Recently, I wrote about the proposal by one neighbourhood group at the waterfront to use hydrogen fuel-cell buses in place of LRT. Many thanks to all who contributed feedback to that piece.
This item contains a lot of technical bumpf and calculations. If anyone finds an error in this, please let me know and I will be happy to correct it, even if that worsens my own argument. I would like some real information to be “out there” on the issue rather than a lot of hype.
At Toronto Hydro, we learn:
In windspeeds of 6m/s, the turbine produces 110 kW and the turbine reaches its rated capacity of 750kW in windspeeds above 14m/s. On average, the 750kW wind turbine will generate 1,400 megawatt hours (MWh) of electricity per year, equivalent to the electricity needs of about 250 homes, and can displace about 494 tonnes of carbon dioxide.
Meanwhile, there is a lot of information available on the site that tracked the European Union’s fuel cell experiment. The ticker on the left side takes you to a collection of reports at this link including the July 2006 final report.
From that report we learn a number of things:
- The number of buses in the trial was 27.
- The total fuel consumed was 192,000 kg of hydrogen.
- The total distance travelled was 841,123 km.
- Ergo, the fuel consumption was 22.8 kg per 100 km, and the average bus travelled 31,153 km.
- The average speed of operation was 12.8 km/hr which, by Toronto standards overall, is low, but not far off the mark for congested downtown operation with frequent stops. Also, the value varies considerably from city to city probably as a function of the type of service, just as speed and diesel fuel consumption in Toronto vary a lot from route to route.
As for fuel production:
- One litre of water produces 1 normal cubic metre or .09 kg of gas. (A normal cubic metre is mesaured at 0 degrees C and 1.013 bar pressure.)
- This process consumes 4.8 kWh for the electrolyser, and 5.1 kWh for the transformer, rectifier and gas cleaning. Thus a total of 9.9 kWh is required to produce .09 kg of gas.
- This translates to 110 kWh to produce 1 kg of gas.
- Note that less than half of the power consumed actually goes into splitting water into hydrogen and oxygen.
- Some future saving may be possible for turbine based production by directly linking the turbine output to the electrolyser. In this project, electrical power was usually drawn from the grid and had to be converted to the appropriate form for use in hydrogen production.
The economics of the trial in various countries were highly sensitive to transportation costs. In other words, if you don’t have the gas right where you need it, you will pay a lot to get it there and this is counter to the purpose of saving energy.
From the TTC’s own stats, we know that an average bus travels about 69,000 km per year, or about 230 km per day (counting Saturdays and Sundays as half days).
One bus day therefore consumes (230/100) * 22.8 kg of gas = 52.4 kg of gas.
The power required to produce this gas is 52.4 * 110 = 5,764 kWh = 5.76 mWh.
For one year, the power required is 5.76 * 300 = 1,728 mWh.
The turbine at the CNE produces 1,400 mWh per year (average) and so is capable of powering less than one bus.
I have not even mentioned the question of fuel storage, maintenance and safety of very large gas volumes. Although the brochures show nice little clusters of gas tanks, these are for very small numbers of buses in each trial city. A reasonable fleet would be at least 100 vehicles, probably 150 or more, and the fuel storage would be correspondingly larger.
Siemens looked at the energy consumption of a Combino LRV in Basel and Potsdam about 10 years ago in this paper, and found that it consumed under 200 kWh per 100 km. I have rounded up the actual numbers cited in the article which were 153 (Basel) and 184 (Potsdam). The lower consumption in Basel was due to a higher rate of energy recovery due to the duty cycle of the vehicle (better regenerative brake recovery).
A hydrogen bus needs 22.8 kg of hydrogen to travel the same distance, and that costs 22.8 * 110 = 2508 kWh to produce. Even a huge reduction in the conversion losses would not reduce hydrogen’s energy cost per vehicle km to anything near that of an LRV. Oh yes, there’s also the little matter of vehicle capacity — the Siemens tests were conducted with an equivalent passenger load of 65, and that’s not a full vehicle. That’s well above the service design capacity of a bus.