# 70% of fuel is wasted generating power? **URL:** \ **Category:** Factual Questions\ **Created:** [February 10, 2009, 7:04pm UTC](https://boards.straightdope.com/t/70-of-fuel-is-wasted-generating-power/485258 "2009-02-10T19:04:49Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Mithra](https://avatars.discourse-cdn.com/v4/letter/m/e47774/32.png) [@Mithra](https://boards.straightdope.com/u/Mithra)\ **Post date:** [February 10, 2009, 7:04pm UTC](https://boards.straightdope.com/t/70-of-fuel-is-wasted-generating-power/485258/1 "2009-02-10T19:04:49Z")
“How much energy is lost getting electricity from the power plant to your PHEV or BEV? Plenty. In the U.S. right now, about 70 percent of the energy used to make electricity — more than four million gigawatt-hours — comes from fossil fuels. About 70 percent of that amount is wasted generating the power and transmitting it to your door. Additional energy is lost when charging batteries and running electric motors. Overall, electric cars use fossil fuel at 20 to 25 percent efficiency, but dismal as that sounds, it beats an internal-combustion car, which typically operates at about 15 percent efficiency. An HEV uses around 0.48-0.74 kilowatt-hours per mile, while PHEVs in electric mode and BEVs use 0.18-0.46 kWh per mile. By contrast, a conventional car getting 25 MPG uses 1.35 kWh/mile. To put the issue in more familiar terms, a PHEV or BEV offers fuel economy equivalent to as much as 188 miles per gallon.” Took this from [Do “green” vehicles really save energy? Is a Prius worse for the environment than a Hummer? - The Straight Dope](http://www.straightdope.com/columns/read/2759/are-electric-cars-really-more-energy-efficient) Not sure I understand how 70% is wasted, from what I know only 2-3% is lost when transmitting the energy which would mean power plants themselves waste 67-68% of the energy contained by the fossil fuels? ---
**Author:** ![Dervorin](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Dervorin](https://boards.straightdope.com/u/Dervorin)\ **Post date:** [February 10, 2009, 7:09pm UTC](https://boards.straightdope.com/t/70-of-fuel-is-wasted-generating-power/485258/2 "2009-02-10T19:09:16Z")
Indeed. Thermal power plants are limited by the laws of thermodynamics, which means they typically run at an operating efficiency of 35 - 50%. Not the best, but you can’t beat those dang laws of physics. The rest of the energy leaves the power plant as heat, hence the massive cooling towers with their clouds of steam. > **[Thermal power station](https://en.wikipedia.org/wiki/Thermal_power_station)** > > A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a steam turbine connected to an electrical generator. The low-pressure exhaust from the turbine enters a steam condenser where it is cooled to produce hot condensate which is recycled to the heating process to generate more high pressure steam. This is known as a R... ---
**Author:** ![Dromish](https://avatars.discourse-cdn.com/v4/letter/d/b77776/32.png) [@Dromish](https://boards.straightdope.com/u/Dromish)\ **Post date:** [February 10, 2009, 7:49pm UTC](https://boards.straightdope.com/t/70-of-fuel-is-wasted-generating-power/485258/3 "2009-02-10T19:49:37Z")
Most conventional power plants boil water, to produce steam which turns a turbine. It makes me somewhat sad to know that the latest and greatest designs for the most advanced nuclear power plants on the planet break down into “It’s a steam engine”. Energy is lost: chemically due to the burning process, thermally in the boiler (heating up things that don’t produce power, like the boiler itself, or the surrounding air, and mechanically to friction of spining the turbine shaft. Of course the turbines themselves are lossy systems, which is why most plants chain multiple turbines together in series. ---
**Author:** ![YamatoTwinkie](https://avatars.discourse-cdn.com/v4/letter/y/cc9497/32.png) [@YamatoTwinkie](https://boards.straightdope.com/u/YamatoTwinkie)\ **Post date:** [February 10, 2009, 8:31pm UTC](https://boards.straightdope.com/t/70-of-fuel-is-wasted-generating-power/485258/4 "2009-02-10T20:31:25Z")
For any heat engine, even the theoretical _maximum_ efficiency is limited to something called [Carnot Efficiency](http://en.wikipedia.org/wiki/Carnot_efficiency#Efficiency), so even with a _perfect theoretical_ machine, unless your “hot” source is reaaally hot and your “cold” sink is reaally cold, you’re still going to end up with crap efficiency.