Nuclear vs renewable energy and the critical importance of independent research

This is an adapted version of a blog by Prof Benjamin K. Sovacool and Prof Andy Stirling, to accompany the publication of their paper “Differences in carbon emissions reduction between countries pursuing renewable electricity versus nuclear power” in Nature Energy. A University of Sussex press release also summarises the paper’s findings and policy recommendations.

The role of nuclear power in a low-carbon future has been subject to a long and contentious debate. Is a nuclear or a renewables pathway the best way forward, or do we need a “do everything” approach where every deployable technology is rolled out to decarbonise our electricity supply as soon as possible?

Many influential climate scientists and international organisations argue that a global shift towards nuclear power offers the best pathway to tackling the climate emergency and meeting the world’s increasing demands for electricity.

Others argue that renewable sources of energy are the best pathway towards a low-carbon electricity system and assert that they are cleaner, safer and more economically sustainable than nuclear.

In an attempt to negotiate these contending positions, a frequent mantra is that energy strategies should “do everything” in order to address the climate emergency. But – as a number of commentators have noted (for example, here and here) – this would actually be a highly irrational course of action.

Where “doing everything” involves making investments that are slower or less cost effective, which divert resources away from preferable options, or which in some other way impede them, the result would be potentially disastrous for carbon emissions mitigation.

Amidst many uncertainties, the real questions we should be addressing are about which investments offer the most cost-effective and beneficial ways forward.

Our new paper, Differences in carbon emissions reduction between countries pursuing renewable electricity versus nuclear power, seeks to contribute towards this debate.

Nuclear vs renewable energy – what this paper tells us

Our paper focuses specifically on situations in which real-world constraints mean strategic choices must be made on resource allocation between nuclear or renewables-based electricity.

Our research explores this dilemma retrospectively, examining past patterns in the attachments (i.e. investments) of different countries to nuclear or renewable strategies. Our paper addresses three hypotheses:

  1. A “nuclear climate mitigation” hypothesis: that countries with a greater attachment to nuclear power will tend to have lower overall carbon emissions.
  2.  A “renewables climate mitigation” hypothesis: that countries with a greater attachment to renewables will tend to have lower overall carbon emissions.
  3. A “crowding out” hypothesis: that countries with a greater attachment to nuclear will tend to have a lesser attachment to renewables, and vice versa

Across the study countries as a whole we found that the “nuclear climate mitigation” hypothesis is not sustained by the evidence at an appropriate level of statistical significance. The renewable climate mitigation hypothesis is confirmed with substantial significance. And the crowding out hypothesis is also significantly sustained.

Put plainly – if countries want to lower emissions as substantially, rapidly and cost-effectively as possible, they should prioritise support for renewables rather than nuclear power. Pursuit of nuclear strategies risks taking up resources that could be used more effectively and suppressing the uptake of renewable energy.

A windmill next to a body of water

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What causes these patterns?

What might explain these patterns? Technologically, nuclear systems have been prone to greater construction cost overruns, delays, and longer lead times than similarly sized renewable energy projects. Thus, per dollar invested, the modularity of renewables projects offers quicker emissions reductions than large-scale, delay-prone, nuclear projects.

Furthermore, renewables tend to display higher rates of positive learning where increased deployment results in lower costs and improved performance, especially for wind farms and solar energy parks. This contrasts with the experience of nuclear power in France which has been prone to negative learning,” rising costs or reduced performance with the next generation of technology.

In terms of policy, the incidents at Three Mile Island (1979), Chernobyl (1986), and Fukushima (2011), all resulted in significant tightening of regulatory requirements for nuclear reactors.

Finally, wider social factors may also work against nuclear energy, and for renewable energy, facilitating faster acceptance, permitting and deployment.

Of course, these are just informed speculations, beyond the scope of the paper itself. Other commentators will favor contrasting interpretations.

But here, perhaps the most important issue – especially given the prominence of the topic and the scale of what is at stake – is that this kind of analysis has been so remarkably neglected over recent years.

Given how highly charged and hotly contested the associated policy controversy is, it is rather strange that there is not a large body of work on these questions. Either way, the many open questions and issues of detail acknowledged in the paper show that much work remains to be done.

The critical importance of independent research – our view

We have presented the findings of our research. Now we must acknowledge the uncertainties and errors, divergent interpretations and clashing interests that make it difficult to achieve the comprehensive prioritising analysis called for at the beginning of this blog – while making a case for the vital importance of scientific scrutiny.

In an ideal world of “evidence-based policy”, energy and climate policy would only go ahead after comprehensive research into every relevant positive or negative aspect of all possible energy resources.

The resulting self-evident “facts” would be examined by objective analysts and any uncertainties eliminated, until a point where a single unambiguous ‘truth’ is determined – with grateful policy makers adopting the identified energy pathway or portfolio.

Unfortunately, we do not live in an ideal world.

Across various energy debates – and not restricted to any political constituency – crucial roles are often played by deliberate mis-representation of information, manipulation of discourse, co-option of leading opposing voices, direct subversion of opponents and stifling of meaningful public debate. 

