for FCVs. It must be said, however, that there are not currently many hydrogen refueling stations around the country–the DOE counts only 10 publicly accessible stations, but many more are in development: California, for example, plans to have 68 stations in operation by 2016.
The BEV Advantage This is not to say that BEVs don’t have advantages over FCVs. The efficiency of a BEV is unsurpassed, and it will always take more energy to get from point A to point B in an FCV. The most efficient production BEV currently available is the 2014 Chevrolet Spark EV, shown below in Figure 5, which achieves an EPA rating of 260 Wh/mile City/310 Wh/mile Highway/280 Wh/mile Combined (equivalent to 128 MPGe City/109 MPGe Highway/119 MPGe Combined). The higher efficiency is due to the electrochemical reaction in batteries being more efficient than the reaction in a PEMFC but also because the PEMFC requires a balance of plant (BOP) system that delivers the external reactants to the reaction sites. The efficiency of the PEMFC is increased dramatically with higher reactant pressure, and the air compressor consumes the most energy of the BOP components, thereby reducing the efficiency the most. (The H2 is already compressed in the H2 tank.)
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Fuel Cells vs Batteries In the Automotive Sector
Figure 4. 2014 Chevrolet Spark EV, the most efficient production EV currently available Source: http://www.engadget.com/2012/11/27/chevy-details-2014-spark-ev/
The BEV is also simpler technology that does not cost as much to build. In fact, for a commuter or city car, and especially for a driver that never needs to drive very far and can charge their EV in the garage at night, a BEV is very tough to beat. As shown in Figure 6, the efficiency spectrum ranges from conventional vehicles to EVs, with FCVs somewhere in the middle but more efficient than even hybrid electric vehicles (HEVs). The efficiency is given as the “tank-to-wheel” (TTW) efficiency, which ignores the efficiency of the fuel and/or electricity extraction, refining, and delivery to the vehicle; including these losses would allow for a “wellto-wheel” (WTW) efficiency calculation. www.Intertek.com/Automotive
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Fuel Cells vs Batteries In the Automotive Sector
Figure 5. Approximate TTW efficiencies of conventional vehicles (both SI and CI), an SI HEV, an FCV, and a BEV Source: Helmers and Marx Environmental Sciences Europe 2012, 24:14 (adaptation) http://www.enveurope.com/content/24/1/14
Competing or Complementary Technologies? It is apparent that with current technology, BEVs and FCVs are both imperfect replacements for conventional vehicles in some ways, and expecting either to become the dominant transportation propulsion technology is far from a sure bet: BEVs have range and recharging limitations, while FCVs boast an efficiency that is
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Fuel Cells vs Batteries In the Automotive Sector
higher than ICE vehicles but do not offer a large enough gain to overcome the higher purchase price and lack of hydrogen refueling infrastructure. It should be noted that the FCVs that are being commercialized are really hybridized designs that use a battery as well as a fuel cell. The reasons for this hybridization are that without an ESS, the FCV cannot capture regenerative braking energy—a distinct efficiency advantage of a vehicle with an electric motor—and the slow responsiveness of the PEMFC would make vehicle transients less dynamic than desired by vehicle consumers. For FCVs to recapture regenerative braking energy, the PEMFC system would have to also work in reverse as an electrolyzer to split water into H2 and O2. This would require a source of water on board the vehicle that could be pumped through the fuel cell. This water source would take up space and could become depleted over long trips, and would also need to be replenished. Obtaining water exiting the cathode of the fuel cell would add to system complexity, and obtaining it from an off-board source requires extra plumbing. A method for eliminating the produced O2 would also be required. More problematic would be how to store the produced H2, which would be at a much lower pressure than the H2 stored in the tank, and thus would have to be pressurized. This would require some time in which hydrogen exiting the tank for propulsion would not be possible. Regenerative braking performed by the fuel cell would therefore be less efficient and make the vehicle less responsive than regenerative braking by batteries. The responsiveness of an FCV without an ESS is exacerbated by the lower transient capability of the PEMFC, and an ESS as a buffer is highly advantageous: It is faster to get current from the ESS than it is to (1) draw hydrogen from the tank and (2) www.Intertek.com/Automotive
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supply air to the fuel cell to (3) produce the equivalent electricity in a PEMFC to power the electric motor that propels the vehicle. As a result, the FCVs that are coming to market can actually be classified as fuel cell hybrid electric vehicles, or FCHEVs. An on-board battery to support the PEMFC provides the quick response required - and desired - by drivers. In fact, it is unlikely that FCVs will be built without energy storage. Even better, they can be designed as plug-ins that can drive on pure electricity for a portion of the range to tap into that high battery efficiency. Thus, having a battery paired with a PEMFC in an FCHEV makes the vehicle more responsive and more efficient. In this way, fuel cells and batteries become complementary - and not competing – technologies.
