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tarheel91 on 29 December 2010
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O-D-C said:
silicon said:
mrstickball said:

Electric vehicles have an efficiency of 80% or more. Regular cars are in the area of 20-30%.

The problem with combusion engines is that they do not convert gasoline (or most fuels for that matter) into energy very effectively. Electric motors are far more efficent, and certainly cheaper (cost per KwH vs. cost of fossil fuel), too.

Here is a pretty good breakdown:

http://www.fueleconomy.gov/feg/atv.shtml

For an electric car, you do not lose energy when idling (as the engine is not being turned), the engine does not lose any energy, and you usually have regenerative breaking. Therefore, the only losses are due to aerodynamics, accessories and drivetrain.

For the OP, I'd like to add that while the electric motor may be 80%, there are additional losses from charging the battery. Plus, depending on where you live, electricity can be generated using coal or natural gas which still has really low efficiencies.

Everything adds up. Efficiency is an odd thing. It's hard to compare since it's hard to know what boundaries to set.

true, but is the amount of energy used to power an electric battery for a 100km drive the same as driving a fossil fuel car for 100km?


Depends on the electric car.  A lot of the energy/pollution stuff for an electric car happens before the car is driven.  Aside from simply the effects of generating electrical energy, the components of an electrical car frequently require more energy to create (i.e. the infamous Prius components that are created/assembled accross several continents).  It's not as cut and dry as many people on both sides of the arguement want it to be, and a lot is dependent on the specific car and the manufacturing process used to make it.

To answer the OP's question, traditional piston engines are around .4 lb/HP-hr.  Diesels are around .3 lb/HP-hr, and rotaries are around .5 lb/HP-hr.  Any of those can vary by as much as .05 lb/HP-hr depending on the specific engine.  The efficiency also varies with how much power is being made.  For example, rotary effieciency approaches piston engine efficiency at peak power values.

I'm sure those numbers don't mean much to you, but it gives you an idea of the different types of engines' relative efficiencies.