In 2009, I obtained my PhD in electrical engineering from TU Delft. My research was about the large-scale integration of wind energy into the power system. And (amongst other things) about what would happen during low-wind periods, when wind turbines are idling. Below, you find a summary of my thesis. If you want, you can find the full thesis here: Grid Integation (researchgate.net). The storyline and conclusions of the research still hold – but I am happy to see that we are now (2024) exploring much higher levels of wind power than I researched at the time!
Reason for the research
Our society revolves around electricity. Most electricity comes from electric power stations that use coal and natural gas. These are reliable and affordable fuels, but they also have disadvantages. The supply of fossil fuels is finite and unevenly distributed across the earth. Besides, conventional power stations emit greenhouse gases. There is an urgent need for sustainable alternatives, such as wind power. The disadvantages of wind are that sometimes it is blowing and sometimes it is not and that it is unpredictable. The generation of electricity must however equal demand at all times. That makes the integration of wind power in the electricity system more difficult.
Goal and method
My Ph.D.-thesis was about the question what are the consequences of the integration of a lot of wind power for the existing power system. What problems do we run into and what solutions are available? Is it possible to produce one third of the electricity demand with onshore and offshore wind energy? To come to an answer to these questions, first, it was calculated how much electricity the future wind parks would produce, and when. This information was added to an existing power system simulation model. This simulation model calculates which power stations must be turned on and off at which moment to provide in the electricity demand throughout the year. Electricity exchange with other countries is also calculated. The simulations provide a picture of the reliability, costs and emissions of the generation of electricity, with and without wind power. A second simulation model, developed in this research, computes how the power system reacts to wind energy during certain circumstances, for example during a storm. By combining the two models, possible problems with the integration of wind power in the existing power system become clear. The possible solutions, such as flexible electric power plants and energy storage, are also investigated by using those models.
Wind variations and forecast errors
Electricity demand changes continuously: for example, during the day we use much more electricity than at night. On top of that, the supply of wind power changes, because sometimes it is very windy and sometimes there is almost no wind. These two uncertainties are examined simultaneously in the simulations in order to explore the worst combinations. The results indicate that more wind power demands for more flexibility of the existing power stations.
Sometimes more reserves are needed, but much more often the power stations must reduce their output to make room for wind power. It is important to compute the commitment of the power stations again and again using the latest wind forecast. Then it is possible to reduce forecast errors and to integrate wind power better into the system.
If the wind is or is not blowing…
It turns out that the Dutch power stations will be able to set off the variations in demand and wind supply at any moment in the future, provided that actual and improved wind forecasts are taken into account. There are however limits to the integration of wind power. This is, for example, because coal-fired power plants cannot be turned off just like that. Therefore, if there is a lot of wind and little demand, there will be a surplus of wind power. Instead of the often posed question ‘What to do when the wind does not blow?’, the question ‘What to do with all the electricity if it is very windy at night?’ is much more relevant. An important solution for this lies in the international trade of electricity, because foreign countries can often use this surplus. Besides, expanding the ‘opening hours’ of the international electricity market is favourable for wind power. At present, electricity companies determine how much electricity they will buy or sell abroad one day ahead. Then, the international market closes. The wind forecast is still inaccurate one day ahead. Wind power can be integrated better if the time difference between trade and the making of the wind forecast would be smaller, for example one or only a few hours.
Integrating wind power into the power system
The integration of wind energy in the Dutch system would provide a reduction of the operating
cost of the system as a whole of EUR 1.5 billion a year. This is because the wind is free,
while coal and natural gas are not. By using less coal and natural gas, also the emission of
CO2 decreases by 19 million tons a year. This research also shows that with the amounts
of wind energy investigated here, no facilities for energy storage have to be developed. The
results indicate that international electricity trade is a promising and cheaper solution for the
integration of wind power. Also making power stations more flexible turns out to be a better
solution. For example, the use of heat boilers allows for a more flexible operation of combined
heat and power stations, which consequently can clear the way for wind during the
night. Also a second electricity cable to Norway seems to be a good alternative for building
pumped hydro power energy storage in the Netherlands itself.
Recommendations for further research
This Ph.D.-research focuses on the Netherlands especially. Further research should consider
the situation in other countries in a better way, especially that in Scandinavia. The electricity
markets should be investigated on a European scale. Further research is also needed on the
capacity of the electricity network in Europe. The future lies in a better cooperation between
different countries and markets; this way, differences in electricity demand and the supply
through sustainable energy sources can be bridged better and more easily.
