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Low Capacity Factors: challenges for a low carbon energy transition

Robert Wilson's picture
University of Strathclyde

Robert Wilson is a PhD Student in Mathematical Ecology at the University of Strathclyde.

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  • Oct 15, 2013

Low capacity, mo' problems

A transition to low carbon energy faces multiple challenges, here I discuss two: that posed by the low capacity factors of renewable energy and the challenge posed by the requirement for power plants to run with reduced capacity factors.


On a sunny Saturday afternoon in May 2012 Germany got over half of its electricity from its solar panels. This story was heralded by too many environmentalists as showing that solar power was now contributing large amounts of energy – in some accounts Germany now gets 50% of its electricity from solar year round – and that the German roll out was a resounding success story. Instead it indicated that solar power is a far from appropriate technology for a cloudy country such as Germany. This is shown by contrasting the electricity Germany got for a couple of hours on that May afternoon with the rest of the year. In descending order: it got around 20% of its electricity from solar that day, around 12% from solar that month, and only 4.6% from solar for the entire year.

In other words if Germany was to get only 10% of its electricity from solar, it would have days when it gets 100% of its electricity from solar. And quite clearly expanding beyond 10% will pose significant challenges. Here we have a simple illustration of the multiple challenges posed by the preferred capacity factors of low carbon power plants.

Capacity Factors: A Primer

The capacity factor of a power plant is defined rather simply, it is its average power output divided by its maximum power output. Actual capacity factors vary significantly and are determined by multiple factors.

The first is the role a power plant plays in the electricity grid. In fundamental respects the total generating capacity on a conventional electricity grid (i.e. one with little intermittent renewables) is determined by peak electricity demand, which for example is 60 billion watts (60 GW) in the UK. Power plants are not always available to supply electricity into the grid, so the total capacity is normally peak demand plus change, around 10% in many countries. However electricity demand is mostly below peak demand, for the simple reason that very few people are awake at 5 AM in the morning to consume large amounts of electricity. In the case of the UK average demand is about 40 GW, which translates to an average capacity factor of around 60%.

However not all power plants have identical capacity factors. Turning to the United States, in 2009 the average capacity factor for coal plants was 63.8%, for gas plants 42.2%, and for nuclear plants 90.3%. The reasons for these differences is primarily that their running costs are different. Typical electricity grids buy electricity from power plants on the basis of which has the lowest running osts at that particular time. The typical order here is nuclear cheapest, then coal and then gas. However this has recently been upended by the diffusion of shale gas in the US. Cheaper natural gas has resulted in a significant increase in capacity factors for US gas plants, and a reduction in both the capacity factors of coal plants and in turn carbon dioxide emissions. A transition from low to high capacity factor gas plants and from high to low capacity factor coal plants has the potential to be a significant climate change mitigation wedge.

Low Capacity Factors of Solar and Wind

In contrast typical renewable energy plants currently do not have capacity factors determined by market forces. Their main determinants are when the sun shines and when the wind blows. Solar panels have capacity factors below 10% in cloudy Germany, whereas they are 20% in the more suitable Arizona. Average solar radiation in Arizona is 22% of its maximum, therefore a capacity factor of around 20% should be viewed as a physical upper limit to capacity factors in Arizona. The difference between peak output and average can be significant, last year peak output (22 GW) was seven times higher than average output (3.2 GW) in Germany.

Wind speeds vary significantly globally. Therefore it is unsurprising that capacity factors will also. Boccard (2007) calculated that European wind farm capacity factors varied from a low of 18% in Germany to a high of 26% in the United Kingdom. The past however should not necessarily be viewed as an accurate reflection of the future. Diffusion of onshore wind farms may result in a reduction of average capacity factors as better sites are used up. In contrast diffusion of offshore wind farms should see increases to average capacity factors. Germany provides a good illustration of this. At the start of 2012 it had 28.8 GW of wind power installed, and wind farms produced 45.9 TWh of electricity, which equates to an average capacity factor of 18%. However offshore wind farms rarely have capacity factors below 30%, and future German offshore wind farms are more likely to average much closer to 40% than the national onshore average of below 20%. Therefore German wind farm capacity factors should increase significantly if more offshore wind farms are built.

