Monday, January 4, 2010

Post # 8: The Carbon Footprint of Electricity Production

I've been searching for credible information on the "life-cycle" carbon footprint of electricity generation from different sources. By "life-cycle", I mean the total effective carbon footprint ( CO2 emitted / unit of electricity generated) including resource extraction, power plant and equipment manufacturing and construction, and power production operations. Reliable information is difficult to come by - principally because it is devilishly hard to calculate these life-cycle CO2 footprints in a consistent manner.

The five studies I've chosen to summarize here are referenced at the end of this post. The studies were conducted by a variety of organizations for different purposes over a 9-year period between 1998 and 2006. I've summarized the results of the five studies in the graphic below, which displays the range and the average value of the emissions estimates from the five studies for each of the generation types. All generation types were not evaluated by each study, and in some cases (Wave/Tidal and Oil) only point estimates were give. (Note to reader: g CO2/kWh = kg CO2/MWh = MT CO2/GWh). You'll probably need to click on the image to see the expanded version if you want to read the values from the chart.

Several conclusions can be drawn from the chart above and from a more detailed review of the actually reports from which the data are taken:

(1) there is no significant difference between the life-cycle carbon footprint of hydro, nuclear, and wave/tidal power; and all three electricity generation sources are substantially better (by two orders of magnitude or more) than coal and natural gas.

(2) wind and biomass have ~ twice the CO2 emission footprints of hydro, nuclear, and wave/tidal - but still far superior to natural gas, coal, and oil

(3) solar-PV appears to have a significantly higher CO2 emission footprint than hydro, nuclear, wave/tidal, wind and biomass. There's some interesting details in the analysis. While the majority of studies place it's CO2 footprint near that of hydro, nuclear, and wave/tidal, some studies estimate a significantly higher footprint (hence the range shown the plot). Some of this may be due to different assumptions regarding the specific solar-PV technologies employed, differing assumptions regarding the deployment location of the solar-PV systems,and some may be due to the specific analysis methodologies employed.  I find it difficult to believe solar-PV's CO2 footprint could be even close to that of natural gas, but I need to understand this better.

(4) the three fossil sources (natural gas, coal, and oil) are all problematic unless/until we overcome the carbon capture/storage challenge . Breakthroughs in carbon capture and sequestration technologies for these fossil-driven electricity sources would tremendously improve our chances of achieving the global green house gas emission reductions we need.

Last words... if you're interested in reducing CO2 emissions, and you believe in dealing with the facts, you must give serious thought to the "low-carbon portfolio": hydro, nuclear, wave/tidal, geothermal, and biomass. I'm not putting solar in this category just yet. Solar probably belongs in the low-carbon portfolio, but I want to understand the wide variation in CO2 emissions footprints noted above, before I draw that conclusion..


REFERENCES:

1. "ExtremE - Externalities of Energy. National Implementation In Germany,"Krewitt, Mayerhofer, Friedrich, et al., IER, Stuggart, 1998

2. "Hydropower-Internalized Costs and Externalized Benefits," Frans H. Koch, International Energy Agency (IEA), Implementing Agreement for Hydropower Technologies and Programs, Ottawa, Canada, 2000

3. "A guide to life-cycle green house gas (GHG) emissions from electric supply technologies", Daniel Weisser, PESS/IAEA, IAEA Bulletin 2000

4. "Life-Cycle Assessment of Electricity Generation Systems and Applications for Climate Change Policy Analysis," Paul J. Meier, University of Wisconsin - Madison, August, 2002 (http://fti.neep.wisc.edu/pdf/fdm1181.pdf)

5. "Carbon Footprint of Electricity Generation", Science and Technology Postnote # 268, UK Parliamentary Office of Science and Technology, October 2006 (http://www.parliment.uk/documents/upload/postpn268.pdf)

12 comments:

