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What is the Greenest Source of Electricity?

Carbon Intensity of ElectricityEarlier this week the new French Prime Minister Manuel Valls reiterated President Hollande’s plan to cut French dependence on atomic power to half of all output by 2025, down from almost 75% currently.  The plan is to curtail nuclear and ramp up renewables.  In his speech he noted that:

The climate is probably the area where regulation is most needed . .  It’s a major challenge for the planet and we will respond with a real low-carbon strategy.

I’m not sure if the context of this quote has gone missing in translation, but I’m guessing that switching from nuclear to renewables is not how France intends to cut its emissions by 40% by 2030. I’m sure it isn’t, because that simply isn’t a mitigation strategy.

In the map above we can see that France already has very low carbon electricity, just 79 g CO2/kWh in terms of carbon dioxide emitted at plants.  This figure is so low precisely because they have so much nuclear.  In fact their carbon productivity of 0.15 kg CO2/$ makes most countries look like climate laggards (the US is 0.4 for example, and China is 2.1).

Reading this story made me wonder how well people understand the carbon intensity of electricity generation.  So here is a quick primer, based on an excellent IPCC meta-study of the issue, looking at full lifecycle emissions of electricity production.

carbon intensity of electricity

It’s basically pretty simple.  Fossil fuels are high carbon sources of electricity while other generation sources are low carbon.

Coal is the most carbon intensive, followed by oil and then natural gas.  Solar PV and geothermal are slightly more carbon intensive than other non-fossil sources, but still very low carbon compared to any fossil fuel.  If you dig into the study you can see the range of data points across different studies for each technology.

So what is the ‘greenest source of electricity’?

If you are looking just at carbon then hydro is a decent bet, closely followed by ocean power, wind and nuclear.  If we could actually make it work biomass with carbon capture and storage (CCS) would be quite something, preferably using the waste from some fast rotation food staple. In the IPCC meta-study biomass with CCS has estimates from -1,368 to -598 g CO2eq/kWh.  Sadly this option looks like it is a very long way from being commercially scalable.

So which do you think is the greenest source of power?  Does your definition of green extend beyond just carbon?

Content Discussion

Bob Meinetz's picture
Bob Meinetz on April 14, 2014

Lindsay, you touch on the critical point of scalability late in your article.

Other factors aside, nuclear is the only low-carbon generation technology with the proven scalability to address climate change.

“Greens” have been making the most noise about the new proposed law – but it’s not a law yet, and a significant majority in France support nuclear energy.

Robert Wilson's picture
Robert Wilson on April 14, 2014


There is of course a caveat with the solar CO2 figures. They vary a lot depending on where the solar panel was made and where it is located. Solar can actually vary by a factor of around 4, i.e. the carbon intensity of electricity from a Chinese made solar panel located in the UK will be about four times higher than that from electricity from a US made solar panel in Arizona.

Recent DECC figures estimate that it is around 90 g CO2/kWh for Chinese solar panels in the UK.
Whether that is too high is a matter of debate, however the fact that most of those emissions are in China means that the point is not likely to be debated much.

Lindsay Wilson's picture
Lindsay Wilson on April 14, 2014

Hey Robert, I’d say some of the other technologies actually deserve far greater caveats.  Solar PV are reasonable constrained in the 20-150 g range.  Natural gas, oil and coal all vary more at an absolute level.  And as you know quite well the carbon neutrality of biopower really depends a lot on the rotation speed of the biomass and its inputs. To be honest this was more of a beginners primer.  The actual study is pretty decent.

Lindsay Wilson's picture
Lindsay Wilson on April 14, 2014

Hey Bob, when I do get around to opening a nuclear vs renewables can of worms I’m really going to open it.  I actually think generalisation on the topic leaves much to be desired.  Geography, politics and current grid mix dictate very different attractiveness for competing technolgies

Bob Meinetz's picture
Bob Meinetz on April 14, 2014

Lindsay, if you think “generalisation on the topic leaves much to be desired” you might avoid asking a general question like, “What’s the Greenest Source of Electricity?”.

