Vehicle Electrification - Quo Vadis?

N. Brinkman, GM Global Research & Development, Warren, MI, USA;

Dr. U. Eberle, Dr. V. Formanski, Prof. Dr. U. D. Grebe, R. Matthé, General Motors Europe, Rüsselsheim, Germany

Vehicle Electrification – Quo Vadis? Fahrzeugelektrifizierung – Quo Vadis? Fortschritt-Berichte VDI, Reihe 12 (Verkehrstechnik/Fahrzeugtechnik), Nr. 749, vol. 1, p. 186–215, ISBN 978-3-18-374912-6

N. Brinkman, GM Global Research & Development, Warren,Michigan, U.S.A.; Dr. U. Eberle, Dr. V. Formanski, Prof. Dr. U.D. Grebe, R. Matthé, General Motors Europe, Rüsselsheim, Germany

Fahrzeugelektrifizierung – Quo Vadis? Vehicle Electrification – Quo Vadis? Kurzfassung Die Entwicklung der elektrischen Fahrzeugantriebe von der Erfindung des Kraftfahrzeugs bis zur Gegenwart wird in dieser Veröffentlichung beschrieben und es wird ein Ausblick auf den zu erwartenden Fortschritt gegeben. Unter Berücksichtigung der Randbedingungen verschiedener Energieketten und technischer Grenzen aller Systemkomponenten eines elektrischen Antriebsstrangs werden sinnvolle Einsatzfelder elektrifizierter Fahrzeugantriebe aufgezeigt. In Zukunft werden die Antriebstränge zunehmend elektrifiziert. In einigen Anwendungen werden batterieelektrische Fahrzeuge wettbewerbsfähig, was besonders für den Einsatz im städtischen Kurzstreckenverkehr gilt. Für solche Anwendungsfälle eignen sich Fahrzeugkonzepte vom Kleinwagen bis zum Stadtbus. Elektrofahrzeuge mit Reichweitenverlängerung erlauben weitere Fahrtstrecken und können somit vollwertige Erstfahrzeuge darstellen. Dadurch wird das Elektrofahrzeug für größere Kundengruppen einsetzbar. Wasserstoffbetriebene Brennstoffzellenfahrzeuge fahren jederzeit ohne lokale Emissionen und lassen sich schnell betanken. Die Anwendung der Brennstoffzellentechnologie ist für die meisten Fahrzeugsegmente sinnvoll und im wesentlichen technisch nur durch die notwendigen Baugrößen der Antriebskühlung und der Wasserstoffspeicher für besonders hohe Anforderungen begrenzt. General Motors ist davon überzeugt, dass der Marktanteil der elektrischen Antriebe signifikant zunehmen wird, geht aber auch davon aus, dass die konventionellen Antriebe mit Verbrennungsmotoren noch eine lange Zukunft haben – wenn auch viele eine Unterstützung durch Hybridisierung erhalten werden.

Abstract This publication describes the development of electrified propulsion systems from the invention of the automobile to the present and then provides an outlook on expected technology progress. Vehicle application areas for the various systems are identified based on a range of energy supply chains and the technological limits of electric powertrain components. GM anticipates that vehicle electrification will increase in the future. Battery-electric vehicles will become competitive for some applications, especially intra-urban, shortdistance driving. Range-extended electric vehicles provide longer driving range and offer full capability; with this technology, electric vehicles can serve as the prime vehicle for many customers. Hydrogen-powered fuel cell-electric powertrains have potential for application across most of the vehicle segments. They produce zero emissions during all phases of operation, offer short refueling times, but have powertrain cooling and hydrogen storage packaging constraints.

33. Internationales Wiener Motorensymposium 2012

While the market share of electrified vehicles is expected to increase significantly, GM expects conventional powertrains with internal combustion engines to also have a long future – however, a lot of them will be supported by various levels of electrification.

1. History of Vehicle Electrification [1-6] In the early days of the automobile, various propulsion systems competed. The internal combustion engine used by Carl Benz in his Tricycle vehicle (1885) continues to dominate the market today, but the first vehicle to exceed 100 km/h was “La Jamais Contente,” an electric vehicle driven by Camille Jenatzy, a Belgian race driver and vehicle constructor.

Figure 1 – Early history of vehicle electrification, 1899-1973 [1-6]. Bild 1 – Frühgeschichte der Fahrzeugelektrifizierung, 1899-1973 [1-6]. Countless companies in the United States and Europe built electric vehicles, e.g., the Detroit Electric Car Company, Oldsmobile, and Siemens. In the 1910s, electric cars were popular in North America and owners included Thomas A. Edison and Clara Ford. They were considered luxury vehicles because they were quiet and easy to operate. GMC also produced electric trucks from 1911 to 1917. In 1911, Charles F. Kettering [1] invented an all-electric starting system that was introduced in the 1912 Cadillac. The electric self-starter made the internal-combustionengine car easier to operate since it no longer required a “chauffeur” to crank the engine by hand. The electrification of the internal combustion engine helped to defeat the “electric car” in the first decades of the 20th century. Its arrival signaled the rapid expansion of combustion-engine-powered vehicles. In Kettering’s words, it was a perfect example of “the right thing to do at the time it has to be done.” The last electric vehicle companies went out of business in the 1930s and it was not until the 1960s when General Motors began to develop electric vehicle studies based on the rear-motor-driven Chevrolet Corvair. The Electrovair 1 (1964) and 2 (1966) were equipped with silver-zinc batteries used in the aerospace programs of that era. Around the same 33. Internationales Wiener Motorensymposium 2012

time, GM also developed the Electrovan (1966), the first fuel cell vehicle to use hydrogen and oxygen as fuel. It was powered by an alternating-current (AC) induction motor. GM’s early electric vehicle research was motivated by (1) the search for clean automotive propulsion to address air pollution and (2) technical progress on aerospace technology gained from a number of GM divisions, including Delco Electronics, contracted to build the “Lunar Rover,” the vehicle used by the Apollo astronauts to drive on the moon. In 1973, the Electrovette, which was based on the Chevrolet Chevette and used nickelzinc batteries, was considered as an option to address increasing gasoline prices, but gas prices did not exceed $2.50 per gallon (10 Ah) are mainly made in a prismatic pouch or metal-can form. The cell voltage is dependent on the chosen cathode and anode material and typical nominal voltages range from 3.6-3.8V, with an operation range from 4.2V (high state-of-charge) down to 3V (low state-of-charge). This enables the design of battery systems with higher voltage and a smaller number of cells. Mass and Cost Contribution of Lithium-Ion Cells

Cathode and Anode Material Effect

Cathode material Anode material Electrolyte Separator Current collector

Cell Voltage Specific energy (Wh/kg) Energy density (Wh/liter) Cycle and calendar life Abuse tolerance

Cell housing

Cost

Both cell design and the electrolyte impact specific power (W/kg) and cost.


