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Why Wind Farms Can Be Relied On For Almost Zero Power

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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Wind Farms and the Necessity of Back Up

Modern society is fundamentally dependent on a reliable and on-demand supply of electricity. This electricity comes almost entirely from burning coal and natural gas, fissioning uranium or by large hydro-electric dams. On aggregate, these power plants can be relied on to supply electricity around the clock; a reliability that would seem miraculous to people living only a few centuries ago when light availability was completely dependent on whether the sun shone. Wind farms, however, cannot currently provide this reliability. In fact, on the scale of most countries aggregate wind farm output can be assumed to have almost zero reliability. In this sense, every wind farm must have a fossil fuel power plant sitting in wait for when the wind does not blow.

Let me begin by unpacking a banal statement: All power plants need back up. A century of technical innovation has resulted in electricity grids that are ultra-reliable by any reasonable standard, but power plants still cut off on occasion; they are vastly complex industrial machines and things will sometimes go wrong. When a power plant does goes off-line, others will respond by changing their output. In this sense, all power plants are backed up by each other.

Coal power plant outages, however, are always independent of each other. I live in Scotland, and the probability of Longannett power station – a short drive from where I live – going off-line at exactly the same time as Drax power station – a 3 hour train journey away – is close to zero. The same cannot be said for wind farms.

Anyone who regularly watches weather forecasts knows that wind speeds over large areas, e.g. the whole of Britain, are closely linked. If you are comforted by the claim that “if it is not windy in one place, it will be windy elsewhere”, I suggest you watch a weather forecast.

How much the aggregate output of countries’ wind farms varies can be discovered by looking through spreadsheets produced by grid operators And the lesson is clear: In every country aggregate wind farm output often goes close to zero. I will illustrate this for Britain and Germany.

Wind farms can reliably supply less than 1% of installed capacity

Britain is perhaps the windiest country in Europe; while Germany is more or less the least windy. In 2009, Boccard estimated that the average capacity factor of Germany’s wind farms was 18.3%, while in Britain it was 26.1%. In other words 10 GW (GW = billion watts) of installed capacity in Britain will deliver about 2.6 GW on average, but the figure will be 1.8 GW in Germany. Recent production data in Germany and Britain indicate that these are still reasonable estimates. (Britain’s government publishes annual figures here.)

How much does wind farm output vary in these countries? Let’s look at Germany first.  Last year the power output of Germany’s wind farms peaked at 26 GW at 6 pm on the 5th of December (see technical note for details of calculations). In contrast, minimum power output of Germany’s wind farms was 0.128 GW at 2 pm on the 4th of September. Minimum power output was therefore only 0.5% of maximum power output. Not quite zero, but not much higher either.

GermanyOverall, Britain has a much better wind regime than Germany, with higher average wind speeds and fewer lulls. However, it also sees periods of close to zero wind.

Britain’s total wind farm output peaked at 6 GW at midnight on the 21st of December. Its output reached a minimum of 0.025 GW at 11 pm on the 16th of June. The minimum was therefore only 0.4% of the maximum. Britain installed some new capacity between June and September. However, the lesson is reasonably clear; Britain and Germany’s aggregate wind farm output can be expected to go below 1% of total installed capacity with reasonable regularity.

The day of the peak in Britain is also notable for another reason; it shows how much wind farm output can vary in a single day.  By the end of that day wind farm output was 1% of what it was at the start of it. As the graph below shows output went from around 2.5 GW to almost 0 GW in a single day. This is a switch from average output to almost zero output in 24 hours.


 Wind farms should be viewed as fuel savers

The immediate consequence of this is that wind farms cannot be total replacements for fossil fuel or nuclear power plants. If we build wind farms, we need to acknowledge that we will also need conventional power plants to be ready to increase their output when wind farms produce almost no electricity. This will hopefully change with future innovation in energy storage or with the erection of continent sprawling super-grids, but it will likely remain the case for a while to come.

Wind farms, then, should be viewed as “fuel savers”. When they are generating electricity they save fuel, and CO2 emissions, because you need to ramp down a fossil fuel power plant. In other words, they displace electricity generation from fossil fuel power plants, but not the power plants themselves; the power plants will largely still be needed for when it is not windy.

