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Can Nuclear Power and Renewable Energy Learn to Get Along?

Full Spectrum: Energy Analysis and Commentary with Jesse Jenkins

Nuclear power and variable renewable energy sources like wind and solar power “don’t play well together.”

That’s a commonly accepted nugget of wisdom these days. I heard the argument most recently during an interesting colloquy on Twitter this week with Fresh Energy CEO Michael Noble, reporter Matthias Krause, and author and editor of Renewables International Craig Morris.

If true, the idea that renewables and nuclear don’t mix has important implications. It would mean that if we want to build an ultra-low carbon electricity system to confront climate change, we may face two mutually exclusive paths: one path dominated by nuclear energy (call it the French paradigm) and the other dominated by variable renewables (call it the German paradigm).

(In fact, supporters of the German Energiewende use this argument that large penetrations of renewables are incompatible with nuclear as one of the justifications for the nuclear phase-out underway there now).

The more I think about this, however, the more I’m convinced that the accepted wisdom that renewables and nuclear mix like oil and water is true only up to a point.

In fact, if we want to build an ultra-low carbon system powered by variable renewables, we’re going to have to solve precisely the same technical challenges that will make a hybrid renewables and nuclear power system possible as well.

My thinking is as follows, and I present this as a hypothesis for discussion and with plans to analyze this in more detail in the future (i.e. using power systems modeling)…

I begin with this basic point: In rough terms, once a variable source of renewable energy, such as wind or solar power, reaches an energy penetration level (measured as the share of total energy supply) equal to that source’s average capacity factor, aggregate output from that variable renewable energy source will routinely fluctuate between 0 and 100 percent of total electricity demand.

For example, if the average capacity factor of solar photovoltaics is 10 percent (about what it is in Germany), once solar PV reaches about 10 percent of the system-wide energy mix, solar output will vary from 100 percent of demand when producing at full capacity on a bright mid-summers day and 0 percent when night falls. Wind turbines in the breezy American Midwest have a capacity factor closer to 35-45 percent, so wind would reach a ceiling at about 40 percent of energy share in that region. 

There are two important implications of reaching this point where a renewable energy source’s share equals its capacity factor.

First, without energy storage, high penetrations of renewables don’t leave much room in the power system for nuclear power plants (or any other “baseload” power plant).

While nuclear reactors can technically “ramp” or vary output up and down to follow loads (albeit less flexibly than gas turbines), “cycling” or shutting down entirely and start up again later is too challenging for a nuclear plant to do routinely. Yet at high penetrations of variable renewables, every other plant on the system would have to be capable of routinely cycling on and off.

  • Summary: it’s true then that absent energy storage and flexibility, high penetrations of variable renewable energy sources doesn’t play well with nuclear.

Second, increasing the penetration of renewables beyond the point where energy share equals capacity factor would mean the renewable source would begin to regularly produce more electricity than demanded. Without storage or energy sinks willing to buy up excess power, renewable generators would then have to curtail a growing share of their output and waste any associated revenues.

In practice, this ceiling could actually be reached before renewable energy penetration equals capacity factor, as production would begin to regularly exceed demand on high output/low demand days long before this point.

In addition, if renewables are exposed to wholesale prices (and not subsidized outside the wholesale market, i.e. with feed-in tariffs), the market prices earned by renewables would be negatively correlated with their output. Wholesale prices are lowest precisely when renewable generators are all cranking out power (again, this assumes no energy storage/sinks.) At some point, adding more renewables just wouldn’t be profitable any more. If renewables have to pay for the system balancing services and flexibility needs they contribute to, this economic limit is reached even earlier.

This point where energy share = capacity factor is probably a generous ceiling for renewable energy penetration absent storage then.

If solar capacity factors typically range from 10-20 percent and wind from 25-45 percent, that makes it awfully hard to reach an ultra low carbon energy system powered principally by renewables. Once these sources reach a combined share of maybe 30-40 percent of the energy mix, technical and economic constraints will make it very hard to increase their share further.

  • Summary: absent energy storage and sinks that can make profitable use of excess energy and massive system flexibility to handle variations in renewable output from 0 to 100 percent of load, penetration of variable renewables is effectively constrained below the point where their energy share equals their capacity factor.

If we want to increase renewable penetration beyond these levels and drive truly deep decarbonization of the power system, we therefore need massive amounts of new system flexibility to match demand with varying renewable energy output.

We’d need electric batteries and thermal energy storage to shift output to when its needed, dynamic load shifting and demand response to align demand with output, and ‘energy sinks’ to make productive use of excess output.

But here’s the kicker: if we have the massive amounts of storage and flexibility needed to achieve an ultra-low carbon electricity system dominated by variable renewables, we also have the storage and flexibility needed to make a hybrid nuclear-renewable power system feasible as well.

With that kind of system flexibility, we could store energy and shift loads to avoid having to cycle off and on nuclear plants and limit their ramping only to when it’s the most economical way to provide system flexibility.

  • Here’s my contention then: If you want an ultra-low carbon renewable energy system, you need storage and flexibility. And if you have storage and flexibility, then renewables play just fine with nuclear.

Maybe renewables and nuclear can learn to get along after all. Maybe they won’t offer competing visions for a low-carbon power system in the end.

Let’s discuss…

(A note for comments thread: this post isn’t asking whether you want a nuclear-renewable hybrid power system. It’s asking whether a renewable-hybrid system is technically and economically feasible if we did want one. This is a post about what options we have, not which ones we want to chose. So let’s save those discussions on which you’d choose for another day. Thanks! -Jesse)

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Schalk Cloete's picture
Schalk Cloete on Apr 15, 2014 12:31 pm GMT

Well, if we have super-cheap storage, we can really do lots of cool things. The issue is just that by “super-cheap” I mean batteries below $30/kWh of capacity (fully installed with no O&M, connection or disposal costs). Under the assumptions of 2000 cycles at 50% depth of discharge with a 75% efficiency and 8% cost of capital, such storage facilities would need a spread between buying and selling electricity prices of about $60/MWh to break even. I just don’t know if this is possible. And then of course we are still left with the seasonal variation issue which batteries will never be able to solve. 

