Study Into Grid Integration of Variable Renewable Energy In Ethiopian Power System
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Date
2024-06
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Addis Ababa University
Abstract
Energy has been a crucial factor for the survival of mankind since early primitive societies began
to make fire from timber wood. Since then, there have been significant revolutions in using energy
sources from fossil fuels such as coal and gasoline and the development of energy conversion technologies
such as electric energy generators up to the more recent use of renewable energy sources
(REs). The uneven distribution of fossil fuels in the world, the growing economic and social
need for energy, the difficulty of tackling climate change, advances in energy technology, rising
oil prices and the emergence of low-carbon societies have all contributed to the recent revolution
towards renewable energy sources.
However, REs especially variable renewable energies (VREs) such as wind and solar energy,
pose an additional challenge for electric grid operators due to their inherent variability and unpredictability
nature. Because of these characteristics of VREs, the grid integration of VREs can
potentially jeopardize the reliability of the power grid.
Countries need to conduct grid integration studies to overcome the challenges of integrating
VREs. In this regard, utilities are increasingly relying on the traditional grid integration model,
which ignores the various operational characteristics of VREs. Accordingly, it is important for
the grid integration study to either develop new models or modify existing models to study the
characteristics of VREs in the power sector. In developing countries, especially in Ethiopia, there
is currently little research of this kind due to the slow development of VREs.
Thus, this dissertation deals with the study of grid integration of VREs into the power system
of Ethiopia according to local as well as global needs. The specific objectives are to assess the
variability of existing VREs, simulate wind energy production for grid integration studies, estimate
the maximum integration of VREs, and assess the difficulty of integrating them into the grid. To
achieve these goals, the following four specific objectives are defined and briefed: To assess the
variability of existing wind power in the grid of Ethiopia. This objective is pursued to evaluate
and assess the magnitude and frequency of variability of individual and aggregate wind power in
the Ethiopian power grid. A step-change and correlation are used to examine the variability of wind
power generation. The results indicates that variability of Ethiopian wind power is significant. This
huge variability is due to the small installed capacity. However, this variability does not have much
influence on system operation because of the smaller magnitude of the wind compared with system size.
Modeling Ethiopian wind power production for grid integration study using ERA5 reanalysis
data is the second specific objective. The objective of this particular purpose is to produce
wind power time series considering the various factors affecting wind power production including
wake effect, diurnal and seasonal bias, and the loss in upcoming wind speed. The modeling was
performed using wind speed data from ERA5 of the European Center for Medium-Range Weather
Forecasts (ECMWF) and wind farm data from Ethiopian Electric Power (EEP). Moreover, the
model has used spatial statistical down-scaling and interpolation to obtain the required result. The
outcomes show that the model result and the measurements agree well, with a low root mean square
error. This means that this model can be extended to other regions of the country to predict future
wind power generation and to show the potential areas for simulating wind power generation for
planning and operating wind turbines using ERA5 data.
The third specific aim is to estimate a maximum variable renewable energy integration
with a goal of 100% renewable energy and a high share of hydropower under different scenarios
. This particular objective aims to determine the maximum integration of wind and solar
PV into the power grid of Ethiopia. The current national VRE integration plan for the year 2030 is
analyzed using the model along with eight alternative scenarios that consider dry years and annual
variations in VRE for minimum load shedding and VRE curtailment. GenX, a modified version
of capacity expansion planning, has been used for this work. The findings showed that Ethiopia
could integrate more VRE into the grid than EEP had anticipated.
The fourth specific objective is to study the challenges of system balancing and curtailment
of wind power in Ethiopia grid under different scenarios. In addition to analyzing the
challenge of system operation with wind, developing an hourly dispatch model and simulation of
the Ethiopia power grid is the specific aim of this work. This model will be useful in analyzing
future wind power curtailment and system balancing issues. The developed model was used
to analyze the grid for the year 2030 under different scenarios and verified using historical data.
With an annual wind energy share of 14.5%, 17.8%, and 25.2%, the study analyzed the impact
of transmission capacity, regulation reserve needed, and daily minimum hydropower production.
The result showed that the curtailment was less than 0.2%, 1.1%, and 9.8% for each wind share
respectively.
The cost of wind energy is also directly related to the extent of curtailment and the capacity of transmission lines. A better balance between production and consumption and fewer wind power
curtailments is the result of a reduction in the minimum electricity production from hydropower
and full utilization of transmission lines to neighboring countries.
Description
Keywords
Balancing, Curtailment, Ethiopia, Grid integration study, Model, PV, Uncertainty, Wind, VRE, Variability