ScoobyChris wrote:BMW have "Brake Energy Regeneration" on a lot of their new cars which has helped them to get better fuel consumption figures.
I think that all the BMW system does is to disconnect the alternator for most of the time, and only connect it under braking. This allows the alternator to get enough power to keep the battery charged while the engine is using no fuel, and never having to use valuable energy to drive the alternator. I think the alternator can be reconnected under power if necessary to keep the battery charged.
No doubt this system makes a worthwhile but modest contribution to economy. The new M3 has it but will be lucky to achieve as much as 20 mpg.
However BMW diesel engines in particular are in the forefront for their low emissions levels in relation to the power outputs. For example the X5 3.0D comes in under 220 g/km of CO2 output (the Band G threshold) whereas no Range Rover or Mercedes ML models do so, in spite of generally less good performance. Similarly the 118D is one of the best performing cars in Band B which is taxed at only £35 pa.