Cathode Material Acronym LCO

LNMC

LMO

Cathode Material full Lithium Cobalt Oxide

Application Notebook, Phone

EREV, EV Lithium Nickel Manganese Cobalt Lithium EREV, EV Manganes Oxide

NCA

Lithium Nickel Cobalt Aluminium

HEV, Notebook, Phone,

LFP

Lithium Iron Phosphate, "Olivine"

Power tools, EV

Pro Power

Life

Low material cost, Safety Power, cycle life, calender life Low material cost, Safety

Con Cost of cobalt (high content), abuse tolerance Nickel and cobalt cost Life at temp >40°C Cost of nickel and cobalt (high content), limited abuse tolerance Lower energy density

Table 2 – Commercially used cathode materials. Tabelle 2 – Kommerziell angewandte Kathodenmaterialien. The future will see the continued evolution of lithium-ion battery cell cost due to better manufacturing processes, which will lead to higher yields resulting from better process control. Improvement of known “lower-cost” cathode materials and methods such as particle coating will also facilitate lower cost and longer cell life. The future for battery systems will also see cost reductions due to higher production volumes, reduced part count, optimized cell controllers, and application of the learnings from production of the first-generation units.

Figure 9 – Battery progress, past and future. Bild 9 – Fortschritte in der Batterietechnologie.


Concepts that promise significantly higher energy density – such as silicon anodes, lithium-sulfur cells or lithium-air batteries – have just entered the research stage; it will take many years before they are qualified for use in a vehicle program. Nevertheless, the further development of the battery technology will result in less expensive batteries with higher energy density and greater durability. For the simultaneous improvement in cost and energy density, a factor of one-point-five to two seems reasonable in the future. Whether this is biased toward vehicle cost or vehicle range depends on the chosen vehicle architecture. 3.2 Motors Direct-current (DC) motors, which were used up to the early 1990s, were replaced by alternating-current (AC) induction motors and soon by permanent-magnet (PM), excited synchronous motors. Development of rare-earth magnets in the 1980s, led by GM’s Magnequench, enabled compact motors with high torque and efficiency. In recent years, prices for raw materials such as neodymium have been very volatile due to increasing demand and a limited production base, which is concentrated in China. Future optimization thus must balance cost, mass, volume, and efficiency. This makes motor concepts such as the separately excited synchronous motor or the AC induction machine very attractive. In addition, the permanent-magnet synchronous motor has a future at reduced cost as production volumes grow and competing manufacturers enter the business. Designs will also be optimized for manufacturing, since PM synchronous motors allow torque-rich, compact designs and integration of small motors into transmissions. Examples include GM’s e-Assist™ light electrification system or the motors in its extended-range electric vehicles and hybrid-electric vehicles. Large motors for electric vehicles could also be designed as AC induction motor and synchronous motor.

Figure 10 – Electric motor and power electronics progress, past and future. Bild 10 – Fortschritte bei Elektromotoren und Leistungselektronik. Going forward, the focus for the electric motor is on cost reductions while keeping efficiency high and further reducing mass.


3.3 Power Electronics The thyristor had been the semiconductor used to control the rotor current in DC machines, using a transistor for the small rotor current. Three-phase AC motors require six “switches,” which should operate with low conduction losses and high frequencies. The first MosFETs allowed efficient control of AC machines, but required a high number of components, leading to reduced reliability. The development of the insulated-gate bipolar transistor (IGBT) in the 1990s allowed high switching frequencies for low noise and high propulsion efficiency. Integrated modules contain 6 IGBTs and diodes in one component. Inverters today are also smaller, lighter, and cheaper. The cost will be further reduced by higher production volumes, improved IGBT modules, and optimized inverter design. Longer-term improvements will be based on new semiconductor materials. Power inverter efficiency, size, and mass have progressed greatly in the last two decades and will further improve slightly in the future. 3.4 Fuel Cell Systems In the late 1990s, the polymer-electrolyte membrane (PEM) fuel cell had been developed with higher power density to power electric drives in light-duty vehicles. The cost for fuel cell stacks was reduced significantly due to improved materials and designs. With specific power [kW/kg] and power density [kW/l] increases, fuel cell propulsion systems became more cost-competitive. The durability of the fuel cell systems has also been increased substantially. The next-generations fuel cell systems will require reduced catalyst loading, lower-cost membranes, and improved manufacturing processes. Scaling up production will enable significant cost reduction.

Figure 11 – Evolution of the fuel cell system. Bild 11 – Evolution der Brennstoffzellensysteme.


3.5 Hydrogen Storage Systems Currently, high-pressure hydrogen storage systems show better performance than liquid hydrogen storage and hydride storage. Today’s systems are 70 MPa (700-bar) pressure vessels designed using carbon fiber and a plastic or aluminum liner. Since an automotive system must be able to store at least 4 kg of hydrogen to achieve customer-acceptable range in a compact car, the cost of the hydrogen storage system is driven by material (carbon fiber) and processing. Higher-volume production and improved manufacturing processes will decrease cost significantly and refined designs will slightly reduce the mass of the system.

