THE moment I jump aboard Howard Ross’s bus, I realise something’s missing. With rows of cloth-covered seats, it looks perfectly normal: there’s plenty of space for the usual crush of commuters, pensioners and pushchairs. But this bus is powered by electricity. Electric buses are usually stuffed full of heavy batteries to stop them grinding to a halt between stops. So what’s Ross’s secret? The answer is that his vehicle recharges its modest load of batteries on the fly, with energy sucked from electrical “power points” laid beneath the surface of the road. And thanks to his design, these power points can be laid anywhere – at bus stops, junctions, even on three-lane highways.
Ross, a mechanical engineer and long-time transportation consultant whose client list includes General Motors, Ford and the Electrical Power Research Institute in Palo Alto, California, has spent 20 years developing this technology. “These buses will be the first commercially viable, all-electric city buses,” he says. And he aims to prove it early next year when the prototype makes its maiden voyage from Boston’s Hyde Park to the Massachusetts Bay Transportation Authority station at Forest Hill, a round trip of 6.8 kilometres. If the tests are successful, Ross believes the next step is to fill the street with electric cars, a green dream come true.
Ross first became convinced that conventional electric vehicles could never be practical during the 1970s. He realised that the range of these vehicles would be limited by the weight and size of their batteries. And he began to wonder if a century-old technology could provide the key.
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In the 1890s, engineers found that they could use magnetic fields to send electrical energy over short distances through air, with little loss. This is how electric transformers work: the magnetic field created by current flowing through one coil can induce a flow of current in another coil nearby. If you could drive a suitably modified vehicle through a magnetic field, you should be able to transfer electrical energy to it, and use this to keep its batteries topped up. Ross reckoned it was the only way to make electric vehicles viable.
However, the most efficient way to beam power through the air to a vehicle is to transmit the energy as close to the vehicle as possible. Ross worked out that to do this safely you’d need to provide the power from beneath the vehicle – from the street itself.
So he came up with a unique charging system. It uses two specially designed plates, one of which is connected to the mains electricity supply and is buried about a centimetre beneath the surface of the road. The other is suspended just beneath the chassis of the vehicle.
These plates are designed to behave like the coils in a transformer. Usually the energy in a magnetic field would flow in a spherical pattern around the plate. But Ross has changed the shape of the magnetic field by making each plate from thousands of paper-thin strips of a steel alloy, with the strips arranged vertically like slices in a loaf of bread, each insulated from its neighbours by a thin layer of epoxy resin. The laminated structure and orientation of the metal strips channels the magnetic field vertically instead of horizontally, maximising its overlap with the plate above.
When the plate in the bus is aligned with the plate in the road, the magnetic field from the current in the buried plate induces a flow of current in the vehicle’s plate. This gives the vehicle enough juice to make it to the next charging station.
In the early 1990s, while Ross was consulting for General Motors, he explained his concept to some company executives who liked the idea and encouraged him to develop it. However, potential investors seemed discouraged by the costs of modifying cars and laying electric power points in the road. Then in 1997, Ross visited New England on business and dropped in on Boston Edison’s electric-car research programme. żěè¶ĚĘÓƵs working on the programme put Ross in touch with the Massachusetts Bay Transportation Authority (MBTA), which operates the city’s bus system. By the following year, with help from the MBTA and the state’s Executive Office of Transportation and Construction, Ross and Boston Edison had secured $3 million in federal funding to develop a system for powering electric buses. In April 2000, Ross and Edison signed a contract with the MBTA. Unfortunately, Ross’s partnership with Edison ended a year later when Edison’s electric car programme was shut down. But by then Ross and the MBTA had drawn up plans for a demonstration project and the agency had forked out $750,000. So with extra funding from private investors, Ross started work.
The system he has come up with uses a plate slung beneath the chassis of a bus, and matching plates sunk in the road at intervals – perhaps even at every bus stop. Each plate is a metre wide, five metres long and two centimetres thick. Sensors buried in the ground detect when the bus has come to a stop overhead and switch on current to the buried plate. This induces a current in the plate beneath the bus, which is connected to the batteries. However, the alternating current induced in the plate has to be turned into direct current in a rectifier before it can be stored in the batteries (see Diagram). Sensors on the bus can gauge how much charge its batteries need and switch the plate off when they’re topped up.
Charging batteries this way isn’t especially difficult, and Ross admits that many people have already worked on the idea: for example, some electric toothbrushes and cordless power tools use similar technology. “But we’ve been the most persistent,” he says. And to make the idea practical, Ross and his research team have had to work out how to improve the efficiency of energy transfer, even when the metal plate on the bus isn’t perfectly aligned above the one in the road.
Running an efficient bus service would be impossible if buses had to halt at stops for half an hour. Fortunately, the speed of energy transfer for a particular pair of plates depends on the frequency of the alternating current that’s fed to the lower plate: the higher the frequency, the faster it transfers power. Ross and his team found that the 60 hertz used in US domestic electricity supplies is far too slow so they tried an alternating current with a frequency of around 9000 hertz. Even that wouldn’t do it: buses would either lose precious time at each charging stop waiting to fill up, or not have enough power to make it all the way to the next one. But you can’t simply keep ramping up the frequency: at some point the plates’ ability to handle high-frequency alternating current is overwhelmed and efficiency drops. So Ross settled on a supply with a frequency a little above 10,000 hertz, just below the point at which efficiency starts to fall. With this supply, a bus can top up its batteries in less than five minutes.
His team also had to find a way to alter the frequency on the fly. As a bus takes on or lets off passengers, its chassis rises or drops slightly relative to the pavement. But the separation between the two plates is a crucial element in determining the optimum frequency for energy transfer. So the design team created circuitry that would sense the distance and adjust the frequency to match. “There’s a feedback loop that lets the system know how transfer is progressing,” Ross says.