Under conditions like this, the line between advocacy and scholarship (porous at the best of times) can become especially loose when analysts become passionate about their topic. The reasons for such passion can be as trivial as disciplinary identities or sectoral interests, or as deep as wider political ideologies. On all sides “theorising” can be reduced to a search for validation, and “investigation” to the selective collection of data. 

Energy debates suffer gravely from these syndromes. “Energy evangelists” on all sides are convinced they have found “the solution” to societies’ energy problems—whether this be solar energy, hydrogen fuel cells or nuclear reactors. The intensity of this advocacy (and the scale of the interests often behind it) can lead to everyone else’s solutions being treated as sacrilegious.

So, exchanges of ideas can become hostile battlefields where proponents are unable to reconcile their underlying differences.

There seems to be an especially pernicious asymmetry in this field. Those whom comparative analysis leads to be generally critical of nuclear power are labelled “anti-nuclear”, whilst no such generally-established terminology exists to the same degree for those who are (entirely legitimately – if debatably) critical of renewable energy.

The situation is aggravated by so much research in this field being (unlike our own) funded (directly or indirectly) by organisations with prior entrenched interests on one side or another.

Despite this, we have often found valued opportunities to bridge the divide with those who hold “opposing” views, but with similar open mindedness and good faith.

It is in this spirit that our analysis is offered. We are open about its background and limitations. We acknowledge that our evidence does not compel only one supposedly definitive interpretation. We are clear about the conditions attached to our own interpretations. By publishing our full dataset and the detailed procedures undertaken in our regression analyses, we offer a basis for others to contest our findings.

The “truth” of our study is in this sense not something arrived at by particular analysts claiming individually-transcendent authority, but by contrastingly-oriented analysts contending with each other in an open and pluralistic way, such as to arrive collectively at more robust understandings. This is the organised skepticism of independent science.

If our analysis stimulates reactions in the same vein, then the cause of scientific scrutiny is reinforced. If, on the other hand, it leads to less qualified assertions and ad hominen labelling, then the chance of bridging the polarised divides is sadly diminished. We hope it will do the former.

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27 comments on “Nuclear vs renewable energy and the critical importance of independent research
  1. Colin Megson says:

    “…nuclear systems have been prone to greater construction cost overruns, delays, and longer lead times than similarly sized renewable energy projects…”

    GE Hitachi’s BWRX-300 Small Modular Reactor (SMR) changes all of that. It has a 2-year build programme – no different to Wind And Solar Plants (WASPs). GE Hitachi openly proclaim on their BWRX-300 webpage, a capital cost of US$2,250/kW for the NOAK. The FOAK will be operational in 2027 and should be available for manufacture under licence in the UK by 2030, for a capital investment of £587 million.

    For 3,200 MW, the capital investment required would be £5.6 billion, that’s 72% below Sizewell C’s 2 x 1600 MW EPRs, at £20 billion. And it’s easy to see why, if you have a bit of engineering nous.

    These pseudo-green fund managers will be clawing at one another’s throats to get their pots out of WASPs and into BWRX-300 NPPs. When the BWRX-300 is up and running, it will be the beginning of the end of the insane decades of our energy-inept politicians being suckered into gambling on get-rich-quick WASP technologies by obfuscating lobbyists, like renewableUK, not-of-the-real-world academics and other slick individuals.

    Government ‘money’ is not necessary. Commercial investors can earn many times more for every £1.00 invested in advanced Nuclear Power Plants (NPPs) than £1.00 invested in WASPs:
    Onshore Wind – 7.2X more. Search for: bwrx-300 blogspot. Scroll to Sunday 24 May 2020.

    Offshore Wind – 12X more. Search for: bwrx-300 blogspot. Scroll to Sunday 10 May 2020.

    Solar PV – 15.5X more. Search for: bwrx-300 blogspot. Scroll to Sunday 17 May 2020.

    • Andy Stirling says:

      Thank you Colin for this detailed account of your views on one particular example among what are many different prospective candidates for an entirely new (as yet largely untested) generation of nuclear power reactors. There is much wider discussion of the history, pros and cons of these kinds of claims. But in short, our article does not set out to address this issue. We are simply looking at empirical patterns over the past 25 years.

  2. This post talks about the importance of independent review, which I think is laudable. I think sharing one’s data and information about what one has done in their analyses should be a basic requirement of all publication. That said, is it possible for people to obtain a copy of the article itself in a similar fashion?

    I know paywalls are a part of life for academia, but they can be a painful hurdle for many people who might be interested in learning about new work.

    • Andy Stirling says:

      Thank you Brandon for making this very relevant point, with which I entirely agree. We do publish all our data in its entirety through Nature Energy. If you email me or any other among the authors, we would be happy to send you the paper and additional material.

    • Hi Brandon, happy to share, here is an open access link to ReadCube (free to all, but it cannot be downloaded or printed): Any other questions, feel free to ask.

  3. Nick Greenacre says:

    “Nuclear vs renewable energy”

    Is that a reasonable premise?
    Is it even in question – after all, no one plans exclusive nuclear.
    We are currently pursuing a mix of renewables WITH nuclear power.