While the framing is somewhat provocative and draws attention to your article, be prepared to expect general responses.

Lindsay Wilson's picture
Lindsay Wilson on April 14, 2014


Yep, I guess I was trying to write something basic about the subject for my readers (at my blog).  I think the hypocrasy of my comment was probably a reaction to the fact I expected someone to make such a comment about nuclear. Point taken, no offense intended.  Lindsay



Bob Meinetz's picture
Bob Meinetz on April 14, 2014

We do get a little predictable, don’t we (no offense taken).

Lindsay Wilson's picture
Lindsay Wilson on April 14, 2014

But at what cost?  By that measure solar will dwarf all comers.  I really don’t know much about OTEC.  But surely its lack of traction currently implies it struggles to be commercial?

Jesper Antonsson's picture
Jesper Antonsson on April 14, 2014

The greenest source of energy is clearly solar. However, the most environmentally sound source of energy is as clearly nuclear, with solar perhaps a distant fourth or fifth.

It’s important to realize that “green” is a label and a hype that is used to sell you something. It has little to do with the environment. Renewables is yet another term that people sometimes confuse with “green” or “environmental”. However, palm oil and whale oil is renewable, but perhaps neither green nor environmentally sound. Sustainable is another term that has little to do with the rest.

Of course, nuclear is outstanding in the important aspects. It is low cost (yes, really), environmentally sound, sustainable and delivers base load electricity. Wind and solar wins in the unimportant aspects, such as being green and renewable, but largely fail the important ones.

Lindsay Wilson's picture
Lindsay Wilson on April 14, 2014

I’ll give it a read.  Should know more about it

Engineer- Poet's picture
Engineer- Poet on April 18, 2014

A little BOTE thing I worked up last night:

In 2011, nuclear energy delivered just under half (45.6%) as much power to the grid as coal.  In the same year, the electric power sector emitted 1.718 billion tons of CO2 from coal.  Had the nuclear-generated electricity been replaced by coal, the extra emissions would have come to 783 million tons.  Even assuming $4 billion a year in subsidies as claimed by some opponents, nuclear saved CO2 emissions at a cost of only $5.11 per ton.

That is eminently affordable; we could de-carbonize the entire US economy if that’s all it cost us.

Wind was far less cost-effective.  In the year 2011, wind’s 120 million MWh of generation times the $22/MWh PTC came to $2.64 billion in direct cost to the US treasury.  If it was also displacing coal emissions 1:1 (no diminishing returns) it saved a mere 119 million tons of CO2 at a cost of about $22/tCO2.  If you count research subsidies through NREL and other expenditures, it cost even more.

donough shanahan's picture
donough shanahan on April 15, 2014


Irish data is reported and is easily accessible. I wonder are there any other such data mines?

Robert Bernal's picture
Robert Bernal on April 16, 2014

Closed cycle nuclear, for sure. The CO2 intensity of nuclear is mostly for the mining operations of the once through and for building the huge, individually built somewhat inherently dangerous structures. Mass produced molten salt reactors (based on a re-development of already proven designs and new tech) would reduce that footprint by two orders of magnitude. An ever increasing share of renewables will create a lot of variables, and since we can’t really throttle the nuclear baselod to match perfectly, the nuclear must make synthetic fuel as the storage buffer. The high temp nuclear could be coupled to gas turbines (of a higher max rating) designed to burn the synthetic fuel already hot, more efficiently and “instantly” variable. Theoretically, we wouldn’t need the RE, but this would vastly minimize fission products and allow for the continued expansion of wind and solar as well.

Edit: Or I could be wrong, we can now add batteries to nuclear! So, we need to figure which is more efficient: nuclear thermal to ammonia or methanol and then the thermal losses or thermal losses to electricity to battery at 75% round trip efficiency?

