Specific Energy Production II – Wind and Solar PV

In one of my previous posts I took a closer look at the specific energy production of both nuclear and hydroelectric energy. We saw that there are significant differences between the two.

In the recent past other energy sources have continuously gained ground against them. In particular, wind and solar PV are considered to be production modes of the future, and maybe one day they may be the backbone of our energy-hungry society. However, for the time being, we are still far from this point. One of the reasons is that both of these renewable energy sources do not provide the necessary stability which is cruciall for running the power grid of a post-modern information society.

Now let us look into the details. First we consider wind energy which has seen breathtaking growth rates in terms of installed capacity. However, installed capacity is not the last word when is comes to the actual performance of a particular production mode. Fig. 1 shows the average figures for wind energy for the period 1996 to 2010.

Fig. 1  Sspecific energy production in MWh/MW inststalled for some selected countries.

Fig. 1 Sspecific energy production in MWh/MW installed for some selected countries.

Germany, one of the countries with the largest installed capacity, is doing significantly worse than the other countries shown in the picture. Overall we observe that  the specific production figures are well below the ones we calculated for hydroelectric energy (Specific Energy Production – Nuclear and Hydro).

Fig. 2 provides the same data for some countries which recently have done a lot of effort to promote the use of solar PV. Again, Germany is the performing worse than its competitors which in this case does not come as a surprise since sunshine hours are much more abundant in Spain and Italy. The data represent average values for the period 1990 – 2010.

Fig. 2  Specific energy production for solar PV

Fig. 2 Specific energy production for solar PV

Solar PV is no match for wind in terms of specific output. To produce the same amount of energy in MWh one has to install a much larger capacity of solar PV than wind mills, since the former ones have an average specific output corresponding to only 54% of wind energy plants.

Similarly, the specific output of wind mills is equivalent to roughly 58% of the one for hydroelectric plants. Quite astonishingly, a similar relationship exists between hydro and nuclear with the specific output of hydro corresponding to about 50% of the one for nuclear plants.

In a nutshell, in order to obtain the same production figures as nuclear power installations one needs to install almost seven times as much capacity of solar PV and more then three times as much capacity of wind generating power.

 

Germany´s Energy Future – part 2

One year ago Germany decided to quit producing nuclear energy by 2022. Since nuclear power plants are a central pillar the German energy mix, contributing some 22.5% to the entire electricity output in 2010, this means that until 2022 the equivalent of 140.6 TWh (2010) has to be replaced by other sources. This is a minimum estimate ignoring increase in consumption.

Already at this moment Germany begins to face the consequences of last year’s decision. As nuclear plants are successively being phased out, more strain is put on other sources, in particular renewables. In addition, the power grid is experiencing severe tensions as more controllable sources of energy are being replaced by less controllable (and predictable) ones. Especially the latter is a constant, or rather growing source of trouble.

One the one hand, it’s a clear goal of German policy to increase the share of renewables substantially. On the other hand, it seems implausible to be able to replace the entire nuclear bloc by wind and solar capacities only. Thus, it appears inevitable to commission a number of conventional, i.e. thermal power plants which are supposed to act as a backup for the fluctuating input from e.g. wind farms.

In my view, it is pretty obvious that wind will be the main source of renewable energy in the future, considerably outnumbering all other renewable sources taken together.

In 2010 the total capacity of German wind farms amounted to some 27190 MW which produced some 36.5 TWh. Taking into account the average specific output of wind farms as calculated in one of our previous postings we may estimate the extra capacity needed in order to fill the gap. Then we could show that the average output of wind power installations amounts to some 1600 MWh annually per MW of installed capacity.

Having these figures at hand we may easily estimate how much extra wind capacity is needed in order to replace nuclear in its entirety. Thus if wind power is supposed to be the only substitute (which is certainly an oversimplified approach) it would mean that Germany needed almost 88000 MW of additional wind power by 2022, thus an extra three times as much as was installed up till 2010. This in turn would mean that the country needed more than 115000 MW in wind turbines by the time the last nuclear power station is decommissioned.