The progress that has been made over the last 15 years in terms of the cost, mass, reliability, and durability of electric-drive systems has been tremendous. It has enabled market introduction of a range of electrified systems, from e-Assist™ mild hybrids to extended-range electric vehicles and full battery-electric vehicles. EREVs, a category of vehicle that GM created, set the standard for today’s electric vehicle technology because they are the first electric vehicles where customers do not have to worry about being stranded by a depleted battery. Once the all-electric driving range is exhausted, a gasoline-powered generator can power the electric motor for hundreds of additional kilometers of highway driving. The trend to lower cost will continue and in future years we will see increased market share of partly to highly electrified propulsion systems and even fuel cell-electric vehicles across all vehicle classes.

4. Energy Sources and Supply Chain for Mobility The global transport sector uses a staggering 2.1 billion tonnes of oil every year (45 million barrels per day) [15], more than half of total oil use. Maintaining the oil supply chain and creating new transport fuel supply chains are enormous tasks. We will: (1) review history and projections of transport energy sources, (2) assess grid stability and its potential impact on automotive fuels, and (3) evaluate the fuel lifecycle from resource to vehicle usage. 4.1 Liquid Fuel History and Projections The transport sector in general, and light-duty transportation specifically, have developed almost exclusively around the use of gasoline and diesel produced from crude oil (conventional and unconventional) and natural gas liquids. The IEA [15] historical data and projections of total world liquids fuel supply is shown in Figure 12. From 1990 until today, world liquids demand increased at a rate of about 1% annually. Although the growth in total liquids supply slows to a rate of about 0.6% annually, transportation liquids demand is expected to continue increasing at about 1% per year, driven largely by increased transportation in the developing world. Figure 12 shows that the growth in liquid fuels will be provided by biofuels, unconventional oil, and natural gas liquids, as crude oil supplies remain flat. However, flat supply of crude oil does not mean continuing only to produce from currently producing fields. Supply from currently producing fields will decline roughly 70% by 2035, leaving a gap (shown within the dotted red line) to be filled by fields yet to be developed and fields yet to be found.


Figure 12 – World liquid fuels supply showing investment required to maintain crude oil production; source: [15]. Bild 12 – Weltweite Versorgung mit flüssigen Energieträgern verdeutlicht den Investitionsbedarf um die Produktion zu sichern; Quelle: [15]. Most experts do not anticipate the world running out of oil (estimated 5,500 billion barrels of recoverable resources). However, the amount of capital required, timing of investment of that capital, and carbon footprint of unconventional sources could be issues. The inset in Figure 12 projects that $10 trillion of cumulative investment will be required to maintain conventional oil supply and increase unconventional oil supply from 2011 through 2035. Nearly $9 trillion of that investment is required for exploration, well development, and equipment for transport of oil from wells to refineries. If future oil demand and supply were entirely predictable and there was no time lag between investment and production, timely investments would be expected to match supply with demand. 4.2 Electricity and Hydrogen Electricity is produced from a diverse set of resources throughout the world. The mix of resources varies regionally, as shown in Figure 13. Electricity from coal comprises about 20%, 50% and 80% of electricity in the EU, U.S., and China, respectively.

EU

US

China

Figure 13 – Current mix of resources for electricity production [13,14,15]. Bild 13 – Aktueller Energiemix bei der Stromerzeugung [13,14,15]. Non-fossil resources, including nuclear, hydro, and renewables, have the greatest share in the EU and smallest share in China. Shares of non-fossil resources are expected to increase. In its New Policies Scenario, IEA [15] projects world annual generation increases of 7% for biomass, 9% for wind, 6% for geothermal, and 15% for solar. Shares of nonhydro renewables in 2035 are projected to be 15% globally and over 30% in the EU. 33. Internationales Wiener Motorensymposium 2012

Infrastructure to generate and distribute electricity is well-developed in most regions. Addition of vehicle charging is not expected to substantially impact generation or transmission of electricity in the near future, because transportation demand is expected [15] to be a small share of total generation. Impact of vehicle charging on the distribution requires more study. What is required at the point of charging is a compatible plug socket and an electric vehicle supply equipment (EVSE) interface to the vehicle. Charging interfaces have been established [16] for Level 1 (120V/1.4 kW), Level 2 (240V/3-19kW), and are being developed for DC “fast” charging. The high electrical-power demand of fast charging might drive significant additional investment. Although technology for hydrogen production is well known, infrastructure for distribution and vehicle refueling is small, consistent with the small number of hydrogen-fueled demonstration vehicles available. Hydrogen can be produced from electricity by electrolysis or by catalytic reforming of natural gas, other fossil fuels, and biomass. Largescale production of hydrogen from natural gas by catalytic reforming uses well-developed technology and is employed by petroleum refineries. Electrolysis of hydrogen is also welldeveloped, but used at moderate scale. Vehicle refueling stations could produce hydrogen onsite by electrolysis or small-scale reformers, or hydrogen could be distributed from large plants to refueling stations by pipeline or truck. When available and used at large scale, hydrogen costs are expected to be competitive with petroleum fuels. What is expected to be a challenge, however, is the transition between essentially zero hydrogen refueling stations to a density sufficient to meet the expectations of customers of hydrogen-fueled vehicles. Most favor addressing the transition issue by regional introduction of vehicles and fuel. Examples of cities with hydrogen refueling stations and plans for more are Los Angeles, San Francisco, New York City, Tokyo, Seoul, Shanghai, Hamburg, Frankfurt, Stuttgart, and Berlin. 4.3 Grid Stability, Large-Scale Renewable Energy Storage, and the Automobile In this section, the challenges in Europe arising from the integration of renewable energy sources like wind and solar power into the overall energy system and the corresponding importance and usage of green energy carriers for automotive applications are discussed. The challenge of utmost importance for any country in the industrialized world is to ensure a safe and reliable power supply. Germany is used as a specific example since it is the biggest economy of the European Union and since it has committed to the most aggressive targets for the replacement of fossil and nuclear technologies. To maintain a stable, high-quality electric grid (but also for battery technology reasons), EV charging times of at least one to several hours or even longer periods and the utilization of a sophisticated smart-charging communication protocol (or even a bi-directional energy flow, such as what was pioneered using an Opel Meriva BEV within the MeRegioMobil project [7]) will eventually be required to avoid large load swings due to vehicle charging. One million EVs charging (from a total German car park of 40 million vehicles) at a single point in time in the early morning or the evening would cause a power demand of 3.5 GW when using standard German home sockets and installations. To put this into perspective, a single large-scale baseload power station (nuclear or coal-fired) provides typically only about 1 GW to the grid. Since it will take some time to build up to one million EVs, however, grid operators will be able to react to automotive market sales trends and, in the meantime, establish smart-charging protocols to manage these growing loads.


