It actually is greener to convert your Prius or other hybrid you might own to increase the battery capacity and electric usage. Although the new electric vehicles such as the Nissan Leaf, are well –made cars, it is actually more sustainable to convert the car you have rather than purchasing a new one. The other factor to consider is that Prius cars wear better than normal vehicles. So you might also consider purchasing a used Prius and getting it converted to all electric.
All electric Prius conversions are becoming more popular especially in Colorado with aggressive tax rebates. The State of Colorado is now offering an incentive to convert your Prius to plug-in through a refundable tax credit of 85% of the cost with a maximum credit of $6,000. This is only good through the end of 2011 and might be extended through 2012.
For Denver residents try Green Gears.
For Boulder residents try Boulder Hybrid Conversions.