Portable generators about half as efficient as power plants

Fun fact for electricity geeks. I’ve wondered for a while how home generators compare to big central power plants when it comes to producing electricity. After all, I’ve been living in a country (Venezuela) where more and more of the load is going to be covered by these little portable units, and I wanted to know how this would affect gasoline and diesel exports.

I happened across a spec sheet for Honda portable generators up to 6 kilowatts. According to my math, they convert between 13% and 18% of the power in gasoline into electrical energy, when running at their “rated load,” usually about 10% lower than their maximum load.

This is a little better than half as efficient as fixed power plants.

The gasoline-powered generators produce at best 6.13 kilowatt-hours per gallon of fuel, at worst 4.42, and a median of 5.7.

Fixed power plants in Venezuela (I use it because I have it handy – feel free to correct me) in the first quarter of 2010 produced 11.1 kilowatt-hours of electricity per gallon of diesel.

So, to produce a megawatt of power, you need to feed little Honda generators about twice as many gallons of gasoline as the number of gallons of diesel that you would have fed to power plants for the same amount of electricity. Since both gasoline and diesel are effectively free in Venezuela, this means that providing the same social good will cost the state oil company twice as much per unit of electricity produced using small home power plants.

Thank you for geeking out with me. Now back to the pretty pictures.

About these ads

7 thoughts on “Portable generators about half as efficient as power plants

  1. HalfEmpty

    Hell, if it’s that good (and I don’t know) count yourself lucky.

    Consider the Mean Time Between Failure of your house unit and things might change. Dunno. Diesel, you want it.

  2. Noel Maurer

    In honor of geek week, I’ll point out that your post doesn’t capture the half. Nobody in their right mind would build a diesel plant for baseload generation. Gas has lower capital costs, lower O&M costs, and lower fuel costs per MWh — the go-to stat is the “spark spread.”

    You might use diesel for peakload, if your grid was crappy enough or you lived somewhere (like Chile) with higher-than-normal gas prices. But even that would be weird.

    In fact, Venezuela’s figures are even crazier than the above implies. The U.S., frex, produced 25,792 MWh of electricity in 2009 by burning 43.7 million barrels … for 24.8 KWh per gallon. Venezuelan large-scale plants don’t even reach half the U.S. efficiency for all plants!

    In short, it’s threefer madness! A dumb choice of scale, in a country with inefficient large-scale plants, that should be burning an entirely different kind of fuel anyway.

    There is something impressive about it, I think.

  3. sapitosetty Post author

    Noel – Thanks for the great comment. But a couple things.

    First, where are you getting your USA numbers? If you are including nuclear and other generation in the figure, that will make the U.S. generators look more efficient than they are. What I see at

    http://www.eia.doe.gov/cneaf/electricity/epa/epates.html

    is that in 2008, the USA burned 80,932,000 barrels of petroleum in power plants to generate 46,243 gigawatt-hours. That works out to 13.6 kWh per gallon*, which is better than the number in Venezuela but not the two-fold difference you found.

    (46243000000 kWh )

    over

    (80932000 barrels of petrol *42 gallons/barrel= 3399144000 gallons of petrol)

    = 46243000000/3399144000
    = 13.6

    Second, Venezuela probably should be burning natural gas. But for now, if it were to burn more natural gas, it would have to import the fuel from Colombia. And no, Mariscal Sucre won’t be producing fuel in 2012, or 2013, or 2014.

    :(, as they say.

  4. Noel Maurer

    I used the same source you did. Let me get the exact data from the Electric Power Monthly:

    Table 1.1 – Net Generation by Energy Source, Petroleum Liquids: 25,792 MWh.

    Table 2.2a – Petroleum Liquids, Consumption for Electricity Generation by Sector: 43,672 thousand barrels.

    25,792,000 KWh ÷ (43,672,000 ÷ 42) = 24.8.

    I thought the disparity is that Table ES1 includes fuel burnt for thermal generation as well as electricity, but now I’m not sure. It may be that the Electric Power Monthly figures don’t include residential use … but the disparity is too big for me to believe that.

    Ideas? This sort of thing always worries me …

  5. moses

    I had the opportunity to visit the Tacoa Plant of the Electricidad de Caracas in the early 80’s. This Thermolelecric plant was designed to run on natural gas, but was using a heavy fuel oil to fire the boilers (“Residual Craqueado”, I was told), so heavy that after 6 months of use, the biolers had to be shut down and compressed air hammers (the same you see for repairing concrete roads) had to be used to remove the tar like residue at the bottom of the boilers.

    In the control room there was a big digital display (LED Technlogy) that read the fuel consmption per KWhr. I remember a figure of 0,225 gram or Kg per Kwhr.

  6. Mike

    Generating efficiency is only part of the equation, what matters is the energy consumed vs the energy delivered and there is a significant amount of energy lost through transmission lines – up to 10%.

    In my opinion, the biggest drawback to local generation is the incredible increase in pollution per KW-h that is released. Probably hundreds of times more pollutants released than in a power plant (heavily regulated, measured, and maintained).

  7. thesitrep

    I have a Yamaha EF2000i which produces and amazing 7.83 kwh/ gallon.
    That still isn’t very good considering gasoline in Hawaii is US$4.50/G.
    I have a Lister type generator I built that runs on straight (free) used veg oil that is much more efficient but it weighs about 900 pounds.

    I get an average of about 4 kwh/day from my solar panels. (2000 watts worth)

Comments are closed.