Land Rover goes electric at the Eden Project With just under a million visitors a year, the Eden Project has a lot more people to impress as it moves them around the steep-sided former clay pit. "We reckon that at least a quarter of visitors travel on the road trains," explains Ben Foster, communications officer. So that's between 250,000 and 300,000 people a year who will travel on a Land Rover-pulled road train. "The land train started at the construction of the site," explains Ian Hillyard, land-train supervisor. It was the cheapest, simplest and most cost-effective way of moving people around the site and still is. Initially the tractors used 100 per cent biodiesel, but that became increasingly difficult to source and store. "We were very excited to find an alternative source of traction," says Hillyard. We've been surprised how effective the Defender is, especially the amount of torque it supplies. In fact the 94bhp/250lb ft Defenders aren't fantastically powerful, but use the characteristics of the Nidex Switch Reluctance electric motor, (maximum torque at zero revolutions), and the vehicle's transfer-box gearset to multiply that torque through all four wheels. "In fact, we've had to dial the torque back a bit," explains Jeremy Greenwood, chief engineer on this research project. Otherwise it will spin the wheels even with the diff lock engaged. Switch reluctance (SR) motors aren't the most common electric drives in the automotive world, which prefers AC synchronous motors. They are, however, robust, simple and easy to control, with non-rotating windings and are capable of high rotating speeds. SR motors also offer a limp-home ability if one winding goes down, and it are made of fairly cheap and accessible materials such as iron and copper, rather than rare-earth magnets. SR motors operate from a switched direct current supply, which supplies current in discreet and accurate periods to rotate the motor in a precise series of movements. That certainly proves the case with the Land Rover, which is astonishingly controllable at very low speeds. At one point, we crept at less-than walking speed up a 13 per cent gradient with all four carriages attached. These motors can display a characteristic hunting, or torque ripple, which the Land Rover also exhibits. The peculiar whoa, whoa is felt rather than heard, but Greenwood says it is being worked on. There's also a fair bit of whining from the motor and driveline, although it's not unpleasant and is, in some senses, a perfect example of the kind of motor noise the car industry is looking for to inform the driver and warn the public of an electric vehicle's approach. In all it's been a fine job of refining some pretty agricultural systems by Paul Feetenby of Pi Innovo, the Cambridge firm which did the software mapping. The rest of the driveline is pretty standard electric car, if that's possible to say. There's a 410kg, 300v, 27kWh lithium-ion battery pack and the current converter, which sit under the bonnet. The heavy-duty cycle means Land Rover has fitted an additional battery pack in the pickup bed behind the cab. No battery cooling is required as the 90 China Aviation Lithium Battery Co (Calb), lithium-phosphate prismatic cells are pretty robust. The motor sits in a ribbed casing between the front-seat passengers with the single reduction gear on the back driving the two-speed transfer 'box. On the rest of the seven-strong, single-battery experimental fleet, the normal range is about 50 miles, with a 12.5-mile reserve. Top speed is restricted to 70mph. Recharge time is 10 hours using a three-amp household supply, four with a 32A fast charger. In practice, the twin-battery Eden Project Defender is left on charge overnight. No one knows yet how it will fare in full active service because testing has only just begun. It's a measure of the vehicle's efficient scavenging of momentum that in tests at Land Rover's Gaydon development centre, the battery Defender will travel further cycling between zero to 30mph than it will at a steady 40mph. Travelling down one slope, with maximum regeneration dialled into the hill-descent control, we saw 30kW flowing back into the battery. The project was kick-started by a South African safari park, which wanted a quiet, torquey and environmental vehicle to carry visitors on a game sightseeing tour. They built their own electric Defender and then invited Land Rover to have a look at it. Greenwood was suitably impressed. We spent a bit of time sorting out their vehicle, then our management asked, 'what else can you do with that technology?'. He says. His engineers didn't need any more encouragement... The rest of the experimental fleet are station wagons and Land Rover is looking for placements, with options including another game park and maybe some all-terrain work where high-torque battery power would be a boon. Obviously, a known duty cycle and back-to-base operation is essential, but in those circumstances the battery Defender could be a much more environmental choice than a diesel. This doesn't come cheap - Greenwood says the conversion hardware costs over £20,000, with the batteries between £10,000 and £14,000 each as one-off supplies."Factor in the fuel costs for the tractors and the payback could be between two and three years," he says. Using off-peak electricity, a full fill-up for each battery is about £1.30, so not that much short of the cost of a litre of diesel. It's not something you'd want for your farm, but for pulling 64 people on a road train round a former clay pit, not much else is better or more environmentally-friendly than this car. Pictures: David Shepherd