The nuclear/RE incompatibility (at least as I understand it) is based on a scenario of limited storage capacity. The problem is not so much that nuclear cannot ramp, it is just that it is unprofitable to operate nuclear at low capacity factors (necessary for using it as mid-load balancing capacity). When looking at the overall system LCOE, such operation would greatly increase the profile costs of RE integration because the underutilization of nuclear capacity would result in great costs. This is the reason why the optimal share of variable renewables actually decreases with an increasing CO2 price in the study I wrote about earlier.

Robert Wilson's picture
Robert Wilson on Apr 15, 2014 12:31 pm GMT

Thanks Jesse

This is the view I have held for a long time. As I explained in the post below curtailment of renewables can become a very serious problem at high penetrations. Obviously it varies a lot on location and renewables. Curtailment is a far bigger problem for solar in Germany than for offshore wind.

So getting to a majority share of renewables will almost certainly require lots of storage. Otherwise you have to curtail a vast amount of electricity which will just make higher penetrations incredibly expensive.

Of course some people will point to Denmark and say that they are showing you how it can be done without storage, but Denmark is a unique case. If it is really windy then they can export the electricity due to them having an incredible number of interconnectors.

You raise a good question about what penetration levels renewables can reach. Capacity factor is probably a good rough ball park at the minute, until storage comes along.

For example The National Grid has advised the UK government that there should not be any more than 60% wind/solar on the grid at any time. If this is not relaxed then obviously it places a significant limit on RE in the UK.

However an issue perhaps worth exploring, if you are going to, is looking into how different electricity mixes work with storage.

There is some interesting work out of Stanford that suggested that non-geological storage does not really work for wind, but does for solar.

It might then be interesting to see how well storage works with different nuclear/RE mixes. And it is possible that generalisations such as “nuclear works well with renewables so long as there is storage” are a bit too simplistic.


Robert Wilson's picture
Robert Wilson on Apr 15, 2014 12:37 pm GMT

N Nadir

Jesse has posed an interesting question that is worthy of serious discussion.

Is it possible that we could discuss it in a grown up manner, that does not rapidly descend into a generic renewables versus nuclear debate? Otherwise what is the point in having the comments section.

Nicholas Thompson's picture
Nicholas Thompson on Apr 15, 2014 1:31 pm GMT

The other key thing here is that when renewable output is 0 (or at least low), something has to take up the slack, and in the case in most places, its fossil fuels. 

Many renewable advocates will also argue that since wind and solar peak at different times in the day, you can get to a higher penetration and maintain some reliability since the output is evened out somewhat by the two sources. If this point is true, then nuclear plays with renewables even better. The country that actually proves this is Germany. They have a high penetration of renewables, but also have a steady baseload that they draw from continuously, which is primarily coal. If that baseload were nuclear instead of coal, they would still have a very reliable grid and it would be one of the least polluting in the world. 

Either way, for peaking, some natural gas will probably be needed just to ensure grid reliability. 

Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 1:40 pm GMT

Let’s please stay focused on the question at hand: can a renewables and nuclear powered electricity system work to achieve ultra-low carbon output?

If you hate  nuclear or you hate renewables, this is not the place to start a debate over the relative demerits of “the other guys.” I’d rather the comments thread here didn’t descend into another nuclear/renewables flame war. Thanks,


Joris van Dorp's picture
Joris van Dorp on Apr 15, 2014 2:15 pm GMT

Good article, Jesse. I think you’ve done a very nice, compact write-up of some important issues which have been noted often by many of the most informed participants on this great website. Thank you.

FWIW, I think it’s pretty clear that renewables and nuclear cannot get along, for the simple reason that they are very different categories of energy technology: Nuclear energy is a power generation technology, while intermittent RE are fuel saving technologies.

Intermittent RE is only useful in a power grid dominated by fossil fuels, where there is expensive and/or polluting fuels which needs to be saved or substituted. But in a grid dominated by nuclear power, fuel saving is pointless, because nuclear fuel is inexhaustible, extremely cheap and doesn’t produce pollution. (To be sure, nuclear power certainly produces waste, but it does not produce pollution, where pollution and waste are understood to be completely different things!)

One could say that intermittent RE depends on the existence of ample fossil fuel generation for which it can save fuel in order to justify its economics and environmental benefit. Nuclear – on the other hand – yields its economic and environmental benefit by simply replacing fossil fuel plants altogether.

In as far as intermittent RE tends to promote the use of fossil power plants (for cheap backup power), while nuclear power tends to eliminate completely fossil power plants, it seems clear enough that nuclear and intermittent RE cannot ever learn to get along. Their respective purposes are simply too contradictory.

Paul O's picture
Paul O on Apr 15, 2014 2:16 pm GMT


Here is my 2 cents. I am afraid that I agree with those who say that Nuclear Power and RE do not play well together. The reason is not that it is impossible in the first place, but that with the exception of Tiny/ Impoverished/ Isolated areas, such a concoction appears to be a Choice invented soley to allow RE to be able to participate in a National Grid environment, if they chose thusly, then So Be It.

I say the above because when I ask myself, “WHY” , I get stuck.

1) Why would a  RE oriented grid want/need Nuclear Power if it had adequate  storage. Doesn’t that just add complexity and Headaches  for them?

2) Why would a Nuclear powered Grid want/need RE, if excess power could be diverted to other purposes, like Water Desalination or process heat, as need be?

3) Why would any National Grid give itself more headaches with different kinds of technologies and manpower expertise, by inclussion of both Nuclear and RE?


It is not that the 2 absolutely cannot co-exist, but it’s rather that such coexistence is a forced and/or poorly planned choice. I suppose truly Vast (large and spread out population and geographical base) grid like the Chinese can afford to play around a little with both/each.

In the end Some Nations will choose primarily nuclear others will choose RE, and others will mix both. Over time the  experience from these different grids will help other grids determine how best to proceed under their own uniques circumstances..

