Electrical utilities all over the world are beginning to realize the need for reliable wind power predictions, as the penetration of electricity gener-ated by wind farms in the electrical grids is increasing. As the industry is approaching maturity, the market is shifting from heavily subsidised tech-nology demonstration plant to capital-driven shareholder value. From the description in the following sections it will become apparent, that in order for the wind power industry to survive in the future, new methods that facilitate the reliability of wind power are necessary.
1.1.1 Increasing penetration
Figure 1.1 shows the development in the penetration of electricity pro-duced by wind farms. The numbers shown are from Denmark. In 1999 the raw share of electricity from wind power is close to 9 %, for the nor-malized wind production values the share is more than 10 %. The values are from (Krohn 2000).
0 0,02 0,04 0,06 0,08 0,1 0,12
1980 1985 1990 1995 2000
Year
Share of Wind Energy
Figure 1.1: Share of electricity produced by wind energy in Denmark.
Rectangles correspond to values where the wind power production has been normalized to an average wind year.
If the exponential growth in the share seen in Figure1.1 continues, one could be lead to expect that all electricity will come from wind power after only a few years. This is not the case. It is important to note that the share value shown in the figure is not the same as savings in fossil fuels used by conventional power plants. This is illustrated in the following example.
An example – A storm coincides with low load
In PaperH the power production set-up in the Western part of Denmark is outlined. The power production set-up consists of 6 primary stations with a total capacity of 4.3 GW, a large number of local CHP (Combined
1.1 Background and motivation 3 Heat and Power) units with a total capacity of 1.4 GW and, finally, wind turbines with a total rated capacity of approximately 1 GW. The production from the local CHP units and the wind turbines is treated as priority production, which means that this production has to be accepted in the electrical grid. The annual variation in the load in the Western part of Denmark is in the range 1.2–3.7 GW.
From these numbers it is seen that if a storm coincides with a low load situation, then the wind turbines alone will be able to cover the demand, resulting in overproduction of power if the primary power plants are not shut down. This could be the case if the storm peaks during the night-hours where the load is particulary low. On the other hand, if the storm is predicted, actions can be taken in due time to e.g. shut down pri-mary power plants. As demonstrated by this example, wind power pre-dictions are necessary for optimal dispatch and scheduling of the total power production, and the importance of the predictions increases as the penetration from wind power increases.
In the worst case, this means that if the wind power is completely unpre-dictable, it will not save any fossil fuels at all. In principle there are three ways to prevent this. Accumulation of wind energy, e.g. using batteries, wind power predictions and/or spatial distribution of wind turbines. The first method is evident, but has not yet proved practically feasible, the second method is the subject of this thesis. Predictions can be used for creating an optimal combination of wind power production with other power sources, like hydro power and/or fossile fuel power plants. The final method is a feature of the atmosphere. More specifically, from the assumption that the wind always blows somewhere, distributing the wind turbines over a larger area stabilises the wind power production.
Germany, Spain and Denmark are the leading countries in Europe with regard to installed wind power capacity. In the beginning of 2001 the installed wind power capacity in Europe was close to 13000 MW, in Germany 6100 MW, in Spain 2400 MW and in Denmark 2300 MW.
This means that the three leading countries account for more than 83 % of the installed capacity in Europe. Only two other countries have wind power capacities that are in the same order of magnitude as the leading countries in Europe, these are USA with an installed capacity of 2500 MW and India with an installed capacity of 1200 MW.
The global installed capacity in the beginning of 2001 was 17700 MW, which means that the 5 countries mentioned above account for approxi-mately 82 % of the world wide installed wind power capacity.
1.1.2 Liberalization
The electricity sector is currently subject to liberalization, and as a con-sequence of this, a new structure is emerging. The sector is being divided into three independent groups, which are production, transmission and distribution.
The production companies are both the owners and operators of the con-ventional power plants and some of the wind farms. The transmission companies are the owners and operators of the high voltage transmis-sion network, and the distribution companies are responsible for the low voltage distribution network supplying the individual consumers.
In this set-up, when fully implemented, the dealings between the opera-tors will be based on short-term contracts, typically day to day contracts.
Any deviations from the reported demand or production will be subject to economic penalty. This means that operators with a considerable amount of wind power will be highly dependent on wind power predic-tions.
The same is the case for the players in emerging energy trade markets.
Nord Pool, The Nordic Power Exchange, is an energy trade marked estab-lished in Norway in 1993. In 1995 the national authorities in Denmark, Finland and Sweden agreed to establish a common Nordic energy trade marked. As a result of this, Sweden joined Nord Pool in 1996, Finland in 1998, and, finally, Denmark joined the marked in 1999.
On this marked the value of wind power depends on the availability and accuracy of wind power predictions, as in this market the dealings of power is also based on short-term contracts. One of the key concepts of the short-term contracts, is that the dealings of power for the following day have to be settled at noon the day before. This means that the wind power prediction horizon has to be between 12–36 hours in order to be useful for trading on Nord Pool.