Plenty of room inside
Ross and his team have already tested the design in half-size mock-ups at a lab in Ojai, California. Their trials indicate that the power transfer system is about 80 per cent efficient. His prototype bus will carry a tonne of batteries and store about 400 kilowatt-hours of electricity, giving it a range of around 25 kilometres on a single charge. “We need only about 10 per cent as much on-board energy storage as a conventional battery-powered bus,” he says. The team has also run basic safety checks by walking across the charging plates when they were switched on. Ross says they felt no sign of the magnetic field, and wristwatches, computer discs and credit cards were also unaffected, though he admits that more thorough tests will have to be done before the buses could be a going concern.
The charging system can even run in reverse. In the evening, when demand for buses has fallen and many are back at their garages, bus drivers can dump any leftover electricity onto charging plates and the power is returned to the grid. “That doesn’t mean a lot with one bus, but it means a lot to a city with a hundred of them, or a country with tens of thousands,” he says. In particular, this could help power suppliers meet the surge in residential power demand that usually occurs in the early evening. The buses can then recharge later when demand is lower.
Ross estimates that once in production, his vehicles will cost up to 30 per cent more to buy than conventional diesel buses. Yet their life-cycle costs – the total spent on them from the time they roll off the assembly line until they reach the end of their useful lives – will be 30 per cent less. His analysis also suggests that these vehicles should generate an annual fuel bill 60 per cent lower than the diesel bill for a standard bus. And his buses should last twice as long. “A diesel engine wears out after about 5000 hours, but the best electric motors can go 20,000 hours between failures,” says Ross.
The figures have impressed the MBTA, which now plans to test his concept. Two buses owned by the bus company are being converted in a warehouse in Boston, and early in 2004 the vehicles will begin plying a 6.5-kilometre loop in Boston’s Hyde Park neighbourhood. “We won’t carry passengers or earn revenue,” says Ross. “We’ll run the buses for a few months, shake down the equipment, take the buses apart to see how they’re holding up, then put them back out and run them some more. After that, the agency can decide if they want to fund a longer test or put the buses into service.”
But Ross has his sights set on an even more ambitious scheme – applying the same technology to an electric car. This vehicle would look and weigh about the same as a conventional car. Crucially, it could run indefinitely if someone builds the electrified highway Ross envisaged in the early 1990s for San Diego’s electric power company. An electric car would carry 90 kilograms of batteries – compared with about 480 kilograms for today’s electric cars.
Ross envisions a series of 300-metre-long charging plates buried in the highway at 3-kilometre intervals. It would take roughly 10 seconds for the car to cruise over one of the plates at highway speeds. This would be long enough to take on half a kilowatt-hour of charge, sufficient to take you to the next charging strip. Slow down a little and a car could take on even more power. These strips could be installed in a recharging lane and users would be billed for the power they drew.
By electrifying a strategic 1 or 2 per cent of the roadway in San Diego, for example, Ross calculates that 99.8 per cent of all routine trips through the area could be made in an electric car with little inconvenience to the driver, even allowing for a spell on the electric highway to top up car batteries. And if his electric cars have a range of 65 kilometres when fully charged, most people would be able to manage their daily routines with no problem. Electrify the west coast highway system, for example, and you could drive from Tijuana, Mexico, up the west coast to Vancouver, British Columbia, without stopping.
Ross calculates that the improved energy efficiency of these vehicles means that you would get the equivalent of 30 kilometres per litre of gasoline. And although the electric car might cost 10 per cent more to buy than a conventional internal-combustion vehicle, it would bring down local pollution levels and its maintenance and fuel costs would be on a par with the electric bus design.
Most transportation engineers see no technical reasons why Ross’s scheme can’t work. “But I do see some reasons why it could be problematic,” says Robert Michelson, a robotics engineer at the Georgia Institute of Technology in Atlanta.
Firstly, the frequency at which the charging plates work creates electrical noise that might interfere with nearby receivers. To operate at highway speeds, a car would have to absorb seven or eight kilowatts as it drives over each power strip, Michelson says. “A lot of small TV stations don’t put out that much power. And would the public pay for the cost of installing the strips if only a small fraction of the public drives these kinds of cars?” Ross’s approach to electric vehicles is a great idea, Michelson concedes, “but you have to solve a lot of logistical and political problems in order to make it happen.”
Elizabeth Deakins, director of the Transportation Studies Program at the University of California at Berkeley, agrees. “But I’d never bet against Howard,” she says. “He’s a tenacious fellow and has the energy to push the project until it works. We’ll have to see what the technology’s weaknesses are in daily use and what the maintenance costs actually are.”
Still, she admits that there are areas such as New Jersey’s urban corridor along the Hudson River across from New York City that are particularly keen to solve air pollution problems and cut traffic noise. “Downtown shuttle services, such as in Denver, are a natural application”, she says, “and large university campuses that run buses in large, continuous loops. My own community of Berkeley would love it.”
Ross now plans to spend a year or two developing pilot programmes for his buses in several other North American cities where discussions are already under way with bus companies and power suppliers. After that he will turn his attention to the family car and the kinds of practical details that Michelson raises. Ross hopes to buy several cars, convert them, then run them on a test track at 125 kilometres per hour for days or even weeks “to show what’s possible”. At that point, he’ll call a major car manufacturer where he has an informal invitation to explore collaborations and, he hopes, eventual licensing arrangements.
But can an electric car find a niche in a market already transfixed by fuel cells? As long as fuel cells need a non-renewable energy source such as petroleum for power, and they will do for the foreseeable future, Ross believes the answer is yes. “This technology has a future if we create that future,” he says firmly. “The only technical challenge remaining is how well you do it – not whether you can.”