Back in 1997, Toyota led the charge with the first mass-produced petrol-electric ‘hybrid’ car – the Prius. Now, with limited global oil reserves, and increasing petrol prices, nearly every car manufacturer has either developed a hybrid solution or is seriously looking into it.

Now that 12 years have passed since the first Prius, and Toyota’s third generation Prius has recently been launched in Australia, what will be the next step towards the holy grail of zero emission, low cost motoring?

Enter the plug-in hybrid.

At last week’s Tokyo Motor Show, Toyota demonstrated a plug-in version of the Prius. While it uses the same ‘hybrid’ motor concept, where the combination of small electric and petrol engines deliver similar performance to a larger, hungrier, petrol-only motor. In a conventional hybrid’s case, the electric engine handles all the stop-start and low speed driving, and passes the job over to the petrol engine for cruising speeds beyond about 40km/h. The electric engine runs on batteries, which are topped up by kinetic energy captured by ‘regenerative’ braking, or the petrol motor.

A plug in hybrid is slightly different. It has a full ‘EV’ or electric vehicle mode, meaning the petrol motor doesn’t kick-in, regardless of how fast you’re going. In the plug-in Prius’s case, this is made possible with the help of a high capacity Lithium-ion battery bank, which provides the electric motor with the necessary range and power for short distances. You can charge the batteries with a wall socket, but if you forget, the Prius will run using the petrol motor.

The battery is good for about 20km of driving, and once depleted, the system will switch to the petrol motor for mid and long distance travel.

Plug it in for 20km of electric-only travel.

So with a plug-in hybrid, you get the benefit of an ultra-efficient electric-only mode for hopping around town, and if you run out of juice, the low-consumption petrol motor will kick in. For mid to long range trips, the plug-in hybrid will operate like a conventional hybrid system, meaning top-notch fuel-efficient cruising.

While there are other alternative fuel options on the horizon, such as hydrogen, or electric-only vehicles capable of long distance travel, these are still years away. For the gap in-between, plug-in hybrid technology makes sense, especially since the technology for hybrid vehicles is already established.

A recharge takes just 2 hours with a standard Australian wall socket, not this fancy thing.

Toyota plans to launch its first plug-in Prius in the US and Europe by the end of 2009, but no date has been given for Australia. We may also see plug-in hybrids powered by solar energy or bio-fuels in the near future.

The only downside of more vehicles capable of running in fully electric mode is that you’ll need to be especially careful crossing the road, as you might not hear one coming.