    It is Storage that large scale RE would need were we to remove Firm nuclear from the mix so surely the more pertinent [and perhaps less ideological?] area for study would be: ‘RE firmed with Storage -vs- Nuclear’
    And of course that we will need to retain a grid wide ‘Black Start’ capability to recover from grid failures.

    So what would storage and intermittent support cost without nuclear?
    There’s alarmingly little on this.
    There’s not even a commercial flat grid storage.

    UKERC estimate that a 50% penetration of RE would add up to £50/MWh to wholesale costs.
    They didn’t model beyond that 50%

    If we don’t ask the correct questions now, then we could be reconciling ourselves to a future of RE supported by unabated gas.


    • Andy Stirling says:

      Thank you Nick for this interesting and important comment. As someone who has worked intensively on issues around energy diversity (references in the article we are discussing), I entirely sympathise with your point that it is not helpful unduly to polarise the comparison of nuclear and renewable -based strategies, nor to exclude the many other zero carbon energy service alternatives. This said, it does remain relevant against this background to interrogate carefully (as we do in this paper) particular angles on the relative merits of what must be acknowledged to be these two highest profile broad clusters of electricity supply options. Sadly, it’s not possible to do everything in one paper.

      The questions you raise about costs of addressing intermittency and inter-seasonality are also important. But please don’t be “alarmed”, because it was not the purpose of our article to undertake this kind of comprehensive appraisal. In order to be rigorous, we are simply looking at extant empirical patterns and how they relate to three hypotheses.

      But I would mention by reference to a variety of other recent major reviews of this issue (like the recent UK BEIS estimates of levelised electricity generating costs), that it is now becoming quite difficult to avoid accepting that (even taking account of high estimates for these grid integration costs), that very large tranches of renewable resources are typically available at more significantly favourable costs than nuclear power. So the reasonable burden of proof now goes in the opposite direction to the way you suggest.

  4. Michael Hoffmann says:

    After reviewing your article’s regression analyses, referenced data, and supplemental information, I was very surprised to see that your article made no reference to change in electricity production from fossil fuels (namely coal, natural gas, and fuel oil) between 1990 and 2014.

    (Q1) Did you consider how the consumption of fossil fuels in electricity production might have affected the CO2 emissions per capita figure and by extension, affected the association between increase in nuclear power or renewable energy production and CO2 emissions per capita?

    The main reason I ask this question is because between the period of 1990 and 2014 many countries greatly expanded their electricity production capacity mostly through fossil fuels, especially the most rapidly developing countries such as the BRICS countries — all of which also happen to be nuclear power countries. In the case of BRICS the expansion of nuclear power-based electricity would appear to also increase emissions per capita because of the relatively greater magnitude expansion in fossil fuels-based electricity.

    With this in mind, (Q2) did you consider performing a regression on only those countries that are both nuclear and renewable power producing countries? I imagine this would give a more accurate depiction of the association between CO2 emissions per capita and nuclear power or renewable energy because it eliminates the averaging out effect of including the ~100 renewable-only (i.e. not nuclear) countries.

    • Goetz Walter says:

      Dear Mr. Hoffmann,

      thank you for your post. In short my answer:

      Regarding your first question, we understand your point, and we think it is incorporated in our study design. The changes you describe are usually strongly associated with economic growth. And the first variable we put into our model is “GDP per capita”. Hierarchical regression analysis works based on semi-partial correlation. Meaning the effect of independent variables is measured while keeping constant the effects of variables put earlier into the model. Meaning: All the effects of electricity production we found were calculated under the condition that GDP per capita is constant, because GDP per capita was for this very reason put into the model first.

      Regarding your second question, this is a good idea. However, the sample you describe actually is our nuclear country sample (n=30), since all the countries in this sample also have some renewable electricity production.

      If you have any further questions, or if there is some further clarification needed, do not hesitate to write us once more.

      Best Regards,

      Goetz Walter

  5. Stephen de Souza says:

    Thanks for sharing an interesting and thought-provoking article. As you say, correlation is not causation and, in such a polarised debate, we will all rush to conclusions. For me the takeaways are:
    1. That energy policy does need to make choices, because resources (in the broadest sense) are finite. And that probably doesn’t just apply to nuclear vs. renewables.
    2. It is, as you say, rather strange that this hasn’t been looked at before.
    3. I wonder if its fair to characterise nuclear as a solution looking for a problem. As a physicist, the energy yield promised by nuclear fission is very attractive. Maybe the reason nuclear doesn’t perform well on a carbon reduction metric is because that’s not what it was pursued for. Maybe, rather than jump on the tCO2/£ bandwagon, proponents of different nuclear technologies should be clearer about the pros and cons of their technology.

  6. Many thanks Stephen, for this very acute observations. I would agree strongly with all the enumerated points and queries you raise.

    Some possible light is cast on the third issue you raise by some parallel research that has been underway at SPRU for the last few years. In case this is of interest, anyone can find links to some associated research outputs here:

    • Thank you ‘Todd D’ for drawing our attention to this critical blogpost, that the authors regrettably did not inform us about. As with other such critical commentaries – some of them rather extremely worded – it is a great shame when important debates like these are undermined by efforts to avoid scientific accountability – for instance by anonymous authorship and neglect to inform those being criticised or giving them a right to reply. As might be expected from such flaws, the contents of the post are sadly deeply flawed. We are grateful to you for this chance to correct them.

