Thursday, October 1, 2015

Energy by the Numbers:

A Comparison of Energy Sources

It's no secret that I like numbers.  Therefore, I was pleased to read, in the last few days, two reports that compared various energy sources--one in terms of fatalities, and the other, in terms of resource use.  These are two very different measures, but both are important ones, so I looked eagerly to see how the various energy sources compared.

The greatest concern that most people have, of course, is safety, so I looked first at an article by James Conca in Forbes called "How Deadly is your Kilowatt?"  In this article, Conca presents a table of the mortality rates worldwide for different energy sources (see below).  The results appear to cover all aspects of each fuel cycle.  They highlight the deaths from air pollution for coal, but they also talk about deaths from uranium mining accidents and from maintenance accidents for wind turbines.  They don't actually mention that they include deaths from coal mining, but presumably, if they included uranium mining, they included coal mining as well. 

Energy Source               Mortality Rate (deaths/trillionkWhr)

Coal – global average           170,000    (50% global electricity)
Coal – China                         280,000   (75% China’s electricity)
Coal – U.S.                             15,000    (44% U.S. electricity)
Oil                                           36,000    (36% of energy,8% of elect)
Natural Gas                              4,000    (20% global electricity)
Biofuel/Biomass                     24,000    (21% global energy)
Solar (rooftop)                             440    (< 1% global electricity)
Wind                                            150    (~ 1% global electricity)
Hydro – global average            1,400    (15% global electricity)
Nuclear – global average*            90    (17%  global electricity)

* With Chernobyl and Fukushima.

Some of the results were no surprise to me--coal was the worst globally, while nuclear power was the best, even when worst-case estimates of Chernobyl deaths and Fukushima projections were included.  However the difference caught me by surprise--worldwide, coal had almost 2000 times more fatalities per kilowatt-hour than nuclear power!  There were some other revelations as well.  The extremely high global death rate from coal appears to be dominated by China, so when China and the US were separated out, deaths attributed to coal use in the US were actually less than deaths attributed to biofuel/biomass use. 

I should caution that, like all studies, there are confounding factors.  Some of the energy sources can be used for electricity production, but can also be used in other ways--direct heating, propulsion, etc.  Nevertheless, even if the numbers were adjusted to compare, for example, only electricity production, it is clear that nuclear power is substantially lower than most other energy sources in terms of fatalities. 

The other study I saw is part of the Department of Energy's Quadrennial Technology Review on energy technologies and research opportunities (Chapter 10: Concepts in Integrated Analysis, September 2015).  While the Forbes article talked about materials use, the DOE report has a good table (see below) that shows just how dramatically the materials usage varies from one energy technology to another.  Although we are not talking about scarcity issues for most of the materials listed in this table, we know that some of the materials are energy intensive to produce.  Concrete, which is the dominant material used to build the plants for most of these technologies, is particularly notable in this regard. 

This table doesn't show requirements for rare earths, which has been discussed a lot recently, particularly in the context of wind turbines.  However, the report does cover that separately.

These two studies do not tell the whole story, of course.  There are other measures that need to be considered, ranging from land use, to cost, to different pollutants, to non-fatal health effects.  And the potential for improvements in each technology could change some of the numbers significantly.

Still, seeing these two sets of numbers side-by-side within a couple of days of each other helped me confirm and quantify some facts that I have thought were true for a long time, and that are important to any discussion of energy technologies.  


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