Why renewables need gas back up

Does renewable energy need to be backed up by fossil fuels? The answer is yes, at least until large scale methods of energy storage are invented. However, the question is one that I would argue is uninformative. A more relevant question is: Can renewable energy supply electricity when demand is at its highest?

[A quick note: the following arguments only hold in countries with similar electricity demand patterns. In particular they may not apply to countries with summer peaks in electricity demand.]

There are two key things that vary in an electricity grid: electricity demand and electricity supply. Fundamentally an electricity grid always needs to be able to match demand. Most high latitude countries are like the UK, with maximum seasonal demand in the middle of winter, as shown in the graph below, taken from UK govt. statistics.

UKseasonal

How much electricity can we rely on renewables to supply during winter peaks? Let’s begin with solar PV. Here is Germany’s actual solar production on 5th January 2011.

Transparency in Energy Markets   Actual solar power generation

The difficulty is that Germany’s, like most European countries, actual demand peak is around 6 pm, so you’re clearly going to need something else to cover that. In simple terms without large scale energy storage options solar power cannot displace any fossil fuel capacity as long as the winter peak in demand stays where it is.

Could we rely on wind farms to provide power at 6 pm in Winter? At this stage I will switch over to UK and Danish wind production, because these countries have much more readily available data. This is what wind power production in January 2012 looked like in the UK and Denmark. (I have put average monthly wind power in red)

UKmonthDKmonth

It seems clear that both countries experience occasions when wind power is down close to zero. On such occasions you will have little choice but to burn fossil fuels, or else rely on energy storage (which is currently rather limited.)

Overall it seems reasonable to conclude that the amount of electricity you can rely on wind and solar to provide at the point of maximum annual demand is close to zero. A direct consequence is that an electricity grid with a very high level of non-hydro renewables will either require fossil fuel plants to cover the annual peak in demand, or that large scale energy storage systems can provide the necessary back up. The latter, however is still a work in progress.

Environmentalists must keep these facts in mind when they demand high levels of renewable energy, and complain about new gas plants being built. It currently seems impossible to have the former without the latter.

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32 thoughts on “Why renewables need gas back up”

  1. All very true…

    An additional question is the reliability of interconnectors to supply during peak demand. The Cambridge Econometrics scenarios for Greenpeace/WWF appeared to require a hefty 15GW of interconnector capacity. That is in itself very ambitious, as you have pointed out elsewhere. Interconnectors are very expensive and really need sustained daily trade to justify the investment. They are unlikely to viable for peaking capacity alone. However, even if built it is unsafe to assume these interconnectors can be ‘dispatched’ as though are flexible power stations like CCGTs. The supplying countries may not have the surplus capacity to export. Three reasons:
    (1) Darkness falls across all of Europe at about the same time, so solar is out of commission everywhere at once. Also, it is quite common for cold winter high pressure systems to becalm much of Northern Europe, reducing wind speeds over a wide area.
    (2) Some interconnector capacity (eg. to Ireland) is already used to smooth the intermittency in the other country, so balancing and peaking services are flowing away from the UK.
    (3) Finally, it is quite likely that European countries will have roughly coinciding peaks and periods of high demand – dark late afternoons in December/January. Yet all have had to meet the EU renewable directive so will have tough balancing and peaking challenges themselves.

    The trouble therefore is that interconnector capacity is itself intermittent in practice, and that intermittency is likely to be systemically correlated with periods of low renewables output in the UK. Of course, some interconnector capacity might be linked to renewable sources not correlated with UK intermittency – for example Norwegian hydro, but this also will be in demand to stablise and meet peaks in the Scandinavian Nord Pool grid.

    Alternatively, I guess opportunistic developers on the exporting side of interconnectors could build CCGTs to take advantage of the countries with the most attractive capacity markets – effectively extending capacity markets across the continent. Not necessarily a bad thing, but hardly getting away from gas.

    1. Thanks Clive

      Actually I am currently looking at wind power data throughout Europe to figure out if wind in other countries can provide power when the UK is in a lull. So far I would probably say the answer is no. Your first point is quite true. I recall this happening a couple of Fridays ago. UK wind was close to zero, but Ireland, Denmark, France and Germany were all also all well below average in terms of wind power.