      For instance, right at the outset, this post begins by asserting without references that “[t]he balance of peer-reviewed literature, international energy organizations, and national energy policies are unequivocal: nuclear is a carbon-free energy source with an important role to play in decarbonizing the global economy”. It goes on to repeat this assertion a number of times – each time without evidence. What is deeply unfortunate about this statement, is – despite the many uncertainties, ambiguities and scope for legitimate disagreement in his field – that it is quite manifestly untrue that the existing literature is “unequivocal”.

      Whatever view one takes on these issues, it is very clear that there is in fact considerable – and growing – debate about the credibility of the ‘zero’ claims often noisily made on behalf of nuclear power – as there are indeed with other options. For instance, one high profile recent peer-reviewed survey of the literature, that substantiates the opposite view to that taken in the blogpost is here:

      Unlike this critical blogpost, we frame our own analysis by hypotheses not assertions. And we are always careful to cite references underpinning the basis for these. But perhaps more important than this, is that our own analysis is anyhow not an exercise in the theory around zero carbon claims (whatever this may be considered to be). It is instead concerned with the empirical picture (insofar as complexity and diversity allow this to be scrutinised).

      And further than this, our ‘nuclear climate mitigation’ hypothesis is actually founded on exactly the claims with which this critical post begins. So to this extent, the opening invalid assertions are not (despite their tone) even a criticism of our article at all. And it is also important to recall on this point, that our analysis treated nuclear and renewable hypotheses in precisely symmetrical ways. Our research design was capable equally of supporting or falsifying either.

      In keeping with the aim of our article to interrogate and illuminate this issue (not simply make assertions), then, there is an additional feature of note in the literature that this critical post refers to at the beginning. This is, that despite the very high economic and policy stakes – and the associated volume of theory-based claims-making in this field – there is actually a remarkable dearth of earlier work devoted to empirical examination of the actual associations (or otherwise) that can be discerned between nuclear power, renewable energy and low carbon outcomes. After decades of high profile claims making around nuclear power of the kind that this critical post opens up with, one of the major questions in this field is why there should have been so little basic empirical work that seeks to illuminate this?

      Then, with respect to what this critical blogpost goes on to claim are “three major flaws” in our study, we would say the following in respect of each.

      First with regard to the lack of strong association between intensities of nuclear commitments and national carbon emissions, our conclusions do not rest primarily or in any categorical way on some particular threshold of statistical significance. What is more striking is that the association is – at very least – discernibly less pronounced between lower carbon emissions and nuclear commitments than between lower carbon emissions and renewable commitments. This is the key feature of our empirical results in this regard, on which our conclusions rest. It is odd that this blogpost does not address at all, this crucial feature of our analysis.

      Second, the critical blogpost is correct that we as authors do acknowledge a series of limitations to our analysis. As a pioneering study, it is inevitable that there will be open ended aspects like this. Indeed (as mentioned above), what is remarkable, is that this is a pioneering study at all. Why is there not after so many years, a very large body of empirical analysis on this crucial point? Although purely circumstantial and not causal at all, it is not entirely irrelevant that such a gap seems to exist in questioning assertive claims by a particular privileged energy strategy. That this appears so, is consistent with our ‘crowding out’ hypothesis, that dominant options can exercise influence in various ways in their own interest.

      Anyhow, in acknowledging the limitations of our own analysis, we are also clear that these do not invalidate the conclusions that we do cautiously draw. Yes, our study is just correlative as we highlight. And we are clear that the correlations involved may admit a variety of possible explanations. But this does not mean that the correlations themselves are not relevant. What is required is not denigration of serious studies like ours, but further work of a kind that has been remarkably absent hitherto. Perhaps the intensity of the defensive critical reaction to our findings in some quarters helps explain why work on these questions has for so long been so evidently inhibited?

      As a final point under this issue, we are accused of adopting a “simplistic metric”. Up to a point, this can be accepted (as we acknowledge in the article) to be fair comment. We are very clear about a number of ways in which more detailed work might build on the foundations that we are seeking to help build. But in the absence of an established body of analysis on this same basic level as our own, it is inevitable that initial studies will have to begin by using more straightforward metrics. If this necessity is taken as a target for criticism, then it may also help explain why the important questions we are raising should for so long have been so relatively neglected. We would welcome it, for instance, if the Nuclear Innovation Alliance (behind this critical blogpost), were to undertake exactly this kind of more refined empirical comparative work, that our study opens the way for.