Bob Bingham's picture
Bob Bingham on April 17, 2014

In New Zealand we are 85% renewable for electricity generation. Mostly hydro and geothermal with some wind. Our powerstation has two boilers fired by gas and two currently with coal but these are just about to convert to gas. Our last area to make savingd of CO2 production is transport where we could easily convert a good proportion to our abundant renewable energy. Oil is a diminishing resource with a volatile price and we would be better off financially if we started to reduce our dependance on oil for transport.

Mary Hartman's picture
Mary Hartman on April 17, 2014

The French are currently leading in cold fusion technology, with an expectation of having a commercially viable cold fusion reactor that uses heavy water (hydrogen) and minute amounts of nickel in 30 years.  A Physicist familiar with the project is quite excited by their research because this is a truly clean, green, abundant and affordable means of providing electrical generation without depleting natural resources.  Willem Post made an interesting point about energy sprawl associated with wind and large solar arrays.  An often over-looked financial cost associated with wind and solar are the high costs to ecosystems via the loss of birds, bats and disappearance of creepy crawly things that live in the soil and are sensitive to the vibrations turbines cause.  The surface of the earth is not the only consideration.  Birds spend more than 90% of their time in the air so industrial scale turbines fragment the air column in a way completely unfamiliar to avian species.  Some species avoid them; some do not.  Avoidance, however, is an expression of loss of habitat, which is still the leading cause of extinction.   It is important to consider all costs, not just operational, when comparing one form of electrical generation for another.  Shouldn’t we be viewing our efforts toward sustainability with a broader approach instead of a myopic near-hysteria about carbon?  Is progress that profoundly adversely effects our goal of ecological sustainability by creating environmental sinks really progress?  

Jim Stack's picture
Jim Stack on April 17, 2014

Nega-a-watts. Not using or wasting are the Greenest.

Robert Bernal's picture
Robert Bernal on April 17, 2014

That 40% should easily include efficiency losses to the eventual build out of batteries. Line losses are no more than 10% and the round trip eff for the Eos’s zinc oxide is good at 75%. Very large grids are required for very large populations as most will not have the wind and solar siting to power their “everything” (and they will never be able to put a molten salt reactor, or other appropiate nuclear in their back yard).

As for finite sources, we need to be FAR more concerned about fossil fueled depletion, as they are just buried material that used to be alive as compared to elements which are distributed rather abundantly (from a 21st century extraction capability point of view) in the Earth’s crust and oceans. 

Bob Bingham's picture
Bob Bingham on April 18, 2014

I don’t think it is worth trying to compare wind and nucear as they are like chalk and cheese and neither can supply the whole market..Nuclear is a massive producer from a single power source wheras wind is local,and much smaller, Wind has a start up cost but almost no running cost and very small decomissining cost. Nuclear is a massive enterprise with big running costs, a volatile fuel source and massive decomissioning costs. Each one has a place but some places ( New Zealand where I live) will not take nuclear at any price. We are 85% renewable with hydro and geothermal.

Nathan Wilson's picture
Nathan Wilson on April 20, 2014

solar … lead to .. democatization of energy

Not a chance.  Low cost residential solar will lead to increased income inequality.  Solar (relative to fossil fuel) increases the sustainability of energy, but what we really like about modern energy is the convenience and dispatchability.  These features are absent in the raw output of solar PV panels, but can be added to solar, but a great cost (grid service or batteries).  So the wealthy get to continue enjoying the convenient dispatchable electricity, and the poor get smart meters that tell them when they can have electricity and when they can’t.

Also, what could make the government more intrusive than adding yet another aspect of people’s personal life that must be regulated (the recycling and disposal of materials from a toxic home solar batteries)?

Paul O's picture
Paul O on April 20, 2014


I can’t really agree with the enthusiasm some people have for so-called democratization of energy.

If I use the analogy of growing veggies, We already have a “democratization of Vegetables” since I can grow my own veggies. So, why don’t I do so? Well for starters, I can’t grow veggies quickly enough, or in variable quantities that would meet my varying needs or wants (if I am entertaining guest or in-laws), nor can I store and preserve sufficient veggies for a possible rainy day in the future. Besides, I can’t alway beat the price of veggies at the groccery store.