  1. Solar and wind, although not biomass, have huge addtional emissions beyond those calculated here when used as part of a system due to intermittency.
    Effectively, they build in carbon use for periods of about 60 years, that being taken as the lifetime of the back-up equipment.
    Here is the huge amount of back-up just for one province's wind build in China - more than the whole generating capacity of Chile:
    http://www.npr.org/templates/story/story.php?storyId=121244275
    Other countires will use natural gas rather than coal, but the burn will still be considerable.
    I argue that the carbon advantage of building wind or solar is often low or non-existent as opposed to exporting the natural gas to the consuming country and using it in Combined heat and power schemes.
    A particular egregious example of this is the projected DESERTEC scheme for the Sahara.
    I lay out the position in a number of commments to this article:
    http://seekingalpha.com/article/180582-our-energy-future-two-very-different-visions?source=commenter
    posting as davewmart

    A close analyis of the carbon savings including back-up of the UK's projected 33GW wind build would be interesting too.
    DaveMart

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  2. You raise some interesting points. The intermittency issue is a particularly stickie one. In the absence of coupled electricity storage (batteries, pumped hydro, etc.) the "quality" of a Mw-hr of wind and solar electricity isn't the same as the quality of a baseload Mw-hr because it doesn't RELIABLY off-set load. In order to meet system supply reliability requirements, an equivalent amount of controllable baseload capacity is needed to fill the gap if/when the wind doesn't blow and the sun isn't shining. If sufficient battery or pump-hydro storage is added to make the wind/solar Mw-hr equivalent to a baseload Mw-hr, then the carbon footprint of the storage system manufacturing, installation, and operation must be added to that of the actual wind/solar generation system.

    I'm not aware of any lifecycle CO2emission studies in which such factors are treated and it isn't clear to me how they could be in a generic manner. I would think one needs to consider factors such as the time phasing of the load curve relative to the wind/solar resource availability. It would probably necessary to analyze an actual generation system to fully understand this. Definitely needs additional thought. Good comment. Thanks. Sherrell

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  3. The nearest we have are German studies of the cost effectiveness for each ton of carbon emission saved, which show that renewables are pretty dire:
    http://www.spiegel.de/international/business/0,1518,666156,00.html
    See graph.
    Efforts by Germany to restrict carbon emissions have been almost wholly ineffectual, and simply concentrating on making coal burn more efficient would have had far better results.
    When you are using fossil fuel as back up they don't get used very efficeintly.
    Combined heat and power would almost certainly use the fuel so much more effectively that the wind turbines would be redundant, and just commit you to a system which overall uses more fossil fuels and has the addtional expense of the turbines littering the landscape.
    Another way of getting at it is to look at the carbon emissions of France compared to Germany and Denmark.
    Nuclear France emits around half the carbon of these 'green' countries.

    You are completely correct though, what we need are case studies of individual wind fields which include all associated emissions for back-up and so on.
    DaveMart
    brittanicone2007 at yahoo dot co dot uk

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  4. Does this analysis include the footprint of manufacture and construction of a new transmission system?
    Such a radical change in the use, acquisition and permitting of right of way will require cooperation between politicians that only the Federal Government could provide. The application of eminent domain will raise such voting-public uncertainties as to threaten political security. Not a winning political strategy.

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  5. I'm not sure if your question is referring to Dave Mart's comment or my original posting. I do not recall any analysis of diverse generation technologies that accounts for the transmission line issue you pose. This, of course, is an issue that presents particular challenges for smaller, dispersed/distributed energy generation technologies (unless, of course, the energy is stored and consumed locally).

    Thanks for the question...

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  6. We'd love to invite you to participate in our carbon/environment debate in our facebook page.
    www.facebook.com/climateaction

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  7. See note 3, are you sure Solar PV require turbines??

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  8. Nice catch! I was thinking about wind turbines and writing about solar. I'll correct in the post.

    Thanks again.

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  9. You have some great info on here, Sherrell! would you be interested in sharing a link?

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  10. So say I need a power generation Superior WI. I need it eco clean but pumping enough juice to run a factory. Out of your choices what would you recommend?

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  11. Tom, I'm not sure what you mean by, "pumping enough juice to run a factory". There are factories of all sizes (in terms of electrical load). Can you be more specific?

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