      The third substantive criticism in the critical blogpost, is that our article does not address “why a nation could not pursue both a renewable and nuclear strategy simultaneously”. Again, it really is odd that it should be felt possible to make an assertion that is so manifestly false. In substantiating our third hypothesis, we discuss very directly (and as fully as constrained space will allow) a number of key themes in the literature on exactly this point. Further detailed discussion is also offered in the blogpost on the Nature site that accompanies the article here:

      In short, the depth and diversity of reasons for asking about the mutual compatibility of nuclear and renewables is actually so well documented in many different wider literatures, that what is remarkable is that this critical blogpost should somehow seek to claim that such reasons do not exist. For instance (and simply as examples), potential reasons why intensity of support for nuclear strategies can militate against that for renewable strategies (and vice versa) might include the following:
      – opportunity cost: available investment for any one strategy to a given end is not independent of investment in alternatives;
      – economies of scale: economies of scale may be suppressed by volume reductions due to investment in alternative strategies;
      – regulatory overheads: fixed costs of dedicated aspects of regulation are a greater burden if alternatives are pursued;
      – system optimisation: optimising an electricity system for any one strategy will likely diminish optimality for any different strategy;
      – institutional lock-in: many different mechanisms for this are so amply well documented, that to ignore them would be very odd.

      Simply put, the multiplicity of reasons for recognising that contrasting strategies are likely to display some degree of mutual tensions, are so well grounded as to make the rational burden of evidence and responsibility for persuasion lie with those who wish to argue the opposite. Simply to rule the question out without any evidence or reasons, is a pretty sure sign of a very serious bias at work.

      Whatever may be thought about these arguments, however, what is crucial about these issues – and the way they are treated in our article – is that to ask about them is, prima facie, completely neutral as between advocacy of nuclear or renewables. One does not have to be partisan about either of these two contrasting broad families of energy strategies in order to ask such questions. The approach taken in our study in this regard is entirely neutral as between nuclear and renewables.

      A further assertion in this critical blogpost under this third point is even more problematic. It argues as if any presence of renewables within an energy system (as, for instance, in the USA) somehow refutes an interpretation that there may exist tensions between these strategies and nuclear strategies of the kind listed above. This is again so obviously untrue and partisan, as to raise very serious questions about what kind of debate this is.

      On the contrary, there is absolutely no reason why tensions of the kind that we point to, would be supposed to lead to the complete non-adoption of whichever is the minority strategy. The point is simply that this alternative strategy will be disadvantaged in a number of ways, and might thus be expected to be slower and more costly in its development to any given scale, than it would otherwise be. That disadvantaged interests exist, is not evidence that they are not disadvantaged.

      And if this alternative disadvantaged strategy offers manifestly more cost-effective and rapid reductions in carbon reductions, then the effect of these tensions will of course have been to slow down overall progress towards these ends. So it is notable that this critical blogpost does not seek to refute what we note (but which it is not the purpose of our article to document), that renewable energy technologies of several different kinds are routinely significantly more competitive and rapidly-developed than is nuclear power, with global trends acting to increase this competitiveness gap. To seek to imply that this commonsense interpretation is not at least sufficiently reasonable to be scrutinised, is a further sign of extraordinary bias.

  7. Eero Hirvijoki says:

    Dear Authors

    In your study that appeared in Nature Energy, I think you have overlooked three major factors:

    (1) You have used the total fossil-fuel-emissions-per-capita to assess the mitigation potential of nuclear and renewables, although these energy sources effectively only supply to the power sector.

    (2) You list possible benefits of distributed energy systems but fail to recognize that during 1990-2014, over 90% of the renewable-energy production was from hydropower, which is clearly a non-flexible source with respect to being small in scale and distributable.

    (3) According to your supplementary material, majority of the coutries with a high (>50%) renewable share of the electricity supply were poor developing countries. These countries have overall small emissions not because of high percentage of renewables but because they are poor and have low overall energy-use-per-capita (transportation, agriculture, industry etc).

    Because of these reasons, it is difficult to accept the metric you have chosen and,consequently, the conclusion regarding the hypotheses you come to on the basis of your statistical analysis.

    Eero Hirvijoki

    • Dear Eero Hirvijoki,

      Many thanks for taking the time to give these considered critical remarks. It is only through this kind of measured substantive exchange that these crucial issues can be clarified. It has been to encourage this, that we made all our data available (in supplementary data at the article site), reflect on the background to the article (at the links given above) and undertake to respond to all comments posted on this present blogsite.

      You say our analysis overlooked three major factors. We would state very robustly in response that this is demonstrably not the case. We will explain why below, with respect to each of your particular concerns.

      Before doing this, though, we should repeat here the acknowledgement made in a number of ways in the paper itself. We are very clear that this is simply one pioneering study on a crucial but neglected empirical issue, examining patterns of association rather than causation. Altho’ the results stand as given, we acknowledge many ways in which the analysis can be improved.

      So, there is here a semantic issue around the term you use: ‘overlooked’. In a world where all analysis of this kind must necessarily be incomplete, it will always be possible to point to specific factors that lie outside the focus of any particular study. The real question at any given moment, is whether the addressing of any such factors may confidently be expected to change the picture that has been obtained in any particular direction. Again, we believe for reasons given below that the answer in this regard is also a definite ‘no’.

      So, to take your three points in more detail in turn, the first is a criticism of our use of total fossil-fuel-emissions-per-capita to address mitigation potentials only in the power sector. This is a fair point, that raises an intractable (and under-recognised) challenge in all forms of analysis, whose interpretation involves consideration of ‘life cycle’ relations. This problem is, that the demarcation of ‘system boundaries’ is never self-evident or given.

