General Motors Europe is developing a cost calculator to help potential Opel/Vauxhall Ampera buyers understand the true benefits of owning its extended-range plug-in hybrid.

Frank Weber, head of electric vehicle business at parent company General Motors, said the move was part of the education process which customers would need. The Ampera goes on sale in the second half of 2011 in Europe and a year later in the UK.

GM estimated that it will cost the average driver about GBP150 a year to recharge the Ampera, based on an annual mileage of around 9,000 miles.

"We will have a major education programme ahead of us to teach people the cost benefits of the Ampera," said Weber.

Although the Ampera would be more expensive than an equivalent petrol or diesel powered car because of the cost of the technology, European governments are offering considerable subsidies to buyers, he added.

"The calculations are more complex than those for diesel versus petrol. I think people understand pure electric vehicles and hybrids, but do they understand our extended range vehicle?"

He is certain about one thing: extended range - which uses a small onboard internal combustion engine to recharge the battery when necessary - is here to stay.

"We can fit this technology into any of our existing small and medium sized cars," he said. The next generation Astra - in production later this year - would be an obvious candidate.

While the electric-only range will stay at 40 miles (60km or so), the batteries would become smaller, more efficient and cheaper as the technology matures.

"We don't need an electric-only range of more than 40 miles because that's the average commute in North America and Europe and that won't change," Weber said.