Electric Power Supply Systems With Great Impact Of Renewable Energy

The implementation of wind power in Denmark is developing faster than expected. The amount of energy produced by wind power in Denmark is still increasing, and by the end of 1999 it will be 10%, a level which was not expected to be reached before 2005. Up until now a few medium-sized wind farms and off shore wind farms have been established in Denmark. The rest of the wind power comes from singles windmills or small groups of them. On Zealand the construction of three large off shore wind farms each of 150 MW capacity has been announced. These will be connected to the power grid, and the 450 MW will supply 1/6 of the power consumption on Zealand at maximum load (on a winter day). There is a wish to supply 50% of the total electric energy consumption in Denmark from wind power by the year 2030.
The location of windmills is almost exclusively based on wind properties, and matters concerning the power grid are given little consideration. Frequently, areas with good wind resources are geographically far from the consumers, and are in regions where the power grid is relatively weak.
The fact that the power grid is weak in the areas where the windmills are placed leads to two technical problems:
1. The reliability of electric power delivery from the windmills when a grid fault occurs.
2. Achieving delivery of quality power.
The reliability of electric power supply is no major problem today because most of the electric power comes from large conventional thermal power plants. When a fault occurs in the power grid the windmills are disconnected and the delivery of electric power is left to the conventional power plants. As the amount of electric power supply coming from windmills increases, the need for conventional power plants will reduce and some of them will be removed from the grid. Then, the power reserve, which is necessary for compensating the power loss in case of tripping the windmills when a fault occurs, will no longer be available.