Oct 08, 2011 7:40 PM GMT
The way I understand it, while you’re driving along, the gasoline engine in addition to turning your wheels is also cranking a generator that charges a battery, and when the car senses you need less power, it shuts the gasoline engine down and runs the car on electric power. Seems simple enough.
But, wait – the first law of thermodynamics says you can’t get any more energy out of a system than you put into it. So, charging the battery takes just as much gasoline as if you were using it to run the car during those times when the battery takes over. Otherwise, the battery wouldn’t have enough power to turn the wheels. So, you're using more energy than you need to when the gas engine is running - part of it turns the wheels and the rest is stored in the battery - and that's what the electric motor taps into.
And, the second law of thermodynamics says no system is 100% efficient, so you’d have to use more energy to charge the battery than the battery could put out to run the car. Of course, efficiency is a tricky thing – it might be that running a car is not a terribly efficient use of gasoline. But it seems completely implausible that using a gasoline engine to generate electricity to charge a battery to run an electric motor to turn the wheels of your car is more efficient than just using the gasoline engine to turn the wheels directly.
I can see that you might save energy if the generator only runs when the car is idling – when you’re stopped at a traffic light, for instance. But then again, you’d still need more gasoline to idle as well as run the generator than if you were just sitting there idling. Seems like you could simply tune the engine to idle at a very low rate and use less gas. And anyway, wouldn’t those be the exact times you’d want to shut down the gasoline engine and let the battery take over?
I did hear of one system where the generator is tied in to the braking system, and the momentum you lose while braking is used to crank the generator and charge the battery. But this doesn’t sound like it could possibly produce enough energy on its own to run the car – unless you’re a horribly inefficient driver, and spend all your time gunning the engine and then slamming on the brakes.
I know hybrids do have great gas mileage, but they also have pretty small engines. I have to wonder what the gas mileage of that same engine would be without the generator and the added weight of the battery (it’s super heavy).
Am I missing something? Or is this the scam of the century?
But, wait – the first law of thermodynamics says you can’t get any more energy out of a system than you put into it. So, charging the battery takes just as much gasoline as if you were using it to run the car during those times when the battery takes over. Otherwise, the battery wouldn’t have enough power to turn the wheels. So, you're using more energy than you need to when the gas engine is running - part of it turns the wheels and the rest is stored in the battery - and that's what the electric motor taps into.
And, the second law of thermodynamics says no system is 100% efficient, so you’d have to use more energy to charge the battery than the battery could put out to run the car. Of course, efficiency is a tricky thing – it might be that running a car is not a terribly efficient use of gasoline. But it seems completely implausible that using a gasoline engine to generate electricity to charge a battery to run an electric motor to turn the wheels of your car is more efficient than just using the gasoline engine to turn the wheels directly.
I can see that you might save energy if the generator only runs when the car is idling – when you’re stopped at a traffic light, for instance. But then again, you’d still need more gasoline to idle as well as run the generator than if you were just sitting there idling. Seems like you could simply tune the engine to idle at a very low rate and use less gas. And anyway, wouldn’t those be the exact times you’d want to shut down the gasoline engine and let the battery take over?
I did hear of one system where the generator is tied in to the braking system, and the momentum you lose while braking is used to crank the generator and charge the battery. But this doesn’t sound like it could possibly produce enough energy on its own to run the car – unless you’re a horribly inefficient driver, and spend all your time gunning the engine and then slamming on the brakes.
I know hybrids do have great gas mileage, but they also have pretty small engines. I have to wonder what the gas mileage of that same engine would be without the generator and the added weight of the battery (it’s super heavy).
Am I missing something? Or is this the scam of the century?