      Norway still has about 40% of its hydro untapped. The big problem with this is that Denmark already wants a big piece of the pie, and as it builds more wind it will just get bigger. Sweden, for now, doesn’t want much. However, if it moves away from nuclear and into wind, it will start using Norwegian hydro heavily for balancing. A solution would be for Norway to get heavily into nuclear power, which is currently zero. It has 15% of the world’s thorium reserves, and they are now building a test thorium reactor (http://www.smartplanet.com/blog/bulletin/norway-ringing-in-thorium-nuclear-new-year-with-westinghouse-at-the-party/6421).

      This is all incredibly elaborate, and unnecessarily so. Decarbonising electricity is easy to do, practically, so long as you don’t exclude nuclear power. Economics and financing should be the only real issues. Instead, Greens have pushed us down a route where we need to find solutions to non-problems.

      1. As a complementary point : Nuclear is a high capital investment that demands a very experimented workforce for the specific level of quality it requires. The consequence is that if you built a nuclear plant with workers that have no experience of that kind of job, it’s going to be very long and very expensive. And a sitting duck for criticisms of exorbitant costs.
        And Flamanville demonstrates that if you haven’t built one during ten years, you’ve already lost that level of expertise (one important point, what failed at Flamanville was almost exclusively construction work. The concrete was of poor quality, as well as the soldering of construction steel, and failed the quality checks and had to be redone over and over. Areva actually stills knows how to build the specific nuclear parts, and Taishan 1 is on track to start at end 2013 and be the quickest built of the 3rd generation until now).
        But the experience in France in the 80, in Korea and now China does demonstrate that if you built a number of reactors in a row, the costs do go down as you gain experience.

      2. >”Actually I am currently looking at wind power data throughout Europe to figure out if wind in other countries can provide power when the UK is in a lull. So far I would probably say the answer is no. ”

        I suspect you are correct. This study of intermittency aggregated across northern Europe is informative:

        http://www.poyry.com/sites/default/files/imce/files/intermittency_-_march_2011_-_energy.pdf

        “It is the strong conclusion of this study that
        in Northern Europe the overall output of the
        renewable generation will be highly variable,
        and will not average out because of weather
        and geography.”

        The aggregated charts show that increaing the amount of intermittent generation over the wide area still creates high peaks and very low troughs, almost randomly through the year.

        So dispersion and interconnection does not solve the problem.

  2. Is the reason nuclear (or hydro probably too) won’t work to even out wind or solar supply versus demand is because, unlike gas or coal, you can’t easily and quickly turn up or down the amount generated as needed? It’s been a while since I read McKay’s book but I seem to remember that was one of his points. What production methods other than burning carbon compounds allow the needed load management?

    “the following arguments only hold in countries with similar electricity demand patterns. In particular they may not apply to countries with summer peaks in electricity demand”

    So most regions are going to have some form of alternate peak and even in summer peak regions there is going to be times when solar won’t work (without significant storage improvements). I lived in Arizona for years and while you used AC when it was sunny, you also tended to use it well after dark as it stayed way too warm even past midnight. Reasonable people also tend to turn the thermostat up during the day when they aren’t at home leading to … an obvious load increase when people get home and decide 75F is too warm to spend the evening in.

    1. Rachel

      On the first point. Modern nuclear power plants can be turned up (just google “load following nuclear reactor” to get info on this.) They aren’t as flexible as gas plants, but technically they can provide a large amount of back up. Running them as back for say 70% renewables however doesn’t make economic sense. Most of the costs of nuclear power is upfront, with running costs very low. The exact opposite is true of gas. So, it would be a lot cheaper to run a gas plant 15% of the time than a nuclear reactor. Something like 40/40% nuclear/renewables should be economical as you can slightly reduce the output from reactors when it is very windy. In practice this is what France does. It’s about 80% nuclear, and will vary the output of some of its reactors throughout the day, and some will also reduce their output seasonally. I’m writing a blog on France currently, and should publish it in a couple of weeks or so.