Joris van Dorp's picture
Joris van Dorp on Apr 15, 2014 2:22 pm GMT

I don’t agree about the need for fossil fuels. France has a lot of nuclear power, and some of their nukes do load-following. In effect, France has ‘nuclear peaking plants’. In other words, France proves that nuclear power can be used economically for baseload *and* for peaking purposes, yielding a near-zero greenhouse gas electricity system.

Sometimes the answer to a problem is right under our noses. The answer to the problem of greenhouse gas emissions is France, not Germany. On the contrary! Ironically, it is Germany which will remain a large emitter of greenhouse gasses, as long as it seeks to expand it’s use of renewables. Even more ironic, France seems to be moving in the direction of the German energy system. Certainly, if France actually does this, it will soon start building more natural gas plants because the business case for nuclear power will be undermined by expansion of intermittent RE.

In thirty years, if France adopts the German energy policy, its greenhouse gas emissions will actually grow significantly. In other words: it is unlikely that France will do this, since the French are many things but they are not completely stupid! (are they?)

Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 2:27 pm GMT

Joris, I think you overstate the role nuclear plays in France. Nuclear plants there do some load following, but they rarely cycle, and they don’t match peak load. France has hydro and gas plants for that role, and they are part of a continent-wide interconnected power system with the rest of Europe, where they can import power at times of peak demand and export power at times of low demand. (Imports/exports is also how Denmark manages with a very high penetration of wind btw). So while nuclear looks like a very high share of France’s electricity supply (or wind in Denmark), it is actually a smaller share of the European power system. And that full interconnected system is what I have in mind when talk about this post. I should have made that more clear. Thanks for commenting,


Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 2:56 pm GMT

Hi Paul, thanks for commenting.

The question I’m asking though is can nuclear and renewables work well together? Not do we want them to

I know that many folks here are perfectly happy choosing one of those potentially mutually exclusive paths I outlined at the start of the post: a nuclear dominanted system or a renewables dominated system. For some of you, there’s no reason to consider any other options. 

But I see both of those options as very challenging. Getting to very high penetrations of nuclear is clearly technically possible, but given the social opposition to new nuclear, by no means an easy feat. Very high penetrations of renewables face more technical challenges, and they also face NIMBY opposition to large-scale projects and the transmission needed to bring renewable power to load centers. So neither a high nuclear or high renewables future is fiat accompli.

That leads me to search for more options. Can we design a hybrid system of 30% nuclear, 60% renewables and 10% gas for peaking? What about 60% nuclear, 30% renewable, 10% gas? Something else? 

The conventional wisdom is such hybrids are impossible. This post is about questions that. I’m curious what you think about those questions (not whether or not we’d want to go there, but could we go there if we did want to).



Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 2:59 pm GMT

Hi Joris,

I think your categorization of technologies is a little bit of a simplication. Yes, variable renewables as operated in a system today are primarily used to provide energy (and not really capacity) and thus to save fuel from other power plants. But in a high-renewables system, they would be paired with storage, sinks, and flexible demand in a different operating paradigm. Additionally, nuclear plants aren’t really “power technologies.” As baseload plants, they supply a tremendous amount of energy to the system (operating nearly 24x7x365) and also provide power to match base demand levels. In a conventional system, peaking power plants like gas-fired or oil-fired plants are the ones that primarily contribute “power” or capacity to the system to meet peak demands. But again, in a high nuclear system, operations would have to look different as well. 

So the question is: what could the power system of the future look like (not how do these generation technologies typically operate today). Thoughts?


Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 3:09 pm GMT

Thanks Robert. I forgot about your great post in October on capacity factors and challenges for high penetrations of renewables (and nuclear). I highly recommend folks head over there to read it and then come back to join this discussion. Cheers,


Robert Wilson's picture
Robert Wilson on Apr 15, 2014 3:21 pm GMT

A common myth is that nuclear power plants have two positions: on or off.This myth is one of the reasons many think renewables and nuclear are incompatible.

However France produces easily available output data for all of its nuclear power plants. Available at the link below.

For example Cattentom 1 ran at around 300 MW throughout most of last Sunday and then in the space of a couple of hours ramped up to 1200 MW. If you believe what many people say then this is technically impossible, but the French do it.

Strangely the same myth is believed by many regarding coal plants. Odd given how some countries run their entire grid on coal.

Alan Nogee's picture
Alan Nogee on Apr 15, 2014 3:23 pm GMT

I think this is broadly well-explained, but misses some important points.

The problem with cycling nuclear plants is not only technical, but economic. As capital-intensive plants, where construction costs dominate fuel costs–and particularly where new nuclear plants and some older plants are marginally economic at best–they have to be run at very high capacity factors to be economic. 

Similarly, renewables have to operate at clise to their design capacity factor, and can’t be dumping power, to be economic. 

The ceiling penetration for renewables may be approximately the capacity factor before needing storage or other system flexibility–it varies by system. But whatever thst level, it is higher if there are more flexible resources on the system, like gas, and lower if there are more inflexible resources, like nuclear (coal is in between, probably closer to nuclear.)

So while it is true that at very high levels of either, you need storage, the ceiling is really determined by the combined nuclear and renewables total. You will hit the ceiling earlier in nuclear-heavy systems, and need more (expensive) storage than you would need at lower nuclear levels. Otherwise, one or the other wouldn’t be profitable, depending on the market rules. 

On the other hand, at current levels of nuclear and renewables, there aren’t likely to be conflict in many places. The idea that you have to phase out nuclear now to make room for renewables later seems also exaggerated. 

But going forward, adding new nukes would start decreasing system flexibility and make it less economic to add renewables, or vice versa. And the added storage needed to make them play together would also undermine the economics of both. 




Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 3:35 pm GMT

Hi Alan,

I grant that without lots of economic storage/sinks, you’d hit the cieling on renewables faster if you have a share of nuclear in the system as well. So if your goal is to increase renewables to their highest penetration before hitting their cieling before needing storage, then you’d want to back off of nuclear. But if your goal is to get to the lowest carbon power system as possible before needing storage, then I doubt that’s the best way to go. 

