Who Needs Gasoline? - The Incredible Potential of Plug-ins and EVs

How would you like to power the entire U.S. fleet of cars and light trucks using only half the oil we currently use? What would you say if I told you we could even do it without using a single drop of petroleum?!

Today we're going to talk about how we could do just that, right now, using available technology: electric vehicles and plug-in hybrids. It all comes down to how efficienctly we want to utilize our petroleum (and indeed energy in general) for transportation...

The Current Picture - An Inefficient Waste

Currently, our transport needs are met by petroleum refined into gasoline or diesel and then burnt in internal combustion engines. This process is not very efficient overall. Here's how it breaks down, from the barrels of oil to the energy at the wheels of our cars:

Engine combustion efficiency: ~35% (gasoline engines are about 20-30% efficient and diesels are ~40% efficient so we'll take 35% as a combined average to represent the two)

Engine mechanical efficiency: ~70% (efficiency of tranmitting mechanical energy of pistons to the driveshaft and transmission)

Transmission efficiency: ~70% (efficiency of transmitting mechanical energy of driveshaft and transmission to the wheels

.35*.7*.7 = Total barrel (BBL) to wheel efficiency = .1715 = 17.15%

[Note: This doesnt take into account the efficiency of refining the crude oil into gasoline or diesel (which I don't know, does anybody have any idea?) which would drive this efficiency down even farther.]

Here's how this breaks down in terms of oil consumption: according to the TDB (p. 1-18) we currently use about 13.2 million barrels of oil per day (million bbl/d) for transportation. 56.6% of this or 7.4712 million bbl/d go towards running the U.S. fleet of cars and light trucks (TDB p. 2-1). At 5.8 million BTU energy content per bbl of oil, that's 43,332,960 million BTU per day of energy used by our cars and light trucks. At 17.15% overall efficiency, only 7,431,602 million BTU of that energy makes it to the vehicles wheels.

So, is there a more efficient way to get the energy from the barrel of oil to the wheels of our cars? Fortunately, yes there is.

Electric Vehicles - Who Needs Oil?

What would it look like if we used all that petroleum to generate electricity to power an electric vehicle fleet? Something like this:

Generation of electricity (burn petroleum in a combined-cycle plant): ~50%

Transmission of electricity: ~90%

Battery efficiency (lithium-ion): ~90%

Electric Motor Efficiency: ~90% (notice how much more efficient an electric motor is than an internal combustion engine!)

Transmission Efficiency: ~90% (an electric transmission is also more efficient than one for an ICE)

.5*.9*.9*.9*.9 = BBl to wheels efficiency = .3281 = 32.81%

That's an improvement of 191% or almost double the efficiency of an ICE fuel pathway. Right there, just by burning our petroleum in efficient combined cycle plants, rather than inefficient gasoline and diesel internal combustion engines, to create electricity and run an electric drive-train vehicle, we could cut our oil consumption for cars and light trucks almost in half. We would only need 52.28% of the oil we currently use, for a savings of 3.565 million barrels of oil per day!

[Note: this example doesn't take into account the efficiency of refining the crude oil into something suitable to burn in a combined cycle plant but I didn't take into account the refining of gasoline for ICEs either so this should be a wash. More importantly, this doesn't take into account the gains of regenerative braking since I'm not sure how much they would be. I would imagine that they are not insignificant however and if anyone has a good estimate for me, I'll plug that in and see how that changes things]

OK, but I promised you we wouldn't need a drop of oil and so far I've only cut our oil consumption in half. We've still got a long way to go right? Wrong. The beauty of using electricity as your primary fuel is that it is not dependent on petroleum to generate. Unlike gasoline, electricity can be made from a myriad of sources, some renewable and others not, all of them producable from within the United States (unlike oil which requires us to import almost 2/3rd of our oil needs and is never renewable). That means we could potentially eliminate our dependence on oil for our car and light vehicle fleet completely if we were to transition to an all-electric fleet.

But that would require a whole ton of additional capacity wouldnt it? We were going to use that 3.9058 million bbl/d of oil to generate 11,326,936 million BTU in our combined cycle plants or the equivalent of 3,319,925 MWh per day of electricity (1 million BTU = .2931 MW). To meet the needs of our EV fleet would thus require 138,330 MW of added capacity (1 MW = MWh/d / 24 hours). Put another way, that would require 138 new power plants (average size 1000 MW) to be built. According to the EIA, total U.S. generating capacity in 2004 was about 1,000,000 MW or 1,000 GW. Powering our EV fleet would thus require us to add another 13.83% to our generation capacity with the addition of over 138.3 GW additional of generating capacity. Or would it...

The Zero-Oil Solution - Using What We've Already Got

Peak demand during the day is generally about twice that of nighttime demand. That means half of our current generating capacity is already sitting idle all night. If we were to charge our EVs overnight, we could utilize this idle off-peak generating capacity instead of building new power plants. Let's see where this would get us:

Total U.S. generating capacity in 2004: ~1,000,000 MW

Percentage of generating capacity idle at night (let's say 10:00 pm - 6:00 am): ~50%

Total U.S. generating capacity idle at night: 500,000 MW

Total energy output of idle capacity each night (500,000 MW * 8 hours): 4,000,000 MWh

Total energy output of idle capacity each night: 13,647,219 million BTU

Electrical needs of EV fleet: 11,326,936 million BTU

That means we wouldn't need to construct any additional capacity and we could power the entirety of our car and light truck transport fleet from existing idle off-peak generation infrastructure, essentially eliminating the use of oil to power our light vehicle fleet. [Some of that existing generating capacity we would be using at night would be powered by petroleum still... so I guess I lied, we would use a bit of oil but we wouldn't have to, these plants could easily be replaced by greener sources like wind and solar, the possibilities are wide-open now that we are using electricity...]

