Abstract:This report is the result of a study to assist Georgetown University in the evaluation of flywheel and ultracapacitor technology for use in the US Department of Transportation (DOT) fuel cell bus program. The objectives of the study were to evaluate the current state-of-the-art of these technologies and to estimate the time scale for their use in the fuel cell powered bus program. To accomplish these tasks site visits were made with 8 researchers and developers. Five additional contacts were made with others working in the technology. A simulation was performed using Hybrid (a bus simulation program developed by Georgetown University). Based on the simulation results, the energy storage and power requirements for flywheels and ultracapacitors were established. The likelihood of meeting these requirements with flywheels and ultracapacitors available today and what may be available in the next two years was then assessed based on the current state-of-the-art of these technologies.