This, of course, does not mean that we should not build wind farms. The benefits that result from the carbon dioxide emissions saved by wind farms are obvious. Similarly, wind farms are among the most economical ways of generating low carbon energy.  However, the role wind farms will play in an energy system should be acknowledged. Anyone advocating the large scale expansion of wind farms must recognise that they will have a large number of fossil fuel power plants on the side. Advocating an expansion of wind farms, while opposing almost all new gas power plants, as some environmentalists do, is either hypocritical or a display of ignorance of basic engineering realities. As the great physicist Richard Feynman said, “For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled.

Technical notes

1. Wind farm output covered in the above graphs does not cover all wind farms. Some wind farms are not “visible” to the grid, and are not reported in these statistics. Because I am only interested in variation, not absolute numbers, the exclusion of some wind farms should not be material.

2. Data is taken from PF Bach’s website, who has aggregated the data from the German and British grid providers.

3. Calculations were performed using R and plotted using the package ggplot2.

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Bas Gresnigt's picture
Bas Gresnigt on Nov 24, 2014

“>no energy storage system exists -or is even envisaged- that can cover outages of this length…”.

Why do you think the Germans are busy developing the cheapest methods to convert electricity to gas and liquid fuel? Their bigger pilots concern 6 – 10MW. Those will be needed after ~1935 (at GW scale).
Those power-to-gas plants will operate especially when electricity is cheap. At sunny or windy days there will be overproduction.

The renewable gas can then be stored in gasfields (e.g. in the huge fields of NL) or in the cavities in the south (Bayern stores enough to handle a cut off of all gas during three months).

So cheap peaker gas turbines can be used to burn that renewable gas and fill the gaps during those periods, together with dispatchable renewable (hydro, biomass, geo-thermal, etc.).

Bas Gresnigt's picture
Bas Gresnigt on Nov 24, 2014

Hope you can deliver against a good price.
If you do my congratulations, as then the standard PV-rooftop solar may include a battery that allows a shift for 4-6 hours.

It may imply the end of the duck curve in the load of the grid. And make the PV-solar decision of the household far less dependent on net metering.

Mark Heslep's picture
Mark Heslep on Nov 25, 2014

100% renewable is the target of Denmark “

It may be that most in Denmark favor a 21st century Danish colony on Mars as well, but that is not going to happen either, not domestically.  If Denmark measures renewable energy percentage by including hydro imported from Scandanavia, of what use is that as an instructive example. 

Clayton Handleman's picture
Clayton Handleman on Nov 24, 2014

You are correct.  The UK alone does not have a decorrelated source and therefore it cannot power its grid with wind alone.  This is old news and I am a bit confused why people are repeating this on a blog with relatively technically competent posters.  In industrialized countries, for renewables to have high penetration there are several approaches, that combined lead to a high renewables penetration scenario. 

– A super grid of sufficient size that sources can be decorrelated and a diversity of sources can be utilized: Hydro, wind, solar and yes, some fossil or nuclear contribution.

– Real time pricing so that the loads can also respond dynamically.

– High EV penetration.  In the near term (5 – 10  years ) EVs offer a great way to load shift on a large scale addressing fluctuations on the scale of hours.

– High EV penetration.  In the long term ( 10 – 30 years ) V2G offering round the clock load shifting and sourcing of power.

For Europe the supergrid that is being envisioned spreads from the 30GW of hydro sources in Norway to wind throughout Europe to the high value solar resources in Spain, Italy and North Africa.  Under such a scenario Europe can reach much higher penetrations.

In the US we can tie together the solar in the Southwest with decorrelated wind in the Great Plains and Atlantic seaboard along with massive load shifting from EVs.  NREL has said that with 40% CF wind and no EVs we can make this work at 80% penetration.  Throw in the more recent surveys that indicate we have over a TW of wind at 50% CF along with high penetration of EVs and other load shifing and we have a system that can work with high penetration renewables.  The UK is about the size of California in the US.  A continental scale super grid is what is required to hit the very high levels of penetration that folks like me think are a good idea.  This is true in the US and it is true in Europe. 

To perpetuate the fantasy that mainstream renewables advocates think that the UK can go it alone is doing nothing more than the bidding of the entrenched FF industry.  It has nothing to with reality and is simply designed to undermine credibility by creating a false meme and caricature.