Curtailment of Electricity

Let’s reconsider that hypothetical future where Germany gets 20% of its electricity from solar power. Germany would then often be generating far more electricity from solar than it can consume. Similar conditions to the May 2012 record of 22 GW of solar would result in around 200% of electricity supply from solar and an excess of around 40 GW. However Germany was also producing 4 GW of wind power at the same time. It’s very difficult to see Germany decarbonising without the majority of its electricity coming from wind power. Let’s say then that in this hypothetical future Germany gets 50% of its electricity from wind instead of the 8%. It would therefore be producing 60 GW more power from wind and solar than it would be consuming on this May afternoon. Germany therefore would have three choices: export the electricity, store it, or curtail it. Only the second two are credible long term options. After all if Germany’s neighbours install lots of renewables capacity they too will probably want to export it at the same time, for the simple reason that solar output peaks in Germany at very similar times to its neighbours and wind speeds are very correlated.

Low capacity factor power sources therefore require greater and greater levels of storage as they diffuse, or significant levels of curtailment. And both of these factors will add to the average cost of each unit of electricity produced.  Here I will demonstrate this by considering the possible future expansion of Danish wind farms. At the start of 2012 Denmark had a total of 3.93 GW of wind capacity installed, a figure which rose to 4.1 GW at the end of the year. Average wind farm output was 1.2 GW, while the average electricity load was 3.9 GW. So, 30% of Denmark’s electricity came from wind farms last year. However what will happen if it continues to expand wind power as expected? Below I have estimated how much wind power will not be consumed in Denmark under different levels of wind power penetration. (Note on calculation: I have taken actual hourly electricity demand and wind farm output data from last year. If total wind farm output is below electricity demand in a particular hour, then I assume all of the electricity is consumed in Denmark. If it is higher then I assume that the excess is not consumed in Denmark.)

Denmark appears to be able to get 50% of its electricity each year from wind without significant curtailment. However higher penetrations will cause greater problems. 70% from wind will result in approximately 30% of wind power either being exported, stored or curtailed. Fortunately Denmark is heavily interconnected and can probably export this electricity to hydro heavy Norway and Sweden, or Germany. Denmark’s average electricity demand is 4 GW, yet its export capacity is almost 6 GW, a benefit shared by few other countries.

We can repeat this exercise with German solar. The much lower capacity factor for German solar, 10% versus around 30% for Danish wind, means we expect expansion of solar to be much more problematic. The graph below shows that up to 20% there will be limited curtailment of solar power due to supply outstripping demand. At 40% penetration half of the energy produced cannot be consumed in Germany. These estimates show solar is not very scalable in Germany, however they also underestimate the challenges it faces. Consideration of the effects of the large scale diffusion of wind power would make the graph below much worse. I will leave this point for a future column.

Repeating this exercise for German wind farms gives us the graph below.

These approximations indicate that Germany will need to curtail, or store, two times more wind electricity (in percentage terms) than Denmark if both countries were to get 50% of their electricity from wind power, reflecting the higher capacity factor of wind power in Denmark than in Germany. These numbers however should not be viewed as realistic projections. Low power density of wind power means a large expansion of onshore wind in Germany will face very significant social and political challenges. Therefore the capacity factor of German wind power is likely to increase significantly and potential curtailment will be much lower.

Regions where wind farms have higher capacity factors therefore will in general require less curtailment of wind electricity. This is one of many secondary, but important considerations that need to be considered when weighing up the costs of intermittent energy sources.