      On the second point. I know the seasonal peak in most of the US is in summer due to AC, but I don’t know what time of the day the peak occurs. In Australia there is a summer peak, but the time is about 7 pm. This actually may not matter because hotter countries can build solar thermal plants more easily. Unlike solar PV they can store energy, so you would actually get some power at 7 pm.

      1. Interesting! Thanks! I was under the impression that nuclear basically couldn’t really be a load-smoother (though could provide most of the base load letting wind balance solar during some periods). I get the economic point but for gas you’d have to include the cost of countering the carbon output as well (though I’d guess it’s much cheaper than only partially utilized nuclear).

      2. The secondary issue is that if you built nuclear reactors that can provide most of the peak electricity demand, then it’s more economic just to run them all the time instead of renewables.

  3. The weather impacts both wind and solar dramatically. On many occasions near the winter solstice, I’m managing as little as 1kWh/day for several days in a row; whereas on a sunny-ish winter day, like today, I produced 9.89kWh. In comparison, in June, a sunny day can give me as much as 25kWh, which is more than enough to provide all the energy needs for my house. Wind is similar, though depending on wind speed rather than a cloudless sky, of course.

    As you say, Robert, the game changer for renewables will be the ability to store the energy they capture. Until then, the best way to look upon renewables is as a valuable, if somewhat unreliable, means of reducing the fuel consumption of a fossil-fuelled and nuclear-powered grid. Even viewed in that light, renewables still provide a very valuable service. Even though we can’t predict exactly when the gift of free energy will be received, looked at over a year we can be pretty sure what the total amount of fuel will be that’s saved. And for those who recognise the importance of reducing emissions, it’s a gift that won’t be refused.

  4. An upstart named Jevons has been making rather the same point in his book, The Coal Question
    http://books.google.fr/books?id=gAAKAAAAIAAJ&dq=The+Coal+Question&printsec=frontcover&source=bn&hl=en&sa=X&oi=book_result&ct=result&redir_esc=y#v=onepage&q=The%20Coal%20Question&f=false (p122-123)
    He remarked that “though they were powerful machines, [windmills] were very irregular, so that in a long tract of calm weather the mines were drowned”.
    All that to say that wind intermittency has been the cause of its demise as an energy source in the 19th century. As far as I know, it is the only energy tech to have been nearly abandonned throughout history.

    When connected to the grid, the lack of wind is not the only problem. It’s the first, and the only we have today. The problem is that human activity is not correlated to wind speeds in any way. At least, there is some correlation between solar irradiance and human activity, as most human activity takes place during the day. Wind speeds are only indirectly related to temperatures, which drive the demand for heating. To summarize, I think wind power without storage can be used as a fuel saver.

    The idea of aggregating windmills over Europe to make it a more stable source of supply is a failure. PF Bach, a danish wind proponent, states in his statistical survey that “the aggregated wind power production cannot be considered as a reliable source of power” http://pfbach.dk/firma_pfb/statistical_survey_2011.pdf (p16). He advocates storage in the form of heat to balance the short term variability of wind. http://pfbach.dk/firma_pfb/wind_power_integration.htm I just wish there would be more proposals like those to deal with the very real problem of intermittency.

    1. I really thought PF Bach was an opponent of wind. As the saying goes, with friends like that, who needs enemies ? ;-)

      I’m not convinced that CHP really works, heat storage works perfectly for storing the daily heat until the night, but not really for several days. And a wind production shortage typically lasts for about one week (see fraunhofer germany 2012 report, whilst the production looks regular at the month level p9, it varies very wildly at the week level p19. So one week is not enough to average the production variations http://www.ise.fraunhofer.de/en/downloads-englisch/pdf-files-englisch/news/electricity-production-from-solar-and-wind-in-germany-in-2012.pdf ).

      Seasonal storage sounds very nice, but in concrete terms, how can it be implemented ?

