Hydrogen has for some time been proposed as an alternative energy source to carbon-rich fossil fuels, and there are "Hydrogen Highways" being planned and under discussion in several parts of the world including North America and Europe. In terms of propulsion, the automotive industry has looked at hydrogen for internal combustion engines (ICEs), and for use in fuel cells. Although BMW built a trial fleet of hydrogen ICE cars - the Hydrogen 7 - it too is now focussing on fuel cells. Mazda developed the Premacy Hydrogen RE Hybrid in 2007 as a bi-fuel version of the Mazda5, in which the two-rotor Wankel engine operates with hydrogen or petrol. Mercedes Benz, on the other hand, has developed its own fuel cell technology and the F-Cell has been introduced into the B-Class. Mercedes Benz has been working with fuel cells since 1994, and since 2003 has been running extensive testing of fuel cells in cars, vans, and service buses. Ford has looked at both technologies. Japanese and Asian auto companies have also been highly active in looking beyond the hydrocarbon era. Honda has been running its FCX fuel cell demonstrator cars on US roads for a number of years, and Nissan employs its own fuel cell technology in its X-TRAIL FCV. Generally speaking, a number of mainstream automobile manufacturers including Fiat have exhibited prototype fuel cell vehicles. All these vehicles are limited in number and require significant cost reductions before they can be commercialised.
A great attraction of fuel cells is their relatively high efficiency - currently 60% compared to 22% for petrol or 45% for diesel internal combustion engines. Coupling fuel cells to electric motors, which are more than 90% efficient, converts the chemical energy of hydrogen to mechanical work without heat as an intermediary.
Both hydrogen-fuelled and fuel cell vehicles emit only water at the exhaust, and thus they are able to meet future stringent automotive emission requirements. Thus programmes have been undertaken worldwide to test hydrogen-propelled buses, scooters, bikes and logistics vehicles as well as cars. Fuel cells are also used to propel boats and aircraft (mainly unmanned ones).
The majority of hydrogen generated today is obtained by reforming natural gas using electricity generated from hydrocarbon fuel, and using this hydrogen for "green" propulsion still generates a significant carbon footprint. The electrolysis of water to generate hydrogen similarly has an unwelcome carbon footprint, although utilising electricity generated from renewable sources to generate hydrogen for use in fuel cells and other applications, while relatively inefficient in a "well-to-wheels" calculation, would act as a store for intermittent energy (wind, solar, marine) that might otherwise be dumped if the grid could not take it.
Distributed hydrogen generation by small and medium sized electrolysers would address the lack of a hydrogen infrastructure, and could extend the use of fuel cells in off-grid applications including auxiliary power and recreation.
Hydrogen storage technology is improving, although current capabilities are best suited to return-to-base fleet delivery vehicles, such as logistics fleets, or, on a smaller scale, for fuel-cell bicycles. Storage solutions currently being pursued are high pressure tanks, cryogenic liquid hydrogen and the use of metal hydride storage systems. One reported problem with liquid hydrogen is the significant loss rate of the fuel in transportation. Most fuel cell and hydrogen ICE vehicles now utilise high pressure storage of hydrogen that allows for rapid dispensing and increased vehicle range.
Fuel cells have been around for a long time, and while scientists have been familiar with the principles of fuel cells since the nineteenth century, they first gained prominence in the manned spaceflight programmes of the 1960s. One type, alkaline fuel cells, famously provided electricity and drinking water for the Apollo astronauts, for example. Of the range of fuel cell types developed, the proton exchange membrane, also called polymer electrolyte membrane (PEM), type has been prominent in the "hydrogen economy", and there are many examples under development in the automotive and transport sectors.
In a PEM, hydrogen is channelled to the anode on one side of the fuel cell, and oxygen from the air to the cathode on the other side. A catalyst at the anode (usually platinum) splits the hydrogen into electrons and hydrogen ions, which pass through the membrane to the cathode. The electrons cannot pass through the membrane and thus travel around the external circuitry as an electric current. The hydrogen ions, when they reach the cathode, combine with the oxygen to form water, which exits the fuel cell. As each fuel cell generates a low voltage, stacks are assembled from a number of cells.
The fuel cell industry has been characterised to date by its hand-built, and hence costly, products, but there is a growing focus on volume manufacturing which is expected to produce dramatic reductions in the cost per kilowatt of a fuel cell.
How the land-based transportation sector will exploit the new technologies (battery-based electric vehicle (EV) technology, hydrogen ICE and fuel cells) remains to be seen. Meanwhile, fuel cells are beginning to find a growing application on the water.
In submarine propulsion, for example, the non-nuclear German Type 212 class U-Boat, developed by Howaldtswerke-Deutsche Werft AG (HDW) for the German Navy and the Italian Marina Militare, uses both diesel propulsion and an air-independent1 propulsion (AIP) system based on Siemens 120 kW PEM hydrogen fuel cells. Elsewhere, in Hamburg the Zemship is an excursion ship that began operating on the Alster Lake in the summer of 2008. This is a pilot project, and is due to run for two years as a demonstration that ships powered by full cells offer the ideal solution for ecologically sensitive inland waterways.
While the Zemship is a 100-passenger vessel, smaller electric boats for leisure, powered by hydrogen fuel cells, have appeared on Lake Traunsee, Austria, and elsewhere. In Austria the group of companies Fronius, Bitter and Frauscher has developed what they claim to be the first fuel cell ready for serial production to power a boat. This is a 4 kW fuel cell that currently powers the "Future Project Hydrogen" boat for use on lakes.
On smaller boats, in particular sailing craft, fuel cells are finding use as a replacement for diesel generator sets as auxiliary power units. They also stand to gain as battery replacements for electric leisure boats in use on American and central European lakes.
European lakes are beginning to ban and/or introduce restrictions on the use of hydrocarbon-powered boats on their waters in an effort to reduce pollution. Consequently, Europe has seen the rise in popularity of fast electric power boats for use on lakes and inland waters. As more lakes, marinas, ports and seaside towns are likely to impose tougher restrictions on engine exhaust and similar pollution, the electric power boat could become a common feature in yachting and boating.
Similarly, there is a movement in the US for electric-only lakes. There is a growing number of lakes that ban the use of spark ignition engines in order to reduce noise and emissions.
These boats are primarily powered by batteries, and while doing sterling service, batteries have a number of limitations that are opening the door for fuel cells to replace these batteries, particularly with the availability of hydrogen stored in metal hydride canisters. The main advantage of these hydrogen fuel cell boats compared with conventional battery-powered electric boats is the fact that no time has to be spent charging the batteries. For conventional electric boats, 6-8 hours of charging gives just 4-6 hours of use. The hydrogen-powered electric boat requires just the time that it takes to change the fuel cartridge, only about five minutes.
An approach emerging as highly appropriate for the recreational boating market is the hybrid battery/fuel cell system, in which the motor is driven by the battery which in turn is recharged by a hydrogen fuel cell. The hybrid system has the following advantages:
Such a hybrid system is being used on the HIDRO tender, a hydrogen powered tender developed jointly by Acta Energy and Callegari, shown below.
These are still early days for the commercial use of fuel cells in transportation, but the cost and technology barriers to quiet, emission-free travel on land and on water are falling.
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