The Need for Low Capacity Factor Power Plants

The low capacity factor of renewable energy conversions is often used by nuclear advocates as a key argument for the supposed superiority of nuclear power plants. However the capacity factor of nuclear power plants have their own associated problems. Scalable and affordable forms of energy storage currently remain elusive, and may remain so. Any future electricity grid may be rather old fashioned, requiring power plants to match demand exactly minute to minute by ramping their output up and down. Average capacity factors of 50-60% may still be the norm in the middle of the century. This is rather different to the preferred capacity factor of nuclear power plants of around 90%. Again this can be demonstrated with approximations of curtailment of nuclear power under various penetration scenarios. Here I will consider a simple scenario where nuclear power provides electricity to the UK electricity grid, assuming future load is the same as in 2012. To simplify things nuclear power plants provide electricity at 100% of their capacity, but their total output is capped by the electricity load each hour. Below is the result:


Up until around 60% penetration there is little need to curtail nuclear power plants. However this need grows very rapidly above a penetration level around 75%. This simple engineering appraisal also rules out the likelihood of 100% nuclear power coming any time soon. It will be much cheaper to get 75 or 80% of electricity from nuclear and to use low capital cost gas plants to fill in the gaps. The same holds for renewable energy.

The Challenge of Electrifying Heating

I will close by drawing brief attention to another under discussed issue: the problems caused by the electrification of heating, in this case in the United Kingdom. The British government have proposed to decarbonise heating in large part through the diffusion of heat pumps. Here I will not consider the efficacy of heat pumps, a controversial issue, but will highlight their possible impact on UK electricity demand. As shown by a recent paper, UK gas demand for heating is much more seasonal than current demand for electricity. A consequence of this is that the electrification of heating will significantly reduce the average capacity factors of British power plants.

The challenge posed by this is made clear by a report for the UK government’s independent advisors on climate change. Element Energy estimated that electrifying the majority of UK heating, largely in the form of heat pumps, would result in peak electricity demand for electric heating of 65 GW. This contrasts starkly with their estimate of average electricity demand for electric heating: 11.4 GW. In other words the UK electricity grid would require the addition of around 65 GW of capacity that would only operate at an average capacity factor of 18%. Meeting this load largely with low carbon energy appears extremely difficult, if not impossible. Meeting this with nuclear power would be challenging from an engineering and economic perspective. Meeting it largely with direct, i.e. not stored, wind energy would probably require a politically unfeasible area to be covered in wind turbines. However an alternative approach, now gaining some traction, is to convert excess wind, nuclear or solar electricity into methane and use this directly in gas furnaces in homes (and as back up in gas power plants).

The rough idea of Power-To-Gas is this: you capture carbon dioxide from somewhere (the current trial in Germany captures it from a biogas plant), use excess electricity from wind farms to first produce hydrogen via electrolysis and second to combine the hydrogen and carbon dioxide to produce methane, which can then be pumped into the gas grid. If this is proved workable it is a potential solution to the low capacity factors of renewables. Multiple challenges are faced however. Carbon capture is expected to impose an efficiency penalty of 20-30% on whatever process is producing the carbon dioxide in the first place, and impose greater capital costs on these plants. Conversion of excess wind electricity to methane is also expected to be at most 60% efficient. Therefore if we are converting excess wind energy to methane and then running it through a modern gas plant to produce electricity the overall process is just over 30% efficient, and below 30% if we factor in capturing the carbon dioxide. Things look slightly better if you are running it through a 97% efficient furnace in someone’s house. However the economics of this look challenging.

An even bigger problem may be that we are capturing carbon dioxide from somewhere, moving it around a little, and just pumping it in the atmosphere in the end anyway. The extreme difficulty of decarbonising industrial processes means that partial recycling of carbon in this way may not go that far, however a full life cycle analysis would be necessary to confirm how scalable this would be without requiring the abandonment of emissions targets. A final problem is that we need to find sources of carbon dioxide. Biogas power plants are a far from scalable energy source (and often have dubious “low carbon” credentials), and a decarbonised energy system may lack gas plants that emit large amounts of carbon dioxide to be captured economically (consider that a decarbonised electricity supply will require gas plants to run below 15% capacity factor, hardly “carbon capture ready” capacity factors.) And if you are capturing carbon dioxide why not just shove it underground and be done with it? Scalable low carbon alternatives to 97% efficient gas furnaces then may be difficult to come by.