What I actually really want and need is Cheap Energy when I need it and in whatever quantity I need. Same goes for  veggitables. It’s begining to look to me that “Democratization of Energy” is the latest and newest incarnation of the notion of  “Sticking it to the “Man” “. A compulsion felt by some to want to reject authority figures and/or be suspiscious of busineses (like utilities).

Frankly, democratization of energy, like veggies, is overdone and over-blown in my opinion.


Leonard Phillips's picture
Leonard Phillips on April 20, 2014

This is a simple question and we all know the leading contenders (my favorite is actually ground-source heat-pumps coupled with OTEC and hybrid solar thermal/PV with storage.

The elephant in the room is nuclear. The problem is that we have not yet paid the full cost of nuclear M&O. The final payment will include the liability borne by the public in the event of a nuclear accident, the cost of decommissioning (embrittlement of reactor building materials over time is a fact of chemistry) and fuel disposal–which is itself still a problem without a solution, and the long-term health effects of radiation generated by nuclear wastes, with some isotopes having half-lives longer than the written history of mankind and others deadly even to trees (e.g., Brookhaven cesium-137 forest experiment–see

Have the supporters of nuclear energy, outside those directly dependent on the industry for their livelihood, learned nothing of the true cost of nuclear electricity from Fukushima and Chernobyl, from the on-again, off-again disposal plans and dollars invested at Yucca Mountain, the groundwater pollution at Hanford, the forest of dead trees standing at Brookhaven? Peaceful nuclear technology, born from war, is clearly the most complex means of generating steam to spin electric generators–and when its concomitant risks are monetized, it is the most expensive.

Ask those Japanese citizens displaced by Fukushima about the cost-benefit ratio of nuclear electricity. If the nuclear power industry was fully exposed to the financial liability of accident insurance, the “low cost” of nuclear energy would suddenly be exposed to be far higher–the actuarial exercise is straightforward, but the sum would be so great as to be politically unacceptable. What is cost of lost land and livelihood, as well as of unknown health effects borne by the public?

What is the value of the “Wolf Zone” land now worthless in Ukraine around the Chernobyl plant? Who can calculate the financial damages suffered by the displaced population, let alone the psychological toll on thousands of people who lost their homes, livelihoods, and social structures?

So what is the financial liability of the nuclear industry to the public in the event of nuclear accidents and how does it compare with actuarial calculations? (Source:

  1. Liability is channeled exclusively to the operators of the nuclear installations (legal channelling means exclusive liability of operator, and protects suppliers);
  2. Liability of the operator is absolute, i.e. the operator is held liable irrespective of fault, except for “acts of armed conflict, hostilities, civil war or insurrection”;
  3. Liability of the operator is limited in amount. Under the Vienna Convention the upper ceiling for operator liability is not fixed**; but it may be limited by legislation in each State. The lower limit may not be less than US$ 5 million. Under the 1960 Paris convention, liability is limited to not more than 15 million Special Drawing Rights***  (SDRs – about US$ 23 million) and not less than SDR 5 million.
  4. Liability is limited in time. Generally, compensation rights are extinguished under both Conventions if an action is not brought within ten years. Additionally, States may not limit the operator’s liability to less than two years under the 1960 Paris convention, or three years under 1960 Vienna convention, from the time when the damage is discovered.
  5. The operator must maintain insurance or other financial security for an amount corresponding to his liability or the limit set by the Installation State, beyond this level the Installation State can provide public funds but can also have recourse to the operator;
  6. Jurisdiction over actions lies exclusively with the courts of the Contracting Party in whose territory the nuclear incident occurred;
  7. Non-discrimination of victims on the grounds of nationality, domicile or residence.
  8. Definition of nuclear damage covers property, health and loss of life but does not make provision for environmental damage, preventative measures and economic loss. This greatly reduces the total number of possible claimants, but increases the level of compensation available to the remainder.

