There's been a lot of buzz over a possible plug-in version of the Toyota Prius (along with some home conversion kits). But Fox Business is reporting that Toyota will display a prototype plug-in Prius hybrid at Legislative Plaza in Nashville on Monday, June 16, during a congressional field hearing on electric vehicles.

"When considering the benefit of new technologies, we must understand the relationship between large sales volumes and fuel savings," said Robert Wimmer, Toyota's national manager for Technical and Regulatory Affairs, Energy & Environmental Research, in the report.

"For example, if we double sales of a hybrid model, the fuel savings is greater than doubling its fuel economy with no change in sales volume. Therefore, it is critical that new technologies, such as plug-ins and fuel cells are introduced at a price point and utility that allow for high volume sales. Otherwise, their environmental benefit will be negligible."