Even with America's current power mix, with a heavy dose of coal power generation, electric vehicles are show to reduce total greenhouse emissions, however the picture isn't all rosy. The Department of Energy study also points to an increase in total particulate emissions with the grid pumping power all night. This, however, is much easier to tackle than petroleum-based pollution. As alternative energy gains a greater share of the American power pie chart, we can look for less particulate emissions as well. In the meantime, check to see if your power company offers green power or try to generate your own. Then, when you get your electric speedster, you can rev it up without worry.

Originally published at:  http://www.treehugger.com/files/2007/09/excess_nightime.php

COMMENT:

Electric Cars at night will make use of existing infrastructure that can not quickly change the level of power output. There will continue to be a surplus of energy production at night, and it is better to put this power to use in charging electric vehicles, then to pollute with no benefit by letting the power go to waste.
Solar power does supply energy during the day, and would reduce the need for new fossil fuel burning plants in the short term, and eventually allow or the closure of worst polluting plants sooner once the capacity comes online.
There is no conflict as moving to electric vehicles and charging them at night will reduce pollution immediately in the short term. In the medium term, we will continue to see surplus power at night with some wind, hydro, nuclear, and remaining fossil fuel power plants. In the long term, hopefully we will have enough clean capacity, along with storage technologies (batteries, fly wheels, ultra capacitors) that the cars can be charged day and/or night, and the grid, along with smart power meters and usage controls, will be able to level out power demand with the excess storage mediums and cars keeping track of usage so that they will charge at the most mutually beneficial rates and times for the entire grid.

(deap breath, end rant)