Frequently Asked Questions

1. Why is the Greater New Haven Transit District undertaking this ambitious project?
2. Why Hydrogen?
3. Why Hybrid?
4. What does "hydraulic hybrid" mean?
5. Why has GNHTD decided to base the vehicle on a 30’ transit bus as opposed to a standard 40’ transit bus?
6. What are the differences between the two auxiliary power units being developed?
7. Why is GNHTD testing two auxiliary power units instead of just one?
8. Is either of these auxiliary power units being used successfully on the street now?
9. What is electrolysis technology?
10. Why did GNHTD choose electrolysis technology for its hydrogen fueling system?
11. Is electrolysis being used successfully in a transit application?
12. What distinguishes this project from other hydrogen bus projects?

1. Why is the Greater New Haven Transit District undertaking this ambitious project?

The Greater New Haven Transit District (GNHTD) has a history of promoting green transit through the District’s electric-powered shuttle buses in downtown New Haven.  Fossil fuels are in limited supply.  As availability diminishes, costs increase and reliability as a future sources of energy decreases.  Fossil fuels also produce pollutants that damage air quality and endanger public health.  GNHTD is committed to bringing renewable, non-polluting, green energy transit to Connecticut and to the New Haven region.  Additionally, this project has the potential to create additional jobs and expand technology in Connecticut.  The project goals are ambitious, and so are the benefits to Connecticut residents. Back to top

2. Why Hydrogen?

Hydrogen has the potential to partially address Connecticut's long term energy and environmental challenges.  Over the next few decades, hydrogen fuel and technologies can help reduce petroleum dependency in our transportation sector, improve reliability in our electricity generation system, and provide important environmental benefits.  Development of hydrogen technologies can also help create new jobs and businesses in Connecticut.

Connecticut's transportation sector is nearly 100% dependent on gasoline and conventional diesel, both of which are non-renewable and in limited supply.  Further, the burning of traditional fossil fuels has a negative impact on the environment and is a main contributor to air pollution and related adverse impacts to public health. Expansion of hydrogen technology within Connecticut has the potential to reduce petroleum dependence, yield environmental and public health benefits, and stimulate economic growth. Back to top

3. Why Hybrid?

Hybrid systems generally increase the efficiency of the vehicle, improving fuel economy.  Hybrid systems do this by adding an on-board rechargeable energy storage system (such as batteries, ultra capacitors, and hydraulic accumulators). These systems are able to recapture energy normally lost in braking operations. This extra energy allows the vehicle designer to specify relatively smaller engines, which are generally more fuel efficient, without a loss in overall system performance.

GNHTD believes that by utilizing a hybrid drive train, it will maximize the vehicle’s energy efficiency and reduce overall operating costs by increasing the vehicle’s overall fuel economy. Back to top

4. What does "hydraulic hybrid" mean?

Hydraulic hybrid is a type of hybrid system where mechanical energy is recaptured by a hydraulic system.  Instead of batteries, hydraulic hybrid systems use a hydraulic accumulator as its rechargeable energy storage device. The accumulator is recharged by a hydraulic pump powered by the momentum of the bus as it slows down. The accumulator releases the captured energy by reversing power through the pump to the vehicle’s drive line. This release of energy gives the vehicle an added boost in acceleration.

Hydraulic hybrid systems exhibit several advantages in maintainability over battery-electrectic hybrid systems. Hydraulic systems are based on a mature technology supported by established international companies. Also, hybrid system components have lifespans equal to or greater than the entire vehicle, unlike batteries which require expensive replacement cells every few years.

5. Why has GNHTD decided to base the vehicle on a 30’ transit bus as opposed to a standard 40’ transit bus?

This decision is based on several factors.  First, GNHTD will operate these buses initially throughout the downtown New Haven area, and believes that a 30’ vehicle would provide greater mobility in this environment.   Second, the high turnover in demand on a downtown circulator does not require full-size bus capacity.  Finally, most fuel cell demonstration projects are on full-size buses or on smaller, auto or van sized vehicles.  The 30’ bus will be a new addition to this blossoming industry and will allow for the use of a smaller fuel cell than a 40’ bus might require. Back to top

6. What are the differences between the two auxiliary power units being developed? Back to top

The first vehicle will utilize a hydrogen fuel cell for its main power source. The second will use an internal combustion engine fueled by hydrogen. Back to top

7. Why is GNHTD testing two auxiliary power units instead of just one?

GNHTD is developing this program in conjunction with the Federal Transit Administration to provide them and the transit world with an ‘apples to apples’ comparison to determine which technology has the most potential for commercialization in the transit industry. There has never been a direct comparison between the two technologies on the same transit vehicle platform.Back to top

8. Is either of these auxiliary power units being used successfully on the street now?

Yes, several hydrogen bus projects have been developed across the United States.  Fuel cell auxiliary power units are currently being utilized in hydrogen bus projects at AC Transit (Oakland, California), Santa Clara Valley Transportation Authority (San Jose, California), Hickam Air Force Base (Honolulu, Hawaii), Sunline Transit Agency (Thousand Palms, California), and several others. Historically, hydrogen-powered internal combustion engine projects have been limited to light duty vehicles. Back to top

9. What is electrolysis technology?

Electrolysis technology, as used in this context, refers to a method of generating hydrogen for use as a fuel. This method requires only water and electricity as the inputs to create hydrogen. Other methods, including reformation, require the input of fossil fuels, such as natural gas.

10. Why did GNHTD choose electrolysis technology for its hydrogen fueling system?

Electrolysis was chosen by GNHTD to completely eliminate any dependence on fossil fuel for this program, as GNHTD has set an objective of making this project “all green”. Back to top

11. Is electrolysis being used successfully in a transit application?

Reformer technology is currently the primary technology used for on-site hydrogen generation at various transit agencies. This is due primarily to the historic high expense of electrolyzer technology. However, as many companies are developing commercial products based on electrolyzer technology (such as project team member Avalence of Milford, Connecticut), GNHTD expects the cost of this technology to decrease in the near term.

Several transit agencies with hydrogen bus projects do not generate their own hydrogen on-site but rather truck it in and deposit the hydrogen into on-site storage and dispensing facilities. GNHTD plans to utilize trucked-in technology only as a back-up to its planned electrolysis-based hydrogen generation facilities. Back to top

12. What distinguishes this project from other hydrogen bus projects? 

This project has several distinguishing characteristics that make it unique among other fuel cell transit bus projects, as follows:

1. This project will be “All Green”.  No fossil fuels will be used in its operation.
2. A direct ‘apples to apples’ comparison will be made between fuel cell and hydrogen fueled internal combustion engine technologies.
3. A hydraulic hybrid propulsion system, a first of its kind in the transit industry, will be utilized.
4. A significant focus is placed on improved ADA characteristics, including an advanced automated guidance system, which will allow the vehicle to consistently dock at bus stops with a level curb-to-door clearance of about one inch. This will virtually eliminate the typical bus step and gap, allowing persons with disabilities to board effortlessly.
5. A 30’ transit vehicle will provide the platform.
6. This project hopes to optimize the use of Connecticut industry and train Connecticut students and workers in the maintenance of these new vehicles.

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