Nevertheless, for plug-in vehicles, there exists a strong interdependency between two normally distinct activities, namely “parking” and “refueling.” This interdependency is not the case for FCEVs, where a typical refueling process takes only 3-5 minutes. Additionally, hydrogen offers a different and very important advantage over stored electricity because of hydrogen’s higher energy density (see Figure 6). Hydrogen, methane, or other “designer chemical energy carriers” could serve as the ideal partner for the intermediate storage of fluctuating, renewable energies. In doing so, excess amounts of sustainable energy sources, such as solar and wind power, can be made available not only for stationary but also for automotive applications. Let us consider, for example, the North German electric power grid, the so-called ‘‘TenneT Regelzone’’. In October 2008, the power fed into the grid by wind turbines fluctuated – sometimes within a few hours, sometimes within days – between a maximum of approximately 8000 MW and virtually zero (see Figure 14).

Figure 14 – Fluctuating wind energy in October 2008 in the grid operated by TenneT compared to biggest German pumped hydro storage Goldisthal (a Vattenfall installation in the state of Thuringia) [10]. Bild 14 – Schwankung der Windenergie im Oktober 2008 im Netz von TenneT im Vergleich zur Kapazität des größten deutschen Pumpspeicherwerk Goldisthal (Fa. Vattenfall, Thüringen) [10].

An excess amount of available wind power, for example, at several points since 2009 dramatic caused effects on the energy markets, such as significantly negative prices of up to minus 25 ct/kWh for electric energy at the European Energy Exchange (EEX). According to the German wind energy industry association, in 2010 the nationwide total installed wind power capacity had risen to 27,215 MW, a 5.6% increase over the respective 2009 value [9]. In the first 9 months of 2011, wind power contributed already on average about 8% (solar power accounts for 3%) of the German gross electricity production [9]. But not only these short-term fluctuations need to be covered; wind power also shows significant seasonal dependencies in its electric generation (see figure 15a). During the winter half-year in Germany, typically 3.5 TWh of wind energy was generated per month (2003 to 2009 mean), while during summer this number drops on average to values below 2 TWh [9]. 33. Internationales Wiener Motorensymposium 2012

Figure 15 – a) Wind electricity generation in Germany, 2011, seasonal effects and the winter storms of December 2011; b)Share of electricity produced from renewable energy sources in Germany, statistical data through 2011 and the “Energiekonzept” targets of the German national government [9]. Bild 15 – a) Strom aus Windenergie in Deutschland, 2011, Jahreszeiteneffekte und die Stürme im Dezember 2011; b) Anteil der Stromerzeugung aus erneuerbaren Energiequellen in Deutschland; statistische Daten bis 2011 und Ziele des Energiekonzepts der deutschen Bundesregierung [9]. It will become even more important and urgent to solve these challenges when the already approved or planned off-shore wind farms (e.g., in the North Sea) come online later this decade. This is of particular importance after the Fukushima accident of 2011 when the German government decided to phase out the nuclear power stations providing a major share of the country’s base load and, as compensation, to increase the share of fluctuating renewable energy dramatically (see Figure 15b [9]). Furthermore, these energy sources currently feature low annual utilization numbers (solar: 900h, wind: 1500h; 1 year = 8760h). An additional issue for grid operators arises from the fact that the typical wind power installations are located in the sparsely populated coastal areas close to the North and Baltic Seas, whereas the population and industry centers are to be found mainly in the south, resulting in a very significant energy transmission challenge. The current German grid infrastructure is already operated at its limit. Hence, it is clear that it would be extremely helpful to ‘‘buffer’’ excess energy in intermediate storage systems to handle these supply fluctuations, i.e., to absorb energy during a certain time period from the grid or, vice versa, to provide energy back to the grid in case of a high market demand. [8] Today, this ‘‘buffer’’ is realized as pumped hydro storage facilities (e.g., the largest facility in Germany, Goldisthal [10], offers a maximum storage capacity of 8000 MWh). If hydrogen is used as a storage medium instead, up to 600,000 MWh of energy could be stored in a two million cubic meter salt cavern. Unlike conventional technology, hydrogen therefore offers not only buffer storage for short time periods ranging from a few minutes to 33. Internationales Wiener Motorensymposium 2012

hours, but such a large-scale hydrogen storage facility could also absorb the excess wind energy of several days. The stored gas could eventually be either converted back into electrical energy or could simply be used as a fuel for hydrogen vehicles. By contrast, even large fleets of pure battery EVs are not able to provide a competitive energy storage dimension: if, for example, 5 kWh of the usable energy content of an EV battery (for operating lifetime and customer ease-of-use considerations, 10% of the total nominal energy content should not be exceeded) could be subscribed to and used by the electric utility, just to replace the pumped hydro store of Goldisthal, 1.6 million EVs would be needed. Also, other large-scale stationary battery systems (based, e.g., on Na-sulfur or lithium technology) are by far not able to provide energy storage dimensions comparable to a hydrogen-based system. [8] Since the setup of a viable and sufficiently dense hydrogen infrastructure in the short term is considered a significant challenge by virtually all major stakeholders in both industry and academia, concepts have been presented over recent years to utilize synthetic natural gas as a chemical energy carrier (in particular by Specht, Sterner et al. [11]). In this concept, fluctuating renewable energy (again especially wind energy) is used for the electrolysis of water. The produced hydrogen and CO2 (taken from a CO2-producing industrial or biogas compound) react via the well-known Sabatier process to form methane (in this case, also known as synthetic methane): 4 H2 + CO2 à CH4 + 2 H2O(g) Typically, Ni-based catalysts are used and according to Specht, Sterner et al, the reaction takes place in a fixed-bed reactor at temperatures between 250-500°C at a pressure of circa 0.8 MPa. The produced process gas is not pure methane; it consists roughly of 87% CH4, 6% CO2, and 7% H2. This synthetic natural gas (SNG) product could be fed into the existing natural gas pipeline and storage network in many industrialized countries. By doing so, additional energy storage capacities of the TWh dimensions could be reached. Unfortunately, although the Sabatier reaction is highly exothermal, the conversion step from hydrogen to methane is not for free. The Sabatier chemical equation directly states – based on mass flows – that 8 kg of hydrogen (corresponding to an FCEV range of 650 km) would be needed to produce 16 kg of methane (equivalent to an ICE range of 250 km). Furthermore, the energy usage also has to be assessed. Under ideal conditions, a conversion efficiency for the methanization of maximum 80% may be reached. For detailed numbers of different paths and usage, see Table 3.


