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Monday, June 05, 2006

EROEI - measure for "real" energy gain

Before review some other issues about energy, I want to highlight the very important concept of:

EROEI: “energy return on energy invested” = Er/Ei

The measurement of EROEI is a valuable tool for really understand the "value"of a potential energy source and make comparison among different energy sources.
This method is more affordable than pure price-comparison because the price for a given energy source can quickly change in one day while the Er, Ei and EROEI change as slow as history do (years or decades).

Let´s try to understand how EROEI works with a classical example: petroleum.

How much energy is there in a liter of gasoline? about 30 MJ (mega joule).
But what about the amount of energy spent in order to get this liter of gasoline?
something about 3 MJ, so that EROEI for petroleum today is 10:1.

But this answer has changed in history: at the begin of 1900 only 0,3 MJ and EROEI for petroleum was 100:1, ten times more!!

This big difference is easily to understand: finding new sources of oil and extracting it is became "energetically" more and more expensive. This is because the size of the oil fields is shrinking, the depth at which oil is being found is growing deeper, and the quality of the oil that is being pumped is decreasing.

Let´s take a look at the EROEI estimates nowadays for the most common energy source (this can vary depending on the technology used):

[source: Energy Bulletin]:

Biodiesel- 3:1
Coal- 1:1 to 10:1
Ethanol- 1.2:1
Natural Gas- 1:1 to 10:1
Hydropower- 10:1
Hydrogen- 0.5:1
Nuclear- 4:1
Oil- 1:1 to 100:1
Oil Sands- 2:1
Solar PV - 1:1 to 10:1
Wind - 3:1 to 20:1

FYI: in order to make an investment it is normally requested EROEI > 1 from a company

see you soon!

[source: a lot of information are taken from this very good article of Dana Visalli from the Energy Bulletin: D.Visalli - D.Visalli - Getting a decent return on your energy investment - En. Bullettin 12 Apr 2006 ]

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