Fuel Cell Vehicles
The fuel cell as a propulsion system is in many ways superior to batteries, as it needs to carry less energy storage devices by weight and volume compared to a vehicle propelled by batteries alone. Figure 1 illustrates the practical travel range of a vehicle powered by a fuel cell (FC) compared to lead acid, NiMH or Li-ion batteries. One can clearly see that lead- and nickel-based batteries simply get too heavy when increasing the size to enable larger distances. In this respect, the fuel cell enjoys similar qualities to the IC engine in that it can conquer large distances with only the extra weight of fuel.
Figure 1: Driving range as a function of energy storage.The logarithmical curves of battery power place limitations in terms of size and weight when increasing distances between charges. In comparison, the fuel cell and IC engine share a linear progression.
Note: 35MPa hydrogen tank refers to 5,000psi pressure; 70MPa is 10,000psi.
Courtesy of International Journal of Hydrogen Energy, 34, 6005-6020 (2009).
Although the fuel cell assumes the duty of the IC engine in a vehicle, poor response time and a weak power band make onboard batteries necessary. In this respect, the FC car resembles an electric vehicle with an onboard power aggregate to keep the batteries charged. The battery is the master and the fuel cell becomes the slave. On start-up, the vehicle relies 100 percent on the battery and the fuel cell only begins contributing after reaching a steady state in 5–30 seconds. During the warm-up period, the battery must also deliver power to activate the air compressor and pumps. When warm, the FC provides enough power for cruising, and when the vehicle is accelerating or climbing hills both the FC and battery provide power. During braking, the kinetic energy is returned to charge the battery.
The FC of a mid sized car generates around 85kW, or 114hp. The energy is coupled to an electric motor with a similar or slightly higher power output. The onboard battery has a capacity of around 18kW and provides throttle response and power assist when passing vehicles or climbing hills. The battery serves as a buffer similar to the HEV and does not get heavily stressed by repeated deep cycling, as is the case with the EV.
Hydrogen costs about twice as much as gasoline, but the high efficiency of the FC compared to the IC engine in converting fuel to energy gives the same net effect on the pocketbook, with the benefit of less greenhouse gas and reduced pollution.
Hydrogen is commonly derived from natural gas. Critics might well ask, “Why not burn natural gas directly in the IC engine instead of converting it to hydrogen through a reformer and then transforming it to electricity in a fuel cell to feed the electric motors?” The answer is efficiency. Burning natural gas in a combustion turbine to produce electricity has an efficiency factor of only 26–32 percent, while using a fuel cell is 35–50 percent efficient. We must keep in mind that the machinery required to support the clean FC is far more expensive and requires additional maintenance over the more simplistic burning process.
Complicating matters further is the fact that we have no hydrogen infrastructure, and the cost of building one is prohibitive. A refueling station capable of reforming natural gas to hydrogen for the support of 2,300 vehicles costs over $2 million to build. In comparison, a charging outlet for the EV is less than $1,000, but the refill time would be longer than with the FC. Meanwhile, we have plenty of gas stations that offer a quick fill-up of cheap fuel.
Durability and cost are other concerns with the fuel cell, and there have been encouraging improvements. The service life of an FC in a car driven in normal traffic conditions has doubled from 1,000 hours to 2,000 hours. The target for 2015 is 5,000 hours, or the full life of a vehicle driving 240,000km (150,000 miles). Further challenge is cost. The fuel cell costs substantially more to manufacture than an IC engine. As a simple guideline, the FC vehicle will be more expensive than a plug-in hybrid, and the plug-in hybrid will cost more than a regular gasoline-powered car. Based on our relatively low fuel prices, using alternative conversion methods is difficult to justify in terms of cost savings. The benefit goes to the environment.
Comments
All fuel cells are made up of three parts: an electrolyte, an anode and a cathode.Fuel cells function similarly to a conventional battery, but instead of recharging, they are refilled with hydrogen.Different types of fuel cells include Polymer Electrolyte Membrane (PEM) Fuel Cells, Direct Methanol Fuel Cells, Phosphoric Acid Fuel Cells, Molten Carbonate Fuel Cells, Solid Oxide Fuel Cells, and Regenerative Fuel Cells.
Before the end of the oil/gas era (within 30-50yrs.) and the current “profit based economy”
people should think and consider/apply a new “resource based economy”. Within this we have to calculate the amount of raw materials we would need globally to manufacture some billions of new fuel cell driven cars. That would not only be price limited, but global resource limited activity.
Sincerely yours
Andras KEMERI
Thank you very much for these interesting and most informative aticles. Thank you for making it availibe to ordinary people lke myself.
Yours sincerely - Wynand Bezuidenhout; Bloemfontein; South Africa