The Future Role of Hydrogen in Petrochemistry and Energy Supply DGMK Conference October 4-6, 2010, Berlin, Germany Hydrogen for Automotive Applications and Beyond U. Eberle Adam Opel GmbH, Rüsselsheim, Germany Abstract The energy storage system is of decisive importance for all types of electric vehicles, in contrast to the case of vehicles powered by a conventional fossil fuel or bio-fuel based internal combustion engine. Two major alternatives exist and need to be discussed: on the one hand, there is the possibility of electrical energy storage using batteries, whilst on the other hand there is the storage of energy in chemical form as hydrogen and the application of a fuel cell as energy converter. [1] Considering the latter concept, hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton-exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high-pressure and cryogenic-liquid storage, adsorptive storage on high-surface-area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off-board regeneration are both possible. Reforming of liquid hydrogen-containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared. [2] Introduction Approximately 900 million vehicles worldwide are on the roads today. About 96% of the fuel used for transportation purposes is thereby produced from fossil sources of energy. There are estimates for the year 2020 that the number mentioned above will increase to approximately 1.1 billion vehicles worldwide, in particular due to the economic expansion and industrial development of India and China. This will inevitably have consequences for global crude oil demand and also consequently for worldwide CO2 emissions. Since an increase in demand for oil and CO2 production proportional to the projected number of vehicles is unsustainable for financial, ecological and political reasons, every implementation strategy must aim at the replacement of fossil fuels as a source of energy for automotive applications. [1] Therefore, a key element of the advanced propulsion strategy of many global car manufacturers is the electrification of the automobile and the displacement of gasoline by alternative energy carriers. This would lead to reduced fuel consumption, reduced emissions and also to increased energy security via geographic diversification of the available energy sources. At General Motors, this strategy has its roots with the introduction of the first modern electric vehicle, the 1996 GM EV1. The EV1 was a pure battery electric vehicle (BEV), developed as a mass production car for the average driver. Unfortunately, the market experience with the EV1 and its initial lessees indicated that further significant improvements in BEVs were needed. Some EV1 drivers coined the term ‗‗range anxiety‘‘, describing their omnipresent concern, or even fear, of becoming stranded with a discharged battery in a limited-range vehicle, away from the electric infrastructure. Hence, improvements in on-board energy storage are needed (directly proportional to vehicle range) and shorter charging times were assessed to be essential for a more widespread deployment of BEVs. [1] DGMK-Tagungsbericht 2010-3, ISBN 978-3-941721-07-4 43 The Future Role of Hydrogen in Petrochemistry and Energy Supply Zero-emission vehicles based on hydrogen fuel cells (FCEV) or pure battery-electric systems (BEV) that are fully competitive to conventional vehicles regarding performance and ease-of- use represent the ultimate target of the GM strategy. [1] Fuel cell electric vehicles and battery electric vehicles - a comparison These days, within the general public and also within the automotive and energy R&D community, very often the impression is created that a decision has to be made between hydrogen fuel cell vehicles (FCEV) and pure electric vehicles (BEV), which is seen as a question of either/or. However, this is definitely not the case since both technologies address different areas of the vehicle market. This is caused by the extremely different energy densities of the applied energy carriers (see Fig. 1). [1] Figure 1: Energy densities of various energy carriers (based on a vehicle range of 500 km) The pure battery vehicle is the technology of choice for small urban vehicles with ranges up to 150 km. Besides GM activities (e.g., the EN-V two-wheeler concept for urban mobility) other car manufacturers, mainly Mitsubishi and the Renault-Nissan alliance, are currently working on the development and market introduction of large volume battery electric vehicles for such an application. By contrast, a so-called E-REV vehicle (extended-range EV), such as the Chevrolet Volt or the Opel Ampera, is perfectly suited for those customers who sometimes - but not too often - need longer ranges of up to 500 km; and especially for those willing to