      To concentrate analysis most specifically on a particular focal activity (eg: in this case, the power sector), risks vulnerabilities to idiosyncratic contingencies and missing important indirect connections throughout wider facility life cycles and resource flows. To extend analytical boundaries outwards into a wider political economy, risks swamping any particular signals with regard to focal activities, against a general average background. There is no single inherently most rational or objective answer to this dilemma.

      With it therefore not being self-evident that any one possible system boundary is definitively more valid than a number of others, we chose to adopt for this initial study a “middle ground” focus. The national per capita carbon emissions data that we used are from sources that are as clear and authoritative as possible. Their scope is somewhat broader than electricity alone, but not comprehensive in respect of every industrial source.

      To the extent that this introduces questions of scope, the same would apply to any analysis using these same very well established datasets – which are widely used in international academic and policy debates without such criticisms. So, the best way to address this point, of course, is to repeat the analysis for contrasting assumptions on this, as on other parameters. It is exactly this kind of onward research that we recommend in our conclusions.

      This said, there do not seem to us to be any clear reasons for thinking that the particular system boundaries implicit in our own choice of data sources are in some way serving systematically to bias our findings as between nuclear and renewables. Nor does your question on this point actually suggest so, Eero.

      Your second criticism is that we “fail to recognize that during 1990-2014, over 90% of the renewable-energy production was from hydropower, which is clearly a non-flexible source with respect to being small in scale and distributable”.

      This seems a somewhat confused point. Hydro is in fact (in many of its forms) a rather unusually flexible and dispatchable renewable resource and available on multiple scales. It may be that you have not fully done justice to your own reasoning in the way you phrase this here? But whatever any such detailed thinking might have been behind this point, the general issues at stake n this question are similar to those with respect to system boundaries above.

      Yes, the fact that the composition of renewable portfolios changed radically
      over our two time periods is indeed a complicating factor. There is no way of framing our analysis that would confidently have avoided this. And this is especially so for the most recent years, in which radical acceleration in wind and solar contributions around the world in particular reflects very rapidly improving economics and wider strategic performance.

      Since (as we repeatedly emphasise) our analysis is correlative and not causal, it remains open exactly what kinds of dynamic might be in play. But in the absence of earlier work addressing our three very clear and straightforward hypotheses, the time periods and datasets that we use, do offer the best initial way to interrogate the available information.

      Whilst arguments can be constructed on your lines, that the earlier prevalence of hydro in renewable portfolios constitutes a countervailing factor in our interpretations, it is also possible to conclude the opposite. For instance, equally in terms of scale and provision of base-load power (which is also more dispatchable), large hydro does arguably compete more directly with nuclear than do other renewables. So to this extent, our findings might be thought conservative.

      In the end, this kind of query can only be helped by the further analysis that we urge. But there are no grounds for any fair-minded observer to judge that our own initial analysis is somehow self-evidently flawed in this regard.

      Your third point rests on an observation that a “majority of the countries with a high (>50%) renewable share of the electricity supply were poor developing countries. These countries have overall small emissions not because of high percentage of renewables but because they are poor and have low overall energy-use-per-capita (transportation, agriculture, industry etc).”

      To interpret this as a problem in our analysis, seems a simple misunderstanding. The hierarchical regression analyses that we report on in detail, do directly focus on – and take care of – potential “confounding” effects of differences between countries in overall levels of GDP per capita. GDP per capita was put into the model first, and all other effects were thus calculated while controlling for the effect of GDP per capita. And, of course, the percentage attachment to renewables is a core focal variable for us. The point you make here, then, has already been very directly addressed in our findings.

      Beyond this, it should be pointed out that renewable energy being more affordable than nuclear (and growing rapidly ever more so) is a fact that applies most acutely in lower income countries – and so might more reasonably be thought to be reinforcing of our findings, rather than detracting from them. That it is in many of these countries that greatest increases have been seen in economic growth and energy consumption, arguably makes it even more striking that our analysis showed emissions “advantages” among these countries.

      So, to conclude, we are grateful to you for raising these questions, Eero. But it does seem clear that all can be very robustly answered – and none constitute any kind of significant avoidable flaw in this initial analysis. As with many other points, tho’, these are important queries to bear in mind for future work, which we thank you for.

      Yours sincerely,
      The Authors

      • Eero Hirvijoki says:

        Dear authors

        You have failed to address the criticism I presented.

        My comment (2) clearly used the word “distributable”, not “dispatchable”. In your paper, you claim to confirm a hypothesis that nuclear crowds out distributed power. Hydropower is not distributable.

        My criticism (1) and (3), the more important ones, can be streamlined in the following manner:

        A group of rich countries produces all of its electricity with nuclear and all of their citizens drive a car. A group of poor countries produces all of its electricity with hydro and none of their citizens have cars.

        From this setting, you claim to confirm a hypothesis that renewables have climate mitigation potential while nuclear doesn’t. This conclusion makes no sense and every sensical person can understand why it is void.

