THE RISE OF PLUG-INS AND THE FUTURE OF ENERGY
The end of the petrolhead Jun 19th 2008
From The Economist print edition
Tomorrow’s cars may just plug in
NOTHING ages faster than the future. A few years ago there was general agreement that if the internal-combustion engine ever was replaced by something clean, that something would be the fuel cell. A fuel cell is a way of reacting hydrogen and oxygen together in a controlled way and extracting electricity from the process. It was to be the precursor of what was known as the hydrogen economy, in which that gas would replace fossil fuels and power almost everything.

Leaving aside the problems of transporting and storing a light and leaky gas, what no one was very clear about was where the hydrogen itself would come from. You would have to make it from something else. That something would either be a mixture of fossil fuel and water (fuels can be reacted with steam to make hydrogen and carbon dioxide, but you still have to get rid of the carbon dioxide), or just water itself, via electrolysis.

But why bother? Why not cut out the middleman and plug your car directly into the electricity mains instead? And that, it seems, is what may happen. You don’t hear much about the hydrogen economy these days. Nor fuel cells. The buzz-phrase now is “plug-in hybrid”.

Plug-ins should not be confused with existing hybrid vehicles, such as Toyota’s Prius, which contains an internal-combustion engine as well as two electric ones. Either sort may drive the wheels. The electric motors kick in when they can do a more efficient job than the petrol engine, but even then the electricity comes ultimately, via batteries, from burning petrol. In a plug-in, the electricity comes from the mains, via an ordinary electrical socket. Some intermediate designs retain the idea of two sorts of engine, but the goal is that the car should be powered by electric motors alone. If the batteries run down, a petrol-powered generator will take over. (Existing batteries are too expensive to give such a car the range of a standard petrol-driven machine.) But most cars, most of the time, are used for short journeys. Gerbrand Ceder, a battery scientist at MIT, reckons that if the first 50km of an average car’s daily range were provided by batteries rather than petrol, annual petrol consumption would be halved. Given that the electrical equivalent of a litre of petrol costs about 25 cents, that is an attractive reduction.

The widespread adoption of plug-ins might also reduce carbon-dioxide emissions, depending on what sort of power station made the electricity in the first place. Even energy from a coal-fired station is less polluting than the serial explosions that drive an internal-combustion engine. If the energy comes from a source such as wind or nuclear, the gain is enormous.

Beyond that, the rise of plug-ins has implications for the electricity industry itself. If they succeed, they will put an unanticipated load on the system. In fact, they may remake electricity as well as transport.

Don’t all recharge at once

That is certainly the view of Peter Corsell of Gridpoint, a company based in Arlington, Virginia. His firm hopes to make its living selling the load-management technology required for “smart grids”. There are several reasons why such technology is desirable. Mr Corsell goes one further: he reckons it will become essential if plug-ins arrive in force. At the moment, the grid would be unable to cope if a large number of commuters arriving home plugged in their cars more or less simultaneously to recharge them. Yet if those same cars were recharged at three o’clock in the morning, when demand is low, it would benefit both consumer (who would get cheap power) and producer (who would be able to sell otherwise wasted electricity). Such cars might even act as micro-peakers—reservoirs of electrical energy that a power company could draw on if a car were not on the road. Managing plug-ins, Mr Corsell thinks, will be the smart grid’s killer application.

In sunny climes, plug-ins might also provide another use for solar cells. Google is already experimenting with photovoltaic car parks. These have awnings covered in solar cells which will shade its employees’ cars and simultaneously recharge them. That is an idea which could spread. Supermarkets, for example, might find that car parks with plugs would attract customers who wanted to top up their cars. And the more opportunities there are for stationary cars to be recharged, the more likely they are to be bought.

