efficiency of charging electric car with gas generator?

I've heard it claimed that charging an EV with a gas generator is actually more efficient than driving a car powered by an internal combustion engine.

for the purposes of this discussion, lets define 'efficiency' as available energy in fuel vs energy provided to the wheels. Fluctuating costs of gasoline, generators and batteries might cause my brain to quit...

I can see how this might be true. As I understand it, gas generators tend to be more efficient because they have less moving parts (no transmission, no transfer case, much less friction loss) and they're designed with a much tighter operational range.

However, there is also energy that is inherently lost when being changed from one type to another, such as changing heat energy to pressure energy, pressure energy to mechanical energy, mechanical energy to electric energy and then back to mechanical energy again. Charging an EV with a gas generator adds adds 1 more energy conversion than driving a combustion engine car.

Has anyone actually done the math on this?

 

You cannot get more power or efficiency out of anything than you put into it. Either way, you're still using fossil fuel to power your EV. There's no getting away from it...

 

At some point you still have to drive to the fuel station every so often to refill the fuel containers you are using to power your generator, burning up either more fuel or power from your EV....

 

to a point, we have some cars that get 7 mpg and some that get 20+

so mpg can change

 

This is not directed at you, but even the question of the efficiency of using a fossil fuel generator to recharge an electric vehicle is the epitome of irony....

 

ya but thats not really what I'm asking. Did you read the entire OP?

 

Yes, I read it, and I can't tell you. I'm sure there is someone out there that knows the conversion ratios and mechanics to answer your question. And that someone is not me. Just adding my 2 cents...

 

think is referring to hybrids - at least that is how I took it

 

I thought hybrids can drive from either the ICE or the electric motor. What I'm talking about is a motor that is incapable of propelling the vehicle itself but rather only capable of charging the vehicle. So if the battery runs out, the car can't move until the battery is charged sufficiently to move it (this would be why hybrids dont work this way).

 

Makes no sense.

 

I thought hybrids were basically battery or a gas generator if battery was low

 

looks neither of us are right...

• Electric Motor Drive/Assist. The electric motor provides power to assist the engine in accelerating, passing, or hill climbing. This allows a smaller, more-efficient engine to be used. In some hybrids, the electric motor alone propels the vehicle at low speeds, where gasoline engines are least efficient.

How Hybrids Work (fueleconomy.gov)
So an underpowered gasoline engine drives the car in normal conditions, the electric motor kicks in when more power is needed.

 

interesting, did not know that

 

Good thread! I've never thought of gas generators as being competitively efficient - interesting!

I'd add one bit to this last.

With a hybrid or EV there are systems in place for capturing brake energy, which is totally lost (turned to heating the brakes) if the powerplant is gas engine only.

There are several types of such systems, and this is an area where there is significant engineering effort.

The better systems today use large capacitors, because a capacitor can be charged almost instantly and with almost no overhead - so even small amounts of brake energy can be efficiently captured. Then, the main battery can be trickle charged, since these batteries have significant overhead and heat issues when one attempts to charge them rapidly. The overall effect is more efficient brake energy capture.

There has been a lot of work on very large capacitors. It could be that future EVs will include large capacitors as the main energy storage method, or maybe just a significant portion of it. The advantage would be that EV charge times for the capacitor would be reduced by a MAJOR factor over modern battery performance and the energy loss in charging would also be majorly reduced.

If you could recharge the capacitor half of your EV power supply in less than 10 minutes, that could be a real feature.

 

No but if what you say is correct, then the electric motor would have to deal with the transmission, wheels, etc etc so overall energy spent would still be greater than operating the car on fuel.

 

Most EVs dont have transmissions, at least not 'multi speed' ones that ICVs do. Electric car motors can run up to around 10K rpm without suffering damage or losing torque. Thats one of the ways they achieve higher efficiency.

 

Gas or natural gas generator? A natural gas generator would be cheaper than charging your car from the wall due to how cheap and clean natural gas is. Natural gas is also transported over pipes and there isn't a huge loss in energy efficiency like power lines running long distances.

 

A small generator, like one you can carry with you in the car. So probably gasoline powered. Natural gas is around 10% less efficient than gasoline (tho I believe this is by price, not by weight, so maybe not...)

 

A generator can run continuously at maximum efficiency [if the system is designed well]. It only needs to operate at one speed. A car engine is very inefficient when it has to operate over a wide range of speeds and loads. Electric motors can operate very efficiently over a wide range of speeds and loads. So while you automatically lose 20% by charging a battery, you are more efficient than powering the wheels directly with combustion.

The proof is in the mileage hybrids get.

 

When we talk about efficiency, we are normally referring to energy efficiency. You are talking about economic benefits.

 

In the USA natural gas is several times cheaper than gasoline. I work in the industry.
Power plants that burn natural gas to produce power make their money on natural gas. Sometimes the pressure of the natural gas pipeline fluctuates, drops or whatever and they cannot burn natural gas. This might be due to maintenance, issues with pipelines, compressors, unforseen high usage, or other equipment.
They have diesel and gasoline silos to hold gasoline in an emergency. If they have to burn gasoline instead of natural gas, they start losing money and they are not very happy.
These are turbines producing electricity and not engines though.

From what I read, If you are charging your car with a generator at your house from your natural gas hookup, then it saves you money. If you are going the LNG route and charging your car out and about, you will not be saving much if anything. Maybe now that gas prices are so high...but not always.

 

I think this is pretty doubtful.
First of all it depends on what exactly you mean by "gas generator". But I think whatever you mean by that, it is still unlikely. A portable gas generator is not going to be more efficient or much more energy efficient than a regular car engine. Add in the additional efficiency loses in charging the battery and then converting mechanical energy into electric energy and then back into mechanical energy.

It is true however that trains use a diesel engine to produce electric power which then drives electric motors and that this is the most practical option for that situation. However that is a different situation from cars.

 

It is the entire basis for hybrids, which do get better mileage than non hybrids!

 

Actually 2 or 3 conversions.
A typical car produces mechanical energy.
What you would describe would produce mechanical energy, which has to be converted (1) into electrical energy and then converted (2) back into mechanical energy. If the starting gas generator is separate from the car, then there are also the efficiency conversion (3) loses of electrical storage or charging the battery.

 

Yes but it can run far more efficiently, AS WE SEE EVERY DAY WITH HYBRIDS!

Do you people know how a hybrid works? Apparently not!