How green are electric cars?

There's a huge amount of fuss in the press about a revolution in electric vehicles driven by the government. The 'greenness' of an electric car depends on where the electricity comes from - don't buy the 0gC02/km figures that are bandied about - that is patent nonsense. It is quite difficult to get precise data, but here's a rule of thumb from www.whatgreencar.com:

• Battery-electric cars using renewable energy provide the largest reduction in GHGs of almost 100%. 
  
• If 'standard-mix' electricity is used, battery electrics reduce greenhouse gases by around 40%. 
  
• Commercially produced pure bioethanol and biodiesel also provide significant reductions in greenhouse gases in the range 35%-90%, the reduction depending on feedstock crop used. 
  
• Due to their high fuel-efficiency, most petrol hybrids offer a reduction in greenhouse gases of around 25%. 
  
• Bi-fuel LPG and natural gas cars also produce modest reductions of around 15% due to better combustion and to their lower carbon content.

Tesla - the makers of the £90k electric sports car go further and say their car does 46gCO2/km, compared to an European average of 158gCO2/km, but that figure assumes the electricity comes from a brand new gas fired power station.

So electric is good, but not quite as good as some may claim!