Plug-ins are moving from idea to reality with amazing speed. General production of the Tesla, Elon Musk’s new sports car, began in March (the firm is Californian, but the cars are built in Britain). The Tesla is not even a hybrid. It draws all of its power from lithium-ion batteries (the sort that power laptop computers), and it has a range of 350km. It can manage that because its price of $109,000 buys a lot of batteries; Tesla owners are not the sort who count their pennies.

Nor is the Tesla the only sports car to go down this road. Electric motors may lack a throaty roar, but they actually do a better job than petrol engines in high-performance vehicles. They have higher torque at low revs which makes them accelerate faster. In Britain a new firm called the Lightning Car Company plans to revive the country’s sports-car tradition with the Lightning GT. Mr Musk also faces competition in California, from Fisker Automotive, whose eponymous founder Henrik Fisker helped design the Tesla. (Tesla Motors is now suing Fisker for infringing its intellectual property.)

Mass-production plug-ins are not far away either, and the rising price of petrol makes them look more attractive by the day. General Motors intends to launch a plug-in hybrid called the Volt by 2010, and Toyota plans a plug-in version of the Prius. Most of the other big car firms are making me-too noises. Only Honda and Mercedes seem to be sticking enthusiastically to fuel cells. It is all very encouraging. But what would really make a difference would be a breakthrough in battery technology.

At the moment, lithium-ion batteries are the favoured variety. This kind of battery uses lithium in its ionic form (ie, with the atoms stripped of an electron to make them positive). When the battery is fully charged, these ions hang around one of its electrodes, the anode, which is usually made of graphite. During operation, the ions migrate within the battery from this electrode to the other one, the cathode, and electrons (which are negatively charged) pass between the electrodes through an external circuit. It is that current of electrons which drives the motor. The cathode may be made of a variety of materials. Cobalt oxide is traditional but expensive. Manganese oxide is becoming popular. But the future probably lies with iron phosphate, which has less of a tendency to overheat, a problem that has resulted in battery recalls in the past.

Iron phosphate certainly will be the future if General Motors has anything to do with it. GM is collaborating with A123Systems, a firm started by Dr Ceder’s colleague Yet-Ming Chiang, to develop batteries with iron-phosphate cathodes for the Volt. A123’s particular trick is that the iron phosphate in its cathodes comes in the form of precisely engineered nanoparticles. This increases the surface area available for the lithium ions to react with when the current is flowing, so such batteries can be charged and discharged rapidly.

The Lightning, too, is making use of nanotechnology. Its batteries, developed by Altairnano of Reno, Nevada, replace the graphite anode with one made of lithium titanate nanoparticles. The firm claims that its batteries are not only safer (graphite can burn; lithium titanate cannot), but can also be recharged more rapidly. Using a 480-volt outlet, such as might be found in a roadside service station, the job should be done in ten minutes.

Dr Ceder reckons he may be able to do even better than this. His version of an iron-phosphate battery can charge or discharge in ten seconds. It, too, could be recharged rapidly at a roadside filling station. He reckons the process would have to be controlled to stop overheating, but a safe refill would take only five minutes. And he thinks batteries might get better still.

The 30,000-compound question

At the moment the process of finding better electrode materials is haphazard, but Dr Ceder proposes to make it systematic. Over the centuries, chemists have discovered about 30,000 inorganic chemical compounds (those that are not based around carbon skeletons), almost any of which might theoretically be suitable material for an electrode. Examining the relevant properties of all of them in the laboratory is out of the question, but Dr Ceder thinks he has found a short cut. He is involved in something called the materials genome project, which takes the known properties of inorganic compounds and turns them into extremely sophisticated computer models. These models are able to calculate the quantum-mechanical properties of the chemicals they are mimicking—and they seem to get it right. When Dr Ceder has checked the predictions for hitherto untested materials by conducting real experiments, he has found that the results coincide.

The materials genome project obviously has much wider applications than battery electrodes, but that is where Dr Ceder has started. His computer is now chewing its way through the chemical encyclopedia, looking for the likeliest candidates. Watch this space.

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