  5. Interesting post, but I find the arguments a little glass half-full. It’s clear that basing an argument on the fact that for a small, perhaps even significant, percentage of the time you will have close to zero wind power, you might logically fall on the backup solution of BAU fossil fuels or nuclear. Yet there are some other considerations to bear in mind:

    1. Offshore wind has not been factored in here. And I would suggest its reliability cannot be extrapolated from current onshore wind in Germany and Denmark.
    2. Solar is, as John Russell above mentions, particularly useful in driving down fossil fuel use currently, but given its predictable daily cycle should start – as electric cars are employed more extensively and better grid management means more intelligent matching of industrial and residential use to availability (achieved through price, like most other things) – to play a bigger role. No one predicted just a few years ago the drastically falling costs of solar PV, which has been a real eye-opener for many. Of course stability issues will dominate the headlines for a few years as the necessary infrastructure and storage options play catch up. But now there’s a real incentive to do so. Just look at the cash the US and others are throwing at batteries and grid storage tech. I’m optimistic in the medium term.
    3. You’ve neglected modern biomass generation which I assume can be switched on to cover lows in a predominantly wind-powered renewable contribution?
    4. A further point is that, both as the renewable capacity is expanded, as well as national grids become increasingly linked up (politics will slow this down, given), you will eventually smooth out and balance areas of low and high production. It’s really just about magnitude, like much else. The wind is blowing somewhere pretty much all the time.

    I accept that I’m extending the time horizon somewhat, out to about 2030 perhaps for many of these changes. It’s a long-term project. Exciting as well That is both what I am hoping for and pretty optimistic about.

    Firing up the gas plants to fill in the gaps, while nuclear should always be given a role given its low carbon profile, provided the industry can get a hold on costs, especially around decommissioning which right now is giving France all sorts of headaches.

    1. Thanks Chris

      1. It’s possible offshore wind will reduce the low points, however from what I have read it won’t do so by a significant margin. The lulls still occur.

      2. I would disagree that smart grids can actually do a great deal to balance renewables when there is very little of it. Yes, you could possibly shift the daily peak to the middle of the day when solar is peaking, but in winter that is a pretty small peak.

      On storage, there are plenty of reasons to invest in R&D, but we shouldn’t simply assume that it will come on line. The need for energy storage has existed since the beginning of electricity grids. So far, the only real option found is pumped hydro, and there isn’t a great deal of that available. Frankly I find “solutions” to climate change that depend on still non existent tech irresponsible, when there are other options available that don’t.

      3. As far as I am aware most biomass plants run like conventional power plants, so wouldn’t be used as back up. You maybe could, but whether the economics of that works out versus gas, I don’t know.

      4. “The wind is blowing somewhere pretty much all the time.” What is it about that sentence that I don’t like. Imagine the UK, Ireland, France, Holland, Belgium and Denmark were all connected up, with power moving between countries when needed. Would this mean that close to zero wind in the UK could be met by wind from elsewhere? The answer to this is probably no. UK and Ireland wind power is heavily correlated. So, each time the UK is looking for back, Ireland will be too. Likewise Holland and Belgium are heavily correlated, and France too. The UK isn’t that correlated with Denmark, but if you overlay the graphs above you can see that there is no guarantee that lulls in the UK won’t coincide with lulls in Denmark. The other problem is the wind has to be blowing in excess somewhere else, not just blowing. Countries need too much wind to start exporting it. It seems that interconnection will increase the percentage of power you can get from wind, a good thing, but not necessarily reduce the lulls. I’m writing a blog on this at the minute, but still crunching the numbers so look out.

    2. - Offshore wind is no more reliable than onshore. Flocard made another study about that, recording the behavior of the first 18 months of Robin Rigg. Unfortunately that one is in French only, but you can see the figures anyway :
      http://www.sauvonsleclimat.org/images/articles/pdf_files/etudes/111030_texterobinrigg-3.pdf
      Fig 6 page 6 shows the power production. Many points are above 80% which is exceptional and very rare onshore, but many are also extremely low, near 0%. Flocard makes the remarks that the optimization has led to turbine that can frequently have a high load factor, but also vary extremely fast. Fig 7 page 7 shows the percentage of production variation over one hour. We see that sometimes production has varied by 60% over just one hour.
      Finally Fig 9 page 9 show the distribution of efficiency, red is Robin Rigg, blue is the French onshore wind power. We see that 30% of the time Robin Rigg was producing at less than 5% efficiency. We also see that the average efficiency is the one it had the least frequently. Either it was producing next to nothing, or it was producing at max power, more than 95% for 6% of the time. In terms of integration to the grid, this is the worst possible way to reach an average production of 30%

