Let’s talk about EROEI or Energy Return on Energy Invested


EROEI is often cited as a metric to compare fossil fuels with renewables.  

Typically, the claim is made that fossil fuels are way better with much higher EROEI and that a global energy system based on renewables will implode under the burden of its internal energy demand because we will use more energy to build the renewables than we get back from them.

But is there any truth in these claims?

Making comparisons is tricky as the EROEI needs to be considered at the system level to compare apples with apples, and so with this series of articles, we will attempt to do just that.

As a starting point, we will use the following assumptions: ranges I have established through numerous articles on the subject and my in-depth knowledge of fossil fuel energy systems.  

I’m not married to these values, and if anyone has numbers they believe are better, please feel free to provide feedback.

  1. Wind EROEI is ~15-35 at the point of generation,  i.e., over its lifetime, a wind turbine will input to the system 15-35 times the energy put into building, erecting and maintaining it.
  2. Solar is typically ~5-20 depending on year-round insolation levels
  3. Gas is ~10-20 after accounting for the energy consumed in extracting and processing it where it meets the specifications for sale.
  4. Oil is ~4-50, with the extensive range being due to the differences between the energy consumed to mine and process tar sands into synthetic crude ready for transporting vs the energy required to extract and process sweet crude from a free-flowing reservoir, of which there are not so many left.
  5. Coal is ~40-50. 

Important note: The EROEI of wind and solar are steadily increasing as technology advances, whereas the EROEI of oil and, to a lesser extent, gas is in steady decline as it becomes progressively more challenging to find and extract.

But this is only the beginning of the EROEI story because we must transport these energy sources to the point of use as molecules or electrons and, in the case of oil and gas as LNG, to undergo further processing. 

These steps of transporting and processing have significant implications for EROEI and serve to dampen and significantly reduce the range of values for each energy source.

Conclusion 1 – On a straight primary energy-based EROEI assessment, renewables hold their own against fossil fuels.

In the next instalment, we look at how much energy is consumed in getting fossil fuels to the point of consumption in a form that we can use and how that feeds into the system-level EROEI.

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