Hydrogen Use for Transportation

Fuel Cell Vehicles

A technical overview of how a fuel cell works can be seen here in a previous section of the website.

The first vehicle to be powered by a fuel cell was back in October 1959 where propane gas was used as the fuel. The DC power produced by the fuel cell was used to drive a motor rated at 15kW or 20 horsepower fitted to a tractor [1]. Since then, fuel cells have been heavily used in the NASA space programs to produce the onboard electricity required by the spacecrafts as well as the drinking water for the astronauts.

Today, several car manufacturers are involved in developing fuel cell powered cars for the future. Honda recently made the first commercially available fuel cell vehicle known as the FCX Clarity. This mid-sized family car, while only available to lease in the southern California area (due to the available hydrogen infrastructure), is capable of returning an energy equivalent of 68mpg on the combined cycle and delivering zero harmful emissions. The fuel economy demonstrated by the Clarity can only be matched by very few of the most efficient diesel engines found in a smaller cars illustrating the potential for fuel cell technology.

Ballard Power Systems of Vancouver Canada were the first to produce a fuel cell powered bus back in 1993 as a demonstration. This bus used a proton exchange membrane(PEM) fuel cell stacked under the bus floor along with a glass-fibre wrapped aluminium hydrogen tank and electric drive motor. The bus was capable of 160km before refuelling which was some way off the 500km achievable by a diesel equivalent bus. The electric output from the fuel cell was 93kW (125hp) and the bus only seated 21 passengers. Further to this, each bus cost $1.4 million which is roughly 3 times the price of a conventional diesel bus of today [2].

Modern fuel cell buses have improved in performance over the early demonstration models of the previous decade and more efficient designs are continuously being developed. Buses set to enter service from Ballard Power Systems in 2010 are now capable of 3 times the range (500km) between refuelling compared to the buses from the 1993 demonstration and carrying four times as many passengers [3]. This has been achieved through a range of developments such as storing the H2 tanks on the roof along with the fuel cell to free up more interior cabin space for full floor access for passengers. Composite H2 tanks are now safer, lighter and smaller allowing for storage pressures between 350 and 700bar so that more fuel can be carried.

Hybrid-drive technology with brake regeneration fitted to the buses stores up some of the energy lost during braking in an onboard battery to power the ancillary systems and for moving off again instead of drawing power from the fuel cell as before. This is particularly effective for a town or city bus as it operates under ‘stop-start’ conditions.

One of the advantages of fuel cell power over an internal combustion engine (ICE) is that they can reach much higher fuel efficiencies approaching 60% under operating conditions whereas the latter can only manage between 15-25% [4]. Additionally, the only moving parts associated with fuel cell drive are found in the electric motor which reduces maintenance requirements over ICEs. The use of electric motors rather than ICEs also reduces the noise levels emitted from the bus. Typically, the interior noise levels at 35mph in a fuel cell and diesel bus is 65db and 73db respectively [5].

A drawback related to the use of fuel cell power is the large cost associated with the technologies involved. This is largely due to the lack of a hydrogen infrastructure and therefore a lack of a demand for the technology. As the world’s oil supplies begin to dwindle and the use of hydrogen as a replacement increases, the costs of fuel cell technology can be expected to decrease.

Furthermore, when a power-plant to wheel efficiency calculation is carried out for a fuel cell bus operating on electrolysed hydrogen, the efficiency is found to be around 22%. It should be noted that this efficiency figure takes account of transmission losses of hydrogen (as shown below) which would not be present in the Stornoway case study as the filling station is adjacent to the wind farm. Therefore, neglecting transmission losses would see a final power-plant to wheel efficiency of 26% [6].

Finally, fuel cells are known for having problems under ‘cold-start’ conditions i.e. sub-zero temperatures [7]. Stationary fuel cells are given the chance to run through a warm-up procedure but in a transportation application, the user will expect to switch on and go immediately. The cold-start problems are caused by the freezing of any residual water left in the fuel cell from previous use or the freezing of water in fuel cell on initial start-up as it is produced as a by-product. Fuel cell performance can also be adversely affected by the ambient temperature and will not reach maximum efficiency until normal operating temperatures are achieved. This problem can be solved with the use of anti-freezing and hybridisation.

References:

[1] http://www.hydrogencarsnow.com/blog2/index.php/fuel-cells/allis-chalmers-farm-tractor-was-first-fuel-cell-vehicle/

[2] http://www.netinform.net/H2/H2Mobility/H2MobilityMain.aspx?ID=278&CATID=2

[3] http://www.canada.com/topics/sports/story.html?id=7b9c39e1-7de0-4184-af7a-21c6610670e5&k=69154

[4] Fuel Cell Technology Handbook, Author: Gregor Hoogers

[5] Hybrid-Electric Fuel Cell Bus Demonstration, Authors: Jayson Cannon, ISE Corporation; Paul B. Scott, ISE Corporation

[6] Efficiency of Hydrogen Fuel Cell, Diesel-SOFC-Hybrid and Battery Electric Vehicles, Author: Ulf Bossel, European Fuel Cell Forum

[7] A PEM fuel cell model for cold-start simulations, Author: Hua Meng, Center for Engineering and Scientific Computation, School of Aeronautics and Astronautics China

[8] http://www.netinform.net/H2/H2Mobility/H2MobilityMain.aspx?id=278

[9] http://gizmodo.com/286141/2010-olympics-now-with-hydrogen-buses