      BTW decommissioning is not giving headaches in France. The one PWR reactor we are decommissioning, Chooz, is currently on track with schedule and costs. Yes, there’s also a small reactor, built as an experimental and later reconverted to produce commercial electricity, with a unique technology, whose decommission does not advance because of a succession of legal recourses against it by the Greens. The headache here is mostly artificially created, and the part that isn’t (handling of contaminated graphite) simply doesn’t apply to PWR which are 100% of the reactors currently running in France.
      The case of 900 MW Maine Yankee that was fully decommissioned for less than $500 millions (discounting fuel storage costs that are handled by Areva in France), shows there’s no real reason to believe decommission will be really expensive.
      http://www.maineyankee.com/overview/default.htm
      http://www.maineyankee.com/public/MaineYankee.pdf

  6. “On such occasions you will have little choice but to burn fossil fuels, or else rely on energy storage (which is currently rather limited.)”

    Or just use less? Go without? Work out how to meet our needs (or real needs not our current wants) within a variable supply envelope? Having a close to 100% reliable grid is something that’s only been available for a couple of generations in a small region of the world. What’s so scary about have routine brown/blackouts? I know plenty of people living ‘off grid’ and they manage just fine.

    I would suggest one of the biggest problems we face over the coming decades is our “longage of expectations”. If we can find a way to relax our grand expectations the future will be a lot nicer all round.

      1. Allianz study ; cost of a global blackout in the US
        http://www.agcs.allianz.com/assets/PDFs/Special%20and%20stand-alone%20articles/Power_Blackout_Risks.pdf
        2003 blackout in U.S. – Daimler Chrysler: 10,000 vehicles were moving through the paint shop at the time of the outage had to be scrapped.
        Ford : outage caused molten metal to cool and solidify inside one of the plant’s furnaces

        That’s the consequences of a one time event. If it were routine, there would be no heavy industry left.

      2. They probably only scrapped the casing, the cost of manually repainting it (and not getting the same quality level), or stripping it of the paint, foremost at this scale, and given the time/man power it would mobilize, was probably more than it’s value. Especially since the steel can be reused.

      3. I think to some degree Chris has a point, Robert. Energy efficiency at the point of use has huge savings back up the supply chain. There’s still a large amount of incandescent lighting around, for instance, and an investment in LED fittings as a replacement can reduce consumption to one sixth.

        Additionally, though I haven’t done the maths, I would guess that every £ spent on insulation of poor quality housing is worth at least two spent on power generation.

        There’s also the point that as the price of energy rises there’s every reason for people to adopt more of an energy-saving mind-set, being more frugal how they use electricity; switching off lights that are not being used; selecting more energy-efficient appliances at the point of purchase, and so on. Add these things up and we can probably make a considerable reduction to the number of power stations required.

        Personally I’d take it all a step further: why not make the cost of electricity vary according to availability and demand? With a display of the spot price in everyone’s home we would then be incentivised to think about when we switch on the oven or washing m/c. In microcosm it happens already in our house: the sun comes out, it’s washing day.

      4. It is a serious question. Obviously I don’t actually mean the lights going off in London this afternoon – that would be scary. What I’m getting at is that we’ve built a stupidly fragile system were a half second’s, let alone a half day’s interruption causes a crisis. We need to work on rebuilding the system so it can cope, without causing disasters, with a variable supply. The off-grid households I know manage this wonderfully on the micro-scale.

        These discussions, far too often take the demand side as a given and focus on the supply side. I think we need to focus just as much if not more, effort on the demand side.

  7. Grid operators include in their forecasts (like RTE that I know specifically) a certainty of 95% to dispose at all time of 10%-15% of the total installed wind power capacity (not sure if grammatically correct but you get the point).

