Keeping the car in full electric mode

This particular line of discussion around abstract generation efficiency is bizarre. Yes, solar panels are ~20% efficient at capturing the energy from the Sun and coal plants are ~33% efficient at capturing the energy from burning coal. We should therefore burn coal instead of using PV panels?

Abstract efficiency of electricity generation is pretty irrelevant (but efficiency of use is relevant). A much more useful metric is CO2 emissions per kWh. Likewise, there is no fixed rule that driving HV is more CO2 (or cost) efficient than EV.

For example, I've seen no calculations here to indicate that the Prius Plugin (or Volt etc.) are more efficient when driven on the highway in terms of CO2 per mile driven on present-day average USA grid electricity than they are when driving on gasoline. The case that grid power in the battery is only best when used for slower city driving and gasoline is always best at highway driving is not been made in any detail here.

In any case, CO2 emissions vary by region. About a quarter to a third of all Prius Plugins, Volts, and probably other plugin cars in the USA are sold in California which has markedly lower than average CO2 emissions per kWh. Above average sales numbers are also seen in other states with low numbers. It wouldn't surprise me if most plugin cars are sold in regions with lower than the national USA average CO2 per kWh.

 

EPA already calculated CO2. See Beyond Tailpipe Emission site for plugin emission.

50 MPG Prius emits 222 g/mi while 99 MPGe 2011 Leaf emits 220 g/mi.

The breakdown for 2011 Leaf is 106 MPGe City and 92 MPGe Highway.

If an EV gets less than 100 MPGe on the highway, it is better to use 50 MPG gas.

The way I drive my PiP, I get 132 MPGe since I mainly drive it for urban/city and 56 MPG with gas on highway.

It is a shame EPA does not divide their city and highway cycles per fuel. Instead, they ran both city and highway cycles for each fuel. So, PiP figures came out weird.

 

The 2013 LEAF is rated as 115 MPGe combined -- 129 MPGe city and 102 MPGe highway. The emissions show 190 g/mi on the US average and 120 g/mi in California (would be lower in Northern California where I live).

The way I drive my Volt I get 120+ MPGe on battery power on the highway and I suspect you would do similarly in your Prius plugin.

 

Yup, I was using 2011 Leaf model in reference to the equvilency (50 MPG = 100 MPGe) point. It was not used to make the Leaf look bad.

You got 64 MPG with a PiP without charging isn't it? If PiP gets 128 MPGe full electric, that's break even. To pull that kind of MPGe, you need to be below 62 mph.

PiP was very well thought out and state of an art balanced. Very few people understands and can appreciated it.

 

Right, so HV is not "better" than EV for highway driving in the PiP using US average grid and it's CO2 emissions. The ratio of betterness might vary a bit at different speeds but I haven't seen the numbers for that since the Prius is excellent with hybrid gas mpg at city speeds as well as highway. My guess is that the biggest issue is optimizing the avoidance of inefficiency due to starting up a cold gas engine if your trip is farther than your EV range.

Yes, I got about 130 MPGe in the PiP and Volt driving mostly highway at 55-60 mph and some city driving as well.

Yes, I agree. We're among the enlightened few!

PiP's battery was sized according to the space available under the hatchback area and according to cost. It's a good combination for many customers. Other folks find the larger battery in the Energi or Volt work better for their commute, geography, and grid region (and alternative power options).

 

I can do 50 MPG at 70 mph. I am not sure if I can get 100 MPGe on electricity at that speed.

Even if it is a tie, higher energy density fuel that is lighter and (EV bias ppl are going to hate me) refuel much faster, is a better choice.

 

Sorry, but this is a false comparison, IMO.

I "think" what you are saying is as follows:

Gasoline is 85% efficient and coal, NG, etc are about 33% efficient.
This is based on the fact that about 15% of the energy in gasoline is used in the drilling a refining processes, etc.
Whereas, coal, for example, in an electrical power plant has some thermodynamic efficiency (say 40%) and then some electrical line losses bringing it down to 33%.

So, when the energy enters the car, for gas, you have 85% as much as you started with...and for electricity you have 33% as much as you started with. So, in EV driving, you'd need to be traveling 85/33 times (~2.6x) as far in terms of MPGe to break even. for 50 mpg on gas this would be 129 MPGe on electricity.


First, let me say that plenty of us (not all) probably get better than 130 MPGe when driving in EV. But of course many people don't get 50 mpg on gas either.

Second, I don't think you can really compare thermodynamic efficiency numbers unless there are the same thermodynamic cycle (process). For example, let's say that my only methods of generating electricity were one large hydro and one coal plant. The coal plant is traditional, maybe 35% efficient. My hydro power was a very low cost terribly built plant that only got 10% of the power of a well-built plant of similar size, etc. The hydro plant was very cost efficient to build and is 10x the size of the coal plant. My "average" efficiency for electricity is ~12% before line losses. Can you now explain why 85% efficient gas is better than my 12% efficient electricity?

Mike

 

When it comes to renewable, I think efficiency does not matter much because the carbon footprint is so low. That was also Jeff's point and I agree.

However, you charge your PiP from the grid and it may be mixed with other electricity. EPA gives CO2 g/mi numbers down to "region". Some are cleaner than others. If you don't want to go by the grid mix average, you can go with figure for your region emission. Enter your zip code, thats all. I would not claim you electric miles are 100% hydro power unless you have a direct line to it.

Renewables makes up about 7% (last I checked). In term of efficiency, 33% vs 84% gap is bigger. In term of emission, it is about 42% vs 84% (50 MPG = 100 MPGe) boosted by renewables.

 

The science and numbers nerd in me is loving this thread. Definitely a new way to think about all of this that I haven't thought about before.

 

The notion that electricity is not fuel probably started with him and it needs to stop.

 

Oof I'd hate to calculate what the comparable numbers are for my dehumidifier, since I use way more electricity in that in one month than I've used for the PiP in the same month.

 

Well, electricity is not a fuel. It may have been generated from fuel, but it in and of itself is not fuel.
People might not be aware of where their electricity comes from, and what implications that has, but that's another matter.

 

Electricity is considered an alternative fuel under the Energy Policy Act of 1992.

Alternative Fuels Data Center: Electricity Fuel Basics

 

That might mean that relevant policies treat it as if it were an alternative fuel (as it reduces the use of the fuel it is considered an alternative for), but I've not seen anything that says electricity is an actual fuel. It's more of an alternative to fuel (or to using fuel directly, at least). Maybe it was just easier to set it up that way for legislative purposes. In the context of vehicles, it probably doesn't matter too much - it's an energy source the car can use.

Anyway, I'm just being pedantic. Would you consider compressed air a fuel? What about gravity-based potential energy sources, such as dams?

 

Yes. It takes energy to move the car. Energy is in the fuel. The form of energy does not matter if it is solid, liquid, electron, etc.

 

Yes, exactly! Energy is in fuel. Electricity is another form of energy, and is harnessed another way. Even if they are different forms, fuel, electricity, and some others can be used to much of the same effect - in this case, propulsion of a car.

 

Fuels are just a way to store energy. If you use hydrogen to power a fuel cell, the hydrogen probably came from hydrolysis of water. Gasoline is stored prehistoric solar energy. Electricity was created by the fuel that powered the generator. Even the radioactive power sources used in deep-space probes are releasing the energy that was used to to create the radioactive element in some ancient star.