Researchers from the National Renewable Energy Laboratory, commissioned by the California Air Resources Board (ARB), have issued their initial evaluation of the hydrogen fuel cell buses in operation at BC Transit. The report covers two years of revenue service data on the buses from April 2011 through March 2013.
In 2012, NREL developed a guideline for evaluating the technology readiness level (TRL) for fuel cell electric buses (FCEBs). TRLs range from concept design at TRL 1 up to full commercialization and deployment at TRL 9. Using this guide, the NREL team assessed the BC Transit buses to be at TRL 7: full-scale validation in a relevant environment. During the two-year data period analyzed for the report, the FCEB fleet accumulated more than 2.1 million kilometers (1.3 million miles) and more than 156,000 hours on the fuel cell power plants. Overall the FCEBs have an average fuel consumption of 15.48 kilograms of hydrogen per 100 kilometers. This equates to a fuel economy of 4.53 miles per diesel gallon equivalent (mi/DGE). The buses have an average availability of 69%.
The background. British Columbia Transit (BC Transit) has been leading a demonstration of fuel cell electric buses (FCEB) in Whistler, Canada, since early 2010. This 20-bus demonstration was introduced during the 2010 Winter Olympic Games and is the world’s largest FCEB fleet in a single location.
BC Transit used a standard procurement process to purchase the FCEBs. The agency released a request for proposals in February 2007 outlining bus specifications to meet the service requirements of Whistler. After reviewing the proposals, BC Transit selected New Flyer Industries.
BC Transit is collaborating with the ARB and the US Department of Energy’s (DOE) NREL to evaluate the buses in revenue service. While the BC Transit fleet is located outside of the United States, the operation of transit fleets within Canada is similar to that of fleets in the United States. The bus is designed for the North American market, and future models could be built to meet ‘Buy America’ requirements for US transit agencies.
The buses. The FCEBs are 42-foot, low-floor buses built by New Flyer with a fuel cell-dominant hybrid-electric propulsion system in a series configuration. In a series configuration, the fuel cell power system is not mechanically coupled to the drive axle. The 150 kW fuel cell power system and the 47 kWh energy storage system work together to provide power to two 85 kW electric drive motors, which are coupled to the driveline through a combining gearbox.
When the bus needs extra power, the fuel cell power system and energy storage system provide power to the drive motors. When the power requirements of the bus are low, the fuel cell power system provides power and recharges the energy storage system. The hybrid system is also capable of regenerative braking, which captures the energy typically expended during braking and uses it to recharge the energy storage system.
The power plant, which is the primary power source for the hybrid system, is Ballard Power Systems’150 kW FCvelocity-HD6. The energy storage system consists of two lithium phosphate battery packs from Valence. The Whistler buses required a supplemental 20 kW heater to meet winter heating demands.
Fueling a 20-bus FCEB fleet requires a station capable of dispensing up to 800 kg hydrogen per day when the entire fleet is operating. The hydrogen station at Whistler is a liquid hydrogen storage and gaseous dispensing station and is designed to fast-fill (10 minutes or less) up to 20 buses per day.
The findings. From BC Transit’s perspective, there have been many achievements for the demonstration, including:
- Project was delivered on-time and on-budget;
- FCEBs have accumulated more than 3 million kilometers in revenue service, operating up to 22 hours a day in a wide range of temperatures;
- The station has dispensed more than 462,000 kg of fuel over 17,900 fills without a safety incident;
- Operating the FCEBs, the agency has avoided more than 4,400 tons of CO2 compared to using diesel; and
- The FCEBs were incorporated into the fleet, fully maintained by Whistler Transit staff.
However, the project also encountered issues, including:
Bus range. Originally designed to have eight hydrogen tanks, the production buses dropped the number of tanks to six because of weight considerations. Once the buses went into service, BC Transit determined that the performance would not meet the service requirements. Early in the demonstration, the manufacturer then added the two tanks back to each bus. In addition, Whistler Transit added a mid-day fueling to the operation to ensure that the buses could operate all day. This required the agency to hire more staff to fuel the buses. This mid-day fueling was only required for a few specific routes.
Bus suspension. The buses have had issues with the suspension because of the weight and the difficult duty cycle. Components within the suspension, such as sway bars, have experienced higher wear and tear compared to similar components on conventional buses. To address the issue of early failures, Whistler Transit has added these components to its parts inventory and is integrating replacements into the normal preventive maintenance schedule.
Battery issues. The batteries have had issues that have been addressed with a routine procedure to balance the packs. Whistler Transit uses a Brusa charger for this procedure, which can take a few hours to a few days. This takes a bus out of service for the duration of the charging time and also takes up space in the facility.
Air compressor/motor/controller. The air compressor, motor, and controller assembly—part of the fuel cell balance of plant—proved to be one of the biggest issues for the system. Ballard is currently testing another compressor and plans to handle this component as part of its system for future buses.
Dry-out. Ballard had earlier determined that it could lengthen the life of the fuel cell stack by periodically performing a dry-out procedure. For BC Transit, this required removing the module and shipping it to Ballard for the procedure. The demonstration project has two spare fuel cell modules, so this could be done without taking a bus out of service for an extended time. Currently, this procedure is done at Whistler Transit without removing the fuel cell from the bus. Ballard is working on a process to incorporate the dry-out process into the module operation so that it is transparent to the customer.
Changing market players. The current economic climate has resulted in changing players within the FCEB market. Over the years, several companies have left the market through restructuring or bankruptcy. The departure of ISE left the project team with insufficient support for the demonstration. The company’s demise affected other FCEB demonstrations as well. When the partners no longer provide technical support or produce parts needed for repair, this makes conducting long-term demonstrations a challenge.
Evolution of technology and components. As the technology development progresses, components and parts are modified for new designs. This evolution results in components that are now obsolete for current demonstrations. Replacement parts become hard to locate or may become obsolete because manufacturers have stopped producing the older designs. Obtaining replacement battery modules has proved to be challenging for BC Transit because the manufacturer’s new battery design is not the same size or does not have the same operating characteristics.
From BC Transit’s perspective, FCEB development must address the following to make the technology feasible for transit operation:
- Improve the reliability of systems and components;
- Lower the purchase and operational cost to levels approaching that of current technology;
- Reduce the maintenance cost;
- Establish a sustainable parts supply chain;
- Lower the fuel consumption and the cost of hydrogen;
- Further reduce bus weight;
- Improve fueling times;
- Improve diagnostics systems; and
- Define the necessary requirements for hydrogen stations to service larger fleets.
A second report outlining the final performance results is expected to be published in summer 2014.
L. Eudy and M. Post (2014) “BC Transit Fuel Cell Bus Project: Evaluation Results Report,” Technical Report NREL/TP-5400-60603