Wind Energy in Germany

Here are some brief considerations about the performance of German wind energy facilities. Over the past two decades the number of wind turbines installed in Germany has increased dramatically. The surge in capacity amounted to 350 % between 2000 and 2010. The growing capacity lead in turn to a growing production of electricity, 300 % up over the same period.

One question of particular interest to us was how much energy one might expect to be generated per MW installed on average. As the production of this kind of energy is highly sensitive to the availability of wind we were seeking for a model which is able to reflect the variations of the latter. The source data for our investigation were taken from both Eurostat and Bundesverband WindEnergie, the German association of wind energy producers.

We started by looking at the amount of energy produced per installed capacity (Prod/cap) measured in MWh/MW between 2001 and 2010. We may call this quantity the specific production. The result is the blue curve in the figure below showing a clearly increasing trend. It must be noted here that this graph needs to be interpreted with special care, since it is distorted by two major sources of uncertainty. The first source is the varying wind availability. The second source of uncertainty is based on the fact that the number of wind mills is constantly growing over the year as more and more turbines are constructed. The total installed capacity may go up by some 30 % and more during the course of a year. Some of the newly built turbines may take up operation in spring and others may be commissioned towards the end of the year. In each case their contribution to the entire production will be very different. Thus our model has to account for the extra capacity erected during one particular year.

Another factor coming into play is the location of the turbines. Although each of them is supposedly optimized in terms of output, there may be significant differences between various wind farms. However, as more and more turbines come into existence, the influence of individual outliers should diminish compared to the total average. We always have the big picture in mind, thus neglecting the performance of particular locations.

In theory, the specific production should exactly correspond to the amount of wind available. The latter quantitiy is represented by the red curve as a percentage over the long-term average (r.h.s. scale). As can be seen, the variations may be tremendous.

Production of wind energy in MWh/MW(installed) and comparision with wind availability.

We note that the red and the blue curve do not coincide as expected. This lack of coincidence is mainly caused by the addition of extra capacity which, in relative terms, was very large during the first part of the period in question (44 % and 37 % in 2001 and 2002, respectively, compared to the previous year).

In order to find a better agreement between the wind availablity curve and the specific production we developed a statistical model which enabled us to eliminate the distortions caused by the newly built wind mills. The result of our model calculations is shown in the green curve which nicely matches with the availability curve (red). What we got is a new quantity Prod/cap* which allows us to draw meaningful conclusions about the mean productivity of each MW of installed capacity.

Depending on the availability of wind Prod/cap* may vary considerably. At a value of 100 % availability each MW installed should produce slightly more than 1700 MWh annually. During our reference period Prod/cap* varied between a maximum of 1800 MWh and a minimum of 1250 MWh. This is a massive variation which must be taken into account when considering the energy supply stemming from wind farms.

Renewables in Europe 3: Wind Power

In some European countries wind power is contributing significantly to the energy mix. At EU level, wind is the second largest source of renewable energy after hydro. Since its early stages in the 1990s the development of wind-generated electricity can only be described as breathtaking. In 2010 the biggest producers were Spain (44,165 GWh) and Germany (37,793 GWh), followed by UK (10,183 GWh) and France (9,969 GWh). All data for this brief analysis covering the period from 1990 to 2010 have been taken from Eurostat.

To get a feeling for the tremendous growth of the sector we may note that at EU level wind power has soared by a whopping 537,000 % during the past two decades, delivering some 149,000 GWh in 2010. The result of this incredible surge is that in some countries like Germany, Spain, and Denmark wind can no longer be considered a negligible contributor to the energy grid.

Fig. 1 gives an overview of the annual changes of power produced from windmills during the period in question.

Fig. 1 Wind power generation in selected countries, relative change compared to previous year

One stiking feature of this graphic is that the changes may also be negative, indicating that in the year n less energy has been produced than in n-1. This may happen as the amount of wind is fluctuating over the years. However, the negative growth rates are generally quite small, because new capacities are added every year. Moreover, with growing capacities in various areas the influence of prevailing calm tends to get weaker.

The other noteworthy issue is that the growths rates are slowly getting smaller. This is not surprising as the countries in our selection have already sizeable quantities of wind mills operating and the extra capacities added are small compared to the existing ones.

Fig. 2 gives an overview over the indexed production of wind-generated electricity with 1990 = 100.

Fig. 2 Wind power generation in some EU countries, 1990=100.

The picture gives a vivid impression of the potential of this source of renewable energy. Although Spain and Germany are the top producers of wind energy, the top performers are Portugal and Italy. It may be noted that the countries selected are significantly outperforming the EU average. The reason is that in some Member States like Poland (1700 GWh), Bulgaria (680 GWh), Romania (310 GWh), and the Baltic states (550 GWh in total) wind power is still in its infancy stage, contributing very little, both in absolute and relative terms, to primary energy production. That may, however, be expected to change in the future. In Malta and Slovenia wind-generated electricity is virtually non-existing.

In spite of being an ever growing contributor to the energy grid wind power faces some intrinsic weaknesses which, paradoxically, tend to become more serious the bigger its contribution becomes. The main source of concern is the fluctuating availability of wind in the atmosphere. This, in turn, leads to fluctuations in the energy supply which put additional strain on the entire grid. Conventional power plants have to be kept in reserve in order to counterbalance the variable inflow from wind energy. This is one of the most pressing challenges to be tackled in the near future, if wind power is to be not only a significant but also a stable  and reliable player in the whole energy mix.