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Page added on March 31, 2013

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Ahhh EROEI

Alternative Energy

The Ratio of the Energy Returned divided by the Energy Invested in producing electricity. The Green bars are global estimates and the purple bars apply to the US. There is considerable uncertainty in the numbers

The Ratio of the Energy Returned divided by the Energy Invested in producing electricity. The Green bars are global estimates and the purple bars apply to the US. There is considerable uncertainty in all the numbers.

How should we decide on the mix of technologies to use to generate electricity? There are pros and cons for all the choices.

  • Coal is cheap but emits carbon dioxide.
  • Gas is a bit more expensive but emits 50%  less carbon dioxide.
  • Nuclear requires eye-watering up-front investment but is low carbon.
  • Wind energy is intermittent but sustainable

So it is interesting to make quantitative comparisons between the differing technologies. We have many choices in comparing parameters. Initial costs; running costs;  immunity to world fuel prices; sustainability – the list goes on.

One interesting choice is EROEI: the Energy Return on Energy Invested. It is the answer to the sum:

EROEI = Useful energy produced ÷ Energy invested

So for example, if I use one unit of energy to dig coal from the ground, ship it around the world,  and then burn it to power a steam turbine and make electricity, how many units of electrical energy do I generate?

This is a simple question to ask, but a difficult one to answer. For example, one would obviously consider the energy used in shipping the coal. But what about the energy used in building the ship? Or some fraction of it? Using standardised rules one can produce estimates of EROEI and the results – in a chart at the top of the article are interesting.

Several things struck me about this chart

  • First there is massive discrepancy between world-wide coal (18) and US coal (80). This is presumably because of the ease of extraction of US coal, and the short distance from mines to coal-powered  electricity-generating plant. The large numbers in each case help explain the popularity of coal in generating electricity both world-wide and in the US. The energy return of course takes no account for energy which might be needed to cope with the consequences of the massive carbon dioxide emissions, or the appalling environmental legacy of coal mines.
  • Second is the number for wind (20 or 18) – which is more-or less the same as coal. At Protons for Breakfast many people ask whether in energy terms wind power is ‘worth it’. The answer from these studies is a definite ‘Yes’. However I suspect that the time to reap this return on investment may be longer which affects the financial return on investment.
  • On reflection I was not surprised that hydroelectricity represents the best EROEI, but of course this does not cover the environmental costs of such schemes.
  • The low value for gas (7 or 10) surprised me. I suppose this reflects the costs of discovery, transport, storage and delivery.
  • And finally the numbers for solar energy more or less match the numbers for nuclear energy. These are not specific to the UK and so the same numbers are unlikely to hold here. However I was surprised at the low number for nuclear power and the relatively high value of Solar Photovoltaic generation.

EROEI is not a magic number – but it is a fundamental number. If this number is below unity, then in energy terms the activity makes no sense. And if the number is close to unity, then the activity is barely worthwhile unless there is some other benefit. Scientific American suggest that activities where the EROEI is below 5 represent a borderline below which electricity -generating technologies are no longer worthwhile. It is interesting that several current technologies – including nuclear power –  come close to that suggested border.

Protons for Breakfast



9 Comments on "Ahhh EROEI"

  1. Arthur on Sun, 31st Mar 2013 2:59 pm 

    Published EROEI values should be taken with a grain of salt, as you can find any number you like:

    http://en.wikipedia.org/wiki/File:EROI_-_Ratio_of_Energy_Returned_on_Energy_Invested_-_USA.svg

    Above graph from energy pessimist Charles Hall says that natural gas has a value of slightly more than 10 (surprised me as well).

    Consider that the eroei of solar is not too high, but that so far solar was optimized for ** efficiency ** (harvest as much electricity from photons as possible, regardless of the cost of the solar device), not eroei. Gains with thin film solar (solar cells of a few microns thick) could increase eroei. Currently cells achieve 10-30 according to this link:

    http://www.polyera.com/end-user-applications/solar-cells

  2. J-Gav on Sun, 31st Mar 2013 3:36 pm 

    Though the arguments are not particularly clear or well-developed in this article, the basic premise that EROEI is an essential measure is correct. Two others are flow rates and net per capita energy available. Get your head around those and you’ll have a pretty good idea of the challenge we face.