These are only a few examples of the challenges posed by the capacity factors of low carbon energy. None of the above is to suggest one energy source is in general better than another. Solar power may have a lower capacity factor than wind farms in most locations, but this does not necessarily imply that wind is more scalable than solar. As recent research shows solar power, in sunny locations, is more suitable than wind power for battery style energy storage. The relative scalability of energy sources therefore is highly dependent on the future development, or lack of development, of energy storage techniques. Political – how many countries will commit to nuclear energy? -, social – how many wind turbines are densely populated countries willing to accept -, and ideological – the world’s largest solar farm was not built in Germany because of sound economic or engineering analysis – will determine the penetration of low carbon energy sources as much as anything else. However their rates and limits of diffusion will always be limited by physical and engineering realities.

Wind and solar data source: PF Bach

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Schalk Cloete's picture
Schalk Cloete on Oct 15, 2013

Could you provide some more detail about the curtailment plots you provided? For example, do they include balancing by exporting peak capacity?

I suppose they do since, as you pointed out, Germany will already get 100% of its electricity from PV on some days even at 10% PV penetration, but the graph shows that significant curtailment only begins around 20% penetration. It should also be considered that the variable thermal power fleet will not be able to go down to zero power, but probably only to about 25% if pushed to the max. This implies that, in the absence of balancing through exports, PV curtailment will start already at roughly 7.5% penetration (assuming that all nuclear plants are retired by that stage). 

Robert Wilson's picture
Robert Wilson on Oct 15, 2013


I perhaps should have explained that more clearly. The plot shows the percentage of solar electricity that cannot be consumed directly in Germany, as labelled on the y axis. As I mentioned in the text there are other issues that will mean curtailment is a bit higher in reality. Going into them however would really take a separate post, because there are a lot of complexities.

The main reason curtailment does not kick in significantly until 20% is that Germany is cloudy. Days when its solar panels produce over 70% of their total capacity are rather rare. It’s also the case that at 10% penetration the days when solar PV output is 100% of demand will be low demand days on Saturday or Sunday afternoons, so the rest of the week won’t be an issue.

I ignored the export issue, as the post was already too long. Currently Germany exports a huge amount of electricity when it is sunny. This option though may not be available in future, if its cloudy neighbours (for some stupid reason) decide to build German levels of PV.  This issue might be worth exploring in a future post. The ability of Germany to export will be highly dependent on what its neighbours do. It could get rather farsical. Wind farms in one country may need to be ramped down because electricity from another country get a higher guaranteed price. But I’ll leave that for another time.

John NIchols's picture
John NIchols on Oct 15, 2013



Mr. Wilson,

  How much capacity does Germany derive from offshore wind during days of high peak demand?

 I speculate this is the same as in the US, with no more than 8% capacity from wind – or less.

  Doesn’t this mean that reliable energy generation like coal, nuclear, natural gas, or the yet undeveloped cost-effective “storage solution”, must always be equal to peak demand?

Therefore, doesn’t it follow that wind does not add to grid capacity, rather, it only temporarily displaces reliable capacity?

Robert Wilson's picture
Robert Wilson on Oct 15, 2013


You simply seem to be repeating things I said in the column. Or more accurately you are repeating them, but giving them an anti-renewables edge.

And once again, my name is Robert.

Robert Wilson's picture
Robert Wilson on Oct 16, 2013


This is more or less correct. German electricity demand peaks around 6 pm in Winter when there is no sun. And wind power can easily go very close to zero. So you will probably need to have peak capacity in conventional power plants.

It is slightly different in countries where the peak is in summer in the middle of the day. In those countries, solar could displace some peak capacity.

Randy Voges's picture
Randy Voges on Oct 16, 2013


A few comments elaborating on some of your points (and you probably know this stuff anyways):

1) It may be helpful in a future post to elaborate more on the distinctions between types of load (base, intermediate, and peak) and how the characteristics of each form of generation play into that, because this does influence capacity factor (as you put it, the typical order of dispatch is nuclear first, then coal, and then gas).  Because coal and nukes utilize steam turbines, it is more practical and economical to simply run them flat out, which makes them most suitable for base load.  Gas combined-cycle plants have a gas turbine in the mix which makes them more flexible and thus more suitable for intermediate load (or load following) which has the effect of reducing the capacity factor.

