# Porsche announces hybrid SUV



## anf301 (Jul 25, 2007)

This is fantastic! I would definitely be interested in one of these -- and you're right, this is likely the direction that will eventually lead to an all-electric fleet. I live in Minneapolis, and drive 85% of my miles on the interstate (in order to afford to live here, I had to move where there's a cornfield across the street from my house) -- that leads me to a question regarding the efficiency statement. If you can cruise at 70 mph without the use of the engine, how would this car only be 25% more efficient? If it takes the same amount of energy to get up to 70 mph as a regular car, why wouldn't the efficiency variable be much higher (like, say for me, 75%)? Or are these numbers dependent upon the average driver, which is probably the inverse of my driving (maybe 80% in town, 20% highway). 

(Excuse my lack of knowledge -- I'm a noob)


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## xrotaryguy (Jul 26, 2007)

Well, there are quite a few different ways to look at efficiency. A gasoline piston engine is only about 22% efficient and usually less. Take all of the drive train losses, rolling resistance, wind resistance, and that number goes down. 

An EV is about 89% efficient from the batteries to the wheels. Taking into account rolling resistance etc, and that number goes down too. Actually, getting power into the batteries requires excess energy too.

Since Porsche's hybrid would actually run on gasoline some of the time, that figure might be averaged in. That could bring the efficiency rating down quite a bit. It just depends on how often Porsche engineers expect the average driver to use the IC engine. 

In the end though, I am not really sure how they came up with the 25% efficiency number. Maybe more searching about Porsche's plans for their hybrid would make things clearer.


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