Fuel Cell Vehicles for the Masses The commercialization of FCHEVs is certainly not following a straight line path, and has occurred in fits and starts up to this point. There are several reasons for this delay:
Fuel cell performance has been lacking
The fuel cell system is too expensive
Hydrogen storage technology performance is insufficient
Hydrogen production pathways have not developed
Hydrogen refueling stations have not materialized
The technological performance issues are currently being addressed by the industry as well as by a renewed interest in fuel cells and hydrogen research by the US Department of Energy. Governments at various levels are also working on the infrastructure issues. Refueling station projects are being funded in clusters to
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Fuel Cells vs Batteries In the Automotive Sector
promote FCHEV adoption in certain metropolitan areas (especially in California) in advance of FCHEV deployment. Furthermore, there is support for cutting-edge research into hydrogen production via algae and other biological pathways. Interest in fuel cells never waned in Asia and Europe in the same way as in North America circa 2008, shown by growing infrastructure in both areas. There were 17 public stations in Japan at the end of 2012, with plans to build 19 more in 2013 and hit the 100-station mark by 2015. There are currently 15 public stations in Germany, with plans for 400 by 2023. A lot of work is being done to remove the roadblocks and the industry as a whole has made considerable progress since the last failed attempt at commercialization. The automotive companies, for their part, have been forming partnerships to pool resources and reduce R&D costs. Some of these partnerships include agreements between GM and Honda, Ford-Renault-Nissan-Daimler, as well as Toyota and BMW. Several companies, including Hyundai, Toyota, Nissan, and Kia targeted 2015 as the year for FCHEV commercialization, with projected vehicle sticker prices of around $50,000. Hyundai has already begun leasing its Tucson Fuel Cell vehicles with an expected production run of 1,000 cars. Toyota is rumored to be beginning sales or leases by the end of 2014. (The Honda FCX Clarity, shown below in Figure 6, has been available since 2008, but only as a lease vehicle for $600 a month, and only in Southern California where there is access to public hydrogen stations.) Other automakers such as Daimler, BMW, Ford, and GM aim to introduce FCHEVs in the marketplace later in the decade.
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Fuel Cells vs Batteries In the Automotive Sector
Figure 6. Honda FCX Clarity, available for lease in California since 2008 Source: http://automobiles.honda.com/fcx-clarity/
A Place for FCHEVs and BEVs FCHEVs and BEVs can and should co-exist, with each fulfilling its particular niche. BEVs are ideal commuter cars and for use in many commercial applications with repeatable routes, while FCHEVs are suitable for drivers that frequently need to drive longer distances. FCHEVs are also good candidates for larger vehicles like long-haul trucks and buses. AC Transit in the Bay Area has been using fuel cellpowered buses for 13 years, traveling over 750,000 miles. BC Transit in British Columbia purchased the world’s largest fleet of fuel cell-powered buses (20) in 2009 for use at Whistler in time for the 2010 Winter Olympics, one of which is shown below in Figure 7. www.Intertek.com/Automotive
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Figure 7. Fuel cell bus, one of 20 purchased by BC Transit in advance of the 2010 Vancouver Winter Olympics Source: http://smg.photobucket.com/user/billlmf/media/BC%20Transit%20H40LFR/1002_4.jpg.html
Unlike conventional, hybrid, and even plug-in hybrid electric vehicles currently on the market, both BEVs and FCHEVs have zero emissions “at the tailpipe.” This makes reducing and eventually eliminating both greenhouse gas and air pollutants from the transportation system easier because it’s more cost-effective to “green” centralized power plants and hydrogen production facilities than individual fossil fuel-burning cars. While BEVs are currently ascendant and FCHEVs have disappointed in the past, many believe that FCHEVs are a technology whose time will come. Is that time the present, with the introduction of the 2015 Hyundai Tucson Fuel Cell, shown below in Figure 8, marking the beginning of the FCHEV era? It is still unclear. In the meantime, it is important to continually increase R&D funding and focus on www.Intertek.com/Automotive
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making any advanced technology vehicle introduced have the performance and efficiency needed to get the public excited, as well as invest in the refueling and recharging infrastructure required to meet the public’s driving needs.
Figure 8. Hyundai Tucson Fuel Cell, made available for lease in June, 2014 Source: https://www.hyundaiusa.com/tucsonfuelcell/
Intertek Fuel Cell and Battery Testing Activities Intertek is technology agnostic when it comes to advanced vehicle powertrain technologies, and the company’s laboratories are highly engaged in testing and certification of both fuel cells and batteries of all types around the world. Intertek’s testing services include testing and certification of both power sources from micro fuel cell systems and battery cells with power in the mW range to large, stationary systems at the MW scale to electrolyzers and battery management systems. Intertek provides services to test against international and national standards such as SAE, IEC, and ANSI/CSA standards. Intertek also performs www.Intertek.com/Automotive
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customized testing that measures electrical and safety performance, as well as environmental and abuse testing. Intertek’s technical experts have many years of experience of working with fuel cells and batteries and can provide advisory services such as regulatory requirement analysis, technical due diligence, safety analysis, modeling and simulations, technology road mapping, manufacturing facility inspection and certification, and courses and training. For more information, visit the automotive division website at www.intertek.com/automotive.
Contact Us If you would like to connect with an expert to answer your questions, or obtain a quote for a new project, contact Intertek at 1-800-WORLDLAB or
[email protected]. Intertek is the leading quality solutions provider to industries worldwide. From auditing and inspection, to testing, training, advisory, quality assurance and certification, Intertek adds value to customers’ products, processes and assets. With a network of more than 1,000 laboratories and offices and over 35,000 people in more than 100 countries, Intertek supports companies’ success in a global marketplace. Intertek helps its customers to meet end users’ expectations for safety, sustainability, performance, integrity and desirability in virtually any market worldwide. This publication is copyrighted by Intertek and may not be reproduced or transmitted in any form in whole or in part without the prior written permission of Intertek. While due care has been taken during the preparation of this document, Intertek cannot be held responsible for the accuracy of the information herein or for any consequence arising from it. Clients are encouraged to seek Intertek’s current advice on their specific needs before acting upon any of the content. AUT010 Rev 07-14
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