How does Denmark handle wind energy? It exports it

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Denmark is frequently held up as a country that shows how you can get to high levels of wind energy. From a simple factual point of view some things are rather clear.

Last year Denmark produced 39% of its electricity from wind turbines. This is much more than any other country. And four times more than Germany or Britain.

Yet, this high level of penetration is enabled by Denmark’s unique position. The uninformed claim once made in the Guardian that “the intermittency issue is easily dealt with as, for example, demonstrated by Denmark” is simply not true.

Consider the times when Danish wind farms produce more than 100% of its electricity demand. Electricity cannot be stored, at least not on a large scale. So, on these occasions Denmark simply has to export the excess to its neighbours. This option is not available to most countries. Furthermore, getting even close to 100% is currently technically unfeasible except in rare countries such as Denmark.

Wind turbines do not provide what is called inertia to an electricity grid. As a result grid operators think they will have to restrict wind power to somewhere between 60 and 75% of instantaneous demand. Any excess above this limit will have to be shed. As a result, in most countries getting to 40% wind energy would result in a large amount of the energy produced by wind farms being curtailed and thus not used. (The issue is discussed in this recent paper about the Irish grid.)

So, how does Denmark do it?

It’s simple. They are interconnected like crazy. A simple comparison with Britain is revealing

Average electricity demand in Britain is roughly 40 GW, while it is around 4 GW in Denmark. A difference of a factor of, then, in electricity consumption.

Yet, Denmark actually has more interconnectors than Britain. Denmark has around 6 GW compared with Britain with less than 4 GW.

So, if it’s windy in Denmark all they do is export the stuff on a large scale to their neighbours. They don’t need to worry about excessive wind production. But everyone else does.

Britain, for example, would need to build 40 GW of interconnectors to be interconnected like Denmark. So, don’t listen to people who tell you Denmark shows that the problems of intermittency are “easily dealt with”.

And here is some actual data showing just how much of Denmark’s wind power is exported. Using data for 2012, the graph below compares hourly wind generation with net exports. The relationship is clear (the blue curve is a simple regression). More wind generation equals more exports.


Similarly, we can compare hourly wind farm output with actual load. Below I show hourly wind farm output versus how much of the load is met by wind farms. As you can see this frequently gets close to or exceeds 100%. This is not an option for most countries. In fact, the dots you see above 60 or 75% or so are currently not technically feasible outside Denmark.wind_load

So, there you go. Denmark is an excellent example of a country that has been able to massively expand wind energy. It is also an example that cannot be copied by many.


6 thoughts on “How does Denmark handle wind energy? It exports it

    peter2108 said:
    March 10, 2015 at 5:24 pm

    I don’t know what percentage of wind power the UK is aiming for – about 30% I believe. Do you know of any other reason in favour of this apart from reduced CO2 emissions?

    The Danes have the most expensive electricity in the EU because they sell their excess to the Norwegians who can use it for pumped storage – and when the wind fails they can buy it back. They sell cheap and buy dear, it seems, and maybe this is why their power is so expensive?


      Robert Wilson said:
      March 10, 2015 at 5:27 pm

      I like to keep things on topic, so I’m not getting into a debate on the reasons for Britain expanding wind power.


    Proteos said:
    March 10, 2015 at 8:29 pm

    Another useful comparison would be with large european cities like (Greater) London and Paris (Île de France). It may sound rather crazy at first, but Denmark is inhabited by 5.6M people. London and Paris are above 10M.

    Yet Paris (and the surrounding Île de France) produce very little of the electricity it consumes (less than 20%). The logical conclusion is that it’s all imported from elsewhere in France and that Paris has numerous HV lines connecting it to the rest of the country (which is readily visible).

    I bet that London is not that different from Paris in this particular domain: most of the electricity comes from outside the Greater London.

    In essence, Denmark could just stop producing electricity and import everything from its neighbors, just like Paris and London. It would then emit zero CO2 from electricity. Alternatively, it could keep its wind turbines.

    The trick indeed disappears when you look at greater scales: large countries such France or Germany can not be as interconnected as Denmark or Belgium, in part because the ratio border length/area is probably smaller, in part because of their sheer size.


      Robert Wilson said:
      March 10, 2015 at 8:45 pm


      That’s actually the comparison Vaclav Smil has made when it comes to how Denmark manages wind power. He has referred to it as being “just a big European city”.

      Denmark could probably shut down all of its non-intermittent generation and get by. And have “zero carbon” electricity.

      This kind of bullshit accounting is popular. WWF recent published a report explaining how Scotland could become “fossil fuel free” by 2030. Basically, if the wind is not blowing fossil fuel electricity is imported from England.


    Jamie said:
    March 11, 2015 at 11:21 am

    “As a result grid operators think they will have to restrict wind power to somewhere between 60 and 75% of instantaneous demand.”

    If I read this right, the implication of this constraint is that the maximum wind capacity would effectively be limited to between 60% and 75% of lowest demand, say 4 or 5 am. Is that correct?

    That being the case, if a country wishes to maximise wind deployment and minimise curtailment, in addition to increasing interconnector capacity it could also adopt a strategy of increasing demand which would otherwise be satisfied at other times (e.g. electric vehicles) or using other fuels (e.g. remote control immersion heaters).


    jmdesp said:
    March 13, 2015 at 5:25 pm

    The situation of Spain / Portugal is much more relevant because they don’t have much interconnection with the rest of the world, and they have also a very high wind percentage, both of them.
    The solution they’ve found is a centralized Control centre for renewable energies (CECRE), that regulates the wind production, and can request curtailment when needed.


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