EROEI

Among critics of renewable energy, one key idea is that of Energy Returned On Energy Invested (EROEI). The central idea can be illustrated by the case of ethanol produced from corn in the US. It’s argued by critics that the production of ethanol from corn uses more fossil fuel inputs than it displaces. The US Department of Agriculture has an EROEI slightly greater than 1, but it’s still clear that corn ethanol is not going to do much to solve the carbon dioxide problem.

Now lets look at the case of solar PV. The energy-intensive component of a solar PV module is the polysilicon used to produce the wafer, which is produced using an electric furnace. Clearly, if more electricity is used in this process than is generated by cell, EROEI < 1, and the idea does not work. We can do a rough check by observing that a typical wafer uses 5 grams/watt of polysilicon. The cost of polysilicon is $20/kg. To be conservative let's assume this is all electricity, at a cost of 5c/Kwh. Then a quick calculation shows that each watt of PV requires 2 KWh of electricity in production or about 1 year's generation in a favorable location. So, for a panel with a 10-year lifetime, the EROEI is 10. Clearly not much of a problem. The estimate omits the energy costs of the rest of the module, but that's almost certainly more than offset by the conservative assumptions about polysilicon.

Some EROEI fans don't like this calculation. They want to include all sorts of other costs, going as far as the food energy used by the workers who instal the panel. At this point, the exercise becomes one of trying to price all economic activity in terms of energy, an idea that has been tried without success for decades. For everything except energy-intensive activities like smelting, energy costs are a small part of the total, and imputing such costs to any particular energy source is a fools errand.

35 thoughts on “EROEI

  1. Rog, about a third of the heat energy in coal will be converted into electricity. Victoria’s brown coal power stations do worse than this modern super critical coal plants can do better, but were not going to get any modern new coal power stations here and fortunately neither is most of the rest of the world. In additon, about 7% of the electricity generated will be lost in transmission, but this is the case with any utility scale generation.

  2. Japan has field tested fabric and sponge based methods of extracting uranium from seawater. These methods adsorb uranium oxide onto their surface. They are estimated to operate at around $240 per kilogram of yellowcake(55). The normal price of yellowcake is around $110 per kilogram.

    There is approximately 4.2 billion tons of uranium dissolved in the world ocean. Because of the vast amount of uranium in the ocean, there is enough U-235 in Tokyo Bay to build 20-25 Hiroshima-sized bombs. (How much depends on the degree of freshwater dilution.

    55. M Tamada. Current status of technology for collection of uranium from seawater. Erice seminar 2009: NuclearInfo.net; 2009 http://nuclearinfo.net/twiki/pub/Nuclearpower/WebHomeAvailabilityOfUsableUranium/2009_Tamada.pdf.

  3. The exciting thing about that technology, Brian, is that it could actually have a practical use as there are places where ground water used for drinking is contaminated with uranium. Of course, safely disposing of the material in a low level waste dump once it has become saturated might be a costly problem.

  4. Ah, the economist’s EROEI without any energy calculations involved.

    I’m looking forward to the day that solar power powers solar panel production 100% and at a profit. In the same way I look forward to seeing unicorns.

  5. Personally I’m looking forward to the day when South Australia generates electricity equal to 40% of its total consumption from wind and solar. Oh wait, that’s already happened.

  6. “Ah, the economist’s EROEI without any energy calculations involved.”

    Say what? I calculated the electricity produced by a solar cell, and divided it by an estimate of the electricity used to produce it. The only place I used prices was to derive the second estimate. As has already been pointed out in comments, you can find lower numbers for new technologies like fluidized bed reactors

    http://www.solarindustrymag.com/e107_plugins/content/content.php?content.14110

  7. @iain

    I see that Ian Plimer is writing a book called “Heaven and Hell: The Pope condemns the poor to eternal poverty”.

    You probly like his thoughts and calculations.

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