Black cab goes green

A UK team is developing a zeroemission black cab powered by a high-energy battery pack and small fuel cell.

The London taxi will be fitted with two 40kW high temperature Zebra batteries, which have four times the energy density of a conventional lead acid battery, and a 6kW Proton Exchange Membrane (PEM) fuel cell.

Dr Nigel Schofield, the project’s leader and lecturer in electrical and electronic engineering at Manchester University, will this week present a paper on the project at a conference in Texas.

Combining the two technologies will make the vehicle more technically and commercially viable than a battery or fuel cellonly powered cab, he said. The fuel cell will extend the range of the battery-powered vehicle from around 120km–240km, for a combination of urban and suburban driving.

The sodium nickel chloride battery, meanwhile, will provide the bulk of the energy needed, and allow energy to be recovered from the vehicle’s braking, said Schofield.

‘Accelerating a 2.5-tonne London taxi from a set of lights requires something like 80kW peak power. If you went to a total fuel cell solution, you would have to have 80–100kW worth of installed fuel cell on the vehicle, and the cost, mass and volume of that would not be commercially competitive, as compared to a hybrid solution,’ he said.

The voltage regulation of fuel cells is a particular problem, he said. ‘In this case we have a 72V fuel cell when there is no load coming out of it, but when we pull maximum load that voltage drops down to 36V. ‘So it’s a very poor regulation, and that means you would have to install much more fuel cell units to get the peak power levels needed.’

The drivetrain will be fitted to a London taxi by engineers at environmental vehicle specialist Modec, and the electric cab will be tested around a track later this year.

The project also involves Magnetic Systems Technology, which is developing the taxi’s traction machine, and Derby-based Beta Research & Development, which is working on the battery management and supply.

The Zebra battery operates at around 300ºC, but is enclosed in a thermally insulated box. The batteries, which were originally developed by Beta and are now owned and manufactured by Swiss firm MES-DEA, contain no exotic materials. This means they should not be expensive when produced in large volumes, Schofield said.

MES-DEA also developed the fuel cell. The Zestful project is due for completion at the end of 2006. If successful the team hopes to find further funding to build a full demonstration model.