Nathan Wilson's picture
Nathan Wilson on Nov 24, 2014

As we have often discussed, Denmark has a tiny grid, whose variability problems are easily solved by interconnecting with their neighbor’s fossil fuel & hydro dominated grids.

The El Hierro is a perfect example of the high cost of high penetration renewables: According to this article, their system costs about US $8 per peak Watt ($20/W avg?), and was 50% paid for by a European Union subsidy.  The energy produced will replace the expensive output of an oil-fired diesel plant (which will be retained for backup, according to this flyer).  The pumped hydro system uses a 700m path along an extinct volcano (with a naturally occurring bowl on top), and can carry the load for 7 windless days (flyer).  20% of the electrical demand is a dispatchable load – water desal.

Bas Gresnigt's picture
Bas Gresnigt on Nov 25, 2014

Norway’s hydro serves already NL and Denmark.
Plans to connect Germany, UK and Scotland.
So they will serve / cover NW-Europe.

France, S-Germany, Austria, Switserland, Italy, Slovenia have the great Alpin mountains.
Span and Portugal have a.o. the Sierra Nevada and the Pyrenees.

Poland the high Tatra as well as Sweden.
Tsjechie, Slowaky, Hungary the high Tatra as well as the Alpins via Austria/Germany.

So there is no real problem for W-Europe to migrate to 100% renewable.

The issue is tactical: The cheapest mix to deliver 99.999% reliable 100% renewable electriity.
So that is an important subject of German scientific think tanks such as Agora.

Joris van Dorp's picture
Joris van Dorp on Nov 25, 2014

The FiT will become equal to the whole sale price in next decade, still expansion will continue as solar price decrease continues.”

Deutsche Bank has recently reported that they expect solar PV LCOE cost to reach a historic trend bottom within the next 18 to 24 months, after which the cost of PV will join the cost of other established energy technologies upwards together with inflation.

“Solar module prices are likely to remain at record low levels for the next 18 months and beyond that timeframe, we see some inflationary pressures driving prices higher,” it writes.

“While balance of system costs have room to decline further, we expect a rapid decline in these costs over the next 18 months and then expect inflationary wage pressures on overall costs.

“Along the same lines, while overall financing costs have room to decline as solar moves down the risk curve and innovative financing structures drive down costs, we expect rising global interest rate environment from 2015 timeframe to drive upward pressure on overall financing costs.

“Bottom line: we expect solar LCOE to reach a cash bottom over the next 18-24 months and expect a rush for installations during the corresponding period.” 

So that’s it. Solar PV costs will reach bottom soon, after which solar advocates will finally be forced by empirical facts (where ‘mere’ logical reasoning has failed) to give up their strongly held pipe-dream of ever decreasing solar costs. They will have to accept that solar PV will never compete with coal, and therefore that solar PV will never solve the problem of unmitigated coal burning and climate change. Not a moment to soon. The world has wasted 40 years on the pipe-dream of solar PV competitiveness while repressing the nuclear option of solving climate change and resource scarcity.

Pure religious belief in ultimate solar PV competitiveness has already brought the world to the brink of hopelessness, causing the climate change problem to have grown the fastest ever during the last decade, resulting in it being at or near the point of no return today. Callous indifference to the fate of the environment and future generations, and a willingness to substitute lies and propaganda for objective and reliable information lies at the bottom of it all.

It will be a huge relief to many of the most serious energy and environmental experts when this madness is finally over sometime during the next few years, if not earlier, so we can begin seriously to address the horrific prospect of rampant climate change throughout the next centuries with the application of advanced, clean, inexhaustible and competitive nuclear energy. Nuclear is the only known coal killer. Solar PV is (unfortunately) little more than distraction and fig-leaf for chronic unmitigated coal burning.

Clayton Handleman's picture
Clayton Handleman on Nov 25, 2014

It is amusing to watch as nuclear apoligists and fossil fuel advocates, along with the probable occasional paid troll, accuse renewable energy advocates on this board of spreading propoganda.  Yet  it is you that is using hyperbol, and ad hominem insinuations in a post that lacks depth.

After decades of watching the EIA, large institutions and mainstream press grossly underestimate the potential for renewables, their rate of growth and the ongoing cost reduction, I will not hold my breath on Deutch Bank getting it right. 

