Archive for June, 2011

Wind Power

June 30, 2011

As about everywhere else, there is also a strong pro and contra debate going on in Luxembourg concerning wind turbines. The Greens put all their energy eggs into the wind and solar basket, so they can’t readily accept any criticism. My personal opinion is that a reasonable and intelligent use of wind power should be a welcome contribution to the energy mix.  But one should never forget the real production data, which are now available for many wind parks. These tell quite a different story than the usual green hype. I think that the visual aspect on the landscape never has been incorporated as a cost; depending on your sensibility and love of pristine nature, these costs could be extremely high.

I wrote a short paper with real numbers (in French:  Réflexions sur les éoliennes, pdf ).  I heavily used Eirgrid’s excellent website which holds a treasure of production and ancillary data. Ireland makes a  good object for research into real wind power. The country has about 1425 MW wind power installed, and is geographically well delimited and wind friendly.

The most important factor in wind energy generation is the capacity factor, i.e. the percentage of the yearly power produced in respect to the installed power. For Ireland this is about 23% in 2010, a shocking low number for a country with such good wind conditions. More disturbing is the negative trend in this country wide capacity factor: (picture from Eirgrid, red arrow added)

I have calculated the linear trend since 2002:  every year this factor falls by about 0.93  (slope of the regression line). Most certainly this negative trend is caused by lower wind velocities ( in the adequate range for wind turbines).  These numbers are not good news for the wind energy industry. Now 9 years do not yet define a climate change, and one really has to wait if this trend continues, reverses or shows up as part of a cycle. It will be interesting to look up other wind producing nations for a similar trend.


Update 01-Nov-2011:

There is a growing opposition to plans to install a great number of wind-turbines in the french speaking part of Belgium (Wallonny). Read here the open letter of Dr. Alain Marchandise. The home page of the organization “Vent de Raison” is here.


Update 07-Nov-2011:

There is a discussion in NatureNews on the diminishing wind velocities over much parts of the globe: Why winds are slowing and also an article from AWS True Power questioning the results of the Nature paper by Vautard et al.

The report for the second quarter Q2 of 2011 documents below normal wind velocities in many parts of Europe.


Update 15-Dec-2011:

Here a graph from the BDEW with my comments, showing yet another example of diminishing capacity factors during the last years. For Germany this would by a hefty -3.8% per year.

A similar negative trend can be found for 4 Luxembourg wind parks; these are unofficial approximate numbers, taken from graphs, so I will keep the sites anonymous (numbers are percent)

Site     2009    2010   2011 (up to Nov.)

site1     18        16         16
site2     19        17         17
site3     12        10        11   (outch!!!)
site4     14       13         12

These numbers show a grim picture of the efficiency of that green energy which should save the world!


added 29 Mar 2012:

see some burning wind turbines here!

Sunshine duration from pyranometer readings

June 4, 2011


I just finished yesterday a short paper comparing 7 different methods to derive sunshine duration from pyranometer measurements. This is a very old problem, for which there exist many potential solutions; these all are usually heavily localized, i.e. they contain parameters valid only for a certain region. MeteoLCD uses since many years a very simple method developed by Jean Oliviéri, a now retired scientist who worked at MeteoFrance’s  Centre de Radiométrie de Carpentras. I compared his method with 6 others using 11 years data from meteoLCD.  I also used the 11 years monthly reports from the national meteorological station of the Findel airport; they used and still use the Campbell-Stokes sunshine recorder( pictured above,  source =

As a “reference” algorithm I took one published in 2006 by Hinssen & Knap from the Durch KNMI; these researchers made simultaneous measurements with a pyrheliometer (which measures direct solar irradiance) and a pyranometer (which measures global = direct + diffuse + reflected irradiances). The WMO definition from 2003 states that sun does shine if the direct irrandiance is at least 120 Wm-2, so a sun-tracking pyrheliometer is the proper instrument to use. As it is a rather expensive gadget, you won’t find many at “ordinary” weatherstations. This makes the existence of pyranometer-readings  based algorithms so useful, even if sunshine duration, which was formerly one of the essential weather parameters to know has lost much of its importance. Campbell-Stokes recorders are notorious for overestimation sunshine duration, something which we see every year at Diekirch, and which the paper also  points too. As they are manually operated, they tend to disappear completely in a time where most weather stations are working automatically.

The conclusions from the paper confirm that Oliviéri’s method “beats them all”, which will be quite a satisfaction for the inventor (and for meteoLCD which long times ago made the correct choice!).

The full text of the paper can be found here (PDF).