Simple math here but I think this gets at the gist of it: if your system is say 20% nuclear, then you’d hit the renewables cieling roughly when their energy share = their capacity factor x (100% – nuclear’s share). So for solar at 10% CF, you’d hit the cieling at 10% x (100% – 20%) = about 8% of the energy mix from solar instead of 10% if you had no nuclear in the system. For wind at 33% CF, you’d hit the cieling at 33% x (100% – 20%) = about 26% of the energy mix from wind instead of about 33% if you had no nuclear in the system.

So yes, you lose a few percentage points of renewables share if you have 20% nuclear in your system versus if you don’t. But if carbon is your priority, it makes no sense to give up that 20% from zero-carbon nuclear in order to get 2% more solar or 7% more wind! 

So again: if you want an ultra low-carbon energy system with high penetrations of solar or wind, you need massive amounts of economic storage and sinks and DR. And if you have those, nuclear and renewables seem to work just fine together. And if nuclear and renewables aren’t mutally exclusive, the lowest CO2 for the least money may very well be a hybrid system.


Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 3:40 pm GMT

Thanks for this excellent resource Robert! I just spent a while poking through this data set, which is really really helpful. It looks like today, France’s aggregate nuclear output ramped up/down by 4.5 gigawatts already. That’s about as much ramping as we saw from their (very flexible) hydro plants and about 4 times as much ramping as we’ve seen today from their entire coal and gas fleet. So clearly France has figured out how to operate their nuclear plants more flexibly than most anywhere else. The data is clear.

This PDF of a technical presentation from French utility EDF also discusses their flexible reactor operation. It even shows plants cycling off over weekends during low demand periods sometimes (see slide 8), although this obviously comes at a cost, and it does take a couple days to get back online after powering off fully. The slides do note a set of technical and operating challenges to modulating reactor output flexibly. Reactor operators need to be well trained to do this, but its certainly possible.


Robert Wilson's picture
Robert Wilson on Apr 15, 2014 3:48 pm GMT

A secondary issue, which would be interesting to explore at some point, is whether, say, 40% nuclear and 40% renewables works better than 80% renewables, if you get storage figured out. My suspicion is that the technical challenges around a mix are possibly lower than they are for 80% renewables. Curtailment of renewables is a major challenge. And the biggest problem of course is the long stretches where there is no wind.

I have never looked to see if there is tecnical literature addressing the point though.

Alan Nogee's picture
Alan Nogee on Apr 15, 2014 3:49 pm GMT

Math oversimplified, perhaps, but the bottom line is the economics of the proposed change to the system. If one is looking at retiring a typically inexpensive existing nuclear plant, then I agree, doesn’t make economic sense.

If you’re looking at adding a new nuclear plant, though, where many analysts, including me, think they are uneconomic even at full capacity factors, and are at best marginal, and where you’re locking in a large resource for presumably 40-60 years, then the added inflexibility equals reduced future optionality. 

Bottom line: They don’t really play well together, except in small doses. 

Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 3:49 pm GMT

I’ve not seen any technical literature on that question. But I’m talking with one of my colleagues here about doing some modeling to answer just that. This could make for a very interesting paper…

Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 3:52 pm GMT

How do you support that bottom line though Alan? That sounds like an assertion, but it’s not clear how that’s the case. It’s one thing to assert that the most economical low-carbon energy mix is all renewables. It’s another to say that renewables and nuclear “don’t really play well together, except in small doses.” I think I’ve shown how they do, assuming you have storage/flexibility. And assuming you don’t have storage/flexibility, an ultra-low carbon renewables dominated system itself isn’t possible (except at extraordinary cost) due to necessary curtailment. 

Jason Burwen's picture
Jason Burwen on Apr 15, 2014 3:59 pm GMT

From a technical standpoint, I think Jesse is generally correct–a world with a high penetration of renewables is necessarily one with a lot of flexibility technology (energy storage, demand response, etc)–and these are precisely the technologies that would enable other sources, such as nuclear, to integrate and play along well. The devil, of course, would be in the technical details–how much energy storage needed, what capacity nuclear can play–but the general concept makes technical sense.

In an economic sense, maybe it’s less clear. As is referenced in the article, marginal-price based wholesale market clearing means that high (zero-marginal cost) renewables penetration has economic limits. Even with a lot of flexibility technologies, does a high-renewables world (without subisidies) demand a different kind of wholesale energy market system? In a world of overwhelming flexibility, you’d get to a point where wholesale energy has a uniform price over time and location. But how short of “overwhelming flexibility” can you go before you need a different energy market to deal with high renewables penetration? More to the point, can you think of a such an energy market system that would let nuclear play economically too?

Robert Wilson's picture
Robert Wilson on Apr 15, 2014 4:10 pm GMT


The underlying assumption of what you are arguing is that natural gas is preferable to nuclear. And that burning more natural gas is preferable if we can loosen up the system to make way for more renewables. Is this not the case?

The economic arguments of course always feel more than a little half-baked. Imagine if I dangled a renewable power plant in front of you, one that could deliver an identical service as a nuclear power plant, but with the same economics. You can’t honestly tell me that you would be complaining about it being uneconomic.

Paul O's picture
Paul O on Apr 15, 2014 4:11 pm GMT

Dear Jesse,

Firstly thanks for the leadership role you and Geoffery Styles play here in terms of tone and cordiality, much much, appreciated indeed.

Secondly, Yes the two can co-exist. I think I stated as much. Where I am comming from is whether it is even wise to do so and whether that co-existence is not in fact a contrived Rube Goldberg solution.

My thinking is that Both RE and Nuclear energy solutions should/will be developed to their Zenith by Nations which favour either. The Germans, perhaps will show us the extent of how renewables technology is employable, and someone else, perhaps the Chinese will show us the same for nuclear power. Then the rest of the world will pick and choose as they wish as per their needs and or sentiment.If they decide on RE in after rational evaluation, that really is fine with me.

