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15/09/2008
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Tom Shelley reports on state of the art in fuel cell systems for passenger cars and other applications
Nissan expects its fuel cell systems for passenger cars to be on the road – in commercially available vehicles – by 2015.
At the same time, collaborating UK researchers are equally confident they will have truly ‘green’ hydrogen-generating technologies in place by then – and have just won themselves an award for a design for motorsport which will be competing on track next year.
As well as cars, fuel cells are already in serious use in aerospace and defence applications and it is conceivable that we will see fuel cell powered aircraft before much longer.
We were recently able to take one of Nissan’s hydrogen fuel cell powered X-Trail SUVs for a test drive through the London traffic. It was quiet running, accelerated and handled well. We might have placed an order on the spot, were it not for the £1.5 million price tag.
Izuho Hirano, manager of the Nissan fuel cell laboratory in Kanagawa, Japan told Eureka that the company’s target was to have fuel cell powered cars on the road in 2015, but there remained the issue of durability – increasing fuel cell life from a few years to more than 10 – and cutting the manufacturing costs of the cells and the compressed hydrogen tanks. He said that a new thin separator had cut the weight of the polymer electrolyte fuel cell stack in the Nissan car by 50% and size by 4%.
The hydrogen tank we saw was, says Hirano, made of aluminium, wrapped in carbon fibre, and rated at 70 MPa. At this pressure, it would give the car a range of 500km – or 370km if pressured to 35MPa. The car is front wheel drive, powered by a single three phase 90kW motor delivering 280 Nm of torque, fed via an inverter which also delivers surplus power to a lithium ion secondary battery, which can deliver extra current to assist acceleration, or absorb energy produced by regenerative braking.
Even Nissan does not expect fuel cells to totally replace conventional engines: even by 2050, the company thinks that high efficiency internal combustion engine cars will still predominate, even if they are mostly hybrids.
Professor Nigel Brandon, who holds the Shell Chair of Sustainable Development in Energy at Imperial College, said that in order to reduce carbon emissions, it was essential that hydrogen for fuel cells be derived from non-fossil fuel sources – as it would require special (and expensive) purification in order not to ‘poison’ the fuel cell. He drew attention to a fuel cell powered racing car that Imperial College is entering for the Class 1A, low carbon vehicle part of the Formula Student competition next year. The car has four separate motors – one coupled to each wheel.
“Each can each be controlled independently in order to improve the dynamic performance of the car,” said project leader Mark Cordner.
Even if fuel cells never becomes mainstream in passenger cars, the commercial impetus given them by developing fuel cells for such vehicles opens up many other applications that are slightly less price sensitive. They are already in use in various military systems, and mobile phone base stations in Africa, in the former case because of their quietness and efficiency – fuel cells tend to be 50-60% efficient, compared with 40-45% at best for internal combustion engines. They are also being investigated for use in manned aircraft in the Environmentally Friendly Inter City Aircraft powered by Fuel Cells (ENFINCA-FC) project led by Professor Giulio Romeo at the Turin Polytechnic University. Two-thirds of the project cost (2.9m Euros), has been put up by the European Commission. The project is aimed at light and small commuter aircraft. At the same time, Boeing and its industry partners are also developing a light aircraft to be powered by a 20kW fuel cell and a lithium ion battery pack.
Pointers
* Fuel cells are becoming more mature technology, the remaining challenges being to increase lives from a few years to more than ten, and to further cut costs
* Hydrogen storage is best undertaken as compressed gas, but there is a need to reduce the cost of light weight storage tanks
* Drive trains typically involve secondary lithium ion or other secondary batteries to store and deliver peak power.
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Author
Tom Shelley
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