2) Some people may not be clear on how nuclear has the lowest running costs.  Costs for power plants are broken down into capital, fixed, and variable (or fuel) costs, and it is important when formulating policy to have a firm grasp of the tradeoffs with each fuel source.  Everybody knows that nuclear has massive capital costs, but less understood are the low variable costs, and this is the only thing that keeps nuclear in the game.  The only way to recoup the costs are to take full advantage of this and extract every last bit of energy from the fuel.  By contrast, natural gas has a clear advantage over coal and nuclear in its (relatively) lower capital costs, but not when it comes to fuel (although as you mention, the shale gas revolution has cut into coal’s normal base load advantage).

3) Because of the variability of the “fuel”, wind and solar are classified as energy resources as opposed to capacity resources, and this factors into why they must be curtailed.  To put it another way, conventional generation is dispatchable; the fuel can be throttled back and forth as necessary depending on the load curve, whereas wind and solar cannot (though the efforts to make them more grid-friendly should not be overlooked).  For this reason, wind and solar have sometimes been characterized as negative load.

Nathan Wilson's picture
Nathan Wilson on Oct 16, 2013

The problem of sustainable winter heating and sustainable CO2 availability for fuel synthesis are both solved easily using ammonia fuel synthesis. 

As described in this conference presentation, ammonia (NH3), can be synthesized using only water and air (which is 80% nitrogen), hence it will always be less expensive than methane made from hydrogen and captured or farmed CO2.  Ammonia can be used in optimized combustors for direct process heating, space heating, or combined heat-and-power applications, but can also be used in combustion turbine or combined cycle utility-scale generation; hence it is compatible with high efficiency heat-pump or simple resistive electric heaters.  Burning (stored) ammonia in utility plants could be more economical than post-combustion carbon-capture when the power plant operates as a low capacity factor peaker, as the capital cost would be lower (there may also be isolated locations with high transportation cost in which ammonia is cheaper as an imported fuel than fossil methane).

Because large scale fuel synthesis would constitute a large dispatchable load (with ultra-fast response time for electrolysis), in high ammonia use scenarios, most demand matching would be done by dispatching load, which avoids the high cost and poor efficiency of electricity made by burning ammonia (a few hours of batteries are still needed with PV, which would otherwise need a lot of ammonia fueled generation).  Fertilizer applications use ammonia at an energy rate of roughly 1% of the electricity market, heavy duty vehicles (which could be designed to burn ammonia fuel instead of diesel, and have the safety advantage of professional drivers) use an energy rate of roughly 25% of the electricity market (probably enough dispatchable load for 100% nuclear electricity), and all transportation is about the same size as the electricity market (with renewables, some extra peaking generation might be required?).

Ammonia is also more easily stored for seasonal use or transportation than is methane.  Liquefying methane requires the cryogenic temperature of 111K, but ammonia can be stored at atmospheric pressure when refrigerated to -33C, which greatly reduces refrigeration cost. When used at (worst-case) room temperature for vehicle fuel, ammonia is about 25% more energy dense than cng, and has 10x lower pressure.  Of course hydrogen is the least storable fuel, with a liquefaction temperature of only 20K, and only half the energy density of ammonia even at 10,000 psi.

Most importantly, use of ammonia fuel allows us to have low CO2 emissions, whether or not we decide to stop using fossil fuels (to the extent that we have repositories available for CO2 sequestration, and many scientists including energy secretary Moniz say we do), while providing two clear paths for the elimination of fossil fuels (nuclear and renewable).