It matters not the source of our electrical power, save that it be carbon free, it works reliably, it is  without rationing, and it supports growth well into the future.

For my money though I really see no particular advantage in a combined solution, although I could be wrong,  whether in terms of costs, and/or effectiveness.

I do believe that Nimbyism can and should be overcome.

Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 4:13 pm GMT

Thanks Paul!

Dwight Baker's picture
Dwight Baker on Apr 15, 2014 4:16 pm GMT

Although currently operating nuclear power plants may not operate economically in load following mode, that doesn’t mean future ones can’t.  I have personally operated several reactors with very high maneuvering rate capabilities (every nuclear powered ship has one), so that is not a technology limitation. Most new Small Modular Reactor (SMR) designs have high negative temperature coefficients and load following capability, as well as very small staffs. The latter factor is key to making them economical in low capacity factor operation. If designed from the ground up for that mode of operation, they may well be more economical than other storage technologies (other than pumped hydro, which is geographically limited).

The main barrier to SMR development is the highly bureaucratic and sclerotic regulatory system in most countries, which was designed for large reactors with large staffs and potentially large offsite accident consequences. It therefore imposes enormous costs on the new small ones, relative to their size. Given that accidents with offsite consequences are impossible (not just unlikely) with most new designs, a legislative exemption from the old regulatory regime would be technically justified. Perhaps if the renewables community came to regard them as an enabling technology the necessary political support could be achieved. The MIT Nuclear Engineering Department should have lots of resource material on the new SMR designs.

Keith Pickering's picture
Keith Pickering on Apr 15, 2014 4:42 pm GMT

1. The curtailment limit has nothing to do with capacity factor. It is easily determined by the total system demand at the lowest point in the annual cycle, and the lowest point in the daily cycle. If  RE nameplate generation (of any type, and of any capacity factor) exceeds that limit, curtailment will occur. The exception is for solar, where the curtailment limit is determined by the lowest demand load during daytime.

2. As others have mentioned, fast throttling of nuclear plants is entirely feasible. It has nothing to do with reactor design, but depends entirely on turbine design. Put a fast-reacting single-stage turbine on a nuclear plant, of the same type that is put on a gas turbine, and you will get the same fast ramping times as you get on a gas turbine. Of course that’s less efficient in the long run (just as gas turbines are less efficient that combined cycle) but if that’s what you want, you can do it easily.

3. If the goal is to kill fossil fuels (and it is, or at least it should be) then RE advocates had pretty clearly state what power source they want for backup when the sun isn’t shining and the wind isn’t blowing. Because right now the default backup is gas, which is certainly not a long-term solution. The recent study by Budischak et al. 2013 shows that backing up RE with more RE requires overbuilding the system by a factor of three, and tripling the cost of electricity in the process.

Now compare that with nuclear backup for RE, which wouldn’t raise the price of electricity at all. But if you’ve got enough nuclear to back up RE, then you don’t need RE in the first place. It’s just needless window-dressing. Which is what the French are doing right now.

4. The optimal solution from a climate standpoint is to deploy first those technologies that are cheapest in terms of dollars per avoided ton of carbon per MWh. That’s because we want to deploy non-fossil generation as rapidly as possible, so cost considerations are critical. Those technologies are, in order, 1. geothermal, 2. hydro, and 3. basically a tie between wind and nuclear. The first two are dependent on specific geology and are (mostly) already fully subscribed. That leaves wind and nuclear. But wind is cheaper than nuclear ONLY if it is not built beyond the curtailment limit, at which point the cost of wind goes up (and continues to go up the more you build). Which leaves nuclear for the balance, which is will be more than 50% in most countries. 

Bob Meinetz's picture
Bob Meinetz on Apr 15, 2014 5:05 pm GMT

Jesse, thanks for a very interesting and provocative post, which may set a record for responses.

I only object to renewables to the extent they’re held out as an alternative to nuclear – they’re not, and never will be. This popular idea is not only misleading but dangerous in that it furthers reliance on fossil fuels and delays addressing a problem which is intractable enough already.

You write

Getting to very high penetrations of nuclear is clearly technically possible, but given the social opposition to new nuclear, by no means an easy feat.

This is a social/messaging problem which should be addressed accordingly.  What makes no sense at all is basing energy and investment policy on public misperceptions, or searching for alternatives to engineering or safety problems which don’t exist.

Nicholas Thompson's picture
Nicholas Thompson on Apr 15, 2014 5:43 pm GMT

Another way renewables and nuclear cand work together is by using heat for other applications. For instance, a nuclear plant near an ocean could divert some of the heat from making electricityto water desalination while the demand for power is low. Another examle was the recent story about using heat to make gasoline out of ocean water.

Ed Dodge's picture
Ed Dodge on Apr 15, 2014 6:34 pm GMT


I see no reason that nuclear and renewables cannot work together.  It obviously does require flexible energy storage, which is conceivably available as synthetic hydrocarbons.  Germany has been moving forward on this front in a variety of technical platforms, some of which I wrote about here:

CO2 splitting and H2O electrolysis, done together or separately, can provide near limitless scale for storage and upgrade low cost electricity into high value hydrocarbons.

In the USA the low price of natural gas undercuts efforts for producing synthetic gas, but the technology is widely available and it could readily absorb any excess grid power from renewables.  CO2 splitting or CO2 methanation could play the same role, allowing us to utilize at least some captured carbon.  These systems could sit passive on the grid waiting for cheap electricity to be available.  This also bypasses the problem hydrogen has for lack of infrastructure, because hydrocarbons already fit the existing systems.

I find it interesting that Power to Gas gets such little attention in American discussion of renewables when it is an active policy in Germany (of course they pay much higher prices for natural gas).  Renewables do not need to be limited to either electric power or biofuels when synthetic hydrocarbons can bridge the gap.

Taken further, a policy of actively promoting synthetic hydrocarbons could change power grid management away from curtailment and demand-response and towards the enablement of electrolysis systems acting as power sinks ready to absorb all the electricity you can provide.

