Carbon intensity of electric power sources (Weekly pic)

IPCC (2014) median estimates of life cycle carbon intensity of selected electricity sources. The figure includes mining, raw material and waste disposal impacts, but excludes infrastructure requirements such as energy storage, strengthened transmission grid, or backup generators. As a result, the figures are likely to underestimate emissions from variable sources such as wind and solar power.

To avert dangerous climate change, we will need lots and lots of low-carbon energy sources. Electricity is perhaps the most important of these, as it is wonderfully flexible form of energy that can replace fossil fuels in multiple applications. Furthermore, it is easy to deliver and we know how to generate it in quantity with very low carbon emissions.

Of all the methods of low-carbon electricity generation, nuclear power is still the single most important. It alone produces far more low-carbon electricity than all the “new” renewables combined. This is an inconvenient fact for those who try to oppose nuclear power while simultaneously opposing climate change. As a result, one hears constantly claims that nuclear power produces greenhouse gases – and that this makes it unsuitable for climate mitigation.

The first part of this claim is true: In fact, no energy source produces energy without greenhouse gas emissions of any kind. There are emissions associated with wind power, and there are emissions associated with solar power. The second part, the inference, is false, however. In all the serious research on the subject, the carbon balance of nuclear electricity is found to be very low. It compares well with wind power and, in fact, tends to be lower than that of solar electricity.

The most common counterargument we’ve heard at this point is the obvious: “Wait, what about uranium mining, or building of nuclear power plants? Surely they contribute a lot of emissions?” 

Fortunately, we can say that this counterargument does not hold water. The figures quoted here, and in any serious scientific report, are so-called lifecycle emissions. This means that the figures already include impacts from mining, building of power plants, and so forth. In our opinion, it is somewhat insulting even to think that such obvious emission sources would not be included in any serious calculations.

But one thing that’s not included in these calculations is the additional infrastructure that is required to deliver equivalent level of service. For nuclear power plants, not much additional infrastructure is required, beyond obvious power lines. But if we want to deliver equivalent service – equivalent amount of reliable electricity generation – from variable sources, we most probably are going to need more infrastructure. This can be reinforced electricity grid to transfer energy from places where the wind blows or the sun shines to places where electricity is needed; it can be backup generators that provide power when it’s dark or calm; or it can be wind turbines and solar panels that are part of “overbuild” required to ensure that at least some catch the wind or the sun at all times.

So far, as the share of variable energy sources in electricity grid has remained small, this additional infrastructure is not really needed. The existing grid and existing power plants can cope with the limited variability, although this often incurs extra costs already. But as we expand our low-carbon energy production, we will need more and more infrastructure to cope with increasing variability. This causes both economic and environmental costs, resulting to higher carbon balance than these simple calculations would suggest.

This is one of the reasons why we believe that opposing proven solutions that can provide significant quantities of low-carbon energy is, at this point, a gamble with the climate. For more information, buy our book, Climate Gamble – or come to Paris during the COP21 climate negotiations and get one for free!



3 thoughts on “Carbon intensity of electric power sources (Weekly pic)

  1. Excellent post, thanks. One point I would like a better understanding of is “backup generation” for wind and solar, since they are variable and electricity flow, of course, needs to be constant and match demand. For example, here’s a link that accounts for CO2 emissions of backup power. It is my understanding that natural gas is the most flexible and therefore the best source of backup power for variable renewables, your thoughts?


    • Thanks for the comment, and sorry for losing your reply in the approval pile. This is something we would definitely like to understand better as well; unfortunately, we believe it’s likely to prove impossible to provide “one size fits all” estimates of the impacts of backup generation and/or associated infrastructure, since actual solutions to the intermittency problem vary between areas, over time, and as variable renewable penetration increases.

      Gas generation is indeed flexible and theoretically well suited for backup – if one ignores CO2 and fugitive methane emissions – but the situation is more complex. In Germany, for example, it is gas plants that are being mothballed and dismantled. Gas is currently so expensive compared to coal that it’s more profitable to run coal plants in a limited load-following mode. Probably the best power plant for backing up variable generation is hydropower, however (obviously only where available though).

      Furthermore, there are other options for increasing grid flexibility; low-emission ones include improved transmission, demand flexibility, and nascent energy storage and conversion technologies (that is, electricity to gas for example).

      Grid flexibility is something we simply have to solve if we want to decarbonise our economies, no matter whether we use nuclear or not. But the task is likely to be easier if there is more dependable energy generation.


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