Robert Wilson's picture
Robert Wilson on Oct 16, 2013


It’s very hard to see how this is solved “easily” as you claim. Almost all of Europe, large parts of the US and Canada heat their houses using gas furnaces. The infrastructure to simply get the gas to people’s houses took decades to get in place. The creation of an industry that will take multiple GWs of excess wind, nuclear or solar and convert it to chemical energy in ammonia, which can then be piped to people’s houses and burned in yet to be commercialised furnaces is not easy under any definition of the word. And getting GWs of peaker plants that can burn ammonia will take decades. None of this can be called easy.

Robert Wilson's picture
Robert Wilson on Oct 16, 2013

Thanks Randy,

There is always a trade off between over explaining and under explaining. For example in your comment you mention steam turbines and gas turbines. Some readers won’t know what a steam turbine is, or that it is less flexible than a gas turbine. And so it goes down the road…

Nathan Wilson's picture
Nathan Wilson on Oct 16, 2013

Easy is relative, I really just meant that no breakthroughs are required.   The ammonia-vs-methane question is analagous to the nuclear-vs-renewables issue:  methane synthesis is easier to start due to infrastructure, but ammonia is cheaper once it’s established and much better at high penetration.  So yes, the transition to sustainable energy will be hard, and it will take decades.

But note that syn-fuel which is made from (off-peak) electricity will cost around the same as electricity.  So there is little reason to plumb homes for ammonia (plumbing commercial and industrial building may be enough); electric heaters are cheap and heat pumps are economical.  

In the 1970s, the US had a large fleet of oil-fired generators which were all converted to “dual fired” (oil and gas, although only gas is used in them now) for low cost; conversion to ammonia will be only slightly more expensive.

Robert Wilson's picture
Robert Wilson on Oct 16, 2013


The figures you cite are simple not credible. If they were there should be clear statistical evidence for them, i.e. kWh of gas required for each kWh of electricity produced by gas plants should be much higher than expected in countries with above 5% wind penetration. Could you possibly provide that evidence?

It’s also the case that the National Grid, who run the UK’s electricity grid, have performed actual calculations of this and found no evidence of what you are talking about.

Bad calculations based on faulty understanding of how power plants operate should not guide policy on renewables.

Jean-Marc D's picture
Jean-Marc D on Oct 16, 2013

Congratulation, you have just demonstrated why France stopped at 80% nuclear. However, you didn’t integrate in your model the fact that NPP have maintenance periods that can be programmed to occur at the time of lower demand, this explain how France could reach 80% nuclear despite having a higher seasonnality that in the numbers you use here.

There’s also the fact that Germany and Denmark currently export a lot more wind & solar power that the graph here would predict at their penetration level, this reflects that the model is still simplified, and in my opinion probably optimistic. You didn’t actually give much explanation about how you estimated the curtailement/export needed at a given production level. Since it’s not only production that varies but also consumption, the calculation is not so obvious.

From for the example of the Falklands (which is a location with high load factor), it seems that the impact of curtailment start being significant more at 40% penetration. With 3 wind turbines, they were generating about 26% of their electricity from wind, but with 6, only around 40% (despite using flywheels) and then saying they couldn’t go on without batteries.

Robert Wilson's picture
Robert Wilson on Oct 16, 2013


I added a brief note to the text to clarify. 

The model is simplified, which is stated clearly in the text. How much wind and solar Germany can export in future is very hard to predict, and is far outside the scope of this piece. In many respects it is down to what renewables its neighbours develop and how the market is working.

Timing of refuelling etc. is part of the reason France curtails nuclear less than the graph. But at the same time at 80% penetration French nuclear reactors still have to load follow, which is effectively the same thing as curtailment. From memory French nukes have average load factors of 78%, which would be closer to 90% if they didn’t load follow. 

As a rule of thumb curtailment problems will begin around the same penetration point as the load factor, so 40% for the Falklands sounds about right. 

Nathan Wilson's picture
Nathan Wilson on Oct 17, 2013

“…there will be NO fossil fuels in the future; the fossil fuel age is ending.”

I agree, but this is a hard basis for national policy, since it might be very hard to know how much time we have left, and there might not be any price signal that supplies are running low (consider the fracking boom).  If we panick and try to transition too quickly (like Germany), or if we are too slow, we could wreck the economy.