Engineer- Poet's picture
Engineer- Poet on Apr 15, 2014 7:29 pm GMT

Nuclear does not play in a system where intermittent sources like wind and PV have legislated priority in dispatching.

I did a BOTE analysis of the storage issue a few months ago, and found that storage is much more economical with nuclear than wind or PV because of the much smaller amounts required and the ability to cycle daily.  Feel free to pick it apart and tell me if I goofed up:

B W's picture
B W on Apr 15, 2014 7:29 pm GMT

Jesse, great discussion and effort to redirect the focus from in-fighting to working together. Being tolerant and inclusive goes a long way in coercing collective efforts out of polarized groups.

Several have now commented what seems to be obvious: 30 years from now one of the two (nuclear or renewables with storage) will prove itself to be the clear economic superior to the other. That seems highly likely based on technological evolution…..

However we don’t seem to base all energy generation decisions solely on economics. In the US we have a lot of energy diversity which seems to have as much to do with public or policy maker preference as much as economics, and we can’t underestimate how much regional special interests factor into these preferences as well. 


Solar and wind also differ from nuclear in that they can be implemented with little government oversight or involvement (excluding subsidy funding). Nuclear necessitates heavy government oversight and only allows large financial entities to be involved in ownership and operation. Nuclear plants while typically favored by republicans are a much more socialized solution. Solar and wind while typically favored by democrats actually lend themselves much more to conservative ideals especially in so much as they economically favor individuals who can afford the capital costs of these systems or own land in which energy farming systems can be deployed. 


So why would we want to assure that BOTH renewables and nuclear are part of the future even if it isn’t economically optimal? Because we have large groups in this country that want each to be part of the future due to the differences listed above. Diversity may be less efficient, but it again I argue that cultural preferences do over-rule cold logic. Diversity seems like a way to keep things honest and industries accountable.


In my opinion though nuclear is a real solution now, GE has offered the prism for some time and Terrapower will likely succeed in making an evolutionary step in reactor design. Whether it’s demand side mgmt, storage, or HVDC distribution all of these solutions are a better fit to be utilized by nuclear power to increase its penetration due simply to the fact that nuclear power has completely controllable output and can utilize these solutions more and make the economic case for each better. Accomodating shifted load with a nuke is far superior than trying to do so with wind + gas…….

but renewables are cool and a lot of people are really excited about them. Not including these passionate people into this sphere of discussion and not allowing their favored industries to participate in the solution would be a mistake. By remaining more positive with pro renewable people and accepting their preferences we can perhaps enlighten them to the reality that nuclear fission is a natural phenomenon that could be an enormous benefit to human kind. It is essentially in a class of its own when it comes to power generation- but it takes a lot of rigorous inquiry to come to this conclusion.

Engineer- Poet's picture
Engineer- Poet on Apr 15, 2014 7:50 pm GMT

The problem is that the renewables everyone expects to carry the load (wind and PV) have outages lasting from overnight to several days.  A nuclear grid using storage for peaking needs only a few hours of average generation to serve the portion of load above plant output.  A grid reliant on renewables needs on the order of 50 hours of storage, and is still vulnerable to long-term deficits of generation vs. consumption which leave the storage empty. If the RE isn’t given a feed-in tariff and has to compete for dispatch priority with generators with better availability, its revenues will go to zero whenever the storage is full.  It basically goes bankrupt in a fair market (unlike the rigged markets of today, which have PTCs or FITs).

Scott Luft's picture
Scott Luft on Apr 15, 2014 7:50 pm GMT

Assume super-cheap storage

A new punchline to an old joke:

Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 8:07 pm GMT

Thanks for the thoughtful comment. Cheers,


Jesse Jenkins's picture
Jesse Jenkins on Apr 15, 2014 8:16 pm GMT

Thanks for the comment Ed! Power to gas is actually what I had in mind when I wrote about “energy sinks” in the post. Desalination maybe also. But the example “energy sink” I linked to was actually Hydrogenics efforts to use excess power production during peak wind output/low demand days in Denmark to produce electroyltic hydrogen used to upgrade sewage gas into pipeline quality natural gas. It’s a very interesting example of the kind of use of excess power we’d likely see much more of in a high-renewables or renewables-nuclear hybrid system.


Ed Dodge's picture
Ed Dodge on Apr 15, 2014 9:01 pm GMT


I agree on the water desalination point which points to the need for a high energy future.

Here is more info on Dutch analysis of Power to Gas.  They view it as an important element for integrating renewables into the overall energy system.

What I have yet to see, except for a little bit from the US Navy, is analysis on using nuclear power in a power to gas scenario.  Why does nuclear have to be limited to producing electricity?  How about a purpose built nuclear plant for CO2 and H2O electrolysis?  It would change the business model for nuclear entirely, rather than selling power for pennies per kWh one could produce ultra pure Air Force grade jet fuel or natural gas.  The Europeans are not doing this analysis because they are trying to move away from nukes, but there are plenty of nuclear advocates that could make the case.  Nuclear would benefit from high temperature electrolysis which is more efficient than just relying on electric power to do the job.




Bentham Paulos's picture
Bentham Paulos on Apr 15, 2014 9:05 pm GMT


Very thoughtful column.  I look forward to your research.  You might delve again into the bowels of the NREL “RE Futures” study to look at their various scenarios. They were completely agnostic about the “other 20%” but the have so many scenarios that might offer some help.  Their Data Viewer might be the place to start:

One key point that didn’t get enough attention in your post is the effect of aggregated control areas — in other words, bigger power markets are themselves a solution to variability, and reduce the cost of integrating any kind of power source, including wind and nuclear.  They would also increase the total amount of variable RE through sheer statistics — it would reduce the number of times of excess generation, therefore allowing more RE capacity.

Bigger control areas would benefit nuclear too, by reducing the cost of their contingency reserves.  A 2 GW nuke needs a 2 GW backup in case it goes down.  That is easier to accomplish in a 100 GW system than in a 10 GW system, since more plants will be sharing their reserves.


– Ben P.


