Here's another plug-in hybrid concept from an established manufacturer...but when will they become production reality?

Trickle-feeding a battery from the AC mains connection at home is a lot cheaper per kilometre than commensurate quantities of fuel to drive a petrol combustion engine for the same range.

That's why Volvo estimates production versions of its latest concept could save consumers up to 80 per cent of their running costs.

On electric power alone, the Volvo ReCharge Concept can travel 100km before needing its battery re-charged. An on-board 1.6-litre petrol engine will start automatically once the drive battery is 70 per cent depleted.

The system also features a manual override for the driver to use if the trip will exceed 100km and the driver wants the battery topped up.

Motive drive comes from four electric motors (one on each wheel) and the petrol engine does nothing other than re-charge the battery. If the vehicle covers a distance less than 100km between AC mains re-charging, there's no need to replenish fuel for the petrol engine.

Plug-in hybrids such as this concept are likely to be the way of the future for urban drivers. Without the need for the internal combustion engine to start/stop on demand in traffic, future plug-in hybrids such as the Chevrolet Volt (more here) could feature on-board turbodiesel engines running on bio-fuel.

Even without the turbodiesel on bio-fuel scenario, Volvo's concept car reduces reliance on fossil fuels considerably, by virtue of being a 'FlexFuel' engine, one that runs on a mixture of petrol and up to 85 per cent ethanol, by volume.

Ethanol can be fermented from crops and is thus a renewable fuel source. One issue of concern with ethanol is that conventional ethanol production would compromise food production if undertaken in sufficiently large scale. With the low fuel consumption of the Volvo ReCharge, that becomes less of a problem for global economies.

All of this reduces reliance on non-renewable fossil fuels to effectively zero. CO2 emissions would be similarly reduced in those instances where drivers only travel a distance per day less than the vehicle's range and top up the lithium-ion battery from home at night.

It's the battery that's something of a stumbling block at the present. Lithium-ion batteries are a better alternative to lead acid (wet cell) batteries, since they're lighter and pack more charge for their weight, but they're expensive to produce.

In the case of the C30-based concept, the battery pack is described by Volvo as a 'lithium-polymer' type and resides in the luggage compartment. Volvo claims the concept will reach 160km/h top speed and can hit 100km/h in nine seconds. Even driven well beyond the 100km/h electric-only range, the concept will return fuel consumption figures as low as 5.5lt/100km.

One safety advantage that Volvo points out is the concepts 'all-wheel drive', which also comes without the added weight of conventional AWD systems, since each motor is allocated to its own wheel, without the shafts, joints, differential and transfer components to go with it.

The Volvo ReCharge is just the latest plug-in hybrid to be announced by a mainstream manufacturer. American companies are already gearing up for plug-in hybrid production to aid their CAFE figures (a corporate average fuel consumption standard in the US) and continue doing business in environmentally award California.

Volvo will launch the ReCharge concept at the Frankfurt motor show (IAA) later this week.

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