SUMMER/FALL 2003 — Vehicle Systems
Evaluating Energy Storage Requirements for Fuel Cell Vehicles
As part of the FreedomCAR and Vehicle Technologies Program, the Vehicle Systems Engineering and Analysis, Fuel Cell and Battery Technical Teams have been working together to determine the energy storage requirements for fuel cell vehicle applications. Argonne focused on developing realistic transient fuel cell models for current, mid-term, and long-term applications based on the GCtool model. The models were incorporated into CTR's Powertrain System Analysis Toolkit (PSAT) to evaluate the implications for energy storage.
Using a Ford Explorer as a base vehicle, several hybridization degrees were simulated (i.e., several combinations of battery and fuel cell power were analyzed). Using the characteristics of the Saft Li-ion HP6 battery, the analysis showed that a higher hybridization degree (i.e., more battery power) led to an increase in regenerative braking energy and a decrease in fuel cell system cycle efficiency. The increase in efficiency afforded by more regenerative braking does not always overcome the decrease in efficiency caused by downsizing the fuel cell and operating it outside its peak efficiency region, leading to an overall decrease in the fuel economy of the vehicle. CTR researchers also used detailed fuel cell modeling to study the impact of initial temperature on fuel cell vehicle system efficiency.
Higher hybridization degree leads to increase in regen braking.
Higher hybridization degree leads to decrease in fuel cell system cycle efficiency.
The initial battery state-of-charge (SOC) had a significant effect on the results and the impact of the control strategy was assessed. Several options were considered to increase fuel economy by modifying the SOC and the minimum fuel cell power demand. The impacts of driving cycle and energy storage technology were also investigated.
The study is not yet complete, but Argonne's work using GCtool-Eng and PSAT has demonstrated that the best fuel economy is a compromise between hybridization degree, energy storage technology, driving cycle, and control strategies. Future work will refine the results and focus on the most important parameters.
Sponsor
U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, FreedomCAR and Vehicle Technologies Program
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