For extraction of energy from natural resources, an important figure of merit is the
Energy returned on energy invested, or EROEI or EROI for short.
If it is less than 1, then one is getting less energy than one is putting into the process of extracting it, and that means a net energy loss. If it is not much greater than one, then one is getting some energy, but at a high cost. So one wants it to be relatively large.
DFID_Report1_2012_11_02 - DFID_Report1_2012_11_04-2.pdf -- EROI of Global Energy Resources Preliminary Status and Trends
By Jessica Lambert, Charles Hall, Steve Balogh, Alex Poisson, and Ajay Gupta
State University of New York, College of Environmental Science and Forestry
That article has an interesting list of EROEI values for various activities, calculated for conventional sweet crude oil.
[table]What | EROEI
Arts and Other | 14
Health Care | 12
Education | 9 - 10
Supporting Families | 7 - 8
Growing Food | 5
Transportation | 3
Refine Oil | 1.2
Extract Oil | 1.1[/table]
The ones at the bottom are from the published literature, while the ones at the top are highly speculative and hand-wavy.
The EROI for discovering oil in the US has decreased from more than 1000:1 in 1919 to 5:1 in the 2010s, and for production from about 30:1 in the 1970s to less than 10:1 today [72]. The global EROI for the production of oil and gas has declined from 30:1 in the 1995 to about 18:1 in 2006 [80]. It is difficult to establishing EROI values for natural gas alone as these values are usually aggregated in oil and gas statistics [70, 71].
Tar sands have an EROEI of about 5, and oil shales about 1.3.
Coal has an EROEI that in the US has varied from 80 to 30 (1980's) and back to 80 (1990's, from increasing strip mining).
Nuclear energy has an EROEI of about 5 to 15.
Of renewable sources, hydroelectric is the best, at around 75 or thereabouts. Wind energy is good, at about 18.
Photovoltaic cells had 7 - 10 around when this article was published (2012 Nov 4), but this is a rapidly developing technology, and some more recent ones do even better.
Corn ethanol has 0.8 - 1.6 (range of estimates), and biodiesel has 1.3.