    The study from Sauvons le Climat was already quoted but it’s still interesting to check it out: http://www.sauvonsleclimat.org/etudeshtml/vent-de-mer-vent-de-terre/35-fparticles/948-vent-de-mer-vent-de-terre.html

    This is all well integrated into German forecasts: in a eye-opening document from the wind specialist Paul-Frederik Bach (http://www.pfbach.dk/) shows that the German authorities (on top of that the BMU, the ministry that deals with that kind of questions and commissions the technical bodies into heavy weighted reports) clearly have in mind this problem.

    Whatever the installed capacity of renewable in the future, they expect to cover 100% of the peak electricity demand with fossil fuels power plants.

    The conclusion is a simple rule for anyone interested into balancing the grid: don’t expect renewable power plant capacity to cover any of the demand. Sobering thought.

    http://www.pfbach.dk/firma_pfb/german_national_grid_plan_next_year_2011.pdf

  8. I agree that wind and solar can not be totally relied on and other forms of energy generation are required.

    Two things that are not mentioned above are:

    1.
    Reducing demand.
    Our demand is increasing despite energy efficiency, I am sure much more could be done with regards to that, which will help a little bit but (I know it is but still more to be done).
    I see the French light pollution law is expected to save 250,000 tonnes of C02 a year or enough energy to power 750,000 French households for a year. If every country did similar things we could see a significant reduction in demand. I remember when street lights in the UK went out at midnight – I am sure some could still be switched off every night. There is one heck of a lot left switched on all day and night in almost every work place I have visited.
    However, even if demand is reduced through energy efficiency, we shall probably still require power from sources such as gas.

    2.
    Type of gas.
    Many are opposed to new gas plants using fossil fuel gas but how about gas produced from organic wastes such as livestock manure, food processing waste, sewage etc? Almost carbon neutral.
    I am often amazed how little this is exploited.

    3.
    Micro generation.
    Many properties, especially new ones could be constructed with energy generation in mind (as well as efficiency).
    My brother (engineer) lived in a remote cottage (for 3 or 4 years) which was not connected to the grid. He constructed his own wind turbine and solar panels. For much of the year he was able to power most normal house hold appliances as usual or with carful consideration to available supply. He did have a series of heavy duty batteries as back up and he had to carefully monitor the energy usage.
    There were occasional times when there was high pressure and fog resulting in no or very little power and that is where other forms of energy generation would have been required
    My brother became very much more aware of his energy consumption, the inconvenience caused when he was low or out of power but noticed the massive saving on electricity bills.
    The cottage was in a fortunate location as it was exposed to sun and wind and NOT all properties have such astonishing potential.

    But I am using the above only as an example of how I think many homes, business and even local authorities could produce more of their own power from renewables and energy efficiency – I’m certainly not suggesting all should or could do as he did!

    Bio-fuels – have their problems, they could play a very small part but are unlikely to to meet the requirements without significant damage.

    Nuclear – Looks like there are quite a number of problems there.
    – Centrica withdrawing from the UK’s nuclear re-building programme because of increasing costs and delays.
    - The cost of cleaning up the Sellafield nuclear waste site, http://www.bbc.co.uk/news/uk-england-cumbria-21298117
    - Plans for the £12bn underground nuclear waste store in Cumbria have been rejected.
    Is nuclear a realistic long term answer?
    Robert, you have probably done all the sums on this:
    So, I ask how much CO2 is produced and energy used in uranium mining (transportation…..), nuclear waste disposal and storage and then maintenance and decommissioning?
    Then there are the concerns or objections that some would have (justified or not) towards nuclear power.
    If nuclear is considered an realistic option – how long will it take to become fully operational, considering governments aims to reduce CO2?

    So to summarise, we could probably cut our dependence on fossil fuels significantly and as a result reduce greenhouse gas emissions massively (but not totally).

      1. OK,

        I posted my comment as the points I made appeared not to have been considered in your original blog and are issues of genuine debate.

        From what I see, with well backed up data, you just consider wind & solar V nuclear or fossil fuels.

        I shall follow but comment no more.

      2. Chris

        My comment was related to your question about the emissions of nuclear power. That information is easily available online. No problems with the rest of the comment. But

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