I don’t know about you, but I remain unconvinced that nuclear is affordable–let alone the cheapest form of electricity. It may indeed be the “greenest”–but the color refers to the currency that this industry consumes from all of us, quietly and even secretly.



Nathan Wilson's picture
Nathan Wilson on April 20, 2014

Leonard, I’m wondering what country you are from.  Because ever since the 1970s, the world has been divided over nuclear power.  Most countries that had strong domestic fossil fuel industries decided that nuclear power was unacceptable, and most developed countries that were dependent on imported energy decided to embrace nuclear power.  Isn’t that a strange coincidence?

Isn’t it strange to you that that tens of thousands of scientists, engineers, and technical people would work in the nuclear field, if it were so terrible?  Except for a few of the PHDs, most of this technical workforce has portable skills, which would allow them to move into any of many other technical fields if they didn’t think they were doing worthwhile work.

Isn’t it strange that seemingly objective organizations, like the World Health Organization would perform studies on the effects of Fukushima radiation (such as this one), and conclude that there would be no detectable health impacts on the local population?

Isn’t it strange that the IPCC periodically reminds us that we need to stop emitting CO2 into the atmosphere, and the EPA tells us that over 10,000 Americans die each year from air pollution from fossil fuel combustion, and yet it is nuclear power that we are told needs to be phased out?

Isn’t it strange that the 1900s-1960s left the US with numerous toxic waste cleanup sites around the country, filled with toxins that will be hazardous forever (am I the only one old enough the remember the Love Canal?), yet it is the war-era nuclear contamination at Hanford that activists assure us is an indication of an industry that is beyond redemption.

Isn’t it strange that many technologies such as steel and iron production, aviation, rocketry, and computers were all born of war, but it is nuclear technology that we fear?

It is certainly strange to me.  The only explanation I can come up with is that the fossil fuel industry has duped the public to save their own skins.  If this were true, it does not take a stretch of the imagination to understand that the news media and “green” groups would benefit from helping with the fear mongering.  

It is not nuclear energy that is the problem, it is fossil fuel.

Peter Lang's picture
Peter Lang on April 21, 2014

Leonard Phillips,

  It’s amazing how differently we view the facts.  I suspect it is about what we see as most relevant and what we dismiss as of less relevant in the options analysis.  Let me respond to points in your first paragraph.  You said:

  “The elephant in the room is nuclear. The problem is that we have not yet paid the full cost of nuclear M&O. The final payment will include the liability borne by the public in the event of a nuclear accident, the cost of decommissioning (…) and fuel disposal …“

  I disagree.  The costs are included in the cost of electricity for nuclear.  The full costs of renewable energy are not fully included in the cost of electricity they supply.  The costs of accidents are far higher than they should be because of the excessive response to accidents.  The excessive response is driven by a public paranoia and also by the allowable radiation limits which are set much lower than is justifiable based on evidence (see pamphlet explaining the case simply here: ). 

  When the public gets over the paranoia and the radiation limits are raised to where they should be based on the evidence, people will not need to be evacuated.  It was ridiculous to evacuate most of the people around Fukushima.  It cannot be justified on the basis of future health risks.  The excessive response is the reason the cost of nuclear accidents is so high.  And it is not justifiable to expect the owners to pay for the costs that are caused by an irrational fear.  If the costs were determined on a rational basis – such as fatalities and valid projections of future fatalities and health effects – the costs of nuclear would be much lower.  And if the same requirements were also placed on renewable energy and fossil fuel energy, then nuclear would gain an even greater advantage over the others (see deaths per TWh: ).  Nuclear is the safest of all electricity generation technologies on the basis of fair comparisons.

  Importantly, nuclear is by far the cheapest way to supply low emissions electricity.  Franceis one example and here is a cost comparison I did for Australia:

Peter Lang's picture
Peter Lang on April 21, 2014

I don’t see a rational justification for renewable energy as a major component of the electricity system, given that:


  1. Nuclear power has proven it can supply over 75% of the electricity in a large modern industrial economy, i.e.France, and has been doing so for over 30 years.


