Fans of hybrid vehicles have been clamoring for carmakers to add plug-in capability to those models so that they can grab some juice off the grid and leave more in the tank. The problem is that making a useful PHEV is actually not as simple as just plopping in a bigger battery pack and some charging circuitry. Current hybrid models are only designed to run on electricity at light loads and relatively low speeds. At higher speeds or rates of acceleration they operate in a blended mode with both the engine and electric motor running. This of course is still beneficial because it means a smaller less powerful engine is required to meet customer performance expectations while saving gas.

In the real world, PHEVs need more electrical power from the motor in order to actually go farther without starting the engine. A new study done by General Motors using real world data recorded from over 600 cars analyzed how standard and plug-in hybrids would perform in the hands of real drivers. What they found was that to get a real benefit the vehicle needs to be designed to perform at all speeds on electrical power alone. With that much electrical power on board, having a full engine to drive becomes redundant. A small engine to charge the battery however makes sense. An extended range EV (like the Volt) would actually eliminate 70-percent of the engine starts at any time during a drive. AutoblogGreen talked to GM's Pete Savagian about the study and the results.

[Source: General Motors, AutoblogGreen]