Path Electricity-to-Gas

Efficiency

Electricity à Hydrogen

57 - 73%

Electricity à Methane (SNG)

50 - 64%

Electricity à Hydrogen Electricity à Methane (SNG) Electricity-to-Gas-to-Electricity Electricity à Hydrogen à Electricity

64 - 77% 51 - 65%

Electricity à SNG à Electricity

30 - 38%

34 - 44%

Boundary Condition Compression up to 8 MPa (pipeline pressure) Compression up to 8 MPa (pipeline pressure) Without compression Without compression 8 MPa compression, 60% re-conversion efficiency 8 MPa compression, 60% re-conversion efficiency

Table 3 – Large-scale energy storage: Efficiency of various conversion paths [11]. SNG: Synthetic Natural Gas. Tabelle 3 – Großtechnische Energiespeicherung: Effizienz verschiedener Umwandlungsketten [11]. SNG: Synthetisch erzeugtes Methangas.

The basic idea behind the SNG concept – to use the conversion of electric energy into chemical energy carriers and the existing natural gas infrastructure for the integration of renewable energy into the energy system of an industrialized country – is definitely worth considering. But evaluating Table 3, it becomes clear that the gas storage should be carried out at the step in the process chain that provides the greatest advantage in terms of conversion efficiency. The SNG process builds on top of the hydrogen production step and leads to a considerably higher technology complexity and higher investment cost. Energy-wise, 100 GWh of electrical energy translates via the Sabatier process to 58 GWh of SNG compared to 71 GWh of hydrogen. The storage and direct use of the electrolysis hydrogen, therefore, obviously has to be preferred from an energy use point of view, especially since it is also possible to feed hydrogen directly into the existing natural gas grid up to a concentration of 5%. Unfortunately, the SNG picture gets even less attractive when vehicle applications are considered. Due to the comparatively low efficiency of the CNG internal combustion engine and the occurring Well-to-Wheel losses, only about 10% of the primary wind energy would be available at the wheels of a natural gas vehicle. If the process would be stopped at the hydrogen stage and considering a fuel cell-electric vehicle (FCEV efficiency about two times greater than for ICE vehicles [8] [12]), about 30% of the primary energy could be used for transportation purposes at the wheels. In addition, the direct use of the hydrogen also has the advantage of being locally emission-free. In contrast, in the case of an SNG-powered vehicle, NOx and CO2 would be locally emitted by the car. At present, several pioneer projects in Germany testing the storage of wind energy in the form of hydrogen are already ongoing. Additionally, in December 2011, the consortium “Performing Energy” was created to commercialize wind-hydrogen technology. This organization consists of several academic partners, three German states, and major industrial companies like Siemens, Linde, Total, and Vattenfall. The consortium intends to provide a strong link to the transportation sector by interfacing with the German “Clean Energy Partnership” hydrogen vehicle program.


It is highly advantageous, especially for transportation applications, to keep the number of energy conversion steps as low as possible. This is enabled by using batteries as an electrical energy carrier and hydrogen as a chemical energy carrier and employing them in various types of electric vehicles. To enable and commercialize such large-scale energy storage technologies, which are essential to reach the highly ambitious German renewable energy targets of the “Energiekonzept” [9], a technology-neutral incentive scheme for load-leveling applications would be required. 4.4 Fuel Lifecycle If gasoline were the only fuel used, vehicle efficiency alone would be a good tool for assessing the environmental footprint of propulsion options. Adding biofuels, compressed natural gas, hydrogen, and grid electricity to the mix requires analysis of the full fuel lifecycle, including production and delivery of the required resource, conversion of resource to fuel, and delivery of fuel to the vehicle. Another term used for fuel lifecycle analysis is “Well-to-Wheels” (WTW). There have been a vast number of studies of fuel lifecycle of future fuel/propulsion options. In Europe, the most comprehensive and widely used study [14] is that jointly conducted by the European Commission Joint Research Center, CONCAWE (oil industry consortium), and ACEA (auto industry consortium). In the U.S., the most widely used tool for fuel lifecycle is GREET [13], developed by the Department of Energy’s Argonne National Laboratory. To compare greenhouse gas (GHG) emissions across the various fuel/propulsion options, we used a GM-proprietary vehicle simulation tool to assess the U.S. on-road vehicle efficiency of a C-segment passenger car. Combining the GM vehicle efficiency results with the Well-to-Tank assessment (gCO2e/MJ of fuel) from the Joint Research Centre [14] provide the results shown in Figure 16. Fuel lifecycle GHG for conventional diesel and CNG were within the range of conventional gasoline and gasoline strong hybrids. Biofuels and biomethane blends could further reduce lifecycle GHG for these internal-combustion engine options. The BEV, plugged into electricity with the GHG footprint of the average mix of the EU grid, provided GHG about half that of conventional gasoline and 30% below that of a strong gasoline hybrid. If the BEV were powered with wind electricity, fuel lifecycle GHG would be zero. WTW GHG of the EREV, like the BEV, depends on electricity GHG footprint, but also depends on charging and driving behavior. Figure 16 shows results for EREV with 50%, 75%, and 100% of kilometers driven on plug electricity. Increasing the share of kilometers on plug electricity reduces WTW GHG. For the hydrogen fuel cell, sources of hydrogen analyzed include natural gas reforming at a central plant and onsite electrolysis from the EU grid mix or wind electricity. The FCEV operating on hydrogen from natural gas reforming had fuel lifecycle GHG about 35% below those of conventional gasoline. With hydrogen from wind electricity, the low FCEV lifecycle GHG were slightly above zero because of truck distribution and compression. However, the hydrogen fuel cell with hydrogen produced from EU average mix electricity increased fuel lifecycle GHG above that of conventional gasoline. Fuel lifecycle GHG were higher with the FCEV than BEV on the same electricity mix due to energy losses in hydrogen production from electricity.


