A report from Carnegie Mellon University concludes that plug-in hybrids are not cost effective in any scenario:
The Carnegie Mellon study, conducted by engineers from three different departments, constructed computer simulation models to determine the impact of additional batteries on fuel consumption and cost and greenhouse gas emissions over a range of charging frequencies.It found that small-capacity plug-ins that get less than 20 miles per charge are more efficient than conventional hybrids. And it said that large capacity hybrids like the Volt that go 40 miles or further on a charge are never cost-effective, because the batteries cost and weigh too much.
Nearly 50% of U.S. vehicle miles are traveled by automobiles covering less than 20 miles per day, according to the report.