The Lotus range-extender

Range-extender technology could offer the best combination of low emissions and real world practicality. We try the latest system from Lotus.

As the electric vehicle (EV) market grows, one of the major problems facing designers of pure EVs is getting sufficient range from batteries that can’t cope with long journeys.

The alternative is to have a full hybrid such as the Toyota Prius or Peugeot 3008 Hybrid4, in which a petrol or diesel engine combines with an electric motor. However, in such models, electric-only range is restricted to just a few miles.

There is also a third option, though: range-extender technology. An electric car today has a range of about 100 miles, and needs about 45 minutes to achieve an 80 per cent charge and eight hours for a full charge.

However, adding a small range-extender engine to drive a generator and keep the batteries charged allows range to be increased to hundreds of miles. The problem with this solution, though, is cost.

Not only are pricey batteries still needed, but there is the additional expense of the back-up engine. For example, the range-extended electric Vauxhall Ampera will set you back £28,995 – and that includes the £5,000 state subsidy. Its back-up engine is a 1.4-litre, four-cylinder unit. Audi’s solution is to use a rotary range-extender engine for its A1 e-tron concept car, while Jaguar uses micro gas turbines for its highly exotic C-X75. What we’re missing is a cheaper range-extender for everyday cars.

That is where Lotus Engineering and its parent Malaysian company Proton come in. Together they’ve developed a lightweight three-cylinder, 1.2-litre engine with outputs of 47bhp or, with a supercharger, 67bhp.

So far the technology has been fitted as a demonstrator to the Lotus Evora 414e concept, but it has far greater potential in small family cars. With this in mind, Proton has installed it in its Emas concept hatchback, which we sampled on Lotus’s demanding new test track at Hethel in Norfolk.

The Emas, which has a single-speed transmission, scuttles along convincingly, propelled by a 75kW electric motor powered by a lithium-polymer battery. Electric-only performance is reasonable, with a 0-60mph time of just over 14 seconds. But if it had been necessary to suddenly peel off the track and drive home, the petrol range-extender would, after about 35 miles, have started to power a generator and provide sufficient energy to the battery for the trip.

At present, the downside is that the Emas has a top speed of 60mph, which would mean mixing it with the trucks, but the supercharged version of the engine would address this with a cruising capability of 70-75mph.

The big advantage is that the engine is relatively simple, so it is easier and cheaper to manufacture than a conventional car power unit.

Unlike a full hybrid, only the electric motor drives the wheels. When the little range-extender is providing power to the generator, CO2 emissions of the Emas are 60g/km and Combined fuel consumption is in the region of 150mpg.

At the right price, this range-extender technology would make a lot of sense. It represents precisely the kind of engineering brilliance that Lotus is famous for.

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