Figure 16 – Well-to-wheels greenhouse gas emissions for various propulsion types and fuel sources; sources: well to tank – JEC [14], tank-to-wheels based on GM analyses for C segment, U.S. on-road. Bild 16 – Treibhausgasemissionen von Primärenergiequelle bis zur Nutzung für verschiedene Antriebstechnologien und Kraftstoffe; Quellen: Vorkette – JEC [14], Tank-zuRad – GM Simulation für C-Segment-Fahrzeuge, US-Realfahrzyklus. Figure 16 shows that the electrification pathways offer the opportunity to drive transportation toward zero fuel lifecycle greenhouse gas emissions. Reductions in GHG for the BEV may be exaggerated, however, because its limited driving range prevents it from being used for all trips. Trips longer than the driving range would have to be taken with another vehicle or transport mode, and would likely increase the GHG footprint of the trip. The EREV does not have this limitation, nor does the FCEV, as long as hydrogen refueling is widely available. Use of 100% cellulosic biofuels, although not included in this analysis, could also provide near-zero lifecycle GHG. The symbols in Figure 16 also indicate the energy resources in each the fuel/propulsion options. With the gasoline and diesel options, transportation is tied exclusively to oil and subject to oil price volatility. With the addition of CNGVs, transportation can diversify from its dependence on oil. The electrification options, EREV, BEV, and FCEV, provide opportunity for increased diversification from oil.

5. Electric Vehicle Usage Experience In recent years, a great deal of customer experience operating electric vehicles in the real world has been gathered as part of GM’s Project Driveway fuel cell market test and from data collected from Chevrolet Volt owners and Opel Ampera test vehicles.


Additional data was also obtained from other earlier EV vehicles and test programs. From 1993 to 1996, during the Ruegen Field Test, ten electric Opel Impuls vehicles accumulated 250,000 km. One result of this study was that customers reported a favorable impression of battery technology and its potential to help reduce petroleum consumption. The Impact Preview test program in the early 1990s and, beginning in 1996, the lease of production GM EV1 electric vehicles in Arizona, California, and New York provided a wealth of customer feedback and significant lessons learned for engineers working on the technology. They designed the vehicle to be very efficient and, therefore, to achieve a reasonable range; customers responded by competing to drive more efficiently and with minimum energy. Since 2007, 119 Chevrolet Equinox and Opel HydroGen4 vehicles have been tested as part of the Project Driveway market test. These vehicles have operated successfully in six countries through five winters, accumulated 3.8 million km with over 6,000 drivers, logged over 25,000 hydrogen refueling events, consumed 53,000 kg of hydrogen, and gathered real-world experience with retail and fleet customers. During the program, 20 vehicle collisions occurred – two were total losses – with no hydrogen lost. The data recorded is being used to support the design of GM’s next-generation fuel cell-electric vehicle. The Chevrolet Volt extended-range electric vehicle allows data upload through GM’s OnStar mobile communication system and information to the driver through the internet. OnStar data reveals that two-thirds of all Volt miles driven were performed with electric energy in “EV” mode. Furthermore, the average Volt customer had 30 days between and drove almost 1500 km between gas fill-ups. On average, every vehicle is driven more than 50 km per day (20,000 km/year). For comparison, in Germany, diesel passenger cars drive on average 18,500 km per year and passenger vehicles with gasoline engines drive 11,500 km per year. The extended-range electric vehicles – with an EV range of 56 km based on the EPA label, or 83 km based on EU certification – allow significant replacement of petroleum-based fuel (60% to 80%) by electricity. Data of Opel Ampera test vehicles used by engineers over several months show that, in this sample, 45 km per day can be driven in EV mode (see Figure 17). This is more than the average gasoline ICE vehicle in Germany, 31 km per day. The Ampera test vehicles were driven 72 km per day, which exceeds the average driving distance of diesel passenger cars in Germany of 15 km per day. Customers who have had the opportunity to drive or own an electrically driven vehicle have been extremely positive about the driving experience, often saying they “love” their vehicles and that they are “fun to drive.” Drivers of electric vehicles (both battery and fuel cell) also express the thrill of electric torque, the smooth ride and handling of these vehicles, and the quietness of the vehicle. Experience with the EV1 influenced the development of the Chevrolet Volt and Opel Ampera. Data show that a high percentage of EV driving is achieved with an EREV. Real-world energy consumption matches the EPA label in the DoE INL project data and underlines the potential to replace petroleum. Project Driveway has demonstrated the day-to-day potential of fuel cell vehicles.


Figure 17– Ampera test vehicles driven by engineers drove 63% in electric vehicle mode despite the high distance of average 72 km/day exceeding the average daily driving distance in Germany. Bild 17 – Ampera-Versuchsfahrzeuge von Ingenieuren im Alltag genutzt erreichen 63% im elektrischen Modus obwohl die durchschnittliche tägliche Fahrleistung in Deutschland erheblich übertroffen wird.

