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- Electric drive
- Fuel cell stack
- Cooling module
- Anode humidifier
- Water pump
- Water tank
- DC/DC converter
- Cathode humidifier
- Glycol water reservoir
- Coolant pump
- Liquid hydrogen store
- High voltage battery
- Air filter
- Compressor
- Combustor/blower
A fuel cell is a device that generates electricity by a chemical reaction between hydrogen gas and steam. During the reaction, electrons - the particles that hurtle through wires to give us electricity - are given off and collected to be used to power an electric motor. The only by-product is harmless water.
The process might sound space-age - it was perfected to generate electricity in space for the US Apollo programme - but in fact was first demonstrated in 1839 by a Welsh judge, Sir William Grove. The reaction takes place across a platinum catalyst - a bit like the device that scrubs the muck out of a petrol engine's exhaust. But instead of being tubular to fit inside an exhaust pipe, the fuel cell is very thin, just 1.3 millimetres thick. Each cell generates about 1 volt of electricity, so they are connected together in a series. A family car needs about 200 volts, so a typical stack would contain 200 cells.
Use of fuel cells will require plentiful supplies of hydrogen but, fortunately, it is already created in huge quantities for industrial use. According to Matthias Altman of German consultant L-B Systemtechnik, annual worldwide production of hydrogen is 50 million tonnes - enough to power all the cars in the US, Europe and Asia.
But hydrogen is not an easy fuel to deal with, and storing it in a vehicle is tricky. To fit in the confined space of a car, the hydrogen gas has to be liquefied and that can only occur at the incredibly low temperature of 253 deg C - not far off absolute zero. Keeping the fuel at that temperature is technically a huge challenge and, at the moment, very expensive. Today's tanks are like big scuba-diving tanks, but wrapped in incredibly efficient insulation made up of dozens of reflecting layers of foil. Although just 40 mm thick, it's the equivalent of 9 m of the foam used to keep central-heating tanks warm. Even so, the hydrogen does warm up and expand, so the plumbing for a fuel-cell car includes a vent that automatically stabilises the pressure by burning off excess gas - a process that slightly knocks its environmental credentials.
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