Archive for September, 2013

Decline in wind power: the slump in capacity factors.

September 20, 2013

In the preceeding comment I showed using the IWES report that the decadal decline in potential wind power was about 14% per decade during the 1992-2012 time period in Germany (coastal and land locations). Such an important decline of the available wind resource should be show up in the electricity produced by the wind turbines. The easiest metric to use is the capacity factor (CF) or the equivalent parameter “Volllaststunden”. (VLh) prefered in German reports. The relation between both parameters is  CF = VLh/8760.

1. The ThinkAero data

It is not easy to find reliable data,so I will start with the data found at the ThinkAero blog. Here we have a table which gives the average VLh of all German wind turbines and also those located in the Land Baden-Würtemberg.

Volllaststunden_BRD_2004_2011The upper red data points represent the German average, the lower blue squares the numbers for in-land Baden-Würtemberg. Trend lines have been computed with Excel. Clearly both groups show declining VLh’s (or CF’s).

As in the previous comment, we clearly find that the year 2007 was an exceptional good one, both for the whole country as well as for Baden-Würtemberg.

For the whole country, the decline given by the trend line would be 62.5 hours per decade, or about -4%/decade (percentages calculated w.r. to the trend line).  The same calculation made for Baden-Würtemberg gives -181 hours per decade or -14.8%/decade.

The situation in Baden-Würtemberg becomes dramatic during the last 4 years 2008 to 2011:


Here we see a decline of -32% during that short period. Needless to say that such a slump will make all economic predictions a laughing-stock!

2. The BMU data

The website of the BMU (Bundesministerium f. Umwelt…) has a data table with values from 2000 to 2012. To be able to compare to the ThinkAero data let us just use the results from 2004 to 2012:

Volllaststunden_BMU_2004_2012The trend line gives a decadal decline of -4.6%.

If we use the ThinkAero data and add the BMU value of 1530 for the year 2012, the same calculation gives a decadal decline of -3.5%, close to the BMU result.

3. The BWE data

The Bundesverband WindEnergie gives a table with the “Windjahr” percents (actually these are anomalies of probably the wind resource (not the produced wind electricity) over an unspecified period, probably a decade):

Here again we find a decline of -12.2% per decade (computed from the trend line), a number close to those found in the preceding comment. And as is the case for Baden-Würtemberg, the last 4 years are especially worrying.

3. Conclusions

1. Both the wind resource data and the capacity factor (or Volllaststunden) data show a (long-term) decline

The 2 series we have studied give the following decadal declines in percent for the period 2004 to 2012:

ThinkAero (Volllaststunden): – 3.5%
BMU (Volllaststunden) :           – 4.5%
The declines in wind resource given by the IWES report (preceeding comment) and by the BWE are comparable (-14% and -12.2%)

2. Especially instructive is the comment given in “Energiewirtschaftliche Tagesfragen” from September 2013: “Bisher ist ein Trend zu steigenden VLS trotz stetiger technischer Weiterentwicklung durch Serienproduktion und rapide gestiegene Anlagenkapazitäten und Nabenhöhen nicht erkennbar.”

Approximate translation: “Up until now a rising trend in CF’s can not be detected, despite technical progress and fast rising power capacities and wind turbine heights”.

It would be more correct to acknowledge that an uncomfortable declining trend  is clearly detectable!

The dramatic decline in available wind power

September 19, 2013

In two previous comments (here and here) I wrote about declining wind power and declining capacity factors of installed wind turbines in Europe and especially in Germany and Ireland. The German Fraunhofer “Institut für Windenenergie und Energiesystemtechnik IWES” has published a very interesting report “Windenergie Report Deutschland 2012” which I recommend for reading to everyone interested in wind energy, be he a 100% fan or a more skeptic individual. Sure, the IWES must be on the side of the wind power pushers, but this report has serious scientific reflections and, if you read it carefully, they do not refrain to put the finger on spots that hurt (click here for an English version).


I intend to write a couple of comments on this report; this first one will exclusively document the dramatic decline in available wind power over Europe during the last 21 years.

1. The potential wind velocities over Europe.


This picture taking from a EEA report shows the mean wind speed over sea and land (I do not know if this a an average over a certain period neither at what height above ground it is measured, so let us take it simply as a rough indicator). Wind power in W/m2 is proportional to the cube of wind speed and to the air density (P = 1/2*density*speed**3), so to convert to W/m2 multiply the cube by 1.25 as the density of air is about 2.5). This gives approx. 1.25*1000 = 1250 W/m2 for offshore locations , and this number must be approximately divided by 3. The main unsurprising result is that offshore potential is much higher that onshore. Onshore potential at 5 m/s is only  5**3/10**3 = 0.5**3 = 1/8 of offshore potential.

2. The year 2012 with respect to the long time mean over 20 years


This picture from the report clearly shows that at most locations the 2012 wind potential is considerably lower than the 20 year mean: onshore locations in Germany are about 20% lower than this mean. The blue color describing lower potential is dominant if we neglect the offshore locations at great distances from shorelines.

3. The trend over 21 years for German locations.

The IWES report has another figure, that documents the real dramatic decline for various German wind power locations. I have digitized the curves relative to the coastal (“Küste”) and northern plain regions (“Norddeutsche Tiefebene”) using the wonderful UNSCAN-IT software, and calculated the linear trends:

Winddargebot_1992_2012_annotatedThis figure (modified fig.34 of the report) shows an eye-opening decline from 1992 to 2012, with the 2007 peak being a real exception. The trend lines have approximately the same slopes: at coastal and plain locations, potential wind power decreased by ~100 W/m2 (-29%), which gives a decrease of roughly 14% per decade (percentages calculated w.r. to the start point of the trend line) !
This is a very worrying trend for wind power, and one wonders why this trend is mostly ignored in the media and political discussions. The extreme increase in yearly added wind turbines masks this decline of the available resource. But if the installation of new turbines comes to a halt due to saturation, the negative trend (if it continues…) could well spell disaster for wind energy production and investors.

PS: The ZHAO et al. paper I referred to in a previous post finds a decline of  -2.9% for wind velocity per decade (from 1978 to 2008). This results in approx. -24%/3 = -8% per decade in wind power (the divisor 3 represents very roughly the usual efficiency of wind turbines).


IWES: Windenergie Report Deutschland 2012. (link)

MASSEN F., 2013:  Bad wind, lower wind power, exploding costs. (link)

MASSEN F,. 2011:  Wind Power (link)

MASSEN F., 2011:  Réflexions sur les éoliennes (link)

ZHAO et al: Is Global Strong Wind declining? Advances in Climate Change, 2011.