Bob Meinetz's picture
Bob Meinetz on Apr 15, 2014 10:37 pm GMT

Edward, there’s no reason nuclear has to be limited to producing electricity. Nuclear to gas and even nuclear to gasoline, using recycled atmospheric CO2 combined with hydrogen from electrolysis, had a brief flurry of interest in 2008-2009:

The proposal says it’d be worth it to have a payoff of steady, secure streams of methanol and gasoline with no carbon added to the atmosphere (and a price for gasoline at the pump of perhaps $4.60 a gallon — comparable to petroleum-based fuels as oil becomes harder to find)…The concept’s viability has been reviewed and verified by both industrial and semi-independent Los Alamos National Laboratory technical reviews. The next phase will demonstrate the new electrochemical process to prove the ability of the system to both capture carbon dioxide and pull it back out of solution. An industrial partnership consortium will be formed to commercialize the Green Freedom concept.

These technologies are anathema to the petroleum sector business model, so it’s not difficult to imagine why they’re struggling.

Jesper Antonsson's picture
Jesper Antonsson on Apr 15, 2014 10:58 pm GMT

Problem is, the potential 10% solar and 40% wind penetration is relative to the apparent demand. With e.g. 50% nuclear power, the apparent demand is cut in half, so then only 5% solar and 20% wind can be integrated without getting increasing amounts of stranded power.

Sure, with enough storage tech, that might be possible to handle, but I’d argue that storage is a lot harder than just balancing with natgas, hydro and biomass. Also, one might wonder, why make it difficult? If you have 50% nuclear, why not go further to 75-80% rather than littering the landscape with wind towers, strengthen grids, do demand side management, buy storage solutions and live with wild price fluctuations?

B W's picture
B W on Apr 15, 2014 11:27 pm GMT

Whether nukes and renewables are a practical pairing is tied to storage – we would need advanced system modeling to determine if this would be the case. 

My assumption though is that the value of storage increases with nuclear power plants as part of the mix because nuclear power plants being capable of operating near max capacity for prolonged periods can assure a high utilization rate of storage infrastructure so as to lower amortization period and overall cost. Renewables cannot guarantee steady utilization of such storage capacities, or HVDC transmission because their seasonal and day to day, and year to year output is highly variable. Same point applies to accomodating demand side management load shifting. 

Renewables still seem attractive though to the extent that they are practical (integrating them to the greatest extent without introducing large over capacities or inefficincies). The primray reason to me is diversity and reduced oversight. 

So although I aim not to contribute more to polarizing the dialogue, I think it is important to acknowledge that all of the smarter grid technologies which seem to be the missing enablers for renewables are probably a better fit for nuclear due to the fact that it can more fully utilize/accommodate these technologies (storage, HVDC, load shifting).

Alan Nogee's picture
Alan Nogee on Apr 15, 2014 11:54 pm GMT

If natural gas is 20% or less of the system, and the rest is renewables and/or nuclear, system emissions would be dramatically reduced. Renewable Elecricity Futures shows we could do it with 80% renewables, but I wouldn’t rule out say, something like 60% renewables, 20% nukes and 20% gas making economic sense in the US. 

At that point, which will take decades, storage and/or gas/CCS, and/or smart grid would hopefully be well enough along to squeeze out remaining gas emissions.

It also seems possible to me, that SMRs could enable nukes to play a larger role, though I think they face serious challenges. I have many times expressed support for their continued R&D, as the best hope for economic new nukes. 

As for your hypothetical, I do not much appreciate your presuming what my position would be. As it is a hypothetical, it is hard to judge. If it had not shown much potential to reduce costs with scale, and had other significant impacts, like say, a tidal barrage or large-scale hydro, I would have similar concern. If showed potential for reduced costs, like offshore wind, I would support cautious expansion. If I lived in Germany, instead of being a beneficiary, I’d have the same reservations you’ve expressed about relative investment in solar vs wind. 

And if I were as anti-nuclear as you suggest, I would not support continued operation of existing nukes. But where they are economic and don’t have specific safety issues–as is generally the case–I do. 

Michael Keller's picture
Michael Keller on Apr 16, 2014 12:17 am GMT

A pressurized water reactor has only a limited capability to follow the load due to both fuel cycle and equipment restraints.

Routinely following large scale grid changes is unrealistic for most (but not all) reactor types, with the need to pay-off the large debt required to build the plants placing even more restraints.

Combustion turbines are far more adept at dealing with the unreliable nature of renewable energy. Further, the assertion that “ultra low” carbon emissions are required is of doubtful necessity.

I think the more accurate question: Can renewable energy zealots get along with anybody else?

Joris van Dorp's picture
Joris van Dorp on Apr 16, 2014 12:43 am GMT

Hi Jesse, I agree that I simplified, but I don’t think I overdid it too much.

I believe the future energy system will be competitive (i.e. delivering more tax revenues than subsidies consumed), which means it will be either fossils or nuclear that do the heavy lifting. In that case, the choice is clear for me. Fossil fuels have been essential to human development in the past, but the greenhouse gas emissions problem has to be dealt with. Fossils have to be phased out. (CCS would be good temporarily, but seems impractical for quick global implementation.) So for me the obvious choice is nuclear.


You mention the pairing with RE of auxiliary technologies in order to firm them up enough to achieve a quasi-stable RE energy system. There’s good news and bad news about that paradigm. The good news is it’s possible. The bad news is that it is several times more expensive than conventional energy in terms of financial costs. That makes RE – I’m sorry to say – even less practical than CCS. Nuclear can do the job without all the auxiliaries. That makes all the difference, in my opinion.

The future energy system will be at least 50% nuclear – assuming that greenhouse gas emissions reduction is achieved in a timely manner to prevent the worst of AGW.

But if nuclear continues to be sidelined, for example by RE advocates who oversell the merits of RE and confuse the public, then I will not dare hope of seeing the solution to the AGW threat. Besides, without nuclear, I also don’t expect to witness the end of extreme poverty. On the contrary, I fear.

