Engineering Intuition and The Media

I don't really want to ridicule Kevin Drum here for thinking out loud.  I really hate partisan Conservative and Liberal team-politics blogs, but I read a few to stay out of the echo chamber, and Drum is smarter and incrementally more objective (a relative thing) than most.

But this is really terrible, awful engineering intuition:

These two things together reminded me about an energy factoid that's always struck me as slightly odd: virtually every form of energy seems to be almost as efficient as burning oil, but not quite.

For example, on either a power/weight basis or a cost basis, batteries are maybe 2x or 3x bigger and less efficient than an internal combustion engine. Not 50x or 100x. Just barely less efficient. And you see the same thing in electricity generation. Depending on how you do the accounting, nuclear power is maybe about as efficient as an oil-fired plant, or maybe 2x or 3x less efficient. Ditto for solar. And for wind. And geothermal. And tidal power.

I'm just noodling vaguely here. Maybe there's an obvious thermodynamic explanation that I'm missing. It's just that I wouldn't be surprised if there were lots of ways of generating energy that were all over the map efficiency-wise. But why are there lots of ways of generating energy that are all surprisingly similar efficiency-wise? In the great scheme of things, a difference of 2x or 3x is practically invisible.

First, we have to translate a bit.  He mentions power to weight ratios for batteries in the second paragraph.  In fact, batteries have terrible power (actually energy storage) to weight ratios vs. fossil fuels, much worse than 2-3x for energy storage per unit of weight or volume.  That is why gasoline is still the transportation energy source of choice, because very few things short of plutonium have so much potential energy locked up in so little volume.  But I will assume he is comparing an entire electric drive system compared to a gasoline drive system (including not just energy storage but the drive itself) and in this case the power to weight ratios are indeed closer.

But here is the problem:  in engineering, a 2-3x difference in most anything -- strength, energy efficiency, whatever -- is a really big deal.  It's the difference between 15 and 45 MPG.   Perhaps this is Moore's Law corrupting our intuition.  We see electronic equipment becoming twice as powerful every 18 months, and we start to assume that 2x is not that much of a difference.

But this is why Moore's Law is so much discussed, because of its very uniqueness.  In most fields, engineers tinker for decades for incremental improvements, sometimes in the single digit percentages.

The fact that alternative energy supporters feel like their preferred technologies are just so close, meaning they are only 2x-3x less efficient than current technologies, explains a lot about why we skeptics of these technologies have a hard time getting through to them.


  1. delurking:

    The problem isn't the engineering intuition, it is the market intuition. Those things that are close to oil are on the table because they are close to oil. I can give you plenty of energy generation techniques that are on some metric less than 1% as efficient as burning oil. Hell, there are plenty of photovoltaics being researched in academic labs that are 1% as efficient as current silicon photovoltaics. Similarly with fuel cells, biofuels, etc.

  2. Panzersage:

    When Kevin talks about a difference of 2-3x being invisible I burst out laughing. He's asking why we don't have any technology that is 200-300% more efficient when an increase of 5% can cost millions of dollars and take a decade.

    Drum also fails to understand that none of the technology has been standing still. Every decade we have improved efficiency in every area of power generation.

    Finally Drum's post gives all the signs of a conspiracy theorist. He suggests some shadow conspiracy taking place to keep oil on top. He uses fake numbers (I have no idea how he gets the 2-3x number), although they might not be fake numbers, however without the math to show where he starts (i.e. from the power plant or in the battery itself), how the power is generated, etc. He uses the "just asking questions" excuse to keep from having to give any theories yet imply something sinister.

  3. nzc:

    Another point -- these things are (in part) as close as they are in efficiency because people are working hard at optimizing all of them. Because the evil market forces are actually pushing hard to achieve what the greens want. Well. Not all the greens. Some want to return to pastoral/agrarian life, and no rational mechanism will produce that.

  4. NL_:

    Anything that was 100 times less efficient wouldn't even be considered much of a power source. I mean, human propulsion and horse-drawn wagons could be used to compare. But you'd need to house and feed and maintain such a huge number of horses or human servants just to get the same towing capacity as a car at a slower speed that we don't consider it. But certainly it exists. It's just that the less efficient forms are already ruled out.

    So while there might be some energy benefit to burning garbage in your trunk and using the resulting heat to boil water that turns a turbine, we don't use it because the entire process is unwieldy and unreliable and the energy transferred isn't that great and the distribution system required would be silly (dumping your burnable garbage into your trunk, maybe?).

