This master thesis studies the flexibility of Swedish power system. Because of the increase of
fuel price and the environmental issues, renewable energy plays an increasingly important
role. Sweden parliament has a planning frame of 30 TWh wind power energy per year in
2020. Wind power generation is largely dependent of wind speed. Since wind speed varies
all the time and is hard to be predicted, the introduction of wind power will cause variation
of power generation which needs to be balanced. Therefore, it is very important to study the
regulation capacity of the power system in order to balance wind power. In Sweden, it is
hydropower and thermal power that plays the role as balancing power. In earlier studies at
Department of Electric Power Systems KTH, a model has been built to examine the flexibility
of Swedish hydropower system. The aim of this thesis is to further develop this original
model. In the improved model, the flexibility of thermal power in Sweden is included.
Moreover, the improved model further considers the future value of stored water and the
impact of delayed running water released from the upstream power plants at the end of
simulated week.
The whole model is a large short-time planning problem and the objective of this model is to
maximize the profits. In this thesis, the profit is expressed as the future value of hydropower
minus the generation cost of thermal unit. Besides, the profit also includes the income and
the cost for the trading energy. The improved model is built as an optimization problem in
GAMS. The time step is one hour and the time span of each simulation is one week. The load
consumption and wind power production in each area are given as time series. The
constraints considered in this model include the generation limitations, operational
constraints of thermal power plants, hydrological coupling of hydropower plants, load
balance in each bidding area and transmission capacity. Several case studies are performed
in this thesis. Two models, both original model and improved model, will be tested. To find
out how large the regulation capacity the Swedish power system has, four different
expansion levels of wind power: 0 MW, 4000 MW, 8000 MW and 12000 MW are introduced.
The information regarding hydropower is obtained from statistic data in 2009 and the wind
power data for each week is coming from scaling the data in earlier studies. The operational
constraints of thermal power plants are based on the statistics data from 2008 to 2012. The
main finding from these case studies is that spillage will not increase when more wind power
is introduced to the system but only increase when the export capacity is reached and the
surplus power cannot be exported to other countries. Therefore, it can be concluded that
the Swedish power system has good possibilities to balance large amounts of wind power.
However, some simplifications and assumptions are made when the model is built, which
will give rise to some inaccuracy to the result. Therefore, in the end of this thesis, some
future studies are suggested to further improve this model.