PETROL and diesel cars and vans will disappear from Britain's roads by 2050, replaced by electric vehicles that get their energy from wind turbines and nuclear power stations, according to proposals put forward by Chris Huhne, the energy secretary.  He wants Britain's 30m or so cars and light vans, almost all powered by internal combustion engines, to be replaced by a new generation of batterypowered vehicles that can be recharged from low-carbon sources of electricity, such as wind farms.  The controversial scheme is set out in Huhne's new carbon plan, which describes how Britain might cut greenhouse gas emissions by 80% by 2050.  Its key underlying idea is that Britain will replace fossil fuels such as petrol and diesel in vehicles, or the gas used in heating homes and businesses, with electricity generated by low-carbon technologies, such as wind and nuclear.  If implemented, it will mean a huge increase in the demand for power by 2050 to about double that of today. Since that power will have to be green, the carbon plan can be achieved only through the construction of tens of thousands more wind turbines, along with new nuclear power stations.  Perhaps the greatest impact will be felt by drivers. In the plan, Huhne warns that road transport produces 130m tons of CO2 a year - almost a quarter of the nation's emissions. He wants that cut to between 20m and 40m tons by 2050.  The switch to new -technology vehicles will, however, have to begin much earlier than that, ideally in the early 2020s. Huhne said: "The average emissions from new cars will need to fall by at least a half by 2030."  The benefits would be potentially huge. Quite apart from cutting greenhouse gas emissions, it would also dramatically reduce urban pollution, blamed for about 500,000 premature deaths each year. It would also make cities much quieter because low emission engines make less noise.  However, such vehicles could cost significantly more, at least until the technology has advanced. The government would also have to oversee the rewiring of Britain's streets and car parks to provide millions of charging points for electric cars, which are seen as the technology most likely to succeed. In the report, Huhne said Britain would need at least 100 gigawatts of low carbon generating capacity by 2050. at the moment, Britain has only about 80 gigawatts of total generation capacity, and most of that is based on coal and gas.  He said: "Beyond 2030, as transport, heating and industry undergo electrification, lowcarbon power generation will need to rise significantly. Renewable electricity has the potential to provide 40% of power generation by 2030."  Such thinking is proving increasingly controversial, especially because most low carbon power generation systems,