        Put frankly, you cannot escape scientific scrutiny by “[…] examining patterns of association rather than causation”. Science is all about causation. Correlation on its own has no value at all.

        In admitting this openly, yet promoting conclusions based on correlation, one can only come to question your motivation: it appears not as scientific but political and ideological.

        Eero Hirvijoki

        • Thank you, Eero, for these further thoughts. We note that you do not substantively refute any of our responses to your earlier criticisms. We regret that you now resort to more ad hominem points.

          It is unfortunate that our respectful response to the analytical matters you raised with us earlier, now lead to you become more rhetorical. It is no comfort that we anticipated this kind of dynamic in our blogpost on this article for Nature Energy:

          With respect to your use of the word “distributable”, this is not a well established term in this context. This does not matter in itself. But it does make it problematic for you to express such irritation about our reply.

          More important is that (whatever word is used), our point remains relevant concerning the dispatchable features of hydro power. That hydropower is ‘distributed’ across a range of scales (albeit tightly constrained by sites) is of no significant relevance to the degree in which renewable-based and nuclear-based strategies tend to crowd each other out.

          With regard to your feelings about what any “sensical” [sic] person can understand, we repeat: our analysis carefully tests the effects of GDP (that you seem to be raising again here). What are the concrete particularities that you would take issue with in this analysis? Without this kind of detail, your anecdotal generalisations about car ownership are simply not valid.

          More seriously – and contrary to your rather grave accusations – we are manifestly not trying to “escape scientific scrutiny”. We have actually taken unusual care: to acknowledge open-ended aspects of our analysis; to make details of our data and analysis readily available; and to respond to comments on this present platform.

          Likewise, there is nothing that we are not “admitting” “openly” – you have identified no aspect that is not fully acknowledged in our article or these responses. For you to say against this background that “one can only come to question your motivation: it appears not as scientific but political and ideological” sadly says more about you than us.

          And as for your remarks concerning the nature of the scientific process, there is no alternative in reply, except to note that – however this is looked at – you are seriously wrong. You write: “Science is all about causation. Correlation on its own has no value at all”. In short, across all sciences, associations are a crucial window on causation. To seek to invoke the latter independently of the former, is to substitute doctrine for analysis.

          We evidently disagree on many key aspects here, Eero. We believe that you have not been able to refute us on any of these. If we are wrong, please demonstrate this with substantive argument, rather than rhetoric. But either way, your resort to personal allegations it is sign of weakness.

          Yours sincerely
          The Authors

        • prismsuk says:

          It is very reasonable to imply that the lead author of this paper,who has been writing papers over at least 12 years, with titles like this, might have political and ideological motivations:

          “…Nuclear Nonsense: Why Nuclear Power Is No Answer To Climate Change And The World’s Post-Kyoto Energy Challenges…”

          Worryingly for the Authors, other day-to-day living motivations spring to mind, when the vast number of man-hours going into a paper such as this, seek to remove nuclear power, which has contributed so much to mitigating GHG emissions for more than 60 years, as part of the solution going forward.

          • Benjamin Sovacool says:

            Prismsuk, this is not the place to discuss another paper, but every claim in the article you refer to was fact-checked and substantiated.



          • prismsuk says:

            It would be good if the author of a paper starting ‘Nuclear Nonsense’ would acknowledge the dismissal of a technology, that has benefited humanity so much over the past 60+ years, was ill-judged and apologise for the use of the word ‘Nonsense’.

            The author himself, every member of his extended family and just about every UK citizen has benefited from nuclear power displacing coal-fired power plants over these many decades:

            46,500 premature deaths saved.
            381,281,000 cases of Lower Respiratory Cases prevented.
            10.6 million lost working days prevented.
            £61 billion saved.

            Would any reasonable person think ‘Nonsense’ was an appropriate way to describe nuclear power? I think not!.

            Search for: “the life, lifestyle and health of someone you know – and maybe you”

          • Benjamin Sovacool says:

            Prismuk, from what you write, my guess is you haven’t even read the study. I would suggest you actually read it, and carefully consider it’s arguments, before you make statements about whether a paper is valid or not. After all, critiquing a paper you haven’t even read is not extremely poor practice. I would be happy to share the study with you if you email me.

  8. Matthew Lockwood says:

    Hi authors

    Thanks for a very interesting paper.

    I wondered whether your findings that there is evidence that renewables have crowded out fossil fuels whereas nuclear has not might be due to the contexts in which these have been deployed. Nuclear seems to be a popular choice for governments in situations where electricity demand is rising (UK and US post war, Japan in the 1970s, Spain in the 1980s etc.), whereas renewables have been promoted more by post-industrial countries with stable or even falling overall (Western Europe in the 1990s onwards).

    Clearly, if it has occurred historically more frequently in situations with rising electricity demand, investment in nuclear is less likely to displace fossil fuel generation than in cases of renewables deployment under stagnant or falling demand. However, this doesn’t mean that nuclear couldn’t have this effect under the latter conditions (perhaps it will be the case in Finland, for example).

    This point is about interpreting the patterns you have found. In my mind, there is a separate question about whether nuclear or renewables is likely to be responsible for displacing fossil fuel generation looking forward. Here the answer must surely be renewables because the economics of nuclear is so bad.

