Overview California through transit agencies like AC Transit and SunLine Transit Agency are leading some of the world's most sophisticated hydrogen demonstration projects in transit buses. No less than five generations buses are powered by various hydrogen fueled engine systems and are in or slated for revenue service. The traction configurations range from a large fuel cell engine to fuel-cell hybrid and even hydrogen internal combustion engine hybrid. The latest generation of fuel cell bus is a purpose designed modern bus designed for lower-weight and high-efficiency electronics and accessories to be coupled with a modern, high-durability fuel cell as a hybrid. This paper describes that evolution comparing and contrasting features, performance and anticipated benefits.

Research Starting in 2000, SunLine began operating their first ZE-bus or zero-emission fuel cell bus. During 2000-2001, an Xcellsis (now Ballard) ZE-bus began operations. The ZE-bus Phase VI test used compressed hydrogen to supply a 200-kW PEM fuel cell stack to power the 40' bus. Later, in 2002-2003, SunLine began operating the ThunderPower 30-ft fuel cell bus, a Thor Industries 30' ElDorado National EZ Rider 2 chassis using compressed hydrogen and a 60-kW PEM fuel cell stack from UTC Fuel Cells, then moving on for service at Chula Vista Transit.

The ISE/New Flyer hybrid hydrogen internal combustion engine (HHICE) bus was introduced into service in late 2004 at SunLine. The HHICE combines an ISE integrated electric drive and energy storage with a hydrogen-fueled ICE. Soon after arriving at SunLine, the HHICE bus was shipped to Manitoba, Canada for cold weather testing in February and March 2005. During the 2004-2006 period and continuing, a demonstration project of four fuel cell buses using UTC fuel cell stacks and compressed hydrogen in 40-ft Van Hool buses for AC Transit and at SunLine were developed and integrated by ISE, Van Hool, and UTC Power. Daily rigorous operation of these buses is focused on providing data to UTC Power for engineering development of a next-generation, more durable and reliable fuel cell for public transit but it also is capturing critical operational data in strenuous daily service. In December 2005, SunLine received one of these fuel cell buses. The HHICE and Van Hool fuel cell bus are currently in operation and preliminary evaluation results are available.

Just getting underway at SunLine is the American Fuel Cell Bus (AFCB) development, part of the National Fuel Cell Bus Program which will use an advanced 40-foot reduced-weight bus chassis by New Flyer, a 120 kW fuel cell from UTC Power, and an ISE improved electric traction drive subsystem, featuring a reduced weight power electronics suite, improved gearing to reduce weight and noise, and a lithium-ion battery energy storage subsystem.

Results The paper will compare and contrast such features as configuration, weight and space claim to show how the various hydrogen power-trains are becoming smaller, lighter and yet providing enhanced performance and efficiency. The results translate into lower cost and improved transit operations.