6. The Vehicle Application Map The electrification of the vehicle is a necessity to achieve the agreed targets for fleet emissions of carbon dioxide. Further efficiency improvements in the internal combustion engine are still possible, but that improvement is limited and cannot achieve the environmental friendliness an electric drive can provide. The environmental criteria are important for customer acceptance of a new vehicle propulsion system technology. Equally important in terms of customer acceptance is that a new technology must be able to meet the performance and utility (size and usable space) that customers are used to and expect from currently available technology. A third important factor influencing customer acceptance of a new propulsion technology is cost. Here, the appropriate measure is overall cost of ownership, which includes not only the vehicle price but also costs for fuel and maintenance. The important question now is what the optimal level of electrification for the future vehicle propulsion system will be, considering the listed assessment criteria of performance, environmental compatibility, and total cost of ownership over the bandwidth of vehicle applications? To understand this relationship, an extensive study was conducted using expertise from a variety of arenas available within GM. One basis for the analysis was a vehicle application matrix, shown in Figure 18. This matrix differentiates two types of duty cycles for vehicles, light-load vehicles and high-load vehicles, as well as five vehicle drive cycles – from stopand-go driving, represented by the FTP city driving schedule or the Manhattan Bus Cycle – up to almost continuous driving, represented by the FTP highway cycle. With this approach, a 2x5 matrix was generated and for each section of the matrix a suitable vehicle platform with representative performance requirements was identified. 33. Internationales Wiener Motorensymposium 2012

Figure 18 – Application matrix used to assess optional propulsion systems for various duty and drive cycles. Bild 18 – Anwendungsmatrix zum Bewerten konkurrierender Antriebssysteme bezüglich Last- und Fahrzyklen. Optional propulsion systems for the various vehicle platform applications must fulfill duty and drive cycle performance requirements in order to be considered applicable in a specific section. Using this approach, the vehicle class-specific performance requirements and the vehicle parameter became prerequisites instead of evaluation criteria. They are the starting point used for the configuration of any optional propulsion system. The propulsion systems considered in this study include a gasoline internal-combustion engine (ICE), a diesel ICE, a compressed natural gas (CNG) ICE, a gasoline mild hybrid, a gasoline strong hybrid, a diesel strong hybrid, an extended-range electric vehicle (EREV), a battery-electric vehicle (BEV), and a fuel cell-electric vehicle (FCEV). For each section of the application matrix, each optional propulsion system is configured to meet the vehicle performance requirements. For the purposes of the study, hydrogen was assumed to be produced by steam reforming of natural gas. For electric energy consumption, the European grid mix was used as the basis to determine CO2 emissions and total energy consumption. One example of a section-specific vehicle performance requirement is a vehicle driving range for a specified load cycle. For the C segment (L3), a driving range of 600 km was identified as a minimum, using the LA92 driving schedule as the reference. For a BEV, this range requirement is not realistic, as Figure 19 illustrates. The needed battery capacity must be increased by adding battery mass, and added battery mass leads to further energy requirements (this relation is not considered in Figure 6). To achieve the 600 km driving range target using a battery for a C segment vehicle (L3), the vehicle weight would need to increase by about 290% compared to a conventional ICE vehicle.


Figure 19 – Vehicle curb weight sensitivity to battery-electric vehicle driving range. Bild 19 – Reichweiten-Einfluss auf das Leergewicht eines batterieelektrischen Fahrzeugs. The drive cycle, of course, has significant impact on the necessary battery capacity per driving range, as illustrated in Figure 19. In addition to the driving schedule the auxiliary load for passenger comfort, like heating and cooling, is important to consider in the design of a battery system for a BEV application. The recharge time for the battery is another limitation in increasing the vehicle driving range. With a 3 kW recharge capability and 6 hours recharge time a driving range of 150 km (LA92 cycle) and 220 km (FTP city cycle) is achievable. Considering vehicle cost for this comparison, it is even more obvious that a BEV is not able to achieve the driving range that a customer expects from a compact-class vehicle. A BEV can only be considered for sections in which a reduced vehicle driving range of 100200 km is acceptable for the customer, such as a light-load vehicle for city driving only or a city bus application. Determining the cost of ownership for such a limited-range application must include the complete mobility needs of the customer. Therefore, higher-range traveling must be accommodated in the total cost of ownership by adding expenses that will be incurred for car rental and/or use of other means of transportation providing longdistance traveling. Although fuel cell technology has significantly higher efficiency than internal-combustionengine technology, thermal heat rejection by the vehicle radiator is higher with a fuel cell vehicle. This is due to exhaust gas enthalpy, which is much lower for a fuel cell powertrain compared to an ICE powertrain. In addition, the fuel cell is limited with a maximum coolant temperature of about 95°C. Thus, the thermal cooling task for an FCEV is more challenging than for conventional vehicles and therefore maximum continuous power is limited by maximum possible vehicle radiator area (see Figure 20).


The radiator performance is dependent on air flow, vehicle speed, radiator fan operation, temperature difference between coolant and air, etc., but Figure 20 gives for a typical thermal design case the bandwidth of maximum mechanical power of a FCEV for various vehicle applications, referring to the section definition of Figure 18. This thermal restriction is relevant in assessing a FCEV within the application map. Here, it is important to note that this limitation is affecting continuous mechanical power only and not the peak performance of the FCEV.

Figure 20 – Continuous mechanical vehicle power in relation to maximum available radiator area for various FCEV applications. Bild 20 – Kontinuierliche mechanische Leistungsabgabe als Funktion der verfügbaren Kühlerfläche für verschiedene FCEV Anwendungen. A second considerable restriction for FCEVs is the package space required for the hydrogen storage system; this factor needs additional detailed analysis. Based on the performance requirements identified for this study, however, the FCEV could be applied in each section. The assessment of optional propulsion technologies within the defined application map has led to the following results: With respect to well-to-wheel CO2 emissions, the BEV is the preferred solution in sections L1/L2 and H1/H2, in cases where limited driving range can be ignored. When considering total well-to-wheel energy consumption, BEV, FCEV, and EREV technologies are very close within these sections. For sections L3 to L5 and H3/H4, FCEV and EREV technology provide the lowest total energy consumption and the lowest well-to-wheel CO2 emissions compared to the other powertrain technologies investigated. The electrification of the vehicle powertrain offers regenerative braking and engine load point optimization. Therefore electrification of the vehicle powertrain will increase with the need to improve fuel economy in balance of the total cost of ownership. A prediction on the growth rate for powertrain electrification always contains the uncertainty of cost forecast for fuel and energy, but also for technology cost development, which is again coupled with the production volume. 33. Internationales Wiener Motorensymposium 2012

Fuel cell and battery electric powertrains both offer in addition locally emission-free driving, which is simply not achievable with an ICE engine and only partly achievable with a PHEV or an EREV. Figure 21 shows how limited zero-emission driving compares to customer expectations and the effort to install battery capacity. Fuel cell technology offers a solution that enables emission-free driving while achieving customer expectations for vehicle driving range and moderate performance requirements.