    Anything that's ridiculously underpowered as an energy source is already ignored, leaving us things that might one day be competitive but today are just efficient enough to tantalize.

  5. me:

    Oddly enough, also: wrong. CNG has better energy density, we won't have to wait for those antimatter cars.

  6. Another guy named Dan:

    I think this fits in well with the other posting regarding a bias towards positive results. There are thousands of ways you could move a person from one place to another, ranging from harnessing a billion ants to a chariot to personal jet fighters. It really shouldn't be a surprise then that after a selection process that has been rigorous, the top contenders should be close.

    It is similar to the fact that the two top competitors in the Olympic 100m dash finals should be closer than the fastest and slowest finishers in a sixth-grade gym class.

    To me the salient point should be that even after a rigorous selection process called the free market, pure electric and plug-in hybrids are the best alternative and still not competetive on a performance/price basis with the gasoline internal combustion engine as a personal transportation solution.

  7. samsam von virginia:

    Nuclear power plants operate with steam at a lower temperature than coal-fired plants (for safety reasons). Efficiency of any heat engine is limited by the difference in temperature in the hot and cold sections of the engine. Thus, nuke plants are less efficient.

  8. TJIC:

    You're familiar with the selection bias hidden in the "we only have 10 years of new oil scouted out ! OMG / ONOZ!" story that we hear every few years.

    For those who aren't, the deal is that the 11th year of oil isn't WORTH scouting out. We'll scout it out next year, when it's just 10 years away.

    In a similar war, it's never worth talking about a power source that's 100 times worse than oil.

    Breading a species of hamsters that east seafood then harvesting oysters to feed to the hamsters to generate electricity via a treadmill (tread wheel ?) is 200 times worse than oil...but no one (before me!) has even thought of it, because ideas like "wind power", "solar", and "biomass" are already stupid enough to fill out 10 year quota of idiocy. If we hit peak oil and nuclear, wind, biomass, etc. all move up one notch in the rankings, THEN we'll put "hamsters that eat oysters" on the list as number 10.

  9. perlhaqr:

    And, of course, the electric vehicle hullabaloo ignores the refueling issue.

    Even if an electric car was 1:1 with a gasoline powered car, I still couldn't drive from New York to Los Angeles in one on anything like a reasonable time frame with their 120 mile ranges and 8 hour recharge cycles.

  10. Don:

    "Every decade we have improved efficiency in every area of power generation."

    Not true if you consider the systems as a whole. One of my vehicles is a 2003 Cummins diesel truck which gets (average) 19.5 mpg. The exact same truck in 2008 year model (same size engine, but outfitted for "low sulfur diesel") gets around 12. The same goes for gas, when I had an '87 Civic Si I got 42 mpg, when I looked at them again in 96, they got 32 mpg for an only slightly larger engine (I think it was .1 liter difference).

    Many of the things that manufacturers are FORCED to put only their autos cost us huge amounts of fuel.

    I cannot help but wonder, if we ONLY paid attention mpg, and let manufacturers do whatever they need to do to get there, would we be looking at a 70-80 mpg Honda Civic today? I think we might.

    From an environmental point of view, perhaps it's time to reevaluate HOW cars are regulated. Perhaps we should take into account the amount of emissions at normal use. If an "improvement" reduces the amount of emission X by 10%, but it creates the need for a 20% fuel increase, have we really helped things? I'd say probably not.

  11. Nobrainer:

    My best guess is that the last two times he says "2x or 3x", he intended to write "2% or 3%." Or I'm wrong and he really just has no clue.

  12. eddie:

    Give Drum a salary that's "maybe 3x less efficient" than his current salary and then see if he thinks that's "almost as good, but not quite, just barely worse".

  13. Max:

    Engineering intuition? What he displayed is not even that, it is the intuition of social science majors, who try to understand engineering. 2x-3x the efficiency is a big deal, especially when applied to big numbers. But you said as much already. Car companies f.e. fight for 0.5 % up to 2% efficiency increases in gasoline engines, because they make a difference in consumption that is not small considering that people drive 10 - 15 k miles per year! (2% of 10k = 200 miles already).
    If all people had such an efficiency increase in their energy consumption, we would save Gigawatt/hours or more per year.

    Also, a small correction. Batteries have a really terrible power to weight ratio, but they have a slightly better energy to weight ratio! Unlike Double Layer Capacitors, which have high power to weight ratios and low energy to weight ratios. Of course, all of them are worse than fossil fuels when it comes to energy per weight.