accept a small internal combustion engine in order to ensure the range beyond the initial 60 km of pure EV operation (see reference [1]). Also, further car manufacturers, such as Daimler and Toyota, pursue similar or related technology paths for concept vehicles. On the other hand, fuel cell electric vehicles (FCEV) offer a different set of advantages: they always operate as zero-emission vehicles, can be refueled within three to five minutes, and offer ZEV ranges of about 500 km at full performance for family-sized cars. Due to its comparatively high energy density of 1600 W h per kilogram of tank system weight (70 MPa Compressed Gaseous Hydrogen vessels based on carbon-fiber composite technology, CGH2), hydrogen is the ideal energy carrier to serve as intermediate store of fluctuating renewable energy such as solar and wind power, and to enable the usage of this green energy as transportation fuel. [1] 44 DGMK-Tagungsbericht 2010-3 The Future Role of Hydrogen in Petrochemistry and Energy Supply a) b) Figure 2: a) GM HydroGen4, b) tank-to-wheel efficiencies of the GM HydroGen4 (upper line) and the gasoline-powered base model Chevrolet Equinox (lower line). The fuel cell (FC) running on hydrogen is the most attractive long-term powertrain option for passenger cars. It eliminates CO2 emissions on the tank-to-wheel path, the fuel can be produced from many sources, and it provides very high average efficiencies. The latter is DGMK-Tagungsbericht 2010-3 45 The Future Role of Hydrogen in Petrochemistry and Energy Supply especially based on the fact that the fuel cell reaches its highest efficiency at part load. By contrast, at full load, there exists virtually no advantage over internal combustion engines anymore. However, particularly passenger vehicles are mostly operated at loads significantly below their rated power: For such operating conditions, the gain in efficiency offered by fuel cells is maximal. At very low power output, even the fuel cell system efficiency sharply drops. This is attributed to many balance-of-plant components such as the air compressor, as those have to be operated even at idle power (see Figure 2b). [3] GM HydroGen4 Vehicle Type 5-door , cross over vehicle, front- wheel drive, based on the Chevrolet Equinox Dimensions Length 4796 mm Width 1814 mm Height 1760 mm Wheelbase 2858 mm Trunk space 906 Liter Weight 2010 kg Payload 340 kg Hydrogen storage system Type 3 Type IV CGH2 vessels Operating pressure 70 MPa Capacity 4.2 kg Fuel cell system Type Proton Exchange Membrane (PEM) Cells 440 Power 93 kW Battery system Type Nickel-metal hydride (NiMH) Power 35 kW Energy content 1.8 kWh Electric propulsion system Type 3-phase, synchronous motor Continous power 73 kW Maximal power 94 kW Maximal torque 320 Nm Performance Top speed 160 km/h Acceleration 12 s (0-100 km/h) Range 320 km Operating temperature -25°C to +45°C, vehicle can be parked at ambient temperature < 0°C (without external heating) Table 1: Technical specifications of the GM HydroGen4 The scalability of fuel cell systems also facilitates the adaptation to different vehicle sizes. One example is the fuel cell system that was originally developed for the GM HydroGen3 (a van based on the Opel Zafira) and afterwards was adapted to a small vehicle, the Suzuki MR Wagon FCV, using a shorter fuel cell stack with reduced cell count. Eventually, it was adapted to a GMT800 truck by doubling the stack and some other components. [1] 46 DGMK-Tagungsbericht 2010-3 The Future Role of Hydrogen in Petrochemistry and Energy Supply Typically, 4 - 7 kg of hydrogen have to be stored on-board. This remains to be a serious issue for the vehicle integration. Furthermore, cylindrical vessels are required for CGH2 and most other types of fuel storage. In existing vehicles, without modifications, there is no space for hydrogen storage devices that could provide a sufficient range. Hence, rear body modifications are necessary to integrate the hydrogen storage vessel(s). In an extreme case, one could imagine concepts where the car is built around the hydrogen storage such as the Chevrolet Sequel (total fuel capacity: 8 kg of hydrogen). [3] By doing so, for the very first time, an FCEV operating range of significantly more than 300 miles could be achieved and demonstrated on public roads between suburban Rochester and New York City in May 2007. [1] Since autumn 2007, within the framework of „Project Driveway―, more than 100 cars of the current generation HydroGen4, were deployed to demonstration projects all over the world (e.g. in the U.S. and in Germany). These vehicles offer an improved everyday-capability and a higher performance than their predecessors (see Table 1). For instance, the cars can be both operated and started at very low temperatures down to -25°C.