Between the year 2000 and 2010 an average of 2000 MW was commissioned annually, in total some 20000 MW of wind power. Extrapolating this trend to 2022 implies that some 24000 MW of new capacity could be added to the grid until D-day. However, what is needed is almost four times as much. Thus the annual growth rate should be close to 7800 MW. Even if we assume that wind will only replace half of the nuclear output, a growth rate of about 4000 MW annually would be necessary, i.e. twice as much as has been the case during the boom period 2000-2010.

The figure below shows two different scenarios for Germany´s wind power capacity. The business-as-usual scenario (BAU) is based on the assumption that wind capacity will grow at a rate of 1900 MW per year, which is equivalent to the increase in 2010. The Target scenario on the other hand assumes an annual growth of 7800 MW which would theoretically be sufficient to replace Germany´s entire nuclear production as seen in 2010.

Total installed wind power in Germany.

Given that there is considerable resistance among the population against onshore wind farms, it is indeed hard to see how this can be achieved. In addition, as  subsidies for renewable energies are becoming a serious burden for consumers, they are likely to be reduced in the future. This in turn may jeopardize further investment in wind power, and thus even the more conservative BAU scenario may, in fact, be too optimistic. As a consequence, other energy sources are desperately needed if Germany wants to maintain her standard of living. We will come back on this issue in another posting.

Wind Energy – The European Top Producers

Most European countries are now investing into wind energy. Only very few of them may be considered as “old” players in the field. Among those which used wind power already back in 1990 were Spain, Denmark, the Netherlands, Belgium and Sweden.

Unfortunately, the data quality of some countries in the beginning stages was rather low so that we confine ourselves to comparing the average output in MWh/MW installed over the period 2000-2010. Taking this as a reference we get the following ranking among those countries which have a relatively long tradition of using wind energy:

Netherlands 2273 MWh/MW (low: 2077 high: 2473)

Spain 2233 MWh/MW (low: 1921 high: 2621)

Sweden 2080 MWh/MW (low: 1784 high: 2625)

Denmark 2028 MWh/MW (low: 1760 high: 2293)

Belgium 1929 MWh/MW (low: 1022 high: 2750)

Germany 1586 MWh/MW (low: 1392 high: 1785)

As indicated these are average values over the first decade of the 21st century. Needless to say that these mean values are rather virtual figures since in reality the availability of the driving force behind the facilities, i.e. the wind, is rather varying by nature. By the way, these figures have been calculated using our specific model which enables us to smooth out distortions due to capacity changes during each year.

The graphics below shows the evolution of wind power in those countries since 1990. The missing data points for some countries refer to the fact that the quality of those data does not fulfil our standards. Thus, we omitted them rather than doing guesswork.

Specific output of European wind farms in MWh per MW installed capacity.

It is quite remarkable that the mean performance between different countries can vary a lot. The most striking feature, however, is that Germany is seriously underperforming when compared to the leading producers in Europe. This may well indicate that selecting the location of a wind farm may not always have been the best choice. Other countries have apparently done a better job.

Wind Energy – The Case of Denmark

Denmark is one of the leading producers of wind energy in the world. This is true not in absolute, but in relative terms. Being a small country Denmark simply does not have the capacity to compete with larger countries such as Spain or Germany when it comes to total output. The share of wind power in the electricity grid was 20.1 % in 2010. Portugal and Spain, the numbers two and three in the ranking, had shares of 17.0 and 14.6 %, respectively.

In a previous post we examined the specific performance of German wind farms. Now we will compare those findings with a similar investigation for Denmark. Fig. 1 shows the specific output of Danish wind energy in MWh/MW between 1990 and 2010. As usual we have applied our model to smooth out distortions caused by the building up of new capacity over a year. The remaining fluctuations are due to varying wind availability.

Fig. 1 Specific output of Danish wind farms in MWh/MW installed.

Fig. 2 gives a direct comparison between Germany and Denmark for the period 2001 till 2010. One striking feature of this picure is that Danish performance is consistently and considerably higher than the German one. On the averge, Danish facilities have an almost 29 % higher output in MWh/MW installed. Thus, their efficiency and productivity are much better than the ones of their southern neighbour.

Fig. 2 Specific output of wind farms in Germany and Denmark.

The average performance of German facilities was 1571 MWh/MW whereas Danish wind farms produced some 2026 MWh per MW installed. One of the reasons for this discrepancy may lie in the fact that Denmark has a higher share of offshore wind farms which tend to have a higher efficiency than the ones based on land.

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.