Figure 21 – Electric energy storage capacity of various vehicle electrification schemes and the resulting impact on zero-emission driving range. Bild 21 – Elektrische Energiespeicherkapazität verschiedener Fahrzeugkonzepte und der resultierende Einfluß auf die erreichbare Null-Emission Fahrstrecke. In the future, both electric power and hydrogen production paths will change as a result of the increasing use of wind and solar energy, which will further reduce the well-to-wheel CO2 emissions of EREVs and FCEVs and further improve the environmental compatibility of these technologies. However, the overall emission-free driving provided by FCEV technology makes it a very promising future powertrain technology; it has the potential for broad application and provides the greatest environmental compatibility. It also enables more functional designs and offers refueling times comparable to conventional gasoline-fueled vehicles. Meanwhile, EREV technology is an appropriate technology solution for today and will maximize environmental benefits in the near term.


Figure 22 – GM’s Advanced Propulsion Technology Strategy. Bild 22 – GMs Strategie für zukünftige Antriebstrangtechnologien.

7. Summary Market experiences with the GM EV1, Project Driveway fuel cell vehicles, and the Chevrolet Volt and Opel Ampera extended-range electric vehicles have been very positive. Customer feedback especially underscores the high appreciation consumers have for the driving quality of fully electrified vehicles. With the rapid progress on EV technology that has been made over the last decade, there are many opportunities to electrify more vehicle segments. Although many of the physical limitations of the various propulsion systems have to be addressed, BEV, FCEV, and EREV systems provide the highest potential to reduce CO2 emissions, especially if renewable energy sources are used to produce the required electricity and/or hydrogen. Concurrent with these advanced propulsion technologies, the electrification of more conventional ICE powertrains will also increase as they incorporate mild hybrid or strong hybrid systems across all vehicles classes. In addition, applications that are highly sensitive to running costs, such as long-haul trucks, could also benefit significantly from hybridization. At the current state of technology, the BEV has range and vehicle mass limitations due to the lower energy storage density of batteries, but it has potential in applications such as city buses and small urban vehicles. EREV technology already allows all customers to drive an average of 40 to 60 km per day on electricity without the need for a second vehicle or restrictions to vehicle use. The EREV technology is therefore a significant enabler for the widespread use of electric vehicles.


EREVs and BEVs both provide opportunities for load leveling through smart charging. This makes them a complementary technology to solar and wind power generation. In the longer term, however, load leveling by hydrogen offers the greatest potential. As noted, FCEV propulsion systems are applicable to all vehicle classes, but their continuous power requirements have to be balanced against radiator size and the vehicle package. Nevertheless, the FCEV is the only advanced propulsion option that provides long-range zero-emission driving combined with a reasonably short refueling time. Unfortunately, ubiquitous infrastructure remains a challenge. Establishing a fueling network for hydrogen fuel cell vehicles requires a joint approach by all the major stakeholders (e.g., auto, energy, and utility industries and government) and this must be accomplished in parallel to vehicle rollout into the market. Large investment is required for all future fuel options, including maintaining global oil supply. Ultimately, the degree of electrification across the vehicle application map is a function of energy prices, technology progress, infrastructure availability, the regulatory framework, vehicle performance and fun-to-drive characteristics, and, finally, the overall customer value proposition.

8. References [1] [2] [3] [4] [5] [6] [7] [8] [9]

[10]

[11]

[12]

[13] [14] [15] [16]

http://www.kettering.edu, Richard P. Scharchburg, Thompson Professor of Industrial History. Idaho National Laboratory: http://avt.inl.gov/pdf/EREV/GMJuly-Sept11.pdf. “The Car That Could”, by Michael Shnayerson, 1996, Random House, New York. Matthe, R; Turner, L; Mettlach, H; VOLTec Battery System for Electric Vehicle with extended range, SAE World Conference 2011, 2011-01-1373. Anderman, M; Status of Li-Ion Battery Technology for Automotive Applications, Presentation at SAE International Vehicle Battery Summit, Shanghai November 2011. Tom van Bellinghen, Umicore. Karlsruhe Institute of Technology, “MeRegioMobil” project, retrieved in December 2011, http://meregiomobil.forschung.kit.edu/93.php. U. Eberle, R. von Helmolt, Energy Environ. Sci., 2010, 3, 689–699. a) Statistical information provided by the German wind energy industry association, retrieved in December 2012, http://www.wind-energie.de/infocenter/statistiken. b) statistical information by the German Industry Association of Electric and Water Utilities BDEW, „Arbeitsgemeinschaft Energiebilanzen“, presentation “Stromdaten Jahr 2011”, retrieved in January 2011, http://www.ag-energiebilanzen.de/viewpage.php?idpage=65. Pumped hydro store Goldisthal, technical specifications, retrieved in December 2011; http://www.vde.com/de/Regionalorganisation/Bezirksvereine/Kassel/berichte_mitteilung/Beric hte/2006/documents/mcms/vattenfall.pdf (German language document). Michael Sterner, Michael Specht, Fraunhofer IWES and ZSW Center for Solar and Hydrogen Energy, retrieved in December 2010, http://www.abgnova.de/pdf/Sterner_IWES_Stadt_Frankfurt_ABGnova_2011.pdf and “FVEE • AEE Themen 2009” , page 69 -78. U. Eberle, R. von Helmolt, “Auf dem Weg zur Kommerzialisierung”, Automobil Industrie, December 2010. Also available in html format, retrieved in December 2011: http://www.eauto-industrie.de/energie/articles/295843/. Argonne National Laboratory. (2011). GREET1_2011 (Greenhouse gases, Regulated Emissions, and Energy use in Transportation): http://greet.es.anl.gov/. European Commision Joint Research Centre. (2011). Well-to-wheels Analysis of Future Automotive Fuels and Powertrains in the European Context. Institute for Energy. International Energy Agency. (2011). World Energy Outlook 2011. Copyright OECD/IEA. SAE International. (2010). SAE Electric Vehicle and Plug In Hybrid Electric Vehicle Conductive Charge Coupler.