There we have it, we can power our entire light vehicle fleet with electricity from off-peak power plants, eliminating the need for 7.471 million barrels of oil per day and without constructing a single new power plant. If that isnt impressive, you're not paying attention.

The Added Freedom of Plug-ins - a Suitable Compromise

OK, so about now is where all those folks who complain about the limited range of electric vehicles start chiming in. What do we do when we want to drive to Grandma's house for Thanksgiving or take the kids on that roadtrip to Disneyland or head down to Mardi Gras for Spring Break? We don't want to have to keep two cars in the garage, one for daily trips and another for those longer road trips where an EV's limited range wouldn't cut it?

Well, these are all valid complaints. Although it seems like many people could afford to have two cars (many people already do), most would be reluctant to do so, especially those used to the freedom of a gas-guzzler - you can pull in to a gas station anywhere and in five minutes be back on the road and free to drive another 300 miles.

Well here's a compromise: plug-in hybrids. That is, a hybrid electric vehicle that can be plug-in to charge and can run in all electric mode for 20-40 miles (like an EV) but can also use gas or diesel on extended trips (like an traditional ICE).

This means there are essentially two fuel pathways for this vehicle. The first is the electricity pathway that would be the same as for an EV. The second would use a gas or diesel generator onboard the car to burn fuel and generate electricity to run the electric drive-train when the batteries are dead [this is called a series-parallel hybrid system and is found in the Mitsubishi Concept-CT MIEV for example].

If we assume an all-electric mode with a 40 mile range, we could probably safely say that at least 2/3rds of our trips could run in all-electric mode. According to the Bureau of Transporation Statistics, the average person in the U.S. drives an average of 40 miles per day so most daily trips could be taken using only the electric charge. As we discovered above, this power could easily be provided by existing idle off-peak generation capacity if the plug-in vehicle was charged overnight. That means that just like the EV discussed above, 2/3rds of the driving done in a plug-in could be done without any oil!

So, what about the remaining 1/3rd of the time when the plug-in runs on its gas/diesel generator? Here's what the efficiency of that fuel path looks like:

Engine efficiency (diesel gen-set): ~40%

Generator efficiency: ~80%

Electric motor efficiency: ~90%

Electric transmission efficiency: ~90%

.4*.8*.9*.9 = BBL to wheels efficiency = .2592 = 25.92%

[Again this doesnt take into account refinery losses or gains from regenerative braking]

Notice this is more efficient than the ICE fuel pathway, which is why we use the diesel gen-set to generate electricity and run the electric drivetrain rather than using it to run an ICE engine and drive-train (the latter is what they do in all hybrids currently on the market - Toyota's 'Synergy drive' for example features a split drivetrain that uses both an electric motor and an ICE engine).

What does this mean in terms of oil consumption? Well, we would need to get only 1/3rd of the at-wheels energy from the diesel gen-set or 2,526,745 million BTU. With 25.92% overall efficiency that would mean we would need 9,748,244 million BTU of petroleum (i.e. diesel) fuel or the equivalent of only 1.680 million barrels per day. Thus we would need only 22.5% of the oil we currently consume for our light vehicle fleet for a net savings of 5.79 million barrels of oil per day. This would eliminate 28.38% of total U.S. oil consumption!

So there's the compromise: we don't entirely eliminate our need for oil to run our transport fleet, but we do cut it down to less than one quarter of current consumption and eliminate over 28% of our total oil consumption at the same time. Doing so gives us the freedom and range of a traditional ICE engine while using less than a quarter of the oil.

Conclusions

Clearly using petroleum in internal combustion engines is not the most efficient way to run our light vehicle fleet. Both electric vehicles and plug-in hybrids offer significantly better options. They also allow us to use electricity, giving us the freedom to power of fleet with a variety of energy sources, not just petroleum. Additionally, the United States currently has the existing generation capacity sitting idle every night to power our entire transport fleet if they were EVs or to fully charge the batteries on all of our plug-in hybrids.

Here's the summary:

Traditional Internal Combustion Engine: BBL to wheels efficiency - 17.15%; total oil consumption - 7.47 million bbl/d - % below baseline - 0%

EV with electricity from petroleum-fired combined cycle plants: BBL to wheels efficiency - 32.81%; total oil consumption - 3.9 million bbl/d - % below baseline - 52.28%

EV with power from existing idle off-peak generating capacity: BBL to wheels efficiency - n/a; total oil consumption - 0 bbl/d (excepting petroleum in existing generation mix); % below baseline - 100%

Plug-in with batteries charged from existing idle off-peak generating capacity and extra power from on-board diesel gen-set: BBL to wheels efficiency - batteries: n/a gen-set: 25.92%; total oil consumption - 1.68 bbl/d (excepting petroleum in existing generation mix); % below baseline - 77.5%