  3. econ101 on Sun, 31st Mar 2013 3:59 pm 

    eroei is completly dependend on how much usesfulenergy is eventually extracted. Nobody knows this going forward. The measure is given over to piling on the energy invested and underestimating useful energy produced. Without detailed controls this measure is as none-sensical as peak-oil.

    For an oil well the energy invested is fixed. When oil is discovered there is no more energy in. At that pointe each barrel pumped acts to improve eroei at the wellhead. This process goes on until the well is dry or reworked.

  4. GregT on Sun, 31st Mar 2013 5:16 pm 

    Econ,

    You clearly have no idea what you are talking about.

    Many oil wells initially flow under their own pressure. As the well ages, it requires more and more energy to extract the oil, until it reaches the point where it requires more energy to extract the oil than the oil itself contains. The well is then abandoned.

    The energy investment is not fixed and does not end when the oil is discovered.

  5. Read on Sun, 31st Mar 2013 6:06 pm 

    Greg,
    I think Econ is trying to argue about total lifetime EROEI for a particular play. Of course this can only be an estimate. I think we can agree that the energy requirement will follow a similar curve to the capital required to develop and exploit a play. Energy inputs will be front loaded then will grow throughout the life of the play as it gets harder to extract the remaining energy. Marginal EROEI is relevant because earlier energy investments will be “sunk” and should not be considered from the prospective EROEI.

  6. J-Gav on Sun, 31st Mar 2013 6:14 pm 

    Econ – What a mish-mash! Please translate what you’ve written into some shared language. Or perhaps try and move up to econ201 … Wells drilled 4 miles deep in the middle of the sea are going to cost much more in terms of installation/extraction/getting it to market than Texas Tea ever did … How is that not clear for you?

  7. econ101 on Sun, 31st Mar 2013 9:41 pm 

    The cost to drill those 4 mile wells is not driving eroei into the ground, quite the opposite. You, J-Gav, are letting an incremental increase in inputs overshadow everthing else. For every energy input we are gaining more energy output. Its a profit deal. You put more in get more back.

    You forget about the numerator? How much energy comes out, useful energy and what is the value of the goods and services produced by that energy?

    The cost of the well is fixed. You may have some incidentals in pumping etc but in the end you dont know the eroei of an oil field or an oil well until its dry. Every single barrel is working toward a more profitable eroei.

    Right now the eroei is providing more profit than at any time in history.

  8. BillT on Mon, 1st Apr 2013 1:06 am 

    BS Econ! The costs (Energy/Money) per barrel INCREASE over the life of each well and the overall field. Granted the upfront costs are the major ones, but all of the costs during the life of the well is also causing the overall costs to go up as the well depletes.

    I would like to see the means that were used to come up with these numbers. After all, TOTAL costs for anything would require a lot of facts and a lot of computer time to calculate anywhere nearer than an ‘educated guess’ which is all the above article is.

    Did they factor in the costs for the drilling rigs, the cost to mine the ores to make it? The costs to mine the ores to make the mining machines, etc. The cost to mine the ores to make the trucks that brought the materials to the well site?

    How about the cost of the machines that grow the food and that provide the worker’s salary? After all, anything does not exist in a vacuum. There may be a million inputs that are ignored but mist be there to make that drilling rig/well possible.

    Not just money. ‘Externalities’ are not included or we would find that most energy sources are about breakeven or net losses. We WILL find that out when it gets impossible to keep the whole web functioning.

    For instance nuclear. Nothing is factored in to account for the energy needed to keep those hundreds of thousands of tons of spent fuel safe for the next 1,000 years.

  9. Snoopy on Mon, 8th Apr 2013 4:29 am 

    ahhhhahahahah. Ohhh (Gasps for air whilst grabbing stomach). econ101, please never stop commenting on this site. I absolutely love your comments. It reminds me of driving past a paper mill with my 3 year old niece and on seeing the billowing clouds of steam coming from the chimneys she says, ‘Ahh! Thats where they make clouds.’

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