(Over)blowing in the wind


How can one not like free wind energy? It looks that simple. The wind is plentiful and blows free for everybody. Many green minded people naively believe the idea. Also I previously assumed that when the rotors of a wind mill were turning they were saving energy, because the electricity they produced shouldn’t be produced anymore by a fossil fuel power plant somewhere else. Boy was I wrong!

An example

When looking at the page of the C-Power I found the following statement concerning the first Belgian offshore wind farm:

The capacity of the completed wind farm will be 325.2 MW, enough to provide power to 600,000 inhabitants

This is not an isolated case of reporting it this way. Every time for example the mainstream media reports on wind energy, this kind of statement is given. Sometimes they give it in number of people or in “households” or “homes” that supposedly benefit from the windmill(s).

It is a nice statement on its own, but when digging deeper things don’t seem to add up well. Let’s see about this in more detail. They give more detailed information about this farm on another page on their website:

The wind farm consists of 54 turbines with an installed capacity of 325.2 MW

According to calculations by C-Power, based on over 1.2 million historic wind measurements on the coast since 1986, the wind turbines will run for 8,440 hours per year, being 96% of the time.
The equivalent number of hours when the wind turbines are running at full power (equivalent full load hours) has been calculated to be approximately 3,300hrs/year.

That’s 38% of the time, which is a normal figure for offshore turbines.

Digging deeper

This gives me the information to reconstruct the calculation of the statement. Just a quick calculation. The 54 turbines are erected in three phases and with two different capacities.

Phase Number Capacity (MW) Total capacity MWh
I 6 5 30 99,000
II – III 48 6.15 295.2 974,160
Total 1,073,160

In kWh this will be per person per year: 1,073,160,000 kWh / 600,000 = 1,788.6 kWh. That is a plausible average number in Belgium, so at first glance the statement seems to hold very well.

So, what is the problem then? They will produce 1 TWh in a year (what C-Power acknowledges) and this will be equivalent to the yearly use of about 600,000 people (what the Thornton bank-site said and what the calculation seems to confirm). Yes, that’s all true in theory, but in practice it is a completely different story.

The power produced by these windmills will obviously not really go to a group of 600,000 people. There are no power lines from the farm to their houses. The reality is that the power will be put on the national grid and such an amount of electricity can be used by around 600,000 people with an average power consumption of 1,788 kWh per year. This is a very important difference. The first statement seems to imply that the output of these turbines can fully satisfy the power needs of those 600,000 people. It is not.

If this really was the case, they would have:

  • complete blackouts during the equivalent of 4% of the time (about 15 days per year)
  • a varying amount of power during an equivalent of 96% of the time (about 350 days per year)

Unless they get their power also from other sources.

Indeed, this power is not produced constantly. According to the specifications of the turbines, below the wind speed of 3.5 m/s the turbine doesn’t produce anything. The same above 30 m/s averaged over 10 minutes or 35 m/s peak.
Below about 14 m/s the turbine produces only a part of the installed capacity.

The company estimated the working time of the turbine to 96% according to their wind measurements. But this doesn’t take into account the time the turbine stands still because of defects or maintenance. So those figures are again too rosy. The nice 39% load factor is only for brand new turbines, but according to data of the offshore wind farms in Denmark, the load factor declines over time (in case of Denmark from 45% to less than 15% at 10 years of age). That is 1/3 of the initial value left! There are several reasons for this. There is the wear and tear of the turbines and the blades in the humid, salty sea air. But also the turbines experience more breakdowns, need more maintenance and will take longer to put back on line. If the Denmark data is correct, the capacity could decline to one third after 10 years, which means the farm will only cater for “about 200,000 people” anymore.

Wind energy is intermittent. It is not very suitable for power production which needs a reliable output. Power consumption has a certain pattern over a day, but power generation follows the pattern of the wind and is not necessarily in accordance with actual power consumption. If we really want to rely on wind energy, we will need a backup generator that fills in when necessary, which means such a fast reacting generator will turn mostly at suboptimal speed and use more resources than when running at optimal speed.

This is the little dirty secret of wind energy: when we want to rely on wind energy as a constant power source, we need backup plants that run at a fraction of optimal capacity than when it would be if the wind farm was not there. Or put it in another way: even when wind turbines are working optimal, the backup system is still on stand by AND uses (fossil fuel) resources.

What did I learn?

My previous assumption that windmills were saving us fossil fuel seems to be unwarranted. This assumption was fed by waves of smooth stories from which one side is completely omitted, as the one above. Although the installed capacity of the generators and the wind data (the nice data) were correctly brought, the data of the maintenance, capacity decline and backup needs (the inconvenient data) were completely ignored. When adding this information, it paints a completely different picture than the theoretically capacity story.

An argument that omits relevant evidence appears stronger than it is. No wonder this inconvenient side of the story is hardly been told. No wonder the public at large still has false expectations about wind energy.


2 thoughts on “(Over)blowing in the wind

  1. eSell

    I’ve never seen the actual numbers on wind generation capacity/reliability before–haven’t looked. I think it might be a bit nit-picky to say that the wind turbines don’t really serve 600K houses, but only provide the electricity used, on average, by 600K households.

    That aside, I am disappointed at what appears to be the very steep decline in efficiency within a mere 10yrs. I’m hoping, therefore, that land-based windmills have far better reliability ratings. I’ve seen big huge wind farms in SoCal and up Montana/the Dakotas way and I’m hoping they’re not just a money pit.

    No, wind is not a reliable alternative source of energy–even in Oklahoma “where the wind comes sweeping down the plains”, but I would imagine that every bit of power provided by wind is that much less that fossil fuels are needed to produce. I have heard scattered reports, though, that the “carbon footprint” involved in making the windmills is so large that they’ll barely be able to nullify it through the production of green power. I haven’t looked into this much at all, so I don’t have any data other than some headlines I heard on TV news or some such…

    I am an American currently living in the Netherlands, which is a very Liberal-Progressive country, and one would imagine lots of windmills used here (Holland…Windmills…), but not that much. Partly it isn’t that windy, but partly it is b/c the Animal Rights people are up in arms about it–the windmills kill birds, or the ones out in the North Sea screw with dolphin brains (or something like that). So, everyone wants Electricity, but not Coal, Gas, Nuclear, Hydroelectric (dams destroy ecosystems), and now Wind is bad b/c it kills little birdies. That leaves Solar, but this is a very cloudy country so I don’t know how efficient that will be.

  2. trustyetverify Post author

    Thanks for your feedback, eSell.

    At first glance it seems indeed nit-picking, but I don’t think it is. Stating that a wind farm provides enough power for 600,000 people implies that the output of those mills fully satisfies those 600,000 people (meaning a conventional plant of that capacity could be closed of should not put into service). This is obviously not the case. The reality is that the power is put on the grid when wind blows (but then adds to the already surplus on top of the base load) or a conventional plant should cycle down a bit (but then the power plant will cycle more inefficiently and use more fuel per unit). We have a peak load shaver in Coo, but this installation has only a very limited capacity (maximum 4 hours until full).
    So, it is not because the rotors of a wind mill are turning, energy is necessarily being saved somewhere. I think their capacity and savings are largely overstated.

    All energy sources have their issues. If you wanna make an omelet, you gotta break some eggs. I think the best solution is a system with different energy sources. Especially here in Belgium. We don’t have natural energy resources anymore (except some hydro and some biomass), so we have to import almost everything. The Netherlands have at least some natural gas, I think.

    I have no problem with alternative energy, but I think wind mills and solar panels are not ready for prime time yet. Due to their intermittent properties they are not suited to produce a constant supply of energy in our current grid.


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