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Oil For Electricity is More Efficient than Oil for Gas

An Ironic Pairing

One of the biggest dangers of coasting along in the mentality of business-as-usual is that inefficiencies can become cemented into the forces that are considered to be essential to our daily lives. At some point, rectifying the problem can require more time and effort than most are willing to stomach. Our tendency to allow historical experience to evolve into present-day gospel can lead us to miss opportunities for innovative improvement, especially when it comes to sustainability.

Let's take one of the pillars of American energy usage: our cars. Every living American can look back on the constant of gasoline serving as the energy source for our mobility. Meanwhile we have watched cars become more efficient over time, bolstering our confidence in the system. As part of this mindset, the bulk of our efforts in increasing efficiency have revolved around the puzzle of how to make cars get more miles for every gallon of gasoline they consume. But what if instead of doing more with gasoline it was actually more efficient (maybe much more) to burn oil to create electricity and use it to power cars instead? Perhaps the cultural constants that we assume are the best solution actually don't hold as much as water as we think.

As it turns out, it is true.

Gas Guzzling

According to the EIA, Americans used an average of 367 million gallons of gas every day in 2011. For the year, that's the equivalent of around 16.74 quadrillion Btus of energy or roughly 17.2% of all of the energy the country used for the year.

When Henry Ford first conjured the assembly line for churning out his Model T, who could have imagined how far cars would come 100 years later. With all of the glitz and glam that we can now mold into our automobiles there could be a tendency to point to our cars and laud them as examples of how our innovative spirits have turned a motorized carriage into sleek, comfortable, efficient capsules of mobility. If we needed more proof we could point to our brand new CAFE standards that raised the bar for the efficiency of our vehicular fleet to a minimum of 27.5 miles per gallon for passenger vehicles. To many of us this would come across as a perfectly reasonable argument.

But the truth is that despite the various iterations, classes and likenesses that cars have gone through they are still not all that efficient at turning latent energy into kinetic energy. It's true that cars of today can go much farther on a gallon of gas than their ancestors, but even now most of our internal combustion engines are only 25-30% efficient (actually turning energy into forward motion). The majority of the energy created from burning gas either goes out the tail pipe as heated exhaust or is lost in friction of moving parts.

That alone is a bit disheartening, but it is important to remember that gas is a by-product, not a natural resource, and sits near the end of a long product life cycle. Losing 70% of gasoline's energy is not only throwing away Btu's in your gas tank, but almost three quarters of all the energy that poured into it as well. Comparing the processes of turning oil into gasoline vs. electricity points to an example of the latent inefficiencies that might be baked into our system.

The Life Choices for Oil

In both cases, some of oil's life-cycle is the same. No matter what, crude oil reserves need to be discovered, drilled and harvested. This process alone consumes a significant amount of energy, but for the purposes of our comparison, it is still the same large amount of energy for both. Given that crude oil cannot be used efficiently to do anything, it arrives at the refinery with a latent energy of 132,000 Btu/gallon.

The main component of our oil refining process is distillation where crude oil is vaporized in order to be broken into various refined components. Given the demand for gasoline in this country, about 40% of every barrel of crude oil is turned into gasoline, but this process also costs energy. On average, the refining process for gasoline is around 85% efficient (Wang, 2008) meaning that 15% is lost in the conversion (or about 21,000 Btu. By comparison, No. 4 Fuel Oil (burned in power plants for energy) has a 93% refining efficiency, needing less energy to produce every gallon.

energy to power cars oil vs gas

Coming out of the refinery, barrels of both products are shipped to their point of use–either gas stations or power plants. For the purposes of this comparison, we can once again assume those two numbers are roughly equal.

As noted in the beginning, most of the 114,000 Btu of energy in every gallon of gas burned in an engine doesn't end up turning the tires of the car. If we take a car meeting today's CAFE standards of 27.5 miles/gallon, we get a total energy of 4,145 Btu/mile.

When it comes to electricity, the largest stake holder in the overall efficiency of the system comes at the production level. While the internal combustion engine of a car may still only be able to convert 30% of its energy into useful function, even our oldest coal-fired power plants in this country can keep pace with that. The most recent industry capabilities utilize combined-cycle plants that fire a generation turbine (basically a jet engine) and then recapture the exhaust to produce steam, turning yet another turbine. With these paired processes combined-cycle natural gas plants can reach efficiencies of 60%. (If the heat is captured again and used for heating in nearby buildings, efficiencies can reach as high as 90%.)

It is true that we are not building oil-fired plants anymore due to the affordability of natural gas. In fact most of the oil-fired power capacity we have is in New England and it is seldom used. However, it is fair to assume that we could build an oil-based facility to similar capabilities, achieving a heat rate of roughly 5,690 Btu/kwh. To be fair, ±6% of that energy is lost in transmission so we can boost that number up to 6,031/kwh delivered.

To see how far that gets us on the road we can take the budding star of the Tesla Model S fully electric sedan. Its 60kwh battery pack option can yield 208 miles of travel. That means 3.47 miles/kwh or 1,738 Btu/mile or less than half of the energy per mile of its gasoline-powered counterpart.

Search for Possibility, Acknowledge Opportunity

Before my regular readers raise havoc at the plan outlined above, it is important to note that I am not trying to pitch the consumption of more fossil fuels. In fact, I am not even a proponent of owning a car at all (read: there are few luxuries better than walking to work). Would this be a huge infrastructural shift? Absolutely. And to be successful it would require a wholesale migration of American consumers from gas-powered cars to electric. Furthermore, energy pundits could point out our refining process would need to change in order to shift so much of our crude to distillate fuel production rather than the 40% we now turn into gasoline, which would have an effect on energy prices. All correct. When it comes to a more sustainable society, there is a difference between being more efficient and simply using less. Our planning efforts should still be pushing for development that can afford us convenience without needing cars.

However, in the meantime, the point is that if we were going to keep driving cars and burning fossil fuels, questioning the status quo could leave us with more efficient solutions that would allow us to do more with less. Much like our relationship with coal and power generation, gasoline does not necessarily represent the holistically "best" solution, but maybe just the most convenient. A gradual transition towards cars with more electric capacity (even if that means Plug-in Hybrid Electric as a first major step) could underscore a migration towards a smarter grid that has more flexibility in how we distribute and use energy. We should work to become more diligent in the practice of reassessment rather than waiting for problems to occur. For any technology, letting the societal momentum of a cultural norm roll over the periodical reassessments to challenge our assumptions is dangerous and constricts the innovation that we are trying to promote. We need more comparisons between the "way we've done it" to the "way we are able to do it" rather than letting the former dictate our course forward.