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Fundamentals: Carbon intensity of gas

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  1.  
    • CommentAuthorSeret
    • CommentTimeApr 10th 2013 edited
     
    The oft-quoted figure for the CO2e of gas is 0.1836kg kWh-1, and I've seen this used regularly on this forum to compare the merits of gas vs electricity. However, the published figure for grid intensity (0.5246kg kWh-1) includes factors such as distribution losses, while the figure for gas only includes the actual carbon released at the point of combustion. Digging a bit deeper into the DECC figures it looks like once you add indirect sources of emissions in the gas distribution network the actual figure for natural gas is 0.20155kg kWh-1.

    So what, you ask? Well for a start it means that a mains-powered heat pump would only have to achieve a CoP of less than 2.4 to result in lower emissions than a 90% efficient gas boiler.

    To my mind if we want to assess the actual impact of our consumption we really should be factoring in everything that it takes to get the fuel to us for every fuel, not just some of them.
    • CommentAuthortony
    • CommentTimeApr 10th 2013
     
    My take on fossil fuels is that we should count the cost as the cost of putting it back or making them, not the cost of extraction. This is in carbon or money terms.
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 10th 2013
     
    How would you cost in sequestration in a meaningful way. This is considered the most effective method of reducing CO2e levels in the short term, but it has large future costs.
    Also if you put a price on the cost of releasing, capturing and storing CO2e, would that be open to meddling by governments to control the economy, rather like Corporation, Value Added, Income taxes are today.

    Really the answer is to go for energy generation that does not have a CO2e issue in operation, but that means using land, and we put a much higher price on that. This issue of land usage has to be addressed first, then the rest starts to fall into place.

    But back to the CO2 intensity of gas, how does it compare to other fuels. Is the CO2e costs of coal, oil, biomass, nuclear, hydro, wind, solar, tidal extraction taken into account. I think it usually is.
    Then do they count the environmental costs of the workforce, do tree feller in the Canadian Wild have a bigger personal footprint that a nuclear worker in France. And what would that worker do if they were not in the energy industry?
    •  
      CommentAuthorfostertom
    • CommentTimeApr 10th 2013
     
    Then add in the fact that we shouldn't just limit this kind of accounting to carbon, but to all resources, both the physical kind that is mined, and resources like the planet's capacity to process the mess we make, pouring waste materials and waste energy thoughtlessly out into the biosphere.
    • CommentAuthorSeret
    • CommentTimeApr 10th 2013
     
    Posted By: SteamyTea
    But back to the CO2 intensity of gas, how does it compare to other fuels.


    Fuel Direct GHG Total GHG

    Gas 0.18360 0.20155
    Coal 0.33920 0.39238
    Heating oil 0.24681 0.29245
    Biodiesel 0.00185 0.14867
    Wood logs 0 0.02
    Wood pellets 0 0.04

    All figures in kg kWh-1.

    As far as deciding where to draw the line on externalities, it's somewhat arbitrary, learned opinions differ. They're generally expressed in terms of pence per kWh, as they're talking about more than just global warming potential. So some typical figures for the external cost of various sources of electricity that sit somewhere at the middle of a the various estimates published are:

    Gas = 0.39
    Coal = 5.4
    Nuclear = 0.48
    Renewable = 0.055
    Oil = 6.05.
    (source: Pearce et al 1992).

    Note that these being 1992 figures in today's money you'd probably be looking at more like:

    Gas = 0.71
    Coal = 9.77
    Nuclear = 0.87
    Renewable = 0.10
    Oil = 10.95
    • CommentAuthorShevek
    • CommentTimeJul 29th 2013 edited
     
    Posted By: SeretSo what, you ask? Well for a start it means that a mains-powered heat pump would only have to achieve a CoP of less than 2.4 to result in lower emissions than a 90% efficient gas boiler.

    So how would this affect an EPC/Code for Sustainable Homes/BREEAM rating, given that these standards drive so many decisions?
    • CommentAuthorbarney
    • CommentTimeJul 29th 2013
     
    Not at all, as the methodology refers back to Part L which in turn uses the published values in an asset rating for the EPC and SAP calc.

    Perhaps the most disturbing aspect is the % of gas we lose on distribution and it's GWP

    Regards

    Barney
  8.  
    Posted By: barneyPerhaps the most disturbing aspect is the % of gas we lose on distribution and it's GWP
    have you got any figures for that Barney ? cheers
    • CommentAuthorbarney
    • CommentTimeJul 29th 2013
     
    Depends on who you talk to - anything from 0.6% to 1% of total system throughput

    Thats about 2000 Gigawatt hours with a global warming potential equivalent to around 2 million tonnes CO2 equivalent.

    Regards

    Barney
    • CommentAuthorsnyggapa
    • CommentTimeJul 31st 2013 edited
     
    I wonder if these figures are apples for apples

    Gas 0.18360 0.20155
    Coal 0.33920 0.3923

    my recollection when working for commodity trading company analysing and optimising plant dispatch was than rule of thumb figures were 0.4tonnes/MWh for gas generation and 0.9tonnes/MWh for coal (which should be the same as kg kWh-1 as both are 1000 times bigger)*

    It's possible that the .18 / .33 figures are the emissions from just burning the fuel to generate heat - which does not translate directly into electricity

    gas was about 50% efficient (heat from gas into electricity) and coal about 35% efficient - so 65% of coal's energy went up the power plant chimney quite literally "in smoke"

    applying those plant efficiency ratios to .18 / .33 that brings you to about .4 / .9 that I recall - and closer to the grid intensity value shown (nukes and renewables I guess count as 0 )

    -Steve

    *edit - this was useful maths to do when the price of the carbon EUA allowance was material, as people had an incentive to switch from coal to gas to save and cash in on the allowances - but since the price of the EUA permits has tanked the incentive to switch to cleaner fuels has likewise vanished...
    • CommentAuthorSeret
    • CommentTimeJul 31st 2013 edited
     
    Posted By: snyggapa
    It's possible that the .18 / .33 figures are the emissions from just burning the fuel to generate heat


    Yep, thats exactly what they are.
    • CommentAuthorShevek
    • CommentTimeAug 9th 2013
     
    Bridge Or Gangplank? Study Finds Methane Leakage From Gas Fields High Enough To Gut Climate Benefit
    http://thinkprogress.org/climate/2013/08/07/2426441/methane-leakage-gas-fields/
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 9th 2013
     
    There was a bit in this weeks comic about gas and coal being fairly equal in emission, I need to get hold of the source paper though.
    http://www.newscientist.com/article/mg21929292.000-fracking-could-accelerate-global-warming.html#.UgSbPH_EbN4

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