    Matthew Lockwood

    • Many thanks Matthew for your kind words and characteristically astute comments.

      Given that this is an initial empirical analysis of a very important but oddly neglected question, it is precisely our purpose to help catalyse and inform speculations of the interesting kind you offer. So thanks for picking this up.

      But we have to be careful in exchanges like this (focusing specifically on our article itself), not to be drawn too far into our own speculations as to the causal mechanisms in play here. These are quite a distinct matter – and one for separate research efforts.

      This said, I am not sure I would entirely agree with your unqualified characterising of nuclear as being clearly associated with contexts supposedly requiring of especially high rates of growth in supply. This is not always so.

      And implementation rates for renewables like offshore wind have in several of the other (relatively low demand growth) settings you mention, also compared with or exceeded nuclear growth rates on the supply side. This is so in the UK, for instance, despite formal policy commitments being hitherto more focused on nuclear.

      So, there could be some truth in what you guess. But this is likely only part of the picture. And settling this would need closer examination than we have been able to give. Either way, it is this kind of question that is important, rather than what have hitherto been rather simplistic and under-interrogated (sometimes quite partisan) assumptions.

      As to framing this issue around displacement of fossil fuel generation, the dramatic recent growth – and evidently continuing trend – in the comparative economic performance of wind and solar, do suggest that this framing is becoming a bit dated. What is increasingly evident now in different settings around the world, is that wind and solar (as well as other new renewables in specific contexts) are becoming competitive with fossil fuels in their own right, even without consideration for their climate benefits.

      Either way, the key question now with respect to prospective new build, concerns the most rapid, affordable, secure and equitable way to deliver zero carbon energy services. In a real world of limited time and constrained resources, this is very different to frequent continuing assumptions that the challenge is to ‘do everything’.

      So whatever interpretations are variously adopted of the detailed drivers behind the patterns that we find, our analysis remains salient to this crucial current challenge. There seems little reason to assume as self-evident, that all options display equal efficacy. And it is also perilous to assume that there can be no adverse frictions between them.

      Whatever specific interpretations are made of the patterns illuminated in our analysis, these patterns themselves are important in urging caution about such assumptions. And – as you say – the separate accumulating evidence for the favourable strategic performance of renewables over nuclear power do already seem to making conclusions pretty clear.

      Thanks again,
      Andy Stirling

  9. Eero Hirvijoki says:

    Hi there,

    The results of the paper have been rebuted. See

    I’m curious to hear when Sovacool et al. are planning to retract their paper.

  10. Benjamin Sovacool says:

    Dear Eero, the mere fact that someone posts what they claim is a rebuttal does not make it so, especially when it’s posted without passing any sort of peer review or check on quality, unlike our own manuscript.

    It is unfortunate that the authors of this critical commentary did not at any stage seek to solicit any comments from the authors of the paper they attack.

    Also, the paper linked there is a ‘Matters Arising’ piece that the authors have submitted to Nature Energy, which they are now issuing in advance of publication or peer review there – and again without reference to our own response.

    Nature Energy will shortly publish their critique together with our own comprehensive response. Unlike Hess et al, we will follow the normal academic practice of awaiting peer review before we issue our reply to them. When it is published, we will link to it here.

    • Eero Hirvijoki says:

      This is now the second time that you have tried to publish your results. On both occasions, the results have first passed peer review and then been utterly rebuted. The first time, you had to rectract your paper from the journal Climate Policy. I anticipate a second retraction will follow.

      You are one of the sixteen lead authors of the coming IPCC AR6-WG3 that is supposed to propose technology-neutral, near-to-mid-term mitigation pathways on the basis of scientific research. Simultaneously, your own research is continuously rebuted and biased against nuclear energy, the cleanest and the most reliable energy source we have. Do you see any conflict in this? Are the other AR6-WG3 lead authors aware of these issues?

      The community of researcher who take climate change seriously is growing tired of your nonsense, Mr. Sovacool.

  11. Benjamin Sovacool says:

    Eero, your comment says more than perhaps you realise, about the weakness of your position and kinds of forces at work here.

    What this paper holds in common with the previous one you mention is only the research question. What is the empirical evidence for the comparative carbon reducing potential of nuclear and renewables?

    Why has this question remained so long not only unanswered but unasked. If reactions to this are so aggressive and suppressive, is it not equally science and democracy and climate action that suffer?

    The previous study you mention was indeed withdrawn – but by the authors not the journal. The withdrawal was commended by Retraction Watch as an exemplary case. A regrettable mistake was made (not by SPRU authors, but a fellow author) that we openly and proactively acknowledged to invalidate the argument.

    The present Nature Energy paper has a different lead author, looking at different countries. It is nothing like the Climate Policy paper. Most critical social media and blogging commentary has not been rigorous enough to get in touch with us to check arguments and responses. In every case where they do, we have openly posted the exchanges here.

    Some responses to Nature Energy will also shortly be responded to in that journal by us, fully and decisively.

    It is through substantive analysis and deliberation that science and climate protection progress, not through doctrinaire name-calling and trolling.

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