I think it is very important for governments to use policy and incentives to push the process along.  For example, I think would should use incentives to convert about 10% of our heavy duty vehicle fleet to ammonia fuel  (over a couple of decades);  that will give us an infrastructure basis which will allow us to ramp up quickly if/when needed.  Similarly, we must maintain a capacity to produce new nuclear plants, as well as renewables.

I have no idea how we can use national policy to drive a transition away from fossil fuel, without making expensive (and obvious) mistakes, like putting PV in cloudy places or converting corn to fuel.  Unfortunately, the lobbyists seem to have more influence than the scientists.  Maybe a carbon tax really is the lesser of the evils.

Max's picture
Max on Oct 31, 2013

Very interesting and insightful post! This is the first time I found figures on how much curtailment would theoretically be required at varying wind/solar/nuclear penetration levels in some countries.


I think you make a strong case that Denmark could get a very high fraction of its electricity from wind energy at somewhat reasonable prices. According to your graph, accepting 50% curtailment (dropping the wind capacity factor by half) would allow around 80% of Denmark’s electricity to be supplied by wind alone. The remaining 20% could be supplied by gas turbines, or — even better — by storing some of the otherwise curtailed excess wind output in pumped-hydro installations across the Skagerrak in Norway. 




Robert Wilson's picture
Robert Wilson on Nov 1, 2013


Your final paragraph reads like something a conspiracy theorist would write. Instead of mocking “lay types and others” for somehow being gullible, perhaps you can provide links to some peer reviewed research to back up your point. What I see here are dubious links to studies by anti-wind groups, and a study sanctioned by a fossil fuel lobby group. Why exactly is none of this stuff appearing in the peer reviewed literature? Is it because academics are wanting to “keep their story alive,” or is it because the hypothesis that wind farms don’t reduce emissions does not hold? Somehow I feel that the latter is more likely.

And again, can you please make an effort to make it clear what you are referring to. Too often your comments feel like link dumping and I also feel as if you are just cutting and pasting things in. Your position is far outside the mainstream and making readers go through a bunch of obscure websites to figure out what you are talking about is not a good idea.

Jean-Marc D's picture
Jean-Marc D on Dec 15, 2013

I should have been more precise, I agree the level of curtailment in France is basically what you have predicted, and not less. It seems to me on one side the simplifications in your model make it a bit optimistic, but on the other side careful planning of time of refuelling and other maintenances has allowed to reduce curtailment, and the two aspects more or less cancel each other.

In the case of Falklands, from the available data the 6 turbines should have been able to generate 52% of power, but appear to have been curtailed to 40%. This means about 23% of production seems to have been curtailed instead of the 8% your graph predicts for Denmark, and 18% for Germany. I believe however Falkland chose wind because it’s strong at this latitude, so this ought to ba a scenario with high load factor.

Bas Gresnigt's picture
Bas Gresnigt on Feb 12, 2014

Of course German researches studied how much storage would be needed in case of x% wind & solar etc.
This site reports about one of those studies:

The study shows that name plate capacity of wind can grow toward 100GW and that of solar towards 125GW before storage becomes an issue.
So in general wind+solar can triple before it becomes an issue!
That situation will be reached against 2030.
So there is time to develop good (a.o. storage, and/or replace inflexible power plants) solutions.

Note that: 

  • this also explains why the 35 pumped storage facilities in Germany now make so much losses;
  • wind+solar produce now ~13% of the German electricity (~10% by hydro, biomass, etc).
    So wind+solar can triple towards ~40%, which is ~50% renewable together with hydro/biomass/etc,  before storage or flexible power plants or … become an issue. 
Bas Gresnigt's picture
Bas Gresnigt on Feb 12, 2014


“…CO2 reduction effectiveness of wind energy on the Irish system is about 52.6% @ 17% annual wind energy…

This study of the Fraunhofer IWES institute, analysis mixes of different methods of electricity generation (with/without im-/export), especial wind and solar. 
Your estimation does not fit with the results of this thorough study.

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