I think we can expect to see Rolls-Royce make its future models with two large electric motors -- one front and one rear. Then add a gasoline engine to provide for backup generator power. This would likely be 3.0 liter V6, or basically the BMW i8 multiplied by two.
The battery would likely be at least 16 kWh, and the range would be at least 30 miles, possibly as much as 50 miles. Then the generator would kick in. Basically, an architecture somewhat similar to a Chevrolet Volt (Cadillac ELR) but with 4-wheel drive and with most drivetrain components sized up by two times or more.
Keep in mind that BMW, which owns Rolls-Royce, hired the key program manager from General Motors (GM), who was in charge of developing the Chevrolet Volt 2007-2010. His name is Frank Weber and he has been working for BMW and Rolls-Royce since April 2011. I expect to see a plug-in electric Rolls-Royce by 2018 that reflects this Chevrolet Volt heritage. The BMW i3 has already entered production, and the BMW i8 enters production no later than June 2014.
Longer term, I anticipate an all-electric Rolls-Royce. It would need to beat Tesla by offering a range of at least 300 miles, preferably 400 miles. Most likely, within the next five years, probably in 2018, Rolls-Royce would therefore offer two basic drivetrains for its future cars in several different body styles: One 4x4 hybrid plug-in as I described above, and one pure electric 4x4.At the time of publication, the author was long F and GOOG. Rolls-Royce provided airfare and lunch in addition to the car and a full tank of gasoline to enable TheStreet.com to give you this first-drive report.