DOE Publishes Progress Report on Fuel Cell Learning Demonstration
August 3, 2007
DOE's National Renewable Energy Laboratory (NREL) published an Interim Progress Report (PDF 682 KB) summarizing results from the first two years of the Controlled Hydrogen Fleet and Infrastructure Demonstration and Validation Project. Download Adobe Reader. The project is designed to monitor fuel cell vehicles and hydrogen fueling infrastructure performance in demonstration fleets throughout the U.S. The 5-year project will assess technology readiness and provide data on the status of hydrogen research and development. The industry teams consist of automotive and energy company pairs, including Chevron/Hyundai-Kia, DaimlerChrysler/BP, Ford/BP, and GM/Shell.
The report includes 30 composite data products that show the project's technical results without identifying individual companies. It includes information on fuel cell efficiency, projected fuel cell durability, fuel economy, driving range, and refueling rates. Results to date indicate that the fuel cell vehicles are performing at levels close to DOE baseline targets. NREL will evaluate overall industry and vehicle progress when 2nd generation fuel cell systems are introduced in 2007 and 2008.
Fuel cell system efficiency
Vehicle chassis dynamometer tests confirm that hydrogen fuel cell systems for vehicles can achieve very high conversion efficiency. The system efficiencies at ¼ power ranged from 52.5% to 58.1% from the four teams, very close to DOE's long-term target of 60%.
Projected fuel cell durability
Fuel cell stacks will need to last approximately 5,000 hours to enter the market for light-duty vehicles. For this demonstration project, DOE established targets of 1,000 hours in 2006 and 2,000 hours in 2009. The ultimate goal is to develop fuel cell stacks that last at least 5,000 hours. Vehicles in the project have not yet achieved 1,000 hours of operation, so NREL made projections based on the slope of the voltage degradation. The projections suggest that the time to 10% fuel cell stack voltage degradation averaged over 700 hours. One team achieve a time to 10% degradation that was over 1,250 hours, which exceeds the 1,000 hour DOE target. The 2nd generation stacks introduced beginning in late 2007 will be compared to the 2,000 hour target for 2009. Other tests within the DOE hydrogen program have validated 5,000 hour life in the laboratory. This suggests that more durable materials are still making their way from the laboratories to the demonstration projects.
Vehicle fuel economy
NREL measured vehicle fuel economy from city and highway drive-cycle tests on a chassis dynamometer. These raw test results were then adjusted according to U.S. Environmental Protection Agency (EPA) methods to create the "window-sticker" fuel economy like what consumers see when they purchase conventional vehicles. This resulted in an adjusted fuel-economy range of 42 to 56.5 miles/kg hydrogen for the four teams.
Vehicle driving range
NREL calculated vehicle driving range using the fuel economy results multiplied by the usable hydrogen stored onboard each vehicle. Using the EPA-adjusted fuel economy resulted in a range of 100 to 190 miles from the four teams. The 2nd generation vehicles will strive to increase the range to 250 miles—the 2009 DOE target.
Consumers will require hydrogen vehicle refueling that is as similar as possible to conventional vehicle refueling. NREL analyzed over 3,700 refueling events, and quantified the amount, time, and rate. Refueling took an average of 4.19 minutes with 78% of the refueling events taking less than 5 minutes. The average amount per fill was 2.15 kg, reflecting both the limited storage capacity of these vehicles (~4 kg max) and nervousness about letting the fuel gauge get close to empty. DOE's target refueling rate is 1 kg/minute, and these Learning Demonstration results indicate an average of 0.71 kg/min and a median of 0.75 kg/min. Twenty percent of the refueling events exceeded 1 kg/minute. From the results NREL concluded that hydrogen refueling times and rates close to being acceptable. The challenge, however, is to put enough high-pressure hydrogen onboard the vehicle to provide adequate range. Researchers are also looking for advanced hydrogen storage materials that can replace the need for high-pressure tanks.