  14. Griffin3:

    2x-3x efficiency is very significant, and I take that point. But Kevin Drum is "vaguely noodling" completely wrong numbers. Energy density of gasoline is 47 MJ/kg, of lithium batteries is 1.3 MJ/kg. 30x difference. It doesn't matter if you call it 2-3x difference, it jusr doesn't make it so.

    Drivetrain weight and efficiency might be better with electric, but it never comes close to correcting this curse of low energy density. Same with hydrogen, CNG, propane, compressed-air powered vehicles. Add to that the fact that gasoline is a well-behaved liquid at room temperatures, doesn't need a monstrous steel tank to contain it, and is easily metered and dispensed by customers ... figure out a way to synthesize butane from CO2 with electricity, maybe, else stop holding up progress. You're embarrassing yourself.

  15. EscapedWestOfTheBigMuddy:

    @me: The thing (aside form distribution infrastructure, of course) that limits the take-off of CNG for cars is the volumetric density. Fuel storage in a passenger car is a non-trival fraction of the total volume so lower volumetric density translates to less range.

    Not a big deal for fueling fork-lifts around the warehouse or fleet vehicles that tool around town (both of which are markets where CNG has made some in-roads), but a pain if you want to drive over the hill and through the woods to Grandmother's house a couple of times a month.

    Still, recent trends towards petrochemical production being dominated by natural gas might be a catalyst.

  16. me:


    Given that I recently made the trip from Essen to Luebeck in a CNG car (fully loaded with two kids and three adults plus luggage) on one tank of CNG, I believe the technology eminently practical. That's 260 miles.

  17. EscapedWestOfTheBigMuddy:

    @me: Sure. But the same car outfitted with a efficient gasoline or disel engine would go upwards of 400 miles on a tank.

    The question isn't *if* it will work (it will), but what the people buying them think is the best match for their needs. Now some of the reluctance to buy them could be plain old inertia, but if CNG is economically advantageous people will overcome the force of habit. If they don't you have to wonder what is driving the decision.

    Me, I live in the great plains of North America and sometime drive hundreds of miles in a day. I like that my car will go a bit more than 500 miles on a full tank.

  18. me:

    Concur - in the case of Germany, a price roughly 50% under the price of gas serves rather well as that incentive :)

  19. IGotBupkis, Legally Defined Cyberbully in All 57 States:

    >>> explains a lot about why we skeptics of these technologies have a hard time getting through to them.

    The fact that their entire grasp of science came from watching SuperFriends on Saturday mornings might have even more to do with how difficult it is to get through to them.

    Most people think of an electron as being about the size of a pea.

  20. Smock Puppet, 10th Dan Snark Master:

    >>> Breading a species of hamsters ... but no one (before me!) has even thought of it

    Mmmmmmm, breaded hamsters. Yum!! But would you deep fry them or grill them?

  21. IGotBupkis, Legally Defined Cyberbully in All 57 States:

    >>> 10 – 15 k miles per year! (2% of 10k = 200 miles already).

    Actually 10k to 12k is the standard, and depends an awful lot on the locale one lives and drives in. I'm sure typical people in LA drive a lot further per year than people in a small town that's less than 5mi across.

    As suggested, one of the chief reasons why electric can't take off outside of narrow, targeted usages is the "recharge time". If I'm driving from point A to B, and need to refuel my car, I can do that with a gasoline vehicle inside of about 5 minutes. Any electric vehicle is going to take at least an hour or two, more likely many more.

  22. IGotBupkis, Legally Defined Cyberbully in All 57 States:

    Also as discussed, range is a factor. One more chief advantage of the gasoline/diesel vehicle is the range for a given refueling. With most g/d cars this is in the 250-500 mile range depending on fuel efficiency and size of tank. With most electrics I believe it's more on the order of 120-150 miles.

  23. markm:

    Finally, electric-car batteries will have to be replaced every few years, at a cost currently estimated as $12-15,000. That would buy a lot of gasoline.

    If electrics somehow became practical enough to go into high-volume production, that cost might be cut in half, but that's still more than 10 times the cost of replacing a car's gas tank - which you'll probably never have to do. Rust can eat a metal gas tank, but in my long life in road-salt country, usually the gas tank will still be OK when I will no longer trust the rusted-out unibody to hold together on a bumpy road.

  24. Smock Puppet, 10th Dan Snark Master:

    >>> but that’s still more than 10 times the cost of replacing a car’s gas tank

    Nothing the EPA can't fix with new regulations regarding escaping fumes and puncture/accident safety rules.