Lets take a sampling of your language and think about who is spreading propganda on the board: 

pipe-dream of solar PV

Pure religious belief in ultimate solar PV competitiveness

Callous indifference to the fate of the environment and future generations


horrific prospect of rampant climate change

Solar PV is (unfortunately) little more than distraction and fig-leaf

the most serious energy and environmental experts

When was it that MIT became a not serious place for energy and environmental experts?

Please help me out, I am one of those with advanced physics degree and 30 years of multidisciplinary engineering experience that has ‘a pure religious belief’ that renewables including solar have an important role to play in a low carbon future.  I, along with experts at MIT, NREL and most of the US national labs along with thousands of other highly educated scientists and engineers apparently have much to learn from you and Deuch Bank.





Joris van Dorp's picture
Joris van Dorp on Nov 25, 2014

When solar advocates claim that nuclear power is unnecessary because solar will solve climate change (and i have yet to find one popular solar advocate who does not do this or suggest this), that is when solar power advocacy turns into the disastrous religious belief I refer to in my comment which has prevented nuclear power from solving climate change.

I like solar power, and have experience in the design and costing of a fair number of (commercial sized) systems (its not particularly hard to do of course, but still).

What I don’t particularly like is the politics and culture surrounding it, where parties install solar PV systems for their homes or businesses and claim the very large hidden and direct financial subsidies for solar power, only to then turn around and make a big PR event in which they pound themselves on the chest for being oh so very sustainable and concerned with the environment. Perhaps if they declined the heavy subsidies they would have something to take pride in. As it is, where they are simply making money due to the subsidies, causing their ‘concern’ to really be a financial no-brainer at the cost of society, it is rather pathetic really, and one wonders if the public funds used to subsidise their PR grandstanding was well spent. And when one considers that the solar panels tend to come from asian suppliers who tend to employ prison labor and tend to cause heavy polution due to not having much of any environmental protection laws, one sees even more to call pathetic. And when owners of solar systems deny the need to contribute funds for maintaining the grid and backup facilities, it becomes even more pathetic. All of this is surely not news for you?

Solar power can certainly deliver some environmental and economic benefit at limited penetrations and/or in niche markets (remote off-grid systems, small island nations running on diesel, etc.) I never denied this. I just don’t think its in any way relevant to the serious chalenge of climate change or resource depletion.

The constant refrain of “solar power will solve climate change” just is not credible. It is a religion and a very damaging one at that due to all the hype and misinformation which is hindering real progress on environmental and economic issues.

Wind power has a somewhat different set of characteristics, but in terrms of its ability (together or apart from solar) to make a real dent in the problem of resource depletion and climate change, it is largely similar to solar PV. It simply cannot deliver what is promised, yet it is constantly said to be able to. Pathetic!

Leo Klisch's picture
Leo Klisch on Nov 25, 2014

I think you’re barking up the wrong tree. You should be working to replace all FF with nuclear. Not impeding progress of all the possible carbon free energy sources.

Clifford Goudey's picture
Clifford Goudey on Nov 25, 2014

Roger, how are hydropower and geothermal not dispatchable?  Is there a reason you don’t consider energy storage as a means of turning variable power into dispatchable power?  There are entire countries that operate their grids on 100% renewable power (mostly hydro).  Those countries are nicely poised to adopt wind and solar to become energy exporters and help other countries with their electricity security.  Norway already does this.

Bob Meinetz's picture
Bob Meinetz on Nov 25, 2014

Clifford, Norway is a country with just over 5 million residents. All of Iceland has 330,000 residents, or three times as many people as the town in which I live.

Renewables are fine for tiny clusters of people who happen to live nearby abundant natural energy resources. But there is no other country in the world close to being able to match what these countries have accomplished. All of Norway’s hydro, operating at the worldwide average capacity factor of 44%, can’t  generate half the power required by California on a typical day. California is responsible for 80% of geothermal generation in the U.S.;  its rock solid contribution makes up less than 3% of the state’s peak demand.

Believing renewables can scale to meet the world’s energy demand is wishful (and foolish) thinking.

Bas Gresnigt's picture
Bas Gresnigt on Nov 26, 2014

Neither Solar nor Wind can deliver reliable electricity. But the combination of different renewable can!

And that combination of renewable technologies will also deliver an huge contribution to solve climate change. As these new renewable are expanding rapidly and nuclear is declining.