Jesse Jenkins's picture
Jesse Jenkins on Apr 16, 2014 1:04 am GMT

Hi Ben,

Thanks for the comment. I’ll look again at the NREL Futures report which I included in the recommended resources at the end of my post. 

RE larger balancing/control areas, you are of course correct. As I noted in another comment, when I said “power system” in the post above, I meant the full interconnected, balanced system (i.e. a closed system). The larger that system, the more renewables you can get in there and the less correlated their output is likely to be. But once you get to an energy share equal to about their capacity factor, you certainly can see ramping from 0 to 100% of demanded energy on a regular basis, necessitating lots of storage/sinks/flexibility. So larger balancing issues helps renewables integration (or renewables-nuclear integration) as you say, but it doesn’t really solve the problem.



Jesse Jenkins's picture
Jesse Jenkins on Apr 16, 2014 1:09 am GMT

“…the assertion that “ultra low” carbon emissions are required is of doubtful necessity”

There’s no doubt for this column or this website! Climate change is a pressing global imperative. End of discussion on that matter.

Let’s keep on topic. 


James Hopf's picture
James Hopf on Apr 16, 2014 1:13 am GMT

It’s a little bit too simplistic to lump all renewables in the same category, with respect to this question.  Geothermal and hydro have no issues with respect to combining with nuclear (hydro would be great for use as peaking capacity).  Solar generates its power roughly at the times of peak demand, so unless the penetration level is very significant (too high) it will act to flatten out the demand profile, making the remaining profile MORE able to be covered by baseload nuclear.  It is only wind that has a significant problem combining with nuclear, in the absence of large scale energy storage.

Also, it seems that the discussion is considering one extreme scenario or the other, with respect to electricity storage cost.  In the limit of extremely expensive storage, yes there are issues with mixing nuclear and renewables.  At infinite, zero cost storage, either nuclear or renewables could provide all electricity, and mixing them together will also not be an issue at all.  The answer will probably lie somewhere in between, where storage can make things practically possible, but will cost enough so that the amount of storage capacity will be an important factor, where minimizing the needed amount of storage will significantly reduce overall cost.  It seems clear to me that a mixture of nuclear and renewables would require a significantly lower amount of storage capacity than any renewables only scenario.

James Hopf's picture
James Hopf on Apr 16, 2014 1:30 am GMT

Which technology will be “economically superior” will be more a function of the regulatory playing field and market design (including subsidies and mandates) than of technology.  Also, it’s not a simple matter of the “cost” of given sources (on a pure, per kW-hr basis), but a matter of overall sysem cost.  Renewables will soon (if not already) achieve low per kW-hr costs, especially in some, ideal areas, but their intermittentcy will limit their practical/economic level of penetration, with overall system costs exponentiating as one tries to use them for higher fractions of overall generation.

As for which technology “needs” greater levels of “government involvement”, subsidies (not to mention outright mandates) constitute a much greater form and degree of “involvement” than oversight, in my book.  Alot of that oversight is also, frankly, not necessary (given the lack of health consqeuences of even Fukushima), especially for small modular reactors, whose maximum potential releases are very small indeed.

I find it absurd that RE sources that require large govt. subsidies and outright mandates could be characterized as those more in line with “conservative ideals”, while nuclear is more “socialist”, given that it requires much less govt. intervention on its behalf.  (In fact, the overall effect of govt. intervention on nuclear has been to hold it back, with excessive regulation.)  Fully insured, but relatively unregulated, nuclear power would be far cheaper (an approach truly in line with real, conservative ideals).

Jesse Jenkins's picture
Jesse Jenkins on Apr 16, 2014 1:38 am GMT

Hi James, 

Thanks for the comment. I think you’re probably right about the spectrum of storage costs and nuclear/renewable hybrids. That’s something I hope to explore in future modeling work with a colleague here at MIT. 

Just to be clear: as I noted in the intro sentance, this post is focused on nuclear in combination with variable renewables like wind and solar, not more reliable sources like hydro, geothermal, or biomass.

Also, while solar better aligns with electricity demand than wind, that doesn’t solve the integration issues with nuclear. If it reaches a penetration level where at mid-day, solar is producing close to 100% of load, nuclear will have to cycle off. Solar also is closer to peak, but not really on-peak. In nearly all regions, peak demand is experienced in late afternoon or early evening, not midday when solar systems are at 100%. So what we’re seeing in some of the modeling around here (MIT) of high-penetration of solar is that the remainder of your system (i.e. excluding solar) becomes a “double peaking” system: you get a peak in late morning, then a big trough as solar ramps up around midday, then another sharper peak in the afternoon/evening as solar falls off and peak demand picks up. That actually increases rather than decreases the need for fast-ramping system capabilities. California regulators have dubbed this the “Duck Curve,” while Jeff St. John calls the even more pronounced situation in Hawaii the “Nessy Curve” (both for their shapes). 



James Hopf's picture
James Hopf on Apr 16, 2014 1:40 am GMT

“Given that accidents with offsite consequences are impossible (not just unlikely) with most new designs, a legislative exemption from the old regulatory regime would be technically justified.”

I couldn’t possibly agree more.  NRC’s mandate is to protect public health and safety.  Well, even Fukushima caused no immediate deaths and will have no measurable impact on public health.  SMRs’ maximum possible release would be only a few percent of that, at most.  It’s hard to argue that SMRs can pose a threat to public safety.  All potential consequences will be purely economic (including reactor decommissioning, land cleanup and public compensation).  Thus, we should remove liability limitations for SMRs, but also remove stringent, detailed regulatory oversight.  Decisions on safety measures and practices would be between SMR operators and their insurers.

I discuss this more at:

Robert Bernal's picture
Robert Bernal on Apr 16, 2014 2:52 am GMT

Great, a call to join forces!

Full on closed cycle nuclear, full on rooftop PV and full on wind (and lots of powerlines). Since these 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. Now, the tricky part: figuring if there is enough “room” for smaller reactors, larger turbines and all that synthetic fuel storage in such a wildly fluctuating environment!

Edit: These are probably not options we already have but I’m sure that we have the tech to make it happen.


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