  1. Nuclear power is much cheaper than renewables


  1. Material requirements per unit of electricity supplied through life for nuclear power are about 1/10th those of renewables 


  1. Land area required for nuclear power is very much smaller than renewables per unit of electricity supplied through life


  1. Nuclear power requires far less expensive transmission (much shorter and much smaller capacity in total since the capacity needs to be sufficient for maximum output but renewables run at 10% to 40% capacity factor whereas nuclear runs at around 90%.


  1. Nuclear power is more environmentally benign than renewables.


  1. Nuclear fuel is effectively unlimited.


  1. Nuclear fuel requires a minimal amount of space for storage.  Many years of nuclear fuel supply can be stored in a warehouse.  This has two major benefits:


·        Energy security – it means that countries can store many years or decades of fuel at little cost, so it gives independence from fuel imports.  This gives energy security from trade wars and military conflicts


·        Reduced transport – nuclear fuel requires 20,000 to 2 million times less ships, trains etc per unit of energy transported.  This reduces shipping costs, the quantities of oil used for the transport, and the environmental impacts of the shipping and the fuel used for transport by 4 to 6 orders of magnitude.


I don’t understand what rational justification there is for renewable energy.


Pieter Siegers's picture
Pieter Siegers on April 27, 2014

Peter, you got it completely wrong on number 6 and 7. Nuclear is not safe at all, and its fuel is expensive and hard to get by, and generates potentially environmental malign waste.

Besides, this nuclear waste can be used to create atomic bombs, which is also someting we don’t need to save the planet.

So, in the case of France, how do you explain the massive reduction in nuclear power, if your arguments all were true?

It may be useful to have nuclear at the moment because of its real low CO2 emission, providing baseload power while clean energies are being deployed on great scale. After that, on the long term I’d say that clean and safe energy sources have a much better future.

With respect to the fossil fuels, we need to lower demand, for starters we need to better efficiency, change completely the transport sector, and at the same time work hard to develope energy storage systems like compressed air. There’s so much to be done.

I would love to say otherwise, but nuclear energy does not have a sustainable future at all.


Peter Lang's picture
Peter Lang on April 28, 2014

Pieter Siegers,

Nuclear power is the safest way to generate electricity.  A summary of authoritative studies is here: Excerpt (Deaths per PWh)

Coal electricity – world avg 60,000 (26% of world energy, 50% of electricity) Coal – U.S. 15,000 (44% U.S. electricity) Natural Gas 4,000 (20% global electricity) Biofuel/Biomass 24,000 (21% global energy) Solar (rooftop) 440 (0.2% global electricity) Wind 150 (1.6% global electricity) Hydro – global average 1,400 (15% global electricity) Nuclear – global average 90 (17% global electricity w/Chern&Fukush)

Fuel costs - high for fossil fuel and biomass sources, low for nuclear, and zero for many renewables.
The US Nuclear Energy Institute suggests that for a coal-fired plant 78% of the cost is the fuel, for a gas-fired plant the figure is 89%, and for nuclear the uranium is about 14%, or double that to include all front end costs.
The back end costs for fossil tfules and renewables are not included in their cost of electricity but should be for a proper comparison with cost of electricity from nuclear plants.  Here are the estimated back end costs for nuclear electricity generation:

This ‘back end’ of the fuel cycle, including used fuel storage or disposal in a waste repository, contributes up to 10% of the overall costs per kWh – rather less if there is direct disposal of used fuel rather than reprocessing. The $26 billion US used fuel program is funded by a 0.1 cent/kWh levy.

Decommissioning costs are about 9-15% of the initial capital cost of a nuclear power plant. But when discounted, they contribute only a few percent to the investment cost and even less to the generation cost. In the USA they account for 0.1-0.2 cent/kWh, which is no more than 5% of the cost of the electricity produced.

Nuclear waste cannot be used to make nuclear bombs.  Weapons grade material is made in dedicated nuclear reactors.

Your other points are equally incorrect.  Suggest you do some objective research before posting disinformation.

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