Bas Gresnigt's picture
Bas Gresnigt on Nov 26, 2014

Norway alone has already enough hydro and pumped storage potential to serve the whole of W-Europe. And they are quite happy to do so as you can read at Statkraft’s site.
It’s only a matter of grid extension.

Bas Gresnigt's picture
Bas Gresnigt on Nov 26, 2014

So may be we can agree on a proposal to increase car fuel tax gradual (~20%/a) towards €10/liter = ~$40/gallon, and then continue with an increase 2times the inflation rate (except of course synfuel and with some discount for bio-fuel)?

A more gradual, hence less disruptive, method to reach roughly the same: less toxic and micro-particle in the air as those kill people, and less CO2.

Joris van Dorp's picture
Joris van Dorp on Nov 26, 2014

You’ll find – if you look at some of my other comments here – that I never ‘impede’ any carbon-free energy sources. I don’t even impede CCS for that matter, which is not carbon-free, but has nevertheless become essential in this late stage as a result of obtuse energy policies in the past resulting in a fleet of carbon based generators which need to be either shut down prematurely (not likely to happen at scale) or be fitted retroactively with CCS if we are to have any chance at all of preventing serious damage to our climate in the future..

If there’s anything I do ‘impede’ it is the gross wastage of scarce public funds on symbolic policies that don’t solve problems, but are nevertheless presented as such through the use of blatant misinformation and excruciating propaganda. It is my chagrin over this pandemic (in the West) state of affairs – which makes a cynical mockery of science and stewardship of the earth – which motivates me to protest as vehemently as I do on this website at times. Others are more diplomatic and refined in their protest, which is great – I applaud it – but I choose to play the role of the rabid dissenter which is a role that I feel needs to be played by at a least a fraction of us, lest observers make the mistake of thinking that the issues which are discussed here and elsewhere concerning energy, the environment and our common future are not particularly urgent or not particularly heartfelt, I you understand what I mean.

Clifford Goudey's picture
Clifford Goudey on Nov 26, 2014

Bob, I appreciate your concern but these things take time.  Fortunately they scale well. 

Nathan Wilson's picture
Nathan Wilson on Nov 27, 2014

Norway’s average electricity demand is 14.3 GWatts (Wikipeidia) which is 92% of their hydro production, so their existing hydro fleet could certainly support some variability-smoothing for neighboring countries, though there is a limit, as the total European Union uses 357 GWatt avg (see here).

We should keep in mind that electricity users produce a demand profile with peak to average ratio of about 1.5-2.  Wind has a peak-avg of 3-4, and solar 4-10 (anti-correlated with European seasonal demand).  Nuclear has a peak-avg of about 1.1, and it is well aligned with seasonal demand peaks (scheduled maintenance).

So Norway’s limited existing hydro can supply the variable demand components of zero-carbon grids for something like 3 times as many people with nuclear-dominant grids compared to renewable grids.

As for new construction of pumped hydro:  paying for this new construction will be a tough sell, because as you often point out, the current electricity market does not allow energy storage to operate profitably.  Support for renewables is often based on the presumption that future costs will be low, and funds will be spent locally (i.e. no big expensive projects in other people’s countries).  Also a core belief of the solar PV industry is that the energy is the valuable part, and grid services like energy storage and transmission should be nearly free.

Nathan Wilson's picture
Nathan Wilson on Nov 27, 2014

Clayton, you made a good point upthread about keeping the diaglog civil.

Along these lines, I suggest we refrain from using the inflamatory and devisive term “nuclear apoligists“.  This term is not helpful for civil discussion as it a priory dismissed the core pro-nuclear argument, which is that nuclear power is extremely helpful, not hurtful to society.

I prefer the term “nuclear advocate”.

Nathan Wilson's picture
Nathan Wilson on Nov 27, 2014

reply moved to top for more width.

Bas Gresnigt's picture
Bas Gresnigt on Nov 28, 2014

Agree that wholeale electricity in DK, G, NL, CH, etc. is nowadays so cheap all the time that building (more) pumped storage & hydro is not economical (adding pumped storage to existing hydro may be economical as that requires low investment).

The situation can only change when EU changes the Emission Trading System (ETS) such that emitting CO2 becomes far more expensive.
With the present ETS stopping coal plants does not help the climate, as then the emission rights will be sold on the market and others (e.